RESUMO: Objetivou-se, neste estudo, ajustar modelos volumétricos em diferentes situações de modelagem para obtenção de equações de volume para a espécie Couratari stellata (Tauari) na Floresta Nacional do Tapajós. As informações necessárias foram obtidas da cubagem rigorosa realizada durante a atividade de romaneio de quatro Unidades de Produção Anual (UPAs), onde foram cubadas no total 1431 árvores de Tauari e ajustados treze modelos volumétricos. Os dados foram organizados para três situações de modelagem: 1) total das árvores cubadas das quatro UPAs, 2) por UPA individual e, 3) por classe de diâmetro de DAP. Obteve-se a qualidade dos ajustes dos modelos por meio do R² ajustado, Erro padrão da estimativa (Syx%), fator de inflação da variância (VIF) e análise gráfica dos resíduos, já a validação dos modelos, a partir do teste qui-quadrado (X²). Os modelos que apresentaram melhores ajustes para as quatro UPAs foram Schumacher e Spurr logaritimizado. Nas UPAs individuais, se destacaram as equações de Schumacher para as Unidades 07, 08 e 09 e Spurr log para a 06. Entre as classes diamétricas não foram obtidos resultados satisfatórios. Todas as equações selecionadas foram válidas segundo o teste estatístico realizado.Palavras-chave: cubagem rigorosa, modelagem, volume. ABSTRACT:The objective of this study was to adjust volumetric models in different modeling situations to obtain volume equations for the species Couratari stellata (Tauari) in the Tapajós National Forest. The necessary information was obtained from the rigorous cubing carried out during the romaneio activity of four Annual Production Units (UPAs), where a total of 1431 Tauari trees were planted and thirteen volumetric models adjusted. The data were organized for three modeling situations: 1) total trees cubed from the four UPAs, 2) per individual UPA, and 3) per diameter class of DAP. We obtained the quality of the model adjustments by means of the adjusted R², Standard error of the estimate (Syx%), factor of inflation of the variance (VIF) and graphical analysis of the residues, already the validation of the models, Square (X²). The models that presented the best adjustments for the four UPAs were Schumacher and Spurr logarithmized. In the individual UPAs, the Schumacher equations for Units 07, 08 and 09 and Spurr log for 06 were highlighted. No satisfactory results were obtained among the diametric classes. All the selected equations were valid according to the statistical test performed.

Warming surface temperatures and increasing frequency and duration of widespread droughts threaten the health of natural forests and agricultural crops. High temperatures (HT) and intense droughts can lead to the excessive plant water loss and the accumulation of reactive oxygen species (ROS) resulting in extensive physical and oxidative damage to sensitive plant components including photosynthetic membranes. ROS signaling is tightly integrated with signaling mechanisms of the potent phytohormone abscisic acid (ABA), which stimulates stomatal closure leading to a reduction in transpiration and net photosynthesis, alters hydraulic conductivities, and activates defense gene expression including antioxidant systems. While generally assumed to be produced in roots and transported to shoots following drought stress, recent evidence suggests that a large fraction of plant ABA is produced in leaves via the isoprenoid pathway. Thus, through stomatal regulation and stress signaling which alters water and carbon fluxes, we highlight the fact that ABA lies at the heart of the Carbon-Water-ROS Nexus of plant response to HT and drought stress. We discuss the current state of knowledge of ABA biosynthesis, transport, and degradation and the role of ABA and other isoprenoids in the oxidative stress response. We discuss potential variations in ABA production and stomatal sensitivity among different plant functional types including isohydric/anisohydric and pioneer/climax tree species. We describe experiments that would demonstrate the possibility of a direct energetic and carbon link between leaf ABA biosynthesis and photosynthesis, and discuss the potential for a positive feedback between leaf warming and enhanced ABA production together with reduced stomatal conductance and transpiration. Finally, we propose a new modeling framework to capture these interactions. We conclude by discussing the importance of ABA in diverse tropical ecosystems through increases in the thermotolerance of photosynthesis to drought and heat stress, and the global importance of these mechanisms to carbon and water cycling under climate change scenarios.