Kurt S. Pregitzer

Genotypic variation for condensed tannin production in trembling aspen (POPULUS TREMULOIDES, salicaceae) under elevated CO2 and in high- and low-fertility soil

The carbon/nutrient balance hypothesis suggests that leaf carbon to nitrogen ratios influence the synthesis of secondary compounds such as condensed tannins. We studied the effects of rising atmospheric carbon dioxide on carbon to nitrogen ratios and tannin production. Six genotypes of Populus tremuloides were grown under elevated and ambient CO(2) partial pressure and high- and low-fertility soil in field open-top chambers in northern lower Michigan, USA. During the second year of exposure, leaves were harvested three times (June, August, and September) and analyzed for condensed tannin concentration. The carbon/nutrient balance hypothesis was supported overall, with significantly greater leaf tannin concentration at high CO(2) and low soil fertility compared to ambient CO(2) and high soil fertility. However, some genotypes increased tannin concentration at elevated compared to ambient CO(2), while others showed no CO(2) response. Performance of lepidopteran leaf miner (Phyllonorycter tremuloidiella) larvae feeding on these plants varied across genotypes, CO(2), and fertility treatments. These results suggest that with rising atmospheric CO(2), plant secondary compound production may vary within species. This could have consequences for plant-herbivore and plant-microbe interactions and for the evolutionary response of this species to global climate change.

Integration of Ecophysiological and Biogeochemical Approaches to Ecosystem Dynamics

Our ability to predict the extent to which climate change will influence the composition, structure, and function of ecosystems is contingent on understanding and integrating the response of organisms across all levels of ecological organization (i.e., physiological, population, community, and ecosystem levels). The integration of ecophysiology and biogeochemistry holds promise for working across levels of ecological organization and for increasing our understanding of ecosystem dynamics. In this chapter, ecophysiology is integrated with biogeochemistry using the C cycle of terrestrial ecosystems as a primary example. The fixation, redistribution, and loss of C from terrestrial ecosystems are largely controlled by the physiological activities of plants and soil microorganisms; however, there are several key gaps in our understanding of plant and microbial ecophysiology that limit our ability to predict the response of the terrestrial C cycle to a changing climate. The most significant gap in our understanding lies belowground and centers on the physiological links among the allocation of C to the production and maintenance of fine roots, the longevity of these structures, and the extent to which the metabolism and longevity of plant roots influence substrate availability for microbial activity in soil. In this chapter, we identify how a physiologically based understanding of fine-root production, maintenance, and longevity can be used to understand ecosystem-level patterns of C allocation. We then explore the extent to which the amount, timing, and biochemistry of root-associated C inputs influence the composition and function of microbial communities in soil. Understanding the ecophysiological links between plant roots and soil microorganisms lies at the heart of understanding the belowground C budget of terrestrial ecosystems.

Supporting 13 years of global change research: the history, technology, and methods of the Aspen FACE Experiment

This publication is an additional source of metadata for data stored and publicly available in the U.S. Department of Agriculture, Forest Service Research Data Archive. Here, we document the development, design, management, and operation of the experiment. In 1998, a team of scientists from the U.S. Forest Service, Department of Energy (DOE), Michigan Technological University, and several other institutions initiated the Aspen Free Air CO2 and Ozone Enrichment (Aspen FACE) Experiment. Using technology developed at DOEs Brookhaven National Laboratory (BNL), the experiment fumigated model aspen forest ecosystems with elevated concentrations of carbon dioxide (CO2), or ozone, or both in a full factorial design with three replicates. The Aspen FACE Experiment was one of several free-air CO2 enrichment experiments at the time, but was the only one that incorporated ozone treatment into the BNL design. The experiment operated for 13 years, involved more than 70 researchers from 9 countries, has produced 126 scientific publications to date, held numerous tours and scientific conferences, and was the subject of many reports in the public news media. Findings from the experiment contributed to the supplement to the U.S. Presidents 2002 budget, Our Changing Planet; and to the 2006 rewriting of the U.S. Environmental Protection Agencys ozone pollution criteria document. Data and archived plant samples from the experiment continue to be used in many ways, including meta analyses, global change modeling, and studies examining tree characteristics affected by the treatment gases.