RUI: Measurement and Modeling of Photosynthetic Responses by Temperate Forest Herbs and Tree Seedling to Nearground Enriched Carbon Dioxide and Irradiance Regimes

Franklin And Marshall College, Lancaster PA

Investigators

Abstract

The proposed research has two goals: (1) to measure the interactive effects of naturally-occurring near-ground enriched carbon dioxide (NEC) and fluctuating light on photosynthesis by six herbaceous and woody plant species in a temperate forest ecosystem; and (2) to model daily leaf-level photosynthesis across a wide range of CO2/light combinations in order to determine the potential for NEC/sunfleck interactions to affect survival, growth, and species composition within and across forest stands. The widespread occurrence of naturally enriched CO2 in the herbaceous zone (due to respiration by plant roots and soil microorganisms) and its likely impacts on photosynthesis have been noted for many decades, but no comprehensive effort has been made to measure or model NEC variation or quantify its effects on photosynthesis, especially under the fluctuating light levels (especially sunflecks) typical of the forest environment. Previous research by the principal investigator and his colleagues has shown that the impacts of enriched CO2 on leaf-level photosynthesis are substantial during both background shade and sunflecks. However, it is necessary to measure NEC/light regimes and photosynthesis more extensively in order to accurately predict NEC variation and its effects on plants over longer time periods (days to weeks). The results of this project will increase our understanding of temperate forest ecology in several important ways. First, the data on spatial and temporal NEC/light variation will help fill a major gap in our knowledge of forest resource environments. Second, empirical models of NEC regulation generated during the project should apply in broad outline to other forested systems. Third, the accuracy with which a recently developed dynamic photosynthesis model can predict daily net carbon gain under a range of CO2 levels in the field will be determined. Finally, the data will have implications for estimating the effects of human-caused global CO2 rise on plant species in the herbaceous stratum, including forest regeneration processes. Undergraduate students will play critical roles in all phases of the proposed project, including research planning, field measurements, data processing, data analysis, presentation of results at professional meetings, and publication. A total of nine students will each spend twenty months on the project, including an academic year of preparation for twelve weeks of intensive summer research at the Harvard Forest research site (Petersham, MA), followed by one to two semesters of formal independent study focused on data analysis, presentation at professional meetings, honors thesis preparation, and co-authorship on publications.