Rodolfo Araújo Loos

Asymmetrical effects of mesophyll conductance on fundamental photosynthetic parameters and their relationships estimated from leaf gas exchange measurements

Worldwide measurements of nearly 130 C3 species covering all major plant functional types are analysed in conjunction with model simulations to determine the effects of mesophyll conductance (g(m)) on photosynthetic parameters and their relationships estimated from A/Ci curves. We find that an assumption of infinite g(m) results in up to 75% underestimation for maximum carboxylation rate V(cmax), 60% for maximum electron transport rate J(max), and 40% for triose phosphate utilization rate T(u) . V(cmax) is most sensitive, J(max) is less sensitive, and T(u) has the least sensitivity to the variation of g(m). Because of this asymmetrical effect of g(m), the ratios of J(max) to V(cmax), T(u) to V(cmax) and T(u) to J(max) are all overestimated. An infinite g(m) assumption also limits the freedom of variation of estimated parameters and artificially constrains parameter relationships to stronger shapes. These findings suggest the importance of quantifying g(m) for understanding in situ photosynthetic machinery functioning. We show that a nonzero resistance to CO2 movement in chloroplasts has small effects on estimated parameters. A non-linear function with gm as input is developed to convert the parameters estimated under an assumption of infinite gm to proper values. This function will facilitate gm representation in global carbon cycle models.

BALANÇO HÍDRICO E DE ENERGIA PARA PLANTIOS DE EUCALIPTO COM COBERTURA PARCIAL DO SOLO

Plantios com idade inicial de desenvolvimento apresentam descontinuidade na cobertura do solo, tendendo a apresentar maior exposicao do dossel ao vento e a radiacao solar, o que altera as interacoes solo-plantaatmosfera. O objetivo deste trabalho foi estudar os componentes dos balancos hidricos e de energia ao longo do primeiro ano de desenvolvimento do eucalipto na regiao da planicie costeira brasileira. O sitio experimental esta localizado em uma area pertencente a empresa Fibria Celulose no municipio de Aracruz- ES. O espacamento entre as arvores do plantio de eucalipto da area estudada foi de 3 x 3 m e a data do plantio foi em 15/08/2004. O periodo de estudo foi compreendido entre a data do plantio ate a cultura ter completado 19 meses de idade. Verificou-se maior disponibilidade de energia no periodo de verao e que a precipitacao influenciou diretamente na particao do balanco de energia, sendo que, durante todo o periodo estudado, a fracao da energia disponivel destinada a evapotranspiracao foi sempre maior que a fracao destinada ao aquecimento do sistema solo-planta-atmosfera, apresentando uma relacao de 59,57% de λE/R. Observou-se tambem que o balanco hidrico com a evapotranspiracao modelada apresentou boa correspondencia ao comportamento da umidade observada, apresentando um coeficiente de determinacao de 0,94. Os maiores portes das arvores, maiores indices de area foliar e sistema radicular, favoreceu a evapotranspiracao, mostrando que a maior parte da energia disponivel foi utilizada para mudanca de fase da agua.

VARIÁVEIS-CHAVE PARA DETERMINAÇÃO DA QUALIDADE DA ÁGUA EM MICROBACIAS COM PLANTIOS DE EUCALIPTO

This work aimed to identify the main variables affected by natural factors and, or anthropic, which influence the quality of surface water in watersheds, managed for eucalyptus wood production. Water quality was monitored in four watersheds located in Aracruz, northern ES state, Brazil. The physical and chemical characteristics of the water and the potential presence of pesticides used in forest management were evaluated. Samples were collected after the silvicultural activities and, or, rainfall between the months of January to June 2012. Principal component and factor analysis techniques were used to determine the water variables most sensitive and correlated with forestry activities, soil and climatic conditions of the study watersheds. It was possible to obtain four components that explained 73.1% of the total variance. The components were correlated with the variables and defined as factors mineral, solid, acidity, and pedological. These factors explained 31.6; 18.5; 15.6; and 7.4% of the total variance of the data which are directly related to salinity, the presence of suspended solids, acidity and the inorganic carbon content of the soil, respectively. Sulfluramid (insecticide) and glyphosate (herbicide) were not found. In general, it is possible to reduce from 30 to 12 variables that should be monitored for prediction of water quality, maintaining at least 70% of the precision of the estimates. The evaluation of these key variables allows establishing an adequate monitoring system of water quality considering the eucalyptus forestry activities.

HEIGHT-DIAMETER MODELS FOR Eucalyptus sp. PLANTATIONS IN BRAZIL

The use of height-diameter models have important applications in the management of eucalyptus plantations. The aim of this paper is to provide adequate height models based on the diameter and stand variables that could be easily used and applied to plantation’s management. The data was based on tests located in Espírito Santo and Bahia. A total of 312 plots, including 35 different treatments (different initial planting densities, number and severity of thinning operations, fertilization regimes, among others), and four different clones. This resulted in 2,407 conditions for 85,608 tree measurements. The constructed equations were based on mixed-effect models, in order to accommodate possible autocorrelations, to address variations between sites and to obtain locally calibrated estimates. Among the different model structures and combination of variables tested and presented, the best model showed a coefficient of determination of 0.953 and 0.988, for the fixed and fixed+random parts, respectively. The model included a random factor for measurements-within-tree and tree-within-plot. The bias of the fixed part was 0.208 cm (0.0659%). We believe the models in this study can have broad applications in management and inventory methods applied to plantations. HEIGHT-DIAMETER MODELS FOR EUCALYPTUS SP. PLANTATIONS IN BRAZIL