The thesis summary is included in the 01front.pdf

Crown architecture affects tree growth through the control of leaf area and its display. Yet the linkages between crown structure, leaf traits, and productivity of elite selections of forest trees and responses to intensive silviculture are not fully understood. It was hypothesized that trees with crown and leaf traits governing efficient light capture and photosynthesis at the canopy scale would be the most productive. To this end, families of loblolly (Pinus taeda) and slash pine (Pinus elliottii) were grown at three experimental sites in the West Gulf Coastal Plain of Texas and Louisiana under two silvicultural treatments, including repeated fertilization with control of competing vegetation (HI), and a control (C) consisting of fertilization at planting. Families and species differed in crown traits and aboveground productivity, and genotype differences increased throughout the first 5 years of stand development. Crown shape was important for light interception and growth initially, but at the onset of canopy closure, crown size, stand leaf area and its distribution within crowns affected canopy light interception and tree growth. Among all families and treatments, aboveground biomass productivity was positively related to absorbed photosynthetically active radiation (APAR) and canopy photosynthesis. Light-use efficiency (ε) varied from 0.41 to 0.56 g MJ-1 among families and was lowest in slash pine. Variability in aboveground biomass growth was related more to stand leaf area and APAR than to differences in light-use efficiency in these young stands. Leaf physiological, chemical and morphological attributes changed within crowns in accordance with developing light availability gradients. Physiological attributes, such as net photosynthesis, were better predictors of family performance when integrated at the canopy level than leaf level in the examined pine species. Crown size, light absorption, and aboveground growth generally ranked higher in the HI treatment than in the control, although the effects of the intensive silvicultural treatments did not differ statistically. Family performance was independent of treatment. Crown and canopy attributes, such as high leaf area index and large crowns with low leaf area density per crown volume, may be useful in the selection of highly productive genotypes of loblolly and slash pine under intensive silviculture.

La captación de carbono por la vegetación es a escala global el flujo más grande de CO2 e influencia en gran medida el funcionamiento de los ecosistemas. Sin embargo, su variabilidad temporal y espacial sigue siendo poco conocida y difícil de estimar. Las técnicas de teledetección pueden ayudar a calcular mejor la producción primaria bruta (GPP) terrestre, que es la expresión a nivel de ecosistemas del proceso de la fotosíntesis. El objetivo principal de esta tesis fue encontrar una manera de estimar la variabilidad espacial y temporal de la eficiencia en el uso de la radiación (RUE) a escala de ecosistema y por lo tanto mejorar la estimación de la GPP de la vegetación terrestre por medio de datos de teledetección. Se abordaron cuatro objetivos específicos. El primero fue analizar y sintetizar la literatura científica sobre la relación entre el Índice de Reflectancia Fotoquímica (PRI), un índice espectral vinculado a la eficiencia fotosintética, y diversas variables ecofisiológicas a través de un amplio rango de tipos funcionales de plantas y ecosistemas. El segundo objetivo fue analizar y sintetizar los datos de la variabilidad espacial de la GPP y la variabilidad espacial y temporal de la RUE y sus controles climáticos para un amplio rango de tipos de vegetación, desde la tundra a la selva tropical. El tercer objetivo fue comprobar si diferentes índices espectrales, es decir, el PRI, el NDVI (Normalized Difference Vegetation Index) y EVI (Enhanced Vegetation Index), derivados del Moderate Resolution Imaging Spectroradiometer (MODIS) son buenos estimadores de la captación de carbono a diferentes escalas temporales en un bosque mediterráneo. El cuarto objetivo fue evaluar el uso de MODIS PRI como estimador de la RUE en un amplio rango de tipos de vegetación mediante el uso de datos sobre la captación de carbono de la vegetación derivados de las torres de covarianza turbulenta.Las principales conclusiones de esta tesis son que hay una coherencia emergente de la relación RUE-PRI que sugiere un sorprendente grado de convergencia funcional de los componentes bioquímicos, fisiológicos y estructurales que afectan la eficiencia de captación de carbono a escala de hoja, de cobertura y de ecosistemas. Al complementar las estimaciones de la fracción de radiación fotosintéticamente activa interceptada por la vegetación (FPAR), el PRI permite mejorar la evaluación de los flujos de carbono a diferentes escalas, a través de la estimación de la RUE. Una segunda conclusión apoya la idea de que el funcionamiento anual de la vegetación es más limitado por la disponibilidad de agua que por la temperatura. La variabilidad espacial de la RUE anual y máxima puede explicarse en gran medida por la precipitación anual, más que por el tipo de vegetación. Una tercera conclusión es que, si bien EVI puede estimar el incremento diametral anual de los troncos, y el PRI puede estimar la fotosíntesis neta diaria nivel de hoja y la eficiencia en el uso de radiación, el papel del NDVI es más limitado como un estimador de cualquier parte del ciclo del carbono en bosques mediterráneos. Por lo tanto, el EVI y el PRI son excelentes herramientas para el seguimiento del ciclo del carbono en los bosques mediterráneos. Por último, el PRI derivado de información satelital disponible libremente, presenta una relación positiva significativa con la RUE para un amplio rango de diferentes tipos de bosques, incluso en años determinados, en bosques caducifolios. En general, esta tesis proporciona un mejor entendimiento de los controles espacial y temporal de la RUE y abre la posibilidad de estimar RUE en tiempo real y, por tanto, la captación de carbono de los bosques a nivel de ecosistemas a partir del PRI. / Carbon uptake by vegetation is the largest global CO2 flux and greatly influences the ecosystem functions. However, its temporal and spatial variability is still not well known and difficult to estimate. Remote sensing techniques can help to better estimate the terrestrial gross primary production (GPP), that is the ecosystem level expression of the photosynthesis process or the rate at which the ecosystem's producers capture CO2. The main objective of this thesis was to find a way to estimate the spatial and temporal variability of the Radiation Use Efficiency (RUE) at the ecosystem scale and therefore to arrive to more accurate ways to estimate GPP of terrestrial vegetation by means of remotely sensed data. Four specific objectives were addressed in this thesis. The first objective was to examine and synthesize the scientific literature on the relationships between the Photochemical Reflectance Index (PRI), a narrow-band spectral index linked to photosynthetic efficiency, and several ecophysiological variables across a wide range of plant functional types and ecosystems. The second objective was to analyze and synthesize data for the spatial variability of GPP and the spatial and temporal variability of the RUE and its climatic controls for a wide range of vegetation types, from tundra to rain forest. The third objective was to test whether different spectral indices, i.e. PRI, NDVI (Normalized Difference Vegetation Index) and EVI (Enhanced Vegetation Index), derived from the MODerate resolution Imaging Spectroradiometer (MODIS) can be indicators of carbon uptake at different temporal scales by analyzing the relationships between detailed ecophysiological variables at the stand level in a Mediterranean forest. The fourth objective was to assess the use of MODIS PRI as surrogate of RUE in a wide range of vegetation types by using data on carbon uptake of the vegetation derived from eddy covariance towers. The main conclusions of this thesis are that there is an emerging consistency of the RUE-PRI relationship that suggests a surprising degree of functional convergence of biochemical, physiological and structural components affecting leaf, canopy and ecosystem carbon uptake efficiencies. By complementing the estimations of the fraction of photosynthetically active radiation intercepted by the vegetation (fPAR) PRI enables improved assessment of carbon fluxes at different scales, through the estimation of RUE. A second conclusion supports the idea that the annual functioning of vegetation is more constrained by water availability than by temperature. The spatial variability of annual and maximum RUE can be largely explained by annual precipitation, more than by vegetation type. A third conclusion is that while EVI can estimate annual diametric wood increment, and PRI can estimate daily leaf level net photosynthesis and radiation use efficiency, the role NDVI is more limited as a surrogate of any part of the carbon cycle in this type of forest. Therefore, EVI and PRI are excellent tools for vegetation monitoring of carbon cycle in the Mediterranean forests, the first ones we tested in this thesis. Finally, the PRI derived from freely available satellite information was also found to present significant positive relationship with the RUE for a very wide range of different forest types, even in determined years, the deciduous forests. Overall, this thesis provides a better understanding of the spatial and temporal controls of the RUE and opens the possibility to estimate RUE in real time and, therefore, actual carbon uptake of forests at the ecosystem level using the PRI.Keywords carbon cycle, Normalized Difference Vegetation Index, Enhanced Vegetation Index, Photochemical Reflectance Index, primary productivity, photosynthesis, remote sensing, climatic controls, eddy covariance, radiation use efficiency, terrestrial vegetation.

Crown architecture affects tree growth through the control of leaf area and its display. Yet the linkages between crown structure, leaf traits, and productivity of elite selections of forest trees and responses to intensive silviculture are not fully understood. It was hypothesized that trees with crown and leaf traits governing efficient light capture and photosynthesis at the canopy scale would be the most productive. To this end, families of loblolly (Pinus taeda) and slash pine (Pinus elliottii) were grown at three experimental sites in the West Gulf Coastal Plain of Texas and Louisiana under two silvicultural treatments, including repeated fertilization with control of competing vegetation (HI), and a control (C) consisting of fertilization at planting. Families and species differed in crown traits and aboveground productivity, and genotype differences increased throughout the first 5 years of stand development. Crown shape was important for light interception and growth initially, but at the onset of canopy closure, crown size, stand leaf area and its distribution within crowns affected canopy light interception and tree growth. Among all families and treatments, aboveground biomass productivity was positively related to absorbed photosynthetically active radiation (APAR) and canopy photosynthesis. Light-use efficiency (ε) varied from 0.41 to 0.56 g MJ-1 among families and was lowest in slash pine. Variability in aboveground biomass growth was related more to stand leaf area and APAR than to differences in light-use efficiency in these young stands. Leaf physiological, chemical and morphological attributes changed within crowns in accordance with developing light availability gradients. Physiological attributes, such as net photosynthesis, were better predictors of family performance when integrated at the canopy level than leaf level in the examined pine species. Crown size, light absorption, and aboveground growth generally ranked higher in the HI treatment than in the control, although the effects of the intensive silvicultural treatments did not differ statistically. Family performance was independent of treatment. Crown and canopy attributes, such as high leaf area index and large crowns with low leaf area density per crown volume, may be useful in the selection of highly productive genotypes of loblolly and slash pine under intensive silviculture.

Water availability is a common concern in semi-arid regions, such as Southern Arizona, USA. Hydroponic greenhouse crop production greatly reduces irrigation water use, but the study of water use by evaporative cooling has been limited.This project investigated water use by two evaporative cooling systems: pad-and-fan and high-pressure-fog with fan ventilation. All studies were performed in a double-layer polyethylene film-covered greenhouse (28 x 9.8 x 6.3 m) with mature tomato plants (2.9 plants m-2). Water use efficiency (WUE, kg yield per m3 water use) was calculated daily according to ventilation rate, as well as for a 6-month croppipng period, which used temperature-controlled pad-and-fan cooling.Pad-and-fan water use was 3.2, 6.4, 8.5, and 10.3 L m-2 d-1 for ventilation rates of 0.016, 0.034, 0.047, 0.061 m3 m-2 s-1, respectively. High-pressure-fog water use with a single central, overhead line was 7.9, 7.4, and 9.3 L m-2 d-1 for ventilation rates of 0.01, 0.016, 0.034 m3 m-2 s-1, respectively. For pad-and-fan ventilation rates less than 0.034 m3 m-2 s-1, total greenhouse WUE (20 - 33 kg m-3) was similar to field drip irrigation. For the temperature-controlled high-pressure-fog system, total greenhouse WUE (14 - 17 kg m-3) was similar to field sprinkler irrigation.For the 6-month crop cycle, combining water use by closed irrigation and pad-and-fan systems produced a total WUE of 15 kg m-3. Pad-and-fan WUE increased during monsoon conditions due to lower water use rates.Evaporative cooling water use and air temperature were well-predicted by the energy balance model. Predictions of air temperature improved when outside climate the measured conditions at one greenhouse location. Wind tunnel and full-scale studies of natural ventilation demonstrated the value of knowing airflow patterns when designing and operating a high-pressure-fog systemIt is possible for greenhouse tomato production to have a higher WUE than field production, if ventilation rates are not excessive, if closed irrigation is used, and if control methodologies are improved. Water use can be minimized by knowing how the evaporative cooling system affects greenhouse climate and plant responses.

No description available.

A two-year field study and two incubation studies were conducted to evaluate incorporating urea with a urease and nitrification inhibitor to reduce N2O and N losses from fall banded fertilizer. In each year of the field experiment, five fertilizer treatments (fall banded NBPT-DCD urea, conventional urea, calcium nitrate, spring banded conventional urea and control) were applied at three sites. The effect of incorporating urease and nitrification inhibitors with urea was not consistent in our studies. The application of fall banded NBPT and DCD did not result in greater agronomic performance. Moreover, the addition of inhibitors to urea did not reduce nitrous oxide emissions in the field. The addition of inhibitors resulted in significantly less cumulative nitrous oxide emissions compared to conventional urea in only one of two laboratory experiments. In conditions where fertilizer was not generally susceptible to large losses, the effects of urease and nitrification inhibitors may not be evident.

Hog manure phosphorus (P) can be recovered as struvite or magnesium ammonium phosphate hexahydrate (MgNH4PO4∙6H2O). The recovered struvite has slow-release properties and may be used as a P-source for crops. Two pot experiments were conducted to evaluate the agronomic effectiveness and seedling toxicity of liquid hog manure-recovered struvite for canola (Brassica spp.) and wheat (Triticum aestivum). While wheat was non-responsive to P application, canola dry matter yield (DMY) from struvite (1.9 g kg-1) was similar to that from monoammonium phosphate (MAP) (1.8 g kg-1) and coated-monoammonium phosphate (CMAP) (1.7 g kg-1). Importantly, when P was seed-placed at the higher rate (15 mg kg-1), canola seedling emergence was significantly greater with struvite (90%) and CMAP (85%) than with MAP (60%). The results demonstrate the potential of struvite as an effective P-source for canola in P-deficient soils, which can be safely applied at higher rates than those currently recommended for seed-placed MAP.

A two-year field study and two incubation studies were conducted to evaluate incorporating urea with a urease and nitrification inhibitor to reduce N2O and N losses from fall banded fertilizer. In each year of the field experiment, five fertilizer treatments (fall banded NBPT-DCD urea, conventional urea, calcium nitrate, spring banded conventional urea and control) were applied at three sites. The effect of incorporating urease and nitrification inhibitors with urea was not consistent in our studies. The application of fall banded NBPT and DCD did not result in greater agronomic performance. Moreover, the addition of inhibitors to urea did not reduce nitrous oxide emissions in the field. The addition of inhibitors resulted in significantly less cumulative nitrous oxide emissions compared to conventional urea in only one of two laboratory experiments. In conditions where fertilizer was not generally susceptible to large losses, the effects of urease and nitrification inhibitors may not be evident.

The introduction of dwarfing genes in wheat and rice enabled significant yield improvements and was later termed the “Green-Revolution”. Dwarfing genes in sorghum have not been accompanied by such increases in grain production. On the contrary, some of the commercially employed dwarfing genes in sorghum have been associated with negative effects on grain yield. A positive correlation between plant height and grain yield was also observed in trial data for a diverse range of hybrids tested within the Queensland Department of Primary Industries and Fisheries Sorghum Breeding Program in north-eastern Australia. No attempts have previously been made to examine the physiological basis of the relationship between plant height and grain yield in sorghum. The dwarfing genes that are commercially used in wheat, Rht-B1 and Rht-D1 (formerly known as Rht1 and Rht2, respectively), on the other hand, have been studied extensively. They have been shown to have substantial and positive effects on grain number and harvest index, while not considerably reducing plant biomass, increasing grain yield. Our objective in this study was to examine the effect of height on the physiological and genetic determinants of growth and yield in sorghum to determine whether there was scope to improve yield by increasing the height of sorghum. A positive correlation between plant height and yield was observed in a population that was fixed for the major dwarfing genes, but showed variation in peduncle and panicle length, which are under control of minor dwarfing genes. To study the effects of a single major dwarfing gene (dw3) on biomass production and grain yield, 2- and 3-dwarf isogenic contrasts were developed in three different genetic backgrounds (R931945-2-2, R955343-1, R955637). In some cases, dw3 led to a significant reduction in plant biomass, which was not sufficiently offset by increase in harvest index to avoid yield reduction. This is contrary to the situation in wheat. The observed reductions in plant biomass in sorghum were associated with reduced tiller number and a reduction in radiation use efficiency (RUE) in the short types. Subsequent experiments suggested that an increase in allocation of biomass to the roots, rather than differences in photosynthetic capacity or respiration, was the main cause for the apparent reduction in RUE. However, due to plant-to-plant variability and the difficulty in accurately measuring root-total biomass ratio, studies with greater replication are required to confirm this hypothesis. It was also found that interactions with genetic background (and environment) moderated the effects of dw3, resulting in smaller height, biomass and grain yield reductions in some isogenic pairs. The effects of dwarfing genes on grain yield therefore need to be assessed separately for different genetic backgrounds. As lodging may be controlled by means other than height reduction (e.g. stay-green), we suggest that yield of standard sorghum types used in industrialised countries may benefit from moderate increases in plant height.