The exact quantification of site water budget is a necessary precondition for successful and sustainable management of forests, agriculture and water resources. In this study the water balance was investigated at the spatial scale of canopies and at different temporal scales with focus on the monthly time scale. The estimation of the individual water balance components was primarily based on micrometeorological measurement methods. Evapotranspiration was assessed by the eddy-covariance (EC) method, while sap flow measurements were used to estimate transpiration. Interception was assessed by a combination of canopy drip, stem flow and precipitation (gross rainfall) measurements and soil moisture measurements were used to estimate the soil water storage. The combination of different measurement methods and the derivation of water balance components that are not directly measurable e.g. seepage and soil evaporation is a very complex task due to different scales of measurement, measurement uncertainties and the superposition of these effects. The quantification of uncertainties is a core point of the present study. The uncertainties were quantified for water balance component as well as for meteorological variables (e.g. wind speed, temperature, global radiation, net radiation and precipitation) that served as input data in water balance models. Furthermore, the influences of uncertainties were investigated in relation to numerical water balance simulations. Here, both the effects of uncertainties in input data and in reference data were analysed and evaluated. The study addresses three main topics. The first topic was the providing of reference data of evapotranspiration by EC measurements. Here, the processing of EC raw-data was of main concern with focus on the correction of the spectral attenuation. Four different methods of spectral correction were tested and compared. The estimated correction coefficients were significantly different between all methods. However, the effects were small to absolute values on half-hourly time scale. In contrast to half-hour data sets, the method had significant influence to estimated monthly totals of evapotranspiration. The second main topic dealt with the comparison of water balances between a spruce (Picea abies) and a beech (Fagus sylvatica) site. Both sites are located in the Tharandter Wald (Germany). Abiotic conditions are very similar at both sites. Thus, the comparison of both sites offered the opportunity to reveal differences in the water balance due to different dominant tree species. The aim was to estimate and to compare all individual components of the water balance by a combination of the above mentioned measurement methods. A major challenge was to overcome problems due different scales of measurements. Significant differences of the water balances between both sites occurred under untypical weather conditions. However, under typical condition the sites showed a similar behaviour. Here, the importance of involved uncertainties deserved special attention. Results showed that differences in the water balance between sites were blurred by uncertainties. The third main topic dealt with the effects of uncertainties on simulations of water balances with numerical models. These analyses were based on data of three sites (Spruce, Grass and Agricultural site). A kind of Monte-Carlo-Simulation (uncertainty model) was used to simulate effects of measurement uncertainties. Furthermore, the effects of model complexity and the effect of uncertainties in reference data on the evaluation of simulation results were investigated. Results showed that complex water balance models like BROOK90 have the ability to describe the general behaviour and tendencies of a water balance. However, satisfying quantitative results were only reached under typical weather conditions. Under untypical weather e.g. droughts or extreme precipitation, the results significantly differed from actual (measured) values. In contrast to complex models, it was demonstrated that simple Black Box Models (e.g. HPTFs) are not suited for water balance simulations for the three sites tested here. / Die genaue Quantifizierung des Standortswasserhaushalts ist eine notwendige Voraussetzung für eine erfolgreiche und nachhaltige Bewirtschaftung von Wäldern, Äckern und Wasserressourcen. In dieser Studie wurde auf der Raumskala des Bestandes und auf verschieden Zeitskalen, jedoch vorrangig auf Monatsebene, die Wasserbilanz untersucht. Die Bestimmung der einzelnen Wasserbilanzkomponenten erfolgte hauptsächlich mit mikrometeorologischen Messmethoden. Die Eddy- Kovarianz- Methode (EC- Methode) wurde benutzt zur Messung der Evapotranspiration, während Xylem- Flussmessungen angewendet wurden, um die Transpiration zu bestimmen. Die Interzeption wurde aus Messungen des Bestandesniederschlags, des Stammablaufs und des Freilandniederschlags abgeleitet. Messungen der Bodenfeuchte dienten zur Abschätzung des Bodenwasservorrats. Die Kombination verschiedener Messmethoden und die Ableitung von nicht direkt messbaren Wasserhaushaltkomponenten (z.B. Versickerung und Bodenverdunstung) ist eine äußerst komplexe Aufgabe durch verschiedenen Messskalen, Messfehler und die Überlagerung dieser Effekte. Die Quantifizierung von Unsicherheiten ist ein Kernpunkt in dieser Studie. Dabei werden sowohl Unsicherheiten in Wasserhaushaltskomponenten als auch in meteorologischen Größen, welche als Eingangsdaten in Wasserbilanzmodellen dienen (z.B. Windgeschwindigkeit, Temperatur, Globalstrahlung, Nettostrahlung und Niederschlag) quantifiziert. Weiterführend wird der Einfluss von Unsicherheiten im Zusammenhang mit numerischen Wasserbilanzsimulationen untersucht. Dabei wird sowohl die Wirkung von Unsicherheiten in Eingangsdaten als auch in Referenzdaten analysiert und bewertet. Die Studie beinhaltet drei Hauptthemen. Das erste Thema widmet sich der Bereitstellung von Referenzdaten der Evapotranspiration mittels EC- Messungen. Dabei waren die Aufbereitung von EC- Rohdaten und insbesondere die Dämpfungskorrektur (Spektralkorrektur) der Schwerpunkt. Vier verschiedene Methoden zur Dämpfungskorrektur wurden getestet und verglichen. Die bestimmten Korrekturkoeffizienten unterschieden sich deutlich zwischen den einzelnen Methoden. Jedoch war der Einfluss auf die Absolutwerte halbstündlicher Datensätze gering. Im Gegensatz dazu hatte die Methode deutlichen Einfluss auf die ermittelten Monatssummen der Evapotranspiration. Das zweite Hauptthema beinhaltet einen Vergleich der Wasserbilanz eines Fichten- (Picea abies) mit der eines Buchenbestands (Fagus sylvatica). Beide Bestände befinden sich im Tharandter Wald (Deutschland). Die abiotischen Faktoren sind an beiden Standorten sehr ähnlich. Somit bietet der Vergleich die Möglichkeit Unterschiede in der Wasserbilanz, die durch unterschiedliche Hauptbaumarten verursacht wurden, zu analysieren. Das Ziel was es, die einzelnen Wasserbilanzkomponenten durch eine Kombination der eingangs genanten Messmethoden zu bestimmen und zu vergleichen. Ein Hauptproblem dabei war die Umgehung der unterschiedlichen Messskalen. Deutliche Unterschiede zwischen den beiden Standorten traten nur unter untypischen Wetterbedingungen auf. Unter typischen Bedingungen zeigten die Bestände jedoch ein ähnliches Verhalten. An dieser Stelle erlangten Messunsicherheiten besondere Bedeutung. So demonstrierten die Ergebnisse, dass Unterschiede in der Wasserbilanz beider Standorte durch Messunsicherheiten verwischt wurden. Das dritte Hauptthema behandelt die Wirkung von Unsicherheiten auf Wasserbilanzsimulationen mittels numerischer Modelle. Die Analysen basierten auf Daten von drei Messstationen (Fichten-, Grasland- und Agrarstandort). Es wurde eine Art Monte-Carlo-Simulation eingesetzt, um die Wirkung von Messunsicherheiten zu simulieren. Ferner wurden auch der Einfluss der Modellkomplexität und die Effekte von Unsicherheiten in Referenzdaten auf die Bewertung von Modellergebnissen untersucht. Die Ergebnisse zeigten, dass komplexe Wasserhaushaltsmodelle wie BROOK90 in der Lage sind, das Verhalten und Tendenzen der Wasserbilanz abzubilden. Jedoch wurden zufriedenstellende quantitative Ergebnisse nur unter üblichen Wetterbedingungen erzielt. Unter untypischen Wetterbedingungen (Dürreperioden, Extremniederschläge) wichen die Ergebnisse deutlich vom tatsächlichen (gemessenen) Wert ab. Im Gegensatz zu komplexen Modellen zeigte sich, dass Black Box Modelle (HPTFs) nicht für Wasserhaushaltssimulation an den drei genannten Messstandorten geeignet sind.

Sustainable water management practices for cultivation of bioenergy crops requires a sound understanding of how the different components of the soil-vegetation-atmosphere continuum influence water fluxes at stand scale. In addition, depth to groundwater can influence water accessibility to plants and could potentially determine tree water-use. This dissertation assesses how the meteorological factors and soil hydrological site parameters influence the magnitude of transpiration along a groundwater accessibility gradient in the floodplains of the Morava river, in Slovakia. Specifically, this study examines the influence of the soil texture, soil moisture, and matric potential and the meteorological variables in the transpiration of poplar short rotation coppices stands (Populus spp.) established on loamy sands textured soils, across three sites with high groundwater level, low groundwater level and fluctuating groundwater level. The study was conducted throughout 90 days during two monitoring periods, 2019 and 2021. The first analysis (Section 3.1) examines the meteorological and soil water conditions in combination with the sapflow and transpiration dynamics, between July 3 and September 30, 2019. This study found significant differences in tree and stand transpiration among the study sites. The site with higher groundwater accessibility and the site with fluctuating groundwater level presented larger transpiration rates mainly determined by optimal meteorological conditions, soil water availability and access to groundwater. Contrasting findings were obtained during the analysis of the monitoring period 2021, carried out between July 3 and September 30, 2021. In the monitoring period 2021 (Section 3.5), the sites with fluctuating groundwater level and low groundwater level indicated statistically higher transpiration rates than the site with higher accessibility to groundwater. This research found that the higher transpiration rates may be attributable to soil moisture and accessibility to groundwater. By contrast, the adverse meteorological conditions limited the magnitude of transpiration at the site with higher groundwater level. The examination of the soil physical properties, specifically soil texture and its influence on soil water retention capacity is analyzed on Sections 3.3.2 and 3.8.1. This research found that the sandy texture of the soils in the study area favored a rapid water infiltration at greater soil depths. The accumulation of water at deeper layers may have served as supply for the planted trees. While this characteristic was critical for the site with lower groundwater level, a greater proportion of silt and clay particles on the site with high groundwater level and fluctuating groundwater level were key for improving the soil water retention capacity. The results of this assessment highlight that soil physical properties are critical for water availability for tree water uptake. This research discusses that for reducing the uncertainty in upscaling transpiration from tree to stand level, the determination of water conducting area in poplar trees is critical. Nevertheless, additional uncertainty is brought by the spatial variability of soil physical and hydrological properties. Therefore, this research concludes that upscaling transpiration from tree to larger scales should include not only biometric tree and stand characteristics but it should consider soil spatial properties and their influence on water availability for plants. The overall findings of the dissertation conducted in sandy soils across sites with different groundwater accessibility demonstrated that soil site related factors, namely soil water availability and groundwater accessibility, are critical for tree transpiration and potentially growth at the study sites. Furthermore, a combined assessment of meteorological, soil and groundwater conditions is crucial for the determination of transpiration at larger scales and for the implementation of sustainable bioenergy plantations.:Table of Contents 1. Introduction 1 1.1. Motivation 1 1.1.1. Plant Transpiration is a Critical Flux within the Hydrologic Cycle 1 1.1.2. Main Factors Influencing Transpiration 1 1.2. Research Background 2 1.2.1. Overview of Methods for Estimating Plant Transpiration 2 1.2.2. Methods for Upscaling Plant Transpiration to Stand Transpiration 7 1.2.3. Water Use of Poplar as Short Rotation Coppices 7 1.3. Scope of the work 12 1.3.1. Aim of the Doctoral Thesis 12 1.3.2. Research Hypotheses 13 1.4. Structure of the Thesis 14 2. Materials and Methods 16 2.1. Study Area 16 2.2. Selection of the Experimental Sites 18 2.3. Instrumentation and Continuous Measurements 20 2.3.1. Overview of the Monitoring Periods 2019 and 2021 20 2.3.2. Soil Monitoring 21 2.3.3. Weather Station 23 2.3.4. Sap Flow Measurements with the Heat Ratio Method (HRM) 23 2.3.5. Estimation of Water Conducting Area 28 2.3.6. Estimation of the Leaf Area Index from Sentinel images 30 2.4. Upscaling Method from Sensor to Tree 30 2.5. Data and Statistical Analysis 31 2.5.1. Statistical Analyses 31 2.6. Upscaling Method from Tree to Stand Scale 32 3. Results 33 3.1. Meteorological and Groundwater Conditions for the Monitoring Period July to September 2019 33 3.1.1. Meteorological Conditions 33 3.1.2. Groundwater Conditions 34 3.2. Tree-based Transpiration 35 3.3. Tree Water Use in Relation to Meteorological and Soil Physical and Soil Hydrological Properties – Monitoring Period 2019 40 3.3.1. Site S5-N (higher groundwater level) 40 3.3.2. Site S4-D (low groundwater level) 42 3.3.3. Site S2-F (fluctuating groundwater level) 45 3.4. Principal Component Analysis for Monitoring Period 2019 46 3.4.1. Water Use in Relation to Soil Moisture for the Monitoring Period 2019 50 3.4.2. Quantification of Transpiration at Stand Scale for the Monitoring Period 2019 54 3.5. Meteorological and Groundwater Conditions for the Monitoring Period July to September 2021 56 3.5.1. Meteorological Conditions 56 3.5.2. Groundwater Conditions 56 3.6. Tree-based Transpiration 58 3.7. Tree Water Use in Relation to Meteorological and Soil Physical and Soil Hydrological Properties – Monitoring Period 2021 62 3.7.1. Site S5-N (higher groundwater level) 62 3.7.2. Site S4-D (low groundwater level) 65 3.7.3. Site S2-F (fluctuating groundwater level) 66 3.8. Principal Component Analysis for Monitoring Period 2021 69 3.8.1. Water Use in Relation to Soil Moisture for the Monitoring Period 2021 71 3.8.2. Quantification of Transpiration at Stand Scale for the Monitoring Period 2021 72 4. Discussion 74 5. Synthesis and Future Perspectives 79 5.1. Tree Water Use in Relation to Soil and Meteorological Drivers 79 5.2. Scaling-up tree transpiration to stand level based on sapflow methods 80 5.3. Research Perspectives 81 5.4. Final Remarks 82 6. References 84 7. Appendix 96 / Nachhaltige Wassermanagementpraktiken für den Anbau von Bioenergiepflanzen erfordern ein fundiertes Verständnis dafür, wie die verschiedenen Komponenten des Kontinuums Boden-Vegetation-Atmosphäre die Wasserflüsse auf Bestandsebene beeinflussen. Darüber hinaus kann die Tiefe des Grundwassers die Wasserverfügbarkeit für Pflanzen beeinflussen und möglicherweise den Wasserverbrauch der Bäume bestimmen. In dieser Dissertation wird untersucht, wie meteorologische Faktoren und bodenhydrologische Standortparameter das Ausmaß der Transpiration entlang eines Grundwasserzugangsgradienten in den Auen des Flusses Morava in der Slowakei beeinflussen. Konkret wird in dieser Studie der Einfluss der Bodentextur, der Bodenfeuchte und des Matrixpotenzials sowie der meteorologischen Variablen auf die Transpiration von Pappel-Kurzumtriebsplantagen (Populus spp.) auf lehmigen Sandböden an drei Standorten mit hohem, niedrigem und schwankendem Grundwasserspiegel untersucht. Die Studie wurde über einen Zeitraum von 90 Tagen in zwei Beobachtungszeiträumen (2019 und 2021) durchgeführt. Die erste Analyse (Abschnitt 3.1) untersucht die meteorologischen und Bodenwasser-bedingungen in Kombination mit der Saftfluss- und Transpirationsdynamik zwischen dem 3. Juli und dem 30. September 2019. Diese Studie ergab signifikante Unterschiede in der Transpiration von Bäumen und Beständen an den Untersuchungsstandorten. Der Standort mit höherer Grundwasserverfügbarkeit und der Standort mit schwankendem Grundwasserspiegel wiesen größere Transpirationsraten auf, die hauptsächlich durch optimale meteorologische Bedingungen, Bodenwasserverfügbarkeit und Grundwasserzugang bestimmt wurden. Bei der Analyse des Überwachungszeitraums 2021, der zwischen dem 3. Juli und dem 30. September 2021 durchgeführt wurde, wurden gegensätzliche Ergebnisse erzielt. Im Beobachtungszeitraum 2021 (Abschnitt 3.5) wiesen die Standorte mit schwankendem Grundwasserspiegel und niedrigem Grundwasserspiegel statistisch höhere Transpirationsraten auf als die Standorte mit besserer Grundwasserverfügbarkeit. Diese Untersuchung ergab, dass die höheren Transpirationsraten auf die Bodenfeuchtigkeit und die Zugänglichkeit zum Grundwasser zurückzuführen sein könnten. Im Gegensatz dazu begrenzten die ungünstigen meteorologischen Bedingungen das Ausmaß der Transpiration am Standort mit höherem Grundwasserspiegel. Die Untersuchung der physikalischen Bodeneigenschaften, insbesondere der Bodentextur und ihres Einflusses auf das Wasserrückhaltevermögen des Bodens, wird in den Abschnitten 3.3.2 und 3.8.1 analysiert. Die Untersuchung ergab, dass die sandige Textur der Böden im Untersuchungsgebiet eine schnelle Wasserinfiltration in größeren Bodentiefen begünstigt. Die Ansammlung von Wasser in tieferen Schichten diente möglicherweise der Versorgung der gepflanzten Bäume. Während diese Eigenschaft für den Standort mit niedrigem Grundwasserspiegel entscheidend war, war ein größerer Anteil an Schluff- und Tonpartikeln auf dem Standort mit hohem Grundwasserspiegel und schwankendem Grundwasserspiegel der Schlüssel zur Verbesserung der Wasserrückhaltekapazität des Bodens. Die Ergebnisse dieser Bewertung zeigen, dass die physikalischen Eigenschaften des Bodens für die Wasserverfügbarkeit für die Wasseraufnahme der Bäume entscheidend sind. In dieser Forschungsarbeit wird erörtert, dass die Bestimmung der wasserführenden Fläche in Pappelbäumen von entscheidender Bedeutung ist, um die Unsicherheit bei der Hochskalierung der Transpiration vom Baum auf die Bestandsebene zu verringern. Zusätzliche Unsicherheiten ergeben sich jedoch aus der räumlichen Variabilität der physikalischen und hydrologischen Eigenschaften des Bodens. Daher kommt diese Forschungsarbeit zu dem Schluss, dass bei der Hochskalierung der Transpiration von Bäumen auf größere Maßstäbe nicht nur biometrische Baum- und Bestandsmerkmale berücksichtigt werden sollten, sondern auch die räumlichen Bodeneigenschaften und ihr Einfluss auf die Wasserverfügbarkeit für Pflanzen. Die Gesamtergebnisse der Dissertation, die auf Sandböden an Standorten mit unterschiedlicher Grundwasserverfügbarkeit durchgeführt wurde, haben gezeigt, dass bodenbezogene Faktoren, nämlich die Verfügbarkeit von Bodenwasser und die Grundwasserverfügbarkeit, für die Transpiration von Bäumen und möglicherweise auch für deren Wachstum an den Untersuchungsstandorten entscheidend sind. Darüber hinaus ist eine ganzheitliche Bewertung, die meteorologische, Boden- und Grundwasserbedingungen kombiniert, von entscheidender Bedeutung für die Bestimmung der Transpiration in größerem Maßstab und für die Umsetzung nachhaltiger Bioenergie-Plantagen:Table of Contents 1. Introduction 1 1.1. Motivation 1 1.1.1. Plant Transpiration is a Critical Flux within the Hydrologic Cycle 1 1.1.2. Main Factors Influencing Transpiration 1 1.2. Research Background 2 1.2.1. Overview of Methods for Estimating Plant Transpiration 2 1.2.2. Methods for Upscaling Plant Transpiration to Stand Transpiration 7 1.2.3. Water Use of Poplar as Short Rotation Coppices 7 1.3. Scope of the work 12 1.3.1. Aim of the Doctoral Thesis 12 1.3.2. Research Hypotheses 13 1.4. Structure of the Thesis 14 2. Materials and Methods 16 2.1. Study Area 16 2.2. Selection of the Experimental Sites 18 2.3. Instrumentation and Continuous Measurements 20 2.3.1. Overview of the Monitoring Periods 2019 and 2021 20 2.3.2. Soil Monitoring 21 2.3.3. Weather Station 23 2.3.4. Sap Flow Measurements with the Heat Ratio Method (HRM) 23 2.3.5. Estimation of Water Conducting Area 28 2.3.6. Estimation of the Leaf Area Index from Sentinel images 30 2.4. Upscaling Method from Sensor to Tree 30 2.5. Data and Statistical Analysis 31 2.5.1. Statistical Analyses 31 2.6. Upscaling Method from Tree to Stand Scale 32 3. Results 33 3.1. Meteorological and Groundwater Conditions for the Monitoring Period July to September 2019 33 3.1.1. Meteorological Conditions 33 3.1.2. Groundwater Conditions 34 3.2. Tree-based Transpiration 35 3.3. Tree Water Use in Relation to Meteorological and Soil Physical and Soil Hydrological Properties – Monitoring Period 2019 40 3.3.1. Site S5-N (higher groundwater level) 40 3.3.2. Site S4-D (low groundwater level) 42 3.3.3. Site S2-F (fluctuating groundwater level) 45 3.4. Principal Component Analysis for Monitoring Period 2019 46 3.4.1. Water Use in Relation to Soil Moisture for the Monitoring Period 2019 50 3.4.2. Quantification of Transpiration at Stand Scale for the Monitoring Period 2019 54 3.5. Meteorological and Groundwater Conditions for the Monitoring Period July to September 2021 56 3.5.1. Meteorological Conditions 56 3.5.2. Groundwater Conditions 56 3.6. Tree-based Transpiration 58 3.7. Tree Water Use in Relation to Meteorological and Soil Physical and Soil Hydrological Properties – Monitoring Period 2021 62 3.7.1. Site S5-N (higher groundwater level) 62 3.7.2. Site S4-D (low groundwater level) 65 3.7.3. Site S2-F (fluctuating groundwater level) 66 3.8. Principal Component Analysis for Monitoring Period 2021 69 3.8.1. Water Use in Relation to Soil Moisture for the Monitoring Period 2021 71 3.8.2. Quantification of Transpiration at Stand Scale for the Monitoring Period 2021 72 4. Discussion 74 5. Synthesis and Future Perspectives 79 5.1. Tree Water Use in Relation to Soil and Meteorological Drivers 79 5.2. Scaling-up tree transpiration to stand level based on sapflow methods 80 5.3. Research Perspectives 81 5.4. Final Remarks 82 6. References 84 7. Appendix 96

<p>The removal of vegetation and overburden changes the naturalwater purifying processes and thus decreases the groundwaterprotection in gravel pit areas. The sand and gravel depositsusedfor aggregate extraction in Sweden are also often valuablefor extraction of groundwater as a drinking water resource. TheSwedish legislation requires that gravel pits be restored afterthe cessation of extraction, the aim being to reestablishvegetation and to reinstate groundwater purifyingprocesses.</p><p>The objective of this study was to improve our understandingof the processes governing groundwater protection andvegetation establishment so that these could be applied toimproving restoration methods for reestablishing naturalgroundwater protection. The focus was on the importance of soilphysical properties of the topsoil for vegetation establishmentand groundwater recharge.</p><p>Actual field methods for restoration were reviewed.Conflicts between aggregate extraction and groundwaterinterests were common. In many cases the actual restorationcarried out differed from pre-planned specifications in permitdocumentation.</p><p>Commonly available substrates that might be used forrestoration of gravel pits were investigated. The soils weredescribed as regards texture, organic content, porosity, waterretention and hydraulic conductivity. The way in which acombination of the water retention characteristic and theunsaturated conductivity influenced the behaviour of thesoil-plant-atmosphere system was demonstrated using aprocess-orientated simulation model. Plants with well-developedaboveground characteristics and shallow roots in particularexerted the highest requirements on the soil physicalproperties.</p><p><b>Key words:</b>groundwater protection, soil physicalproperties, CoupModel, unsaturated conductivity, waterretention, transpiration, soil evaporation</p>

The Waiwhero wetland (16 ha) is one of the largest wetlands in the Rosedale Hills, 35 km north-west of Nelson, New Zealand. It has an extensive cover of Salix fragilis L. (crack willow) and has been hypothesised to be a source of groundwater recharge for the Moutere aquifers, an important local groundwater system. However the wetland could also be a groundwater discharge zone, because of the geological boundary that it straddles. The overall aim of this study was to determine the direction of groundwater flux of the wetland by measuring the water balance, with particular emphasis on the transpiration rates from the crack willow trees. The average daily transpiration (measurement was for 230 days) of crack willows in the wetland (6.4 mm/day) was close to twice the potential evapotranspiration (PET) for grassland (3.9 mm/day). The highest measured willow transpiration rate was 12.4 mm/day and the lowest was 0.8 mm/day. High transpiration from crack willows was due to the horizontal energy fluxes (advective energy), tree physiological characters and high soil water content. The study established that the wetland is a groundwater discharge zone with, on average for the two summer periods (2008 and 2009), the net groundwater discharge being 4.8 mm/day. The daily water balance results between two major rainfall events showed that the initial discharge source was from the surrounding hills and later stabilized at around 6 to 14 mm/day. It was believed to be a contribution from the shallow and deep aquifers or a combination of local region inflow and aquifers. The water balance showed that the main loss of water through the hydrological system of the wetland during summer was from the high transpiration of willows (7.7 mm/day). The extent of water savings estimated for the 16 ha wetland through a hypothetical situation of willow removal, and the assumption that it is filled with open water without any canopy cover, was 688 m3/day. However this water savings rate if applied to a large area of crack willow stands would be quite high. On similar lines it is important to understand the transpiration rates of other wetland tree species in New Zealand. This information would help in preparing regional council plans for the introduction of tree species in the wetland for better management of the water resources and sustainable ecosystem management.

Le travail présenté dans ce manuscrit décrit quelques-uns des mécanismes qui régissent les échanges de CO2 et d’eau dans le mésophylle. Nous présentons dans une première partie une méthode originale qui utilise une technique de traçage isotopique et une modélisation deséchanges gazeux pour décrire le transfert du CO2 et la concentration de CO2 aux sites catalytiques des anhydrases carboniques. Dans une deuxième partie, cette approche nous permet de caractériser la diffusion de CO2 intra-mésophylienne et d’aborder l’étude du rôle des anhydrases carboniques et des aquaporines dans la facilitation du transport de CO2. Cette étude est basée sur une analyse fonctionnelle de mutants d’insertions d’Arabidopsis affectésdans l’expression des anhydrases carboniques (ACs) ou des aquaporines. La contribution fonctionnelle d’une AC, bCA4 localisée à la membrane plasmique et récemment identifiée estanalysée plus spécifiquement. Dans une troisième partie, nous montrons par un travail de modélisation que l’approche de traçage isotopique précédemment introduite pour étudier le transfert de CO2 peut être utilisée pour étudier la compartimentation de l’eau mésophyllienne et les flux associés. Cette approche nous permet de démontrer l’existence d’une compartimentation fonctionnelle de l’eau foliaire. La signification de cette compartimentation est discutée, et une nouvelle méthode de suivi quantitatif des flux d’eau entre l’apoplasme etle symplasme est proposée. Enfin, dans une dernière partie nous abordons expérimentalement les effets de l’acide abscissique sur la transpiration foliaire et la régulation stomatique. / N this study, mechanisms that govern CO2 and water fluxes in the mesophyll are investigated. In a first part, an original approach based on isotopic tracing and modeling of gas exchange is presented to describe the CO2 transfer towards sites of carbonic anhydrases catalysis that are used to probe the intracellular CO2 concentration. In a second part, this approach allows to characterize the intracellular diffusion of CO2 and to address the implication of carbonicanhydrases and aquaporins in the facilitation of the CO2 transfer. The functional analysis is based on the characterization of Arabidopsis mutants in which the expression of some carbonic anhydrases (CAs) or aquaporins is impaired. The implication of a recently identified CA, bCA4 located at the plasma membrane, is studied in detail. In a third part a modeling approach is used to show that the method of isotopic tracing introduced to probe the CO2 fluxes can also be used to study the compartmentation of the mesophyll water and the associated fluxes. The basis of this functional compartmentation is analyzed and a newmethod is proposed to quantitatively monitor the water fluxes between the apoplasm and the symplasm. In a last part, the effects of abscissic acid on the leaf transpiration and on the stomatal aperture regulation are addressed.

Student Number : 9402386H - PhD thesis - School of Animal, Plant and Environmental Sciences - Faculty of Science / The upper limit of forest production is constrained by the efficiency of radiation interception and the conversion of carbon dioxide into harvestable products, These processes are limited by water availability and nutrient supply. This study forms part of an international network of experiments aimed at demonstrating the potential yield of a forest species by eliminating water and nutrients as growth-limiting factors. The main aim of this study was to determine the climatic and nutritional controls on the growth of Eucalyptus under a given set of environmental conditions. A field experiement was initiated in the KwaZulu-Natal Midlands, South Africa, to establish the effects of varying levels of water and nutrient availability on the physiological processes controlling tree growth in E. grandis. The experimental design consisted of a control (C), irrigation (I), fertilisation (F), and irrigation and fertilisation (IF) treatments. These treatments aimed to eliminate both water (I and IF) and nutrients (F and IF) as growth-limiting factors. The study focused on three main areas, namely tree-water relations, nutrient dynamics and acquisition, and carbon allocation. Information on these processes was acquired through a combination of field data collection, the application of foliar diagnostic tools, and a modelling approach. The growth of the E.grandis trees in this trial was constrained by poor establishment and management practices. Inadequate vegetation control and vigorous weed growth were a source of competition during the establishment of the seedlings. In addition, the variable seed stock, late fertiliser application and damage from animals resulted in late canopy closure. Consequently, the potential growth of E.grandis at this site could not be determined, and comparisons were made between the different treatments rather than demonstrating maximum growth under optimal conditions. The boimass and nutrient pools were quantified to provide a mid-rotation value of the nitrogen (N) and phosphorus (P) contents contained in the soil, forest floor and above- and below-ground biomass. At age four years, irrigation had a more pronounced effect on growth and biomass accumulation than fertilisation. Increases in diameter, height,, basal area, standing volume and above- and below-ground biomass were observed in response to increased water availability. After four years, the respective totals of the above- and below-ground biomass pools accumulated by the C, I, F and IF treatments were 73, 82, 78 and 85 t ha-1. In irrigated (I and IF) treatments, significantly more above-ground biomass was allocated to the stem, compared to non-irrigated (C and F) trees. The lower root: shoot ratio in fertilised (F and IF) trees indicated that proportionally less mass was allocated to below-ground components compared to non-fertilised (C and I) trees. Irrigated trees accumulated more N and P than non-irrigated trees in above- and below-ground biomass fractions. The 3-PG model has shown considerable potential as a tool for predicting forest productivity. As part of a model validation exercise, 3-PG was applied to this stand. Simulations were run over a two-year period using appropriate initialisation data and a parameter set developed for E.grandis in summer rainfall region of South Africa. The model was validated using observed leaf area index (L) and foliage and above-ground woody biomass, and then used to predict stand volume. The 3-PG model produced accurate predictions of L, foliage and above-ground woody biomass. At four years, the model-predicted L over all treatments ranged from 3.8 to 5.0, in contrast to the observed range of 4.3 to 5.2. Stand volume at four years of age was under-estimated in the non-irrigated treatments. Actual stand volume at this age ranged from 100 to 118 m3 ha-1 across all treatments, compared to model estimates of 82 to 123 m3 ha-1. The 3-PG model can be used as a guide for future research direction, which should focus on a better understanding of nutritional dynamics operatins at a site. Use of a dynamic fertilty rating may improve model predictions and there is a possible scope for improvement in the water-balance component of the model. Results from this study have shown 3-PG to be a robust model by producing accurate predictions of growth under varying levels of resource availability. There is much current interest in predicting the maximum amount of water that can be transpired by Eucalyptus trees. It is possible that industrial waste water may be applied as irrigation water to eucalyptus and it is important ot predict the maximum transpiration rates of these plantations in an attempt to dispose of this contaminate water. A simple model was developed to predict maximum rates of daily transpiration by short-rotation E.grandis plantations experiencing no significant soil water deficits or fertility limitation. Daily sap flow data recorded in a single average tree in the irrigated treatment were used to estimate mean daily canopy conductance. Analysis of daily and seasonal variation in conductance confirmed that solar radiation and vapour pressure deficit are the dominant factors reducing canopy conductance below potential values, when soil water availability is high. A simple canopy conductance model based on these data was then used with the Penman-Monteith equation to predict daily transpiration rates by E.grandis trees at a site situated in Mpumalanga. The modelled transpiration rates agreed well with th oberved daily sap low (R2 = 0.79). The total observed annual sap flow at the Mpumalanga site was equivalent to 1320 mm compared to the modelled value of 1226 mm. Fertilisation is one of the most cost-effective methods of increasing and maintaining the productivity of E.grandis plantations in South Africa. This silvicultural pratice can be optimised by using the foliar nutrient ratios measured in plants at maximum growth as a guideline for fertiliser application. The foiar ratios present at optimum growth are similar across a wide range of plant apecies and can be defined in relation to N. A study was conducted to determine whether the proportions of elements relative to N could be refined specifically for E.grandis through the use of diagnosis and recommendation integrated system (DRIS) norms. The DRIS norms for N, P, potassium (K), calcium (Ca) and magnesium (Mg) wer derived from published studies on E.grandis and compared to targer values recommended by Linder (1995) for optimal growth. The DRIS norms for P and K relative to N corresponded to the target values, but the Ca:N and Mg:N ratios were much higher, indicating luxury consumption of theses elements. A similar trend was observed for foliar nutrient ratios calculated from published data on a wide range of plant species. The DRIS appears useful for diagnosing the nutrient status, provided accurate DRIS norms are used and indices are interpreted correctly. In most cases, the diagnosis made using the DRIS indices was confirmed with the optimal ratio approach. Diagnoses made using these techniques indicated that foliar P and K concentrations were sub-optimal at age four years. The results from this trial suggest that there was an apparent temporal separation of resource limitation experienced at this site. Initially, the trees appeared to be constrained by nutrient availability, whereas water was potentially more limiting to growth than nutrient supply at age four years. However, it is highly unlikely that irrigation of forest species would ever be implemented on a operational scale in this country. Rather than pursuing the potential reponses that could be obtained with unlimited water availability, the forest industry in South Africa would benefit greatly from improved fertiliser recommendations. On the basis of the optimal foliar technique and the DRIS approach, foliar ratios of 100 N: 8 P: 35 K: 2.5 Ca: 4 Mg are suggested for optimal growth of E.grandis trees.

Uma dificuldade para o manejo adequado da irrigação em espécies de plantas perenes, como por exemplo num pomar, é determinar o momento e a quantidade de água que deverá ser aplicada. Há vários métodos tradicionais de medida de consumo diário de água, assim como indicadores do déficit hídrico, mas cada um apresenta seu grau de dificuldade de uso no campo que levam, às vezes, à aproximações pouco exatas. Diante destes problemas e levando em consideração a importância dos citros na economia nacional, o presente trabalho teve dois objetivos principais: a) avaliar dois métodos de determinação de fluxo de seiva para a estimação da taxa de transpiração diária de plantas de lima ácida 'Tahiti' e, b) avaliar o uso da contração radial do ramo ou caule (utilizando um dendrômetro de precisão) e da transpiração relativa da planta (estimada a partir do fluxo de seiva), como indicadores vegetais diretos de deficiência hídrica. Para atingir estes objetivos, foram instalados experimentos em dois pomares, um de plantas jovens e outro de plantas adultas, de lima ácida 'Tahiti'. Os métodos de determinação da transpiração (fluxo de seiva) foram o de balanço de calor (BC) e o da sonda de dissipação térmica (SDT). A comparação entre os dois métodos em um ramo de uma planta adulta, e a comparação do SDT com medidas lisimétricas em plantas jovens, demonstrou o bom desempenho de ambos e sua possibilidade de uso na quantificação da transpiração em citros, principalmente como subsídio à irrigação localizada. No BC há necessidade de precauções para minimizar erros devidos à variações espúrias que os valores de fluxo de seiva sofrem ao longo do período matinal ou de superestimativas no período noturno. No caso da SDT, uma fonte de erro que causa subestimativa é a ocorrência de gradiente térmico natural no caule/ramos nas regiões de medida da sonda, com necessidade de corrigir o erro para medidas mais acuradas. A SDT mostra-se uma técnica confiável e de vantagens em relação ao BC, pela menor complexidade e custo. As variáveis dendrométricas do caule/ramos, recomendadas na bibliografia como indicadoras de estresse hídrico (variação da amplitude diária de contração, da diferença em dias subsequentes do diâmetro máximo e do diâmetro mínimo), mostraram-se problemáticas, pela complexa relação que apresentam com a disponibilidade hídrica no solo, demanda evaporativa do ar e tamanho do caule. A análise da evolução do diâmetro máximo diário e, também, do diâmetro médio mostrou potencialidade de uso como técnica indicadora de estresse hídrico. No entanto, recomenda-se estudos mais aprofundados que considerem regimes hídricos do solo diferenciados e com imposição de secagem mais acentuada, além de se levar em conta características próprias de resposta de espécies cítricas à disponibilidade hídrica do solo e à demanda atmosférica. A transpiração relativa, expressa pela relação entre a transpiração atual e a transpiração máxima (calculada por unidade de área foliar), guardou relação com a variação da disponibilidade hídrica do solo, mas comparada à análise da evolução do diâmetro máximo do caule, mostrou-se menos estável. / A difficulty for the appropriate handling of irrigation of perennial plants like orchards is to determine the moment when and the amount of water that should be applied. There are several traditional methods to determine water nsumption, as well as indicators of water stress.However, they all have difficulties when used in the field because their approaches are not very accurate. Taking into consideration these problems and the importance of citrus in the economy of the state of São Paulo, the present work had two main objectives: a) to evaluate two methods for the estimation of sap flow in the determination of the daily rate of transpiration of plants of 'Tahiti' lime and b) to evaluate the use of the variation of the stem/branches diameter (by using a precision dendrometer) and the relative transpiration (estimated starting from the sap flow) as direct plant indicators of water stress. To reach these objectives, experiments were set up in two orchards of 'Tahiti' lime, one of young plants and another of adult plants. The methods for the determination of the transpiration (sap flow) were: the heat balance method (HBM) and the heat dissipation probe method (HDPM). The comparison between the two methods in a branch of an adult plant and the comparison of HDPM with lisimeter measurements in young plants demonstrated the accuracy of both methods for the quantification of the transpiration in citrus, mainly as a tool for located irrigation. With HBM, precautions should be taken to minimize errors due to spurious variations of sap flow values along the morning or overestimation of the values during night. With HDPM, the occurrence of a natural thermal gradient in the branch or stem is an error source that causes underestimation and that should be taken into account for accurate estimations. HDPM has shown to be a reliable technique with advantages over HBM for its less complexes and lower cost. The use of dendrometric variables of the stem (the variation of the daily contraction, the maximum diameter and the minimum diameter), in the literature recommended as indicative of water stress, is problematic because of the complex relationship that they have with the soil water status, the atmospheric water demand and the size of the stem. The analysis of the evolution of the daily maximum diameter and also, of the mean diameter are potential indicative techniques of plant water stress. However, more profound studies under different soil moisture regimes, with imposition of severe drying of the soil, that also take into account specific response characteristics of citrus species to the soil water status and the atmospheric water demand are needed. The relative transpiration (RT), expressed by the relationship between the current transpiration and the maximum transpiration (calculated by unit of leaf area), was related to the soil water status variation. However, its relation with the analysis of the evolution of the maximum diameter of the stem was less stable.

A recuperação e a restauração florestal de ecossistemas degradados podem não acontecer das maneiras desejadas, se houver carência nutricional ou suprimento inadequado de nutrientes às plantas no estádio inicial de desenvolvimento de espécies florestais nativas. O objetivo da presente investigação foi avaliar os efeitos da deficiência de nutrientes nas plantas na fase inicial de desenvolvimento das espécies florestais nativas Schinus terebinthifolius Raddi (aroeira-pimenteira), Cordia superba Cham. (baba-de-boi) e Cariniana estrellensis (Raddi) Kintze (jequitibá-branco). Foram observadas as alterações ultra-estruturais e teciduais das células do mesofilo das folhas, foi descrita a sintomatologia visual de deficiência nutricional, foram feitas as determinações de teores de macro e micronutrientes, das taxas de assimilação de gás carbônico e de transpiração, e as mensurações da altura e da produção de biomassa. O experimento foi conduzido em casa de vegetação, em blocos ao acaso, com três repetições e treze tratamentos para cada espécie, empregando a técnica de diagnose por subtração (-N, -P, -K, -Ca, -Mg, -S, -B, -Cu, -Fe, -Mn, -Mo, -Zn), sendo que em um dos tratamentos, as espécies nativas foram cultivadas em solução nutritiva completa, com todos os macros e micronutrientes. Durante o experimento e em sua análise, foi observada a seqüência de eventos que motivaram os sintomas de deficiência e a diminuição na produção de biomassa. Sabe-se que falta de um nutriente provoca alteração molecular, o que alterou as ultraestruturas celulares das folhas que foram observadas por microscopia. Essas modificações celulares provocaram alterações no tecido vegetal que induziram nas plantas os sintomas visuais específicos de cada nutriente que foram descritos. Como efeito fisiológico da deficiência nutricional, de forma geral, constataram-se diminuições nas taxas de fotossíntese e de transpiração e, por conseguinte, na produção de biomassa. Estes resultados claramente evidenciam o fato de que projetos de implantação de florestas ou de recuperação e restauração de ecossistemas degradados por meio do plantio das três espécies florestais nativas, em solos que necessitem de suplementação nutricional, poderão ter seu sucesso comprometido se não houver complementação nutricional / The recovery and forest restoration of degraded ecosystems may not be occur as desired if there is a nutritional deficiency or an inadequate supply of nutrients in the initial phase development of native forest species. The objective of this research was to evaluate the macronutrient and micronutrient deficiency effects on Brazilian native species young plants: Schinus terebinthifolius Raddi, Cordia superba Cham. and Cariniana estrellensis (Raddi) Kintze. Ultrastructural and tissue of the mesophyll cells of leaves changes were observed by microscopy, the visual symptom of nutritional deficiencies were described, the nutrient contents were analyzed, the carbon assimilation and transpiration rates were measured, the plant heights and the biomass production were measured. The experiment was carried on a greenhouse in a randomized block design with three replications and thirteen treatments for each species, using the technique of diagnosis by subtraction (-N, -P, -K, -Ca, -Mg, -S, -B, - Cu, -Fe, -Mn, -Mo, -Zn) and in one of the treatments the species were grown in a nutrient solution with all macro and micronutrients. It was observed, during the experiment and its analysis, a sequence of events that caused the visual symptoms and decreased the biomass production. It is known that the nutrient deficiency causes molecular alterations, which consequently led the changes in cellular ultrastructure of the leaves and they were observed by microcopy. These cellular changes caused modifications in the foliar tissue, and the plants showed specific visual symptoms of each nutrient, which they were described. As physiological effect of nutritional deficiency, in general decreases the photosynthesis and transpiration taxes, and consequently the biomass production were decreased. These results clearly project that forest implantation or recovery and restoration of damaged ecosystems by planting the three native species in soils that require nutritional supplementation may have its success compromised if there is no a nutritional supplementation

A cultura da cana é importante para o agronegócio brasileiro. O manejo adequado da palhada da cana-de-açúcar no solo pode influenciar no desenvolvimento e no crescimento da cultura, podendo resultar em ganhos ambientais e econômicos. Neste trabalho, objetivou-se avaliar o efeito do manejo com palha (CP) e sem palha (SP) na evapotranspiração de um canavial irrigado. Um experimento foi conduzido em canavial irrigado com dois tratamentos (mantendo-se 100% da palhada e sem cobertura de palha sobre o solo). Neste experimento, a evapotranspiração foi medida a partir do balanço hídrico \"in situ\" do solo (ETc-BHS) e pelo método da razão de Bowen (ETc-MRB) e a transpiração utilizando-se sensores de fluxo de seiva (FS). A evaporação do solo foi estimada com base em dados da cultura e meteorológicos. A modelagem da transpiração e de seus componentes baseou-se na abordagem no \"modelo da grande folha\" (\"big leaf model\") proposto por Monteith. Para tanto, foram definidos e avaliados submodelos para a simulação do saldo de radiação no dossel, da resistência aerodinâmica, da resistência de cobertura no ambiente da cultura. Ao longo do ciclo da cultura, análises biométricas foram realizadas a cada 30 dias e esses dados utilizados na parametrização do modelo. O desempenho dos submodelos e do modelo parametrizado de Penman-Monteith (PM) foi estatisticamente avaliados. Avalia-se um modelo para estimativa da evaporação em função da cobertura da palhada. O cultivo de cana-de-açúcar utilizando os resíduos vegetais favorece o incremento da transpiração, da evapotranspiração da cultura (ETc) e reduz a evaporação de água no solo. A palha influenciou as variáveis biométricas da cultura, como perfilhamento, massa fresca da parte aérea (MFPA) e massa seca da parte aérea (MSPA). Ao relacionar a transpiração estimada com o modelo de PM com a medida com FS, verifica-se um coeficiente de determinação (R2) de 0,72 e de 0,48 e um coeficiente angular (a) de 1,22 e 0,92, para a área manejada CP e SP, respectivamente. A evaporação de água no solo é maior na área SP, principalmente nos períodos com precipitações acima de 40 mm. Quando se relaciona a ETc-BHS e a ETc-MRB com a ETc estimada com base no método de PM, nota-se um R2 de 0,67 e 0,54 na área CP e 0,59 e 0,54 para a área SP, respectivamente. Independente do manejo adotado, aos 302 dias após o corte, o canavial apresentou ATR, POL e % de fibra ideal para a comercialização. O teor de clorofila na área manejada CP é superior ao manejado SP. O cultivo de cana-de-açúcar utilizando os resíduos vegetais favorece o incremento da transpiração, da ETc e reduz a evaporação de água no solo. / Cane culture is important for Brazilian agribusiness. Proper management of sugarcane trash in the soil can influence the development and growth of the crop, which can result in environmental and economic gains. The objective of this study was to evaluate the effect of trash management (CP) and without trash (SP) on the evapotranspiration of an irrigated sugar cane. An experiment was conducted in irrigated sugar cane fields with two treatments (100% of the trash and without trash cover on the soil). In this experiment, evapotranspiration was measured from soil water balance (ETc-BHS) and the Bowen ratio method (ETc-MRB) and transpiration using sap flow sensors (FS). Soil evaporation was estimated based on crop and meteorological data. The modeling of the transpiration and its components was based on the approach in the \"big leaf model\" proposed by Monteith. For that, submodels were defined and evaluated for the simulation of canopy radiation balance, aerodynamic resistance, and cover resistance in the culture environment. Throughout the crop cycle, biometric analyzes were performed every 30 days and these data were used in the parameterization of the model. The performance of the submodels and the parameterized model of Penman-Monteith (PM) was statistically evaluated. A model for estimation of evaporation is evaluated as a function of the trash cover. The cultivation of sugarcane using the vegetal residues favors the increase of transpiration, evapotranspiration of the crop (ETc) and reduces the evaporation of water in the soil. The trash influenced the biometric variables of the crop, such as tillering, fresh mass of aerial part (MFPA) and dry mass of aerial part (MSPA). When correlating the estimated transpiration with the PM model with the FS measurement, it is verified a determination coefficient (R2) of 0.72 and 0.48 and an angular coefficient (a) of 1.22 and 0.92, for the managed area CP and SP, respectively. The water evaporation in the soil is higher in the SP area, especially in periods with rainfall above 40 mm. When ETc-BHS and ETc-MRB are related to ETc estimated on the basis of the PM method, an R2 of 0.67 and 0.54 is observed in the CP area and 0.59 and 0.54 for the area SP, respectively. Regardless of the management adopted, at 302 days after cutting, the sugarcane plantation presented ATR, POL and% of fiber ideal for commercialization. The chlorophyll content in the managed area CP is superior to the managed SP. The cultivation of sugarcane using the vegetal residues favors the increase of the transpiration, ETc and reduces the evaporation of water in the soil.

O estudo caracterizou as variáveis fisiológicas da fotossíntese, em 7 clones de Eucalyptus de alta produtividade, determinando-se as capacidades fotossintéticas máximas (Amax), e o comportamento da fotossíntese (A), condutância (gs) e transpiração (E) em relação ao Déficit de Pressão de Vapor (DPV). Para isso, um ensaio foi instalado em 2004, na ESALQ/USP, contendo os clones do Projeto BEPP (Brasil Eucalyptus Produtividade Potencial), sendo cada parcela composta de 49 plantas (7x7) no espaçamento de 3,0m x 2,7m. Mediram-se as alturas ou DAPs e selecionaram-se 3 árvores médias para as mensurações fisiológicas, aos 16 e 36 meses. A amostragem para Amax foi composta de duas posições superiores da copa (2 e 3), dois galhos por posição e duas folhas por galho. As medições foram feitas das 8 às 10 horas (baixo DPV). Para o comportamento de A e gs frente ao DPV, as medições continuaram, de hora em hora, das 11 às 15 horas, nas folhas do primeiro galho da posição 2. Ao final as folhas foram coletadas para determinação da área foliar específica (AFE) e do nitrogênio (N). Aos 16 meses, foram feitas curvas A/Ci, para posterior cálculo de Vcmax (taxa máxima de carboxilação), Jmax (taxa máxima de transporte de elétrons) e VTPU (utilização da triose fosfato), pelo programa Photosyn Assistant. As curvas foram feitas em 2 árvores por clone, nas posições superiores e inferiores da copa. Todas mensurações foram realizadas com o aparelho LiCor-6400. Os resultados mostraram que Amax foi similar para as posições 2 e 3. Entre os clones, houve variação, porém não consistente entre idades, e todos mostraram altos valores de Amax na idade de 16 meses (entre 26 e 31, com média de 29 µmol m-2s-1), reduzindo-se aos 36 meses (entre 19 e 26, com média de 22 µmol m-2s-1). A AFE e o N também foram similares entre as posições 2 e 3 e maiores na idade mais jovem (11 versus 8 m²kg-1, 29 versus 21 gN kg-1), podendo estar associados à queda de Amax. A, gs e E também apresentaram menores valores aos 36 meses, para todos os clones (23 versus 18 µmol m-2s-1; 0,41 versus 0,26 mol m-2s-1; 9,2 versus 6,1 mmol m-2s-1). Os clones mostraram sensibilidade ao DPV, reduzindo os valores de gs e A ao longo do dia, sendo a sensibilidade menor aos 36 meses. As sensibilidades foram distintas, evidenciando potencial de seleção de materiais mais aptos a tolerarem estresse hídrico. Em geral, maiores valores de fotossíntese estão relacionados a maiores valores de transpiração, evidenciando a necessidade de se conhecer a disponibilidade hídrica local quando do uso de clones de alta produtividade. Vcmax, Jmax e VTPU foram maiores para as posições superiores da copa, e não diferiram entre os clones. Devido à semelhança fisiológica entre as posições 2 e 3, pode-se sugerir que não haja distinção entre elas em futuras medições de fotossíntese, essenciais para a parametrização de modelos. Não houve relação direta entre crescimento do tronco e fotossíntese, evidenciando a necessidade de integração com estudos relacionados à alocação do carbono dentro da planta. / This study aimed to characterize the physiological variables related to photosynthesis, in seven commercial Eucalyptus clones with high productivity, by evaluating maximum photosynthetic capacity (Amax), and the response of photosynthesis (A), stomatal conductance (gs) and transpiration (E) to Vapor Pressure Deficit (VPD). A trial was installed in 2004, at ESALQ/USP, with the clones that were part of BEPP Project (Brazil Eucalyptus Potential Productivity), and each plot had 49 plants (7x7) in a 3 m x 2.7m spacing. We measured tree height or DBHs and three average trees were selected for measurements, at 16 and 36 months. The sample to estimate Amax was: two crown positions (2 and 3), two branches per tree and two leaves per branch. The measurements which were taken from 8 to 10 am (low VPD). To get the response of A and gs to VPD measurements continued hourly, from 11 am to 3 pm, on the leaves from the first branch and position 2. At the end of the measurements leaves were collected for specific leaf area (SLA) and nitrogen (N) determination. Additionally, at 16 months, A/Ci curves were established, and parameters Vcmax, Jmax and VTPU were estimated through the program Photosyn Assistant. The curves were done for 2 trees per clone, at superior crown positions (2 and 3) and inferior ones (4 and 5). The physiological measurements and A/Ci curves were made using LiCor-6400. The results showed that Amax was similar for positions 2 and 3. There was variation among clones, but not consistent between ages, and all the clones had high Amax at 16 months (between 26 and 31 µmol m-2s-1, with an average of 29 µmol m-2s-1), decreasing at 36 months (between 19 and 26 µmol m-2s-1, with an average of 22 µmol m-2s-1). SLA and N were also similar between positions 2 and 3 and higher at younger age (11,1 versus 8,3 m²kg-1, 29,6 versus 21,1 gN kg-1;), what may be associate with Amax decrease. A, gs and E also showed lower values at age 36, for all the clones (23 versus 18 µmol m-2s-1; 0,41 versus 0,26 mol m-2s-1; 9,2 versus 6,1 mmol m-2s-1). All clones showed sensitivity to VPD, reducing gs and A with increasing VPD. However, the clones showed different sensitivities and all of them were less sensitive to VPD at age 36, highlighting a selection potential of genetic materials for water stress. In general, higher photosynthesis values were associated with higher transpiration, showing the necessity to know the water conditions of sites when planting genetic materials with high productivity. Vcmax, Jmax and VTPU were greater for superior positions compared to inferior ones, and were not different among clones. Due to a similarity in SLA, N and physiological and biochemical traits between positions 2 and 3, no distinction on future photosynthesis measurements between these positions is needed. Finally, there was not a direct relation between stem growth and photosynthesis, at both ages, showing that photosynthesis at crown level by itself can not capture all the ecophysiological processes related to wood productivity, being necessary the integration with studies related to carbon allocation inside the plant.