An understanding of ecosystem-level carbon (C) sequestration, or net ecosystem production (NEP), requires the separation of heterotrophic, microbial respiration (RH) from autotrophic, root-derived respiration (RA) as the components of RS (i.e., NEP = NPP - RH). However, separating these two sources in situ has been problematic since they are closely coupled. This study utilizes two similarly aged Pinus taeda L. stands, 8 and 9 years-old, aimed at quantifying these two respiration components through in-situ root severing. In order to use root-severing treatments to separate RS into RH and RA components, confirmation of carbohydrate depletion coupled to RA decline is crucial. This study evaluated the changes in CO2 flux rates and carbohydrate supply upon root severing in Pinus taeda L. using a controlled laboratory validating a two-part field study. The first field study used root-severing cores to test in-situ if respiration components can be attained based on the depletion of carbohydrate supply. The second field study was aimed at how future changes in climate might affect the ability of forests to store C and how modern forestry practices might affect changes and was conducted over the course of two installations, spring and summer 2012. In this study we examined the effects of fertilization (0 and 100.9 kg N ha-1 ) and throughfall reduction (0 and -30%) on total soil respiration (RS) as well as the heterotrophic contribution to RS, in a fully replicated (n=4), 2x2 factorial design. In the controlled lab experiment RS and RA declined by 86% and 95% respectively by the end of an 86 day trial and NSC carbohydrates declined by 60% for soluble, 29% for insoluble, and 43% for total (soluble + insoluble). The decline of RA was highly correlated to with the decline of NSC’s at 0.90, 0.69 and 0.93 for soluble, insoluble and total, respectively. The companion field study revealed a mean decrease 21±0.5% of over the final three dates when severed root respiration stabilized. In the second study, testing throughfall reduction and fertilization levels there were no fertilization by throughfall reduction interactions on the contribution of RH to RS in either the spring or summer; however, the main effect of throughfall reduction was significant in the spring. During the spring, the mean contribution of RH to RS for ambient throughfall plots was 96±6.4%, while the mean contribution under throughfall reduction was 68±1.9%. During the summer, there were no differences among treatments and the overall contribution of RH to RS was 78±1.6%. Collectively, both of these studies revealed that the severing of roots from their primary energy source and the subsequent depletion of stored NSC that the use of in-situ methods allows for the quantification of soil respiration components RA and RH. Using these estimates to model NEP in the short-term can be variable by season, however, long-term monitoring may simplify future NEP modeling scenarios / Master of Science

Due to concern over the increasing concentration of carbon dioxide in the atmosphere, forest researchers and managers are currently studying the effects of varying silvicultural and harvesting practices on the carbon dynamics of intensely managed forest ecosystems. Soil carbon dioxide efflux resulting from soil microbial activity and root respiration is one of the major components of the total carbon flux in forested ecosystems. In an effort to examine the response of soil carbon dioxide efflux to changes in soil factors, nutrient availability, temperature, and moisture, soil respiration rates were measured monthly over an entire year in a two-year-old loblolly pine (Pinus taeda L.) plantation subjected to fertilization and mulching treatments. A dynamic, closed-chamber infrared gas analysis system was used to measure efflux rates from plots treated with one of four treatment combinations including: nitrogen (115 kg/ha) and phosphorus (11.5 kg/ha) fertilization with black landscape cloth (mulch), fertilization without mulch, mulch without fertilization, and no treatment (control). For each treatment combination, plots were established at the seedling base and 1.22 m away from the seedling base to examine the effect of seedling roots on soil carbon dioxide efflux rates. Soil temperature and moisture were measured at each chamber position monthly and soil coarse fragments, soil nutrient levels, percent carbon, root biomass and coarse woody debris were measured beneath 64 chambers at the end of the study. Fertilization had no significant effect on efflux rates during any of our monthly sampling sessions despite the fact that fertilized seedlings experienced significant increases in both above and belowground biomass. Conversely, regression analysis of growing season soil carbon dioxide efflux rates revealed a slightly negative correlation with both total seedling nutrient uptake and biomass. Rates in plots with mulching were significantly higher than rates from non-mulched plots during five monthly measurement sessions, and higher rates in mulched plots during winter months was attributable to warmer soil temperatures. Rates at the seedling base were always significantly higher than rates in plots away from the seedling. Although rates were always higher at the seedling base, the variability observed was only weakly correlated with the amount of pine roots present beneath respiration chambers. Utilizing soil temperature and moisture, soil carbon, and cuvette fine root biomass in a regression model explained 54% of the variance observed in efflux rates across the yearlong study period. Soil temperature alone explained 42.2% of the variance, followed by soil carbon and soil moisture at 5.2% and 2.7% respectively. The amount of pine fine roots under measurement chambers accounted for only 2.4% of the variance. An additional 1.5% was explained by other factors such as soil phosphorus, coarse woody debris, non-pine root biomass, and soil calcium. An examination of the factors affecting the spatial patterns of soil carbon dioxide efflux revealed that total soil carbon and the amount of fine pine root biomass beneath cuvette base rings explain 38% and 11% respectively, of the observed variability in mean annual soil carbon dioxide efflux from differing plots. The most influential factor affecting soil carbon dioxide efflux during the yearlong study period was soil temperature and modeling of seasonal soil carbon dioxide efflux rates from managed forests using both soil temperature and moisture should be achievable with the establishment of data sets and statistical models covering a range of sites differing in productivity, stand age, and management intensity. The establishment of data sets and statistical models across a variety of forest sites should account for the changing influence of soil carbon levels, aboveground biomass, microbial activity, organic matter inputs, and root biomass on soil carbon dioxide efflux. / Master of Science

The response of global soil respiration (Rs) to climate change determines how long the land can continue acting as a carbon sink in the future. This dissertation research identifies how temporal and spatial variation in environmental factors affects global scale Rs modeling and predictions of future Rs under global warming. Chapter 1 describes the recommend time range for measuring Rs across differing climates, biomes, and seasons and found that the best time for measuring the daily mean Rs is 10:00 am in almost all climates and biomes. Chapter 2 describes commonly used surrogates in Rs modeling and shows that air temperature and soil temperature are highly correlated and that they explain similar amounts of Rs variation; however, average monthly precipitation between 1961 and 2014, rather than monthly precipitation for a specific year, is a better predictor in global Rs modeling. Chapter 3 quantifies the uncertainty generated by four different assumptions of global Rs models. Results demonstrate that the time-scale of the data, among other sources, creates a substantial difference in global estimates, where the estimate of global annual Rs based on monthly Rs data (70.85 to 80.99 Pg C yr-1) is substantially lower than the current benchmark for land models (98 Pg C yr-1). Chapter 4 simulates future global Rs rates based on two temperature scenarios and demonstrates that temperature sensitivity of Rs will decline in warm climates where the level of global warming will reach 3°C by 2100 relative to current air temperature; however, these regional decelerations will be offset by large Rs accelerations in the boreal and polar regions. Chapter 5 compares CO2 fluxes from turfgrass and wooded areas of five parks in Blacksburg, VA and tests the ability of the Denitrification-Decomposition model to estimate soil temperature, moisture and CO2 flux across the seasons. Cumulatively, this work provides new insights into the current and future spatial and temporal heterogeneity of Rs and its relationship with environmental factors, as well as key insights in upscaling methodology that will help to constrain global Rs estimates and predict how global Rs will respond to global warming in the future. / Ph. D. / CO₂ flux emitted from global soil is the second largest carbon exchange between the land and atmosphere. Accurately estimating global soil CO₂ flux and how it responds to climate change is critical to predict terrestrial carbon stocks. The objectives of this dissertation are to evaluate how time-scale affects our ability to estimate global soil CO₂ flux. In Chapter 1, we show that the best time period for measuring daily mean soil CO₂ flux is at around 10:00 am in almost all climate regions and vegetation types. The previously recommended time range (09:00 am and 12:00 pm) reasonably captures the daily mean soil CO₂ flux. The results from Chapter 2 indicate that air temperature is a good proxy for soil temperature in modeling global soil CO₂ flux. However, monthly precipitation is a uniformly poor proxy for soil water content; instead, average monthly precipitation is a better predictor for global soil CO₂ flux modeling. Chapter 3 demonstrates that the time-scale used in parameterizing models strongly affects the prediction of global CO₂ flux. When using monthly time-scale soil CO₂ flux and air temperature data, soil CO₂ flux increases as air temperature increases at air temperatures below 27 ℃, but soil CO₂ flux begins to decrease when air temperature is over 27 ℃. However, when using annual time-scale data, this response to temperature is masked, soil CO₂ flux increases as air temperature increases in all temperature conditions. As a result, the estimate of global annual soil CO₂ flux, based on monthly soil respiration data (70.85 to 80.99 Pg C yr⁻¹ ), is lower than the estimate based on the annual soil respiration data (98 Pg C yr⁻¹ ). Chapter 4 shows that if the level of global warming maintains its current rate (3ºC by the year 2100), then the annual soil CO₂ flux will either decrease or remains the same in arid, winter-dry temperate and tropical climate regions. However, these regional decelerations were offset by large soil CO₂ flux accelerations in the boreal and polar regions. Chapter 5 shows a significant difference in CO₂ flux among the five selected parks in Blacksburg, VA. The Denitrification-Decomposition model, despite having been developed for agriculture and undeveloped lands, closely estimates soil temperature, moisture and CO₂ flux across the seasons and therefore can be used to estimate and understand CO₂ fluxes from urban ecosystems in future studies. This study highlights that the relationship between soil CO₂ fluxes and environmental factors such as air temperature and precipitation differs from region to region. The study also demonstrates that daily and monthly time-scale soil CO₂ fluxes and environmental data help constrain global soil CO₂ flux estimates and help to predict how global soil CO₂ fluxes will respond to global warming in the future.

The tropical forests on the island of Borneo are among of the richest in the world in terms of tree diversity, and their capacity to store a large reservoir of carbon. The Southeast Asian forests are fundamentally different from Neotropical and African forests, with their single-family dominance by dipterocarp trees, and with inherently greater stature and biomass. The carbon productivity and allocation in Asian tropical forests is still poorly quantified, and their responses to environmental drivers are still poorly understood. Almost all recent advances in tropical forest carbon cycling research have occurred in the Neotropics, with very few studies in Asia. The principal aim of this thesis is to quantify the carbon budget of a lowland dipterocarp forest in the Lambir Hills National Park, Miri, Sarawak, Malaysian Borneo. I examined and explored the productivity and carbon cycling processes and their responses to environmental factors across two major and contrasting soil types, in particular the clay and sandy loam soils. I recorded and analysed the Net Primary Productivity (NPP) and respiration for the above- and below-ground components, and observed the responses to seasonal variation and environmental drivers. Total soil respiration was relatively high and contributed a great deal to ecosystem respiration. Variation in soil respiration rates appeared closely related to soil moisture content. I found a strong diurnal cycle in soil respiration. On the basis of the first soil carbon dioxide (CO2) efflux partitioning study undertaken in a tropical forest, the diurnal cycle in total soil respiration appeared to be entirely driven by the diurnal cycle in litter respiration, and in turn litter is strongly controlled by moisture. There was little seasonal variation in allocation of net primary productivity (NPP), but there was evidence showing potential inter-annual variability for several components of NPP. Further, the allocation of NPP showed a strong seasonal shift between the forest plots on clay and sandy loam soils. Combining all the data measured and obtained in this D.Phil. thesis, the overall carbon budget assessed in this lowland dipterocarp forest showed a high level of agreement with other studies in Asia using micrometeorological techniques and the situation appears to be comparable to tropical forests in Amazonia. The key difference is that the aboveground NPP is higher and is the largest component contributing to the overall carbon budget, with relatively higher carbon use efficiency (CUE). The lowland dipterocarp forest in Lambir shows higher allocation in the above-ground NPP, and there were also differences in NPP and its allocation between sandy and clay-rich plots.

Land-use change is the single most important global driver of changes in biodiversity. Such changes in biodiversity, in turn, are expected to influence the functioning of ecosystems and their resilience to environmental perturbations and disturbances. It is widely recognised that the use of functional traits and functional diversity is best for understanding the causes and functional consequences of changes in biodiversity, but conceptual development has outpaced empirical applications. This thesis explores these ideas in grazing systems, which are expected to undergo rapid intensification of fertiliser use and grazing pressure to meet the growing global demand for livestock products. First, a flexible framework for measuring different facets of functional diversity is described, and a new multidimensional functional diversity index, called functional dispersion (FDis), is presented. Second, two vegetation sampling methods are compared with regard to their ability to detect changes in vegetation composition. Third, shifts in plant trait distributions following land-use changes are quantified and compared to null models, and a maximum entropy approach is used to quantify the direction and strength of selection on each trait. Fourth, it is shown that these shifts in trait distributions have cascading effects on primary production, litter decomposition, soil respiration, and ultimately soil carbon sequestration. Finally, data from 18 land-use intensity gradients are used to show that land-use intensification reduces functional redundancy and response diversity, two components of biodiversity that are thought to influence ecosystem resilience to future disturbances. This study illustrates (i) the importance of considering species functional differences to understand how plant communities react to changes in soil resource availability and grazing pressure, and (ii) how such changes directly, indirectly, and interactively control ecosystem functioning, as well as (iii) increasing the vulnerability of ecosystems to future disturbances.

A major uncertainty in soil carbon studies is how inputs of fresh plant-derived carbon affect the turnover of existing soil organic matter (SOM) by so-called priming effects. Priming may occur directly as a result of nutrient mining by existing microbial communities, or indirectly via microbial population adjustments. Soil type and conditions may also influence the intensity and direction of priming effects. However the mechanisms are poorly understood. The objectives of this study were (1) to investigate how additions of labile C4 substrate affected SOM turnover in two contrasting unplanted C3 soils (clayey fertile from Temple Balsall, Warwickshire (TB) and sandy acid from Shuttleworth, Bedfordshire (SH) using13 C isotope shifts; (2) to investigate the influence of rhizodeposition from plant roots on SOM turnover in the same two soils planted with a C4 grass; (3) to assess an automated field system for measuring soil temperature, moisture and photosynthesis sensitivities of SOM turnover in the same two soils over diurnal to seasonal time scales. I used a combination of laboratory incubation, glasshouse and field experiments. In the soil incubation experiment, I made daily applications of either a maize root extract or sucrose to soil microcosms at rates simulating grassland rhizodeposition, and followed soil respiration (Rs) and its δ13 C over 19 days. I inferred the extent of priming from the δ13 C of Rs and the δ13 C of substrate and soil end-members. There were positive priming effects in both soils in response to the two substrates. In the SH soil there were no differences in priming effects between the substrates. However in the TB soil, sucrose produced greater priming effects than maize root extract, and priming effects with sucrose increased over time whereas with maize root extract declined after the first week. I explain these effects in terms of the greater fertility of the TB soil and resulting greater microbial nitrogen mineralization induced by priming. Because the maize root extract contained some nitrogen, over time microbial nitrogen requirements were satisfied without priming whereas with sucrose the nitrogen demand increased over time. In the glasshouse experiment, I planted C4 Kikuyu grass (Pennisetum clandestinum) in pots with the same two soils. The extent of rhizodeposition by the plants was altered by intermittently clipping the grass in half the pots (there were also unplanted controls) and priming effects were inferred from the δ13 C of Rs and the δ13 C of plant and soil end-members. Unclipped plants in both soils generated positive priming effects, while clipping reduced priming in TB soil and produced negligible PEs in SH soil. Microbial nutrient mining of SOM again explained the observed PEs in this experiment. Photosynthesis was a major driver of priming effects in the planted systems. In the third experiment, I found that the tested automated chamber system provided reliable measurements of Rs and net ecosystem exchange (NEE), and it was possible to draw relations for the dependency of Rs and NEE on key environmental drivers. Collectively, the results contribute to a better understanding of the mechanisms of priming effects and highlight possibilities for further research. The methods developed here will allow high temporal and spatial resolution measurements of Rs and NEE under field conditions, using stable isotope methods to separate fluxes into plant- and soil-derived components. Keywords: Soil respiration, soil moisture, soil temperature, Isotope ratio, maize root, flux chamber, climate change, organic matter, rhizodeposition.

A dinâmica do C e do N dentro do ecossistema engloba os processos fisiológicos que ocorrem na planta e no solo. Utilizando o sistema Trop-T-FACE no campus da USP de Ribeirão Preto, que combina os sistemas FACE (Free-air carbon dioxide enrichment) e T-FACE (Temperature free-air controlled enhancement), para enriquecimento e controle do CO2 e da elevada temperatura (aquecimento), respectivamente, foram realizados dois experimentos com duas forrageiras tropicais, Stylosanthes capitata Vogel (leguminosa C3) e Panicum maximum Jacq. (gramínea C4). O primeiro experimento envolveu o aquecimento de 2°C no dossel de plantas S. capitata Vogel e resultou em uma intensificação do ciclo do N em curto prazo provavelmente devido à uma maior fixação biológica de N2 pela leguminosa, além de maiores taxas respiratórias do solo e reduzidas taxas de atividade enzimática do solo. No segundo experimento, plantas de S. capitata e P. maximum foram submetidas a quatro tratamentos: controle, com condições de CO2 e temperatura ambiente; aquecimento de 2°C e concentração de CO2 ambiente (eT), temperatura ambiente e concentração de CO2 elevada em 600 µmol mol-1 (eC) e aquecimento de 2°C e concentração de CO2 elevada em 600 µmol mol-1 (eC+eT). Os resultados da respiração do solo indicaram um efeito do aquecimento sobre os processos biológicos do solo devido ao aumento das temperaturas do solo. Análises isotópicas das plantas mostraram, a partir do 3° dia de experimento, o decréscimo do 13C em ambas espécies nos tratamentos com elevado CO2 como consequência da incorporação do C novo assimilado. Quanto ao 15N, este apresentou apenas valores positivos nas C3, enquanto nas C4 houve tanto valores negativos como positivos, mas ambos não indicaram um padrão muito claro quanto a diferenças entre tratamentos. Análises enzimáticas não revelaram alterações específicas no metabolismo do C no solo, mas foram encontradas alterações no metabolismo do N que indicam uma influência direta deste nutriente no potencial do solo em armazenar C. / The C and N dynamics may be interpreted as a flow within the ecosystem that encompasses the physiological processes that occur in plants and soil. In this study, we used of a new combined FACE and T-FACE system, to allow plants of Stylosanthes capitata Vogel (C3) and Panicum maximum Jacq. (C4) to be exposed to higher CO2 concentrations and temperatures, respectively. The system named Trop-T-FACE was established at the Ribeirão Preto campus of the University of São Paulo (USP). Two experiments were conducted using this system; the first involved the warming of 2° C in the plant canopy of Stylosanthes capitata Vogel and resulted in an intensification of N short term cycle probably due to greater biological N2 fixation by legumes, plus larger soil respiration rates and reduced rates of soil enzymatic activity. In the second experiment, plants of S. capitata and P. maximum were exposed to 4 treatments: a control (ambient temperature and ambient CO2); eT (ambient CO2 concentration and a canopy temperature of 2 °C greater than the ambient temperature), eC (600 µmol mol-1 CO2 and ambient temperature), and eC + eT (600 µmol mol-1 CO2 and a canopy temperature of 2 °C greater than the ambient temperature). Results from soil respiration indicated an effect of warming on soil respiration by effect of increment in soil temperature. Isotopic analysis showed, from the third day of the experiment, the decay of 13C values in both species in the treatments with elevated CO2 as a result of assimilation of the new C. Whereas 15N showed only positive values in C3, in C4 we found negative and positive values, but both did not indicate a clear pattern among treatments. Enzymatic analyzes revealed no specific changes in C metabolism in the soil, but changes in N metabolism might indicate a direct influence of this nutrient in the potential of the soil to store C.

O gênero Pinus ocupa no Brasil uma área plantada de 1,59 milhão de hectares e tem uma ampla faixa de produtividade florestal (18 a 45 m3 ha-1 ano-1), em função das espécies utilizadas, das limitações edáficas, dos tipos de clima, melhoramento genético e, e alguns casos, pela ocorrência de pragas e doenças. Apesar do conhecimento de que o aumento da disponibilidade de recursos naturais (luz, água e nutrientes) eleva a produção de madeira, faz-se necessário compreender como estes recursos influenciam os processos de captura (produção primária bruta ou GPP) e alocação de carbono (C) para os diferentes compartimentos da floresta (raiz, lenho, galhos e folhas). Além disso, o grau de controle genético é de grande importância nesses processos e também deve ser analisado. Assim, este projeto objetivou quantificar as taxas de captura e alocação de carbono em uma espécie de Pinus tropical (P. caribaea var. hondurensis) e em uma subtropical (P. taeda), dos 6,5 aos 8,5 anos de idade, em parcelas controle (sem fertilização e sem irrigação) e parcelas fertilizadas e irrigadas. O experimento está localizado no município de Itatinga - SP e se utilizou o método do balanço de carbono para estimar a produtividade primária líquida da parte aérea (ANPP), o fluxo de carbono para o solo (TBCF), produtividade primária bruta (GPP) e produtividade líquida do ecossistema (NEP). Ao final do estudo, a biomassa do tronco foi 75% superior no P. caribaea var. hondurensis (126 Mg ha-1) do que no P. taeda (72 Mg ha-1), sendo que em ambas as espécies houveram ganhos significativos com a fertilização e irrigação. O primeiro ano avaliado foi mais seco do que o segundo (1195 contra 1487 mm), resultando em diferenças nos fluxos calculados. A produção de tronco do P. caribaea var. hondurensis variou de 722 a 1569 gC m-2 ano-1, enquanto do P. taeda foi de 221 a 452 gC m-2 ano-1. A espécie subtropical obteve os maiores valores de TBCF, variando de 1150 a 2197 gC m-2 ano-1, e para as duas espécies se encontrou relação do TBCF com a ANPP e GPP. Assim, encontrou-se que a maior produtividade da espécie tropical é resultado de seu maior GPP (4964 contra 3744 gC m-2 ano-1 no P. taeda), maior partição de carbono para incremento de tronco (22% contra 9% no P. taeda) e menor partição para TBCF (23% contra 45% no P. taeda). Já a fertilização e irrigação não mudaram a partição da GPP para a ANPP e TBCF comparado ao tratamento controle, e o ganho em produção de madeira foi explicado apenas pelo aumento na GPP (11%). A NEP para ambas as espécies foi positiva, mostrando que essas espécies estão atuando como drenos de carbono. Assim, o conhecimento de como a captura e alocação de C é afetada pela espécie, água e nutrição terá aplicação sobre o manejo florestal, além de propiciar valores de fluxos essenciais para a calibração de modelos ecofisiológicos de produção, ainda inexistentes para essas espécies no Brasil. / The genus Pinus in Brazil has a planted area of 1.59 million hectares and it has a wide range of forest productivity (18-45 m3 ha-1 yr-1) depending on the species, edaphic limitations, climate, breeding and, in some cases, the occurrence of pests and diseases. Despite knowing that the increased resources availability (light, water and nutrients) improves the production of wood, it is necessary to understand how these features influence the uptake processes (gross primary production or GPP) and carbon allocation (C) on the different forest compartments (root, bole, branch and leaf). Furthermore, the degree of genetic control is rather important in these processes and should also be analyzed. Thus, this project aimed to quantify carbon sequestration and allocation rates in a tropical pine (P. caribaea var. hondurensis) and a subtropical one (P. taeda), from ages 6.5 to 8.5 years old, in control plots (no fertilization and no irrigation) and fertilized and irrigated plots. The experimental site is located in Itatinga- SP and the carbon balance approach was used to estimate the above ground net primary production (ANPP), total belowground carbon flux (TBCF), gross primary production (GPP) and net ecosystem production (NEP). At the end of the study, the bole biomass was 75% higher in the P. caribaea var. hondurensis (126 Mg ha-1) than in P. taeda (72 Mg ha-1), and in both species there were substantial improvements with fertilization and irrigation. The first year evaluated was drier than the second (from 1195 to 1487 mm), resulting in differences in the calculated fluxes. The P. caribaea var. hondurensis bole production ranged from 722 to 1569 gC m-2 yr- 1, while the P. taeda showed values from 221 to 452 gC m-2 yr-1. The subtropical specie obtained the largest values of TBCF (from 1150 to 2197 gC m-2 yr-1), and on both species there was relationship between TBCF and ANPP and GPP.Thus, the higher productivity of tropical specie is a result of higher GPP (4964 versus 3744 gC m-2 yr-1 in the P. taeda), increased carbon partitioning to bole increment (22% versus 9% in the P. taeda) and smaller partitioning for TBCF (23% versus 45% in the P. taeda). Fertilization and irrigation have not changed the partitioning from GPP to ANPP and TBCF compared to the control plots, and increase in the production of wood it has been explained only by increased GPP (11%). The NEP for both species was positive, showing that these species are acting as carbon sinks. Therefore, the knowledge of how the carbon sequestration and allocation is affected by the species, water and nutrition will have application on forest management, besides providing values of essential fluxes for calibration of ecophysiological production models, still non-existent for these species in Brazil.

Decisões tomadas no planejamento da implantação florestal, como a densidade do plantio e o material genético, alteram a disponibilidade de recursos naturais tais como nutrientes, água e luz e consequentemente afetam a assimilação do carbono, que está diretamente relacionada ao crescimento da planta. Ainda são escassas as informações de como e quanto a densidade de plantio e o material genético afetam a fixação de carbono pelas ávores. O objetivo desse trabalho foi avaliar os padrões de fixação e alocação de carbono em plantações clonais de Eucalyptus sp. em duas densidades de plantio (3x2 m e 3x4 m), em um Latossolo Vermelho Distrófico T ípico A moderado. O estudo foi desenvolvido na Estação Experimental de Ciências Florestais de Itatinga-SP - ESALQ/USP, com três materiais clonais de Eucalyptus urophylla: AEC 0144, AEC 224 e COP 1404. O delineamento experimental utilizado foi em blocos casualizados, com esquema fatorial 3 x 2, sendo composto por três clones de eucalipto em dois espaçamentos, com 6 repetições para cada tratamento. Durante o intervalo de um ano (dos 40 aos 52 meses de idade) foram determinados a Produtividade Primária Líquida da Parte Aérea (ANPP: incremento da biomassa aérea somada ao folhedo), a Respiração Autotrófica da Parte Aérea (Rp: respiração das folhas e do tronco com base com base na ANPP, assumindo um valor constante de eficiência de uso do carbono (CUE) de 0,53 (GIARDINA et al., 2003)), o Fluxo de Carbono Abaixo do Solo (TBCF: produção e respiração das raízes grossas e finas, exsudatos das raízes e produção de substratos usados por micorrizas) e a Produtividade Primária Bruta (GPP: somatório dos fluxos de carbono) para os seis tratamentos avaliados. A maior produtividade encontrada para o clone AEC 0144 no espaçamento 3x2 m foi resultado de uma maior GPP (5997,45 g C m-2 ano-1), maior partição de carbono para incremento de tronco (30%) e menor partição da GPP para TBCF (34%). A ANPP variou de 1453,99 g C m-2 ano-1 (Clone COP 1404 no espaçamento 3x2 m) a 2288,78 g C m-2 ano-1 (Clone AEC 0144 no espaçamento 3x2 m), sendo os maiores fluxos encontrados para os clones AEC 0144 em ambos espaçamentos e para o clone COP 1404 no espaçamento 3x4 m. A variação encontrada nos valores de respiração da parte aérea seguiram o mesmo padrão dos resultados da ANPP. O TBCF foi significadamente superior para os clones AEC 0144 e AEC 224 no espaçamento 3x2 m com 2056,36 g C m-2 ano-1 e 1903,83 g C m-2 ano-1, respectivamente; e para o clone COP 1404 no espaçamento 3x4 m (1927,43 g C m-2 ano-1). Houve correlação positiva do TBCF com a GPP, mas não com a ANPP. / Decisions not planned for forest deployment, such as planting density and genetic material, alter the availability of natural resources such as nutrients, water and light and consequently affect the assimilation of carbon, which is directed to plant growth. They are still scarce as information on how and how much planting density and genetic material for a fixation of carbon by trees. The objective of this work was to evaluate the carbon allocation patterns in clonal plantations of Eucalyptus sp. in two planting densities (3x2 m and 3x4 m), in a typical Typic A moderate Dystrophic Red Latosol. The study was developed at the Experimental Station of Forest Sciences of Itatinga-SP - ESALQ / USP, with three clonal materials of Eucalyptus urophylla: AEC 0144, AEC 224 and COP 1404. The experimental design was a randomized complete block design with a factorial scheme 3 x 2, being composed of three clones of eucalyptus in two spacings, with 6 replicates for each treatment. During the one-year interval (from 40 to 52 months of age) was determined Aboveground Net Primary Productivity (ANPP: increase of the aerial biomass added to the litterfall), Aboveground Autotrophic Respiration (Rp: leaf respiration and (CUE) of 0.53 (GIARDINA et al., 2003)), Total Belowground Carbon Flux (TBCF: production and respiration of the roots) and Gross Primary Productivity (GPP: sum of the carbon fluxes) for the six treatments evaluated. The higher productivity found for the clone AEC 0144 in the 3x2 m spacing resulted from a higher GPP (5997.45 g C m-2 year-1), larger carbon partition for trunk increment (30%) and smaller partition from GPP for TBCF (34%). The ANPP ranged from 1453.99 g C m-2 year-1 (Clone COP 1404 in spacing 3x2 m) to 2288.78 g C m-2 year-1 (Clone AEC 0144 in 3x2 m spacing) Found for clones AEC 0144 in both spacings and COP 1404 in 3x4 m spacing. The variation found in aboveground autotrophic respiration values followed the same pattern of ANPP results. The TBCF was significantly higher for clones AEC 0144 and AEC 224 at 3x2 m spacing with 2056.36 m-2 year-1 and 1903.83 m-2 year-1, respectively; and for clone COP 1404 in 3x4 m spacing (1927.43 m-2 year-1). There was a positive correlation between TBCF and GPP, but not with ANPP.

O sistema climático global e o ciclo do carbono interagem intensamente, e o CO2 constitui um fator dominante na definição do clima, sendo gerado e consumido pelas plantas e pela atividade de microrganismos em ecossistemas aquáticos, terrestres e na atmosfera. Na atmosfera, esse gás contribui para o efeito estufa. Em um ecossistema de floresta tropical, grande parte da produção de CO2 é proveniente da respiração do solo, e os fluxos de CO2 na interface solo-atmosfera dependem de mudanças nas características físicas, químicas e biológicas na superfície do solo. O objetivo desse estudo foi investigar a variabilidade sazonal dos fluxos de CO2, decorrente da respiração do solo de diferentes florestas nativas da Amazônia, localizadas nos municípios de Sinop (MT), Caxiuanã (PA), Manaus (AM) e Santarém (PA), e determinar os principais parâmetros de correlação dos fluxos de CO2 do solo com a temperatura e umidade. As amostragens foram realizadas durante as estações seca e chuvosa em cada local. Os fluxos de CO2 foram medidos por meio de câmaras dinâmicas, que se baseiam na variação da concentração do gás no interior da câmara em função do tempo e foram calculados utilizando-se de equações lineares. Os valores médios encontrados para as regiões estudadas nas estações seca e chuvosa foram respectivamente: Sinop, 3,03 μmol.CO2 m-2s-1 e 5,76 μmol. CO2 m-2s-1; Caxiuanã, 5,07 μmol.CO2 m-2s-1 e 6,09 μmol.CO2 m-2s-1; Manaus, 5,47 μmol.CO2 m-2s-1 e 5,44 μmol.CO2 m-2s-1 e Santarém, 2,90 μmol.CO2 m-2s-1 e 5,64 μmol.CO2 m-2s-1. Estes resultados demonstraram que houve variação regional e influência da sazonalidade na dinâmica do fluxo de CO2 do solo, sendo que, os maiores fluxos foram obtidos durante o período chuvoso, indicando que a disponibilidade de água e a temperatura do solo foram os principais condicionadores da produção do CO2. Foram coletadas amostras de serapilheira e raízes para estimar o estoque e a influencia sobre os fluxos de CO2 do solo, sendo estas, vias de entrada de nutrientes e principalmente de carbono para o solo. Para todas as regiões os maiores estoques foram encontrados na estação seca. / Carbon dioxide is an important contributor to the greenhouse effect, and by extension, the global climate system as a whole; it is generated and consumed through the activities of terrestrial and aquatic microorganisms. Tropical forest CO2 fluxes at the soil-atmosphere interface depend on changes in the physical, chemical and biological characteristics of the soil surface. The objective of the present study is to investigate seasonal variability of CO2 fluxes from soil respiration in Amazonian native forest located in the municipalities of Sinop (MT), Caxiuanã (PA), Manaus (AM) e Santarém (PA) and to determine the effects of determining parameters such as temperature and soil moisture. The CO2 fluxes were measured using dynamic chambers during both dry and wet seasons at each site. As the concentration of the gas inside the chamber varies with time, samples were taken at given time intervals and fluxes then calculated using linear regression equations. The average values found for Sinop in the dry and wet seasons were 3.03 and 5.92 μmol.CO2 m-2s-1 respectively; for Caxiuanã, 5.07 μmol.CO2 m-2s-1 and 6.09 μmol.CO2 m-2s-1; for Manaus, 5.47 and 5.44 μmol.CO2 m-2s-1; and for Santarém, 5.64 μmol.CO2 m-2s-1 in the wet season and during the dry season and 6.09 μmol.CO2 m-2s-1. Our results showed that there was a seasonal variation of the CO2 flux. The results also showed that there was an influence of the seasonality in the dynamics of the soil CO2 flux, where the greater fluxes were obtained during the wet season, indicating that water availability and soil temperature were the main factors determining production. Litter samples had been collected and roots esteem the supply and influence it on the CO2 fluxs of in the soil, being these, ways of entrance of nutrients and mainly of carbon for the ground. For all the regions the biggest supplies had been found in the dry station.