Causes and implications of dry season control of tropical wet forest tree growth at very high water levels: direct vs. indirect limitations

高水位条件下热带湿润森林树木生长的旱季控制的原因和影响：直接与间接限制

• 批准号: 0842235
• 负责人: Steven Oberbauer
• 金额: $ 81.96万
• 依托单位: Florida International University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-15 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0842235&HistoricalAwards=false
• 关键词: Causes; implications; dry; season; control

Recent research in Costa Rica has shown that the growth of tropical moist forest trees is strongly related to the strength of the dry season across a range of rainfall that by all standard measures would be considered more than sufficient for growth. Understanding the basis for this finding is crucial because tropical moist forests play important roles in the global carbon and water cycles and therefore regional and global climate. Predicted future warming and drying of tropical moist forests could have strong feedback effects on global climate. However, recent satellite studies from the Amazon report that trees have their greatest leaf cover during the dry season, suggesting that the dry season does not affect production. These two findings suggest a serious gap in our understanding of role of the dry season on tropical tree growth and carbon sequestration. Dry-season controls on tree growth could result from both direct water limitation or via other indirect mechanisms. Direct limitation via dry soil and dry air seems unlikely given the high rainfall, soil moisture, and humidity that occur during the dry season. Potential indirect mechanisms include excessive leaf temperatures lowering photosynthesis, premature leaf loss in response to dry air, low light-use efficiency and canopy photosynthesis during periods of direct sun, and changes in allocation of resources to root biomass or reproduction instead of aboveground growth. This project will test hypotheses of direct water limitation and indirect mechanisms to determine the basis for the dry season rainfall correlation with growth. The study will use both observational and experimental approaches to test for direct water limitation, combining measurement of whole forest photosynthesis and the form of energy losses, leaf-and whole-tree water use, monthly tree growth and climate measurements, and a dry-season water-addition experiment. Indirect limitations will be evaluated by measurements of canopy leaf area, leaf temperature, and measurements of root production and metabolism. Measurements of growth and ecosystem carbon, water and energy balance will be used to evaluate the importance of dry season growth reduction for regional climate.This project will support outreach and education components in both South Florida and Costa Rica. In South Florida a partnership has been developed with a local private grade 1-8 school for environmental outreach activities. Project personnel will continue to support the Fairchild Challenge school environmental awareness program at Fairchild Tropical Botanical Garden in Miami. The project will also support the environmental education programs of the Organization for Tropical Studies at the La Selva Biological Station, the location of the study. The project will support one postdoctoral fellow, several undergraduates, and provide training for two Costa Rican technicians. Finally, understanding the basis of the sensitivity of dry season limitation on aboveground biomass production is critical to forecasting the responses of tropical wet forests to future climate regimes.