Made available in DSpace on 2014-06-11T19:28:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-06-21Bitstream added on 2014-06-13T20:37:33Z : No. of bitstreams: 1 teixeira_lg_me_jabo.pdf: 3324980 bytes, checksum: c588c0fe971e863b13d299ae775c6afb (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Usina São Martinho / O preparo do solo tem sido apontado como uma das práticas que causam perda adicional de carbono do solo para a atmosfera na forma de CO2, o principal gás do efeito estufa ampliado. Neste trabalho são estudados alguns aspectos da emissão de CO2 do solo de áreas agrícolas na região de Jaboticabal, SP, Brasil. Os experimentos foram realizados em duas áreas onde estudou-se o efeito do preparo do solo com arado de disco seguido de grade niveladora (convencional), escarificador de arrasto conjugado com rolo destorroador (reduzido) e enxada rotativa sobre as emissões de CO2 do solo. No experimento conduzido com a enxada rotativa, foi considerada sua aplicação sobre parcela com e sem palha de cana-de-açúcar, sendo o efeito da presença ou não de palha na superfície do solo sobre as emissões de CO2 também investigada. Já no experimento que contemplou o preparo convencional e reduzido as emissões totais indicaram que o sistema de preparo arado de disco seguido de grande niveladora foi o mais impactante, resultando em uma perda de carbono do solo próxima a 71 g m-2 (260 g CO2 m-2) em 2 semanas. Com relação à influência da palha sobre as emissões após preparo, essas foram significativas aumentando a emissão em 36% acima daquela da parcela após preparo sem palha. Os resultados apresentaram, invariavelmente, uma queda da emissão de CO2 do solo ao longo do tempo após preparo, que foi melhor modelada em um dos experimentos a partir de uma função exponencial decrescente no tempo somente, enquanto no outro experimento por uma função combinada, exponencial decrescente no tempo e dependência linear com temperatura e umidade do solo, foi a que melhor ajustou-se as variações temporais da emissão após preparo / Soil tillage has been presented as one of the practices responsible for the additional release of carbon from soil to atmosphere as CO2, the major gas of the enhanced greenhouse effect. This work investigates several aspects of soil CO2 emission in agricultural areas in Jaboticabal region, São Paulo State, Brazil. The experiments were conducted in two fields, where the effect on soil CO2 emissions was studied for tillage employing disk plow followed by offset disk harrow, chisel plow followed by clod break roller and rotary tillage. In the rotary tillage experiment, plots with and without sugarcane trash on the surface were considered, being the effect of the presence of crop residues on soil CO2 emission also evaluated. In the experiment comparing conventional and reduced tillage, total emissions indicated that the conventional tillage (disk plow followed by offset disk harrow) was the most impacting tillage system, resulting in a total carbon emission of 71 grams m-2 (260 g CO2 m-2) in 2 weeks after tillage. Concerning the influence of sugarcane trash on emissions after tillage, emissions were significant, increasing 36% over the plot without residues of the crop. In all cases, results consistently showed a decrease in soil CO2 emission in time after tillage, which was best modeled by an exponential decay in time after tillage only, for one of the experiments, while a combined function of exponential decay in time and linear dependence on temperature and soil moisture, in the other experiment, was the best for fitting the temporal variation of emission after tillage

Made available in DSpace on 2015-03-26T13:50:02Z (GMT). No. of bitstreams: 1 texto completo.pdf: 611854 bytes, checksum: 577aff41b49909e4858f6d04d9a63bdd (MD5) Previous issue date: 2009-07-29 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The Amazon rainforest has great biological diversity and it is among the most complex forest ecosystems of the planet. Any forest system is composed of physical components (climatic, edaphic, topographical and among others) and by biological components (animals and plants). Because of the interdependence of these components it is difficult to understand the functioning of the system as a whole. Despite the Amazon forest being the largest continuous reserve of tropical rainforest in the world, there is still little understanding about its functioning, particularly in relation to the carbon cycle. Recent studies have demonstrated the importance of carbon stocks in the soil as a source and potential sink of CO2. However, few experimental studies have been conducted on the quantification of these fluxes and their seasonal variations associated with biophysical variables that influence the magnitude of these fluxes. The objectives of this study are: a) To analyze the seasonal variations of soil rates of respiration with litter in areas of black soil (TP) and yellow Oxisol (LA); b) To identify the function of dependency between the soil respiration rates at the soil surface, with soil temperature, soil moisture and litter production; c) To make a comparation of flux estimates of soil allocated carbon in sites of black soil and yellow Oxisol. The results showed a seasonal variation of the flux soil CO2, the sites of yellow oxisol and black soil in fluxes in both response to the observed seasonality in rainfall, soil temperature and soil moisture. The magnitudes of the CO2 fluxes in the LA site ranged from 1.52 to 3.98 μmol.m-2.s-1 with an average of 2.84 ± 0.20 μmol.m-2.s-1 in LA, while the CO2 fluxes in the TP site ranged from 1.95 to 5.73 μmol.m-2.s-1 and with an average of 3.73 ± 0.35 20 μmol.m-2.s-1. The rainfall in these periods was 37 mm in August and 373 mm in April. The average temperature near the soil surface, in August and April, were 25.3° C and 23.9° C, respectively, while soil moisture ranged from 12.5 % to 21.5 % in respective months. The magnitudes of soil CO2 fluxes, in general, were greater in the rainy season in both experimental sites. The hourly fluxes of soil CO2 in the LA site showed little variation between daytime and night, time in august while in April (rainy season) there was evidence of a diurnal variation. The results of this study indicate a greater allocation of C in TP site compared to the LA site. / A floresta tropical amazônica tem grande diversidade biológica e está entre os mais complexos ecossistemas florestais do planeta. Qualquer sistema florestal é composto por componentes físicos (climáticos, edáficos, topográficos entre outros) e por componentes biológicos (animais e plantas). A interdependência entre esses componentes dificulta a compreensão do funcionamento do sistema como um todo. Apesar da floresta amazônica ser a maior reserva contínua de floresta tropical úmida do mundo, ainda há pouco entendimento sobre o seu funcionamento, particularmente em relação ao ciclo do carbono. Pesquisas recentes têm demonstrado a importância do carbono no solo como estoque, fonte e potencial sumidouro de CO2. Todavia, poucos estudos experimentais têm sido realizados sobre a quantificação desses fluxos e suas variações sazonais associadas com variáveis biofísicas que influenciam a magnitude desses fluxos. Os objetivos deste trabalho são: Analisar as variações sazonais das taxas de respiração na superfície do solo com liteira em áreas de terra preta (TP) e de latossolo amarelo (LA); Identificar a relação de dependência das taxas de respiração na superfície do solo com a precipitação pluvial, temperatura do solo, umidade do solo e produção de liteira; Comparar as estimativas de carbono alocado no solo entre as áreas de TP e de LA. Os resultados evidenciam uma variação sazonal dos fluxos de CO2 do solo, tanto nas áreas de LA como nas áreas de terra preta, em resposta à sazonalidade observada no regime pluviométrico, e da temperatura e umidade do solo. As magnitudes dos fluxos de CO2 variaram de 1,52 a 3,98 μmol.m-2.s-1 e média de 2,84 ±0,20 μmol.m-2.s-1 em LA e em TP os fluxos variaram de 1,95 a 5,73 μmol.m- 2.s-1 e média de 3,73 ±0,35. A precipitação pluvial nesses períodos foi de 37 mm em agosto e 373 mm em abril. A temperatura média do solo próximo à superfície, nos meses de agosto e abril, variou de 25,4o C a 23,9o C, respectivamente, enquanto a umidade do solo variou de 12,5 % a 21,5 % para os respectivos períodos. As maiores magnitudes dos fluxos de CO2 do solo, de um modo geral, ocorreram no período chuvoso em ambas as áreas experimentais. Os fluxos horários de CO2 na área de LA em agosto (menos chuvoso) apresentaram pequena variação entre o período diurno e noturno, enquanto em abril (chuvoso) a variação nos fluxos foi bem mais acentuada. Os resultados desse trabalho indicam uma maior alocação de C na TP em relação a LA, provavelmente pela maior quantidade de matéria orgânica na superfície do solo.

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.

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.

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 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.

Magister Scientiae (Biodiversity and Conservation Biology) / This study examined the magnitude of soil CO2 efflux in an arid South African ecosystem, the flux responses as well as those of key limiting nutrients to soil temperature increases and moisture reductions consistent with a future climate change scenario, and compared measured soil respiration rates with those predicted with empirically and theoretically-based soil respiration models. Measurements of soil respiration rate, temperature, moisture, N and P contents were conducted monthly over a 12-month period in natural environments and those artificially manipulated with replicated open-top warming chambers (average 4.1oC increase) and precipitation exclusion chambers (average 30.1% decrease in rainfall, 26.2% decrease in fog and dewfall) distributed in five different soil-vegetation units.Measured soil respiration rates were over 3-fold less than those reported for temperate and tropical forest ecosystems with 61.5% of the total soil CO2 efflux contributed by root respiration (derived from the differences between moderately vegetated and sparsely vegetated areas) in moderately vegetated soils. Massive increases (up to 15 times) in soil CO2 efflux occurred during wet phases, but even these large CO2 pulses were only comparable in magnitude with soil CO2 effluxes reported for temperate semi-arid grasslands. There was considerable intra-annual and inter-site variability in the magnitude and direction of soil respiration and N and P responses to elevated temperatures and reduced precipitation levels with poor correspondence evident between soil CO2 efflux and soil organic matter content. Soil CO2 effluxes declined in response to precipitation exclusion by 7.1% over all sites and increased in response to warming by 42.1% over all sites. The large increase in response to warming was assisted by a 7.5% enhancement in soil moisture content due to precipitation interception by the chamber walls and its channelling to the soil surface.Relatively smaller respiration increases in response to warming occurred in moderately vegetated soils, these attributed to soil thermal insulation by the plant canopy cover. Soil P and N contents increased in response to warming by 11.3% and 13.3% respectively over all sites, with soil P declining in response to precipitation exclusion by 5.8% over all sites and soil N increasing in response to precipitation exclusion over all sites by 5.8%. Standard least squares regressions quantified the relationships between soil respiration rate and measured soil physical and chemical properties, and their interactions for each of the 5 soil-vegetation units. These relationships were incorporated in an empiricallybased soil respiration (EMR) model which was compared with a theoretically based generalized soil respiration model (GRESP). GRESP model functions included measured Q10 coefficients at soil moisture contents above field capacity, these assumed reduced by half for dry conditions, and maximum retentive and field capacities of soils. EMR modelled soil respiration rates displayed slightly better correspondence with measured soil respiration rates than GRESP modelled soil respiration rates. This apparent from the higher regression coefficients and lower sums of squared residuals, with EMR model residuals also more closely approximating normal distributions. However, despite the EMR model’s slight superiority, it was concluded that more precise laboratory-based measurements of soil retentive and field capacities and their Q10 coefficients at different soil moisture contents could improve the GRESP model’s accuracy thereby providing a more convenient and uncomplicated means of predicting respiration responses to current and future climates over a wide range of arid soil types

This thesis includes two studies. The first study examined changes in soil characteristics as a result of prolonged conifer dominance in successional aspen-conifer forests. Changing disturbance patterns in aspen-conifer forests appear to be altering successional dynamics that favors conifer expansion in aspen forests. The primary objective of this paper was to identify how increasing conifer dominance that develops in later successional stages alters forest soil characteristics. Soil measurements were collected along a stand composition gradient: aspen dominated, aspen-conifer mix, conifer dominated and open meadow, which includes the range of conditions that exists through the stages of secondary succession in aspen-conifer forests. Soil chemistry, moisture content, respiration, and temperature were measured. There was a consistent trend in which aspen stands demonstrated higher mean soil nutrient concentrations than adjacent meadows, mixed or conifer stands. Soil moisture was significantly higher in aspen stands and meadows in early summer. Soil respiration was significantly higher in aspen stands than conifer stands or meadows throughout the summer. The results indicate that soil resource availability and respiration peak within aspen dominated stands that are present during early succession and then decrease as conifer abundance increases along our stand composition gradient, representative of stand characteristics present in mid to late successional stages. Emerging evidence from other studies suggest that these observed changes in soil characteristics with increasing conifer dominance may have negative feedbacks on aspen growth and vigor. The second study examined the facilitation effect between aspen and subalpine fir establishment. In subalpine forests, conifer species are often found intermixed with broadleaf species. However, few if any studies have explored the existence and influence of facilitation between broadleaf tree species and conifers. We have observed the general establishment of subalpine fir seedlings at the base of aspen trees in a subalpine forest, indicating that a facilitative relationship may exist. To explore the potential facilitative relationship during secondary succession in subalpine forests, subalpine fir seeds were planted across a stand composition gradient (aspen dominated → mixed → conifer dominated stands) at six study sites in the Fishlake National Forest. Seeds were placed during the fall of 2010, at distances of 0 cm and 25 cm in each cardinal direction at the base of mature aspen and subalpine fir trees in each of the three stand types. Seeds were also planted within stand interspaces and in adjacent meadows. Seedling emergence was recorded at the beginning of the summer of 2011 and seedling mortality was recorded in October 2011. Soil moisture content was measured at the position that seeds were placed during the summers of 2009 and 2011. Aspen dominated stands had subalpine fir germination that was on average 11 times greater than mixed or conifer dominated stands. Germination was 2.3 fold greater at the base of aspen trees than fir trees and two fold greater at the base of aspen trees than interspaces. Seedling mortality was lower in aspen stands but was not significantly influenced by position relative to mature trees. Soil moisture was highest in aspen dominated stands, with better soil moisture conditions at the base of aspen trees and in interspaces compared to the base of fir trees. Few if any studies regarding conifer facilitation have provided evidence for facilitation at the germination life stage, rather they focus on seedling survival. However, our study illustrates a strong facilitative interaction in which both aspen dominated stands and aspen trees increase the likelihood of subalpine fir seedling establishment by drastically increasing rates of subalpine fir germination. Because of aspen's primary role in initiating secondary succession through post-disturbance sucker regeneration, and the subsequent dependence of conifers on aspen for establishment, aspen mortality via competition with conifers under longer fire cycles, droughts, or intensive ungulate browsing may result in a loss of aspen-conifer forest communities in some locales.

No description available.

Fertilization is a common, cost effective treatment for increasing forest productivity within managed forests of the southeastern United States. However, little is known about how fertilization affects the below-ground processes that drive soil CO2 efflux in loblolly pine (Pinus taeda L.). A thorough understanding of below-ground carbon dynamics is necessary for the estimation of net ecosystem productivity and the carbon storage potential of these managed systems. In April 2004, we began monitoring total soil CO2 efflux (EC), heterotrophic (RH), and root respiration (RR) in response to fertilization with diammonium phosphate (DAP). Respiratory components were measured prior to fertilization, weekly following fertilization, and bi-weekly after respiratory components stabilized using a dynamic closed chamber and an infrared gas analyzer. We found that EC differed significantly (P<0.0001) between fertilized and unfertilized plots, but the direction was dependent on date. In the early period of the study, fertilized plot values were lower than control plots. However, by the latter periods fertilized plot values returned to control levels except for one sampling date in March 2005 when fertilized plot values were greater then control plots. Heterotrophic respiration was consistently and significantly (P=0.0002) lower in fertilized plots. Root respiration was significantly (P=0.0597) increased in fertilized plots when analyzed over the study and showed a 20% increase due to fertilization. We concluded that an increase in RR and possibly root biomass was enough to balance the decrease in RH leading to no difference in EC later in the growing season. We performed a pair of greenhouse studies to observe the effects of fertilization in the form of diammonium phosphate (DAP) on RR. The objectives were to determine how nutrient additions initially affect RR in one-year-old loblolly pine seedlings. Secondly, we wanted to determine if Captan [N-(trichloromethylthio) cyclohex-4-ene-1, 2-dicarboximide], a mild fungicide, could be used to reduce or eliminate ecto-mycorrhizae upon visual inspection. Both studies showed that initially, at a high rate (100 ppm N and 49 ppm P) of fertilization, RR was significantly (P<0.10) increased relative to seedlings that did not receive fertilization. This increase was only temporary with rates returning to, or decreasing below, control levels by the end of the study. No consistent trend was found between low (25 ppm N and 13 ppm P) and moderate (50 ppm N and 25 ppm P) rates of fertilization. Captan was shown to generally have no affect on RR. Captan and fertilization both showed (visual inspection) a decrease in fine-roots and mycorrhizae, which could explain the reduction in respiration rates observed in these treatments by the end of the studies. / Master of Science