Diversity and Abundance of Forest Soil Arthropods Under Elevated Carbon DioxideEPA Grant Number: R825861
Title: Diversity and Abundance of Forest Soil Arthropods Under Elevated Carbon Dioxide
Investigators: Lincoln, David E. , Williams, Ray S.
Institution: University of South Carolina at Columbia
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1997 through September 30, 2000
Project Amount: $332,902
RFA: Terrestrial Ecology and Global Change (1997) RFA Text | Recipients Lists
Research Category: Global Climate Change , Ecological Indicators/Assessment/Restoration , Ecosystems , Climate Change
Description:The extent and manner of effects on biodiversity resulting from globally changing conditions, such as elevated CO2, are not understood, but may be of substantial magnitude. Terrestrial arthropods are widely recognized to constitute the majority of terrestrial species. For example, soil arthropods in temperate forests are a highly diverse assemblage with up to 1000 species per m2 and over 3,400 soil and canopy arthropod species occur at a single site in Oregon. Further, arthropod herbivores, detritivores and predators, and their abundances, are important components in the biotic interactions and the carbon and nutrient dynamics of ecosystems. The present study will experimentally examine the presence and abundance of soil arthropods in the context of forest plots under ambient and elevated CO2 conditions. The goals of this study are to understand the responses of species diversity to globally increasing carbon dioxide and to understand how elevated CO2 environments may alter the processes underlying the trophic structure and function of forest ecosystems.
Convincing evidence of the relative roles of bottom-up and top-down controls of food webs using experimental ecosystems has been obtained from aquatic habitats, but terrestrial ecosystems, particularly trophic webs dominated by arthropods, have proven to be more recalcitrant in yielding data. Large plant-mediated changes are predicted for grazing and detrital food webs under elevated carbon dioxide. One of the major responses of plants derives from the increased photosynthetic rate under elevated CO2 leading to an elevation of leaf carbohydrate content and a depression of leaf nitrogen content, resulting in an increase in the leaf carbon:nitrogen ratio and apparently also an increased lignin:N ratio. These effects have been identified as a primary means by which elevated CO2 effects may be transmitted from plants to other trophic levels. Thus, the quality of the food supply (bottom-up variable) for litter decomposing biota is very likely to be changed by the elevated CO2 conditions which are projected to occur within 50-75 years.
Approach:This study will be conducted in two plantation forests, an eight year old sweetgum forest and a 14 year old loblolly pine forest, using 25 m or 30 m diameter, respectively, plots which will receive supplemental CO2 to raise the concentration in the canopy by +200 ppm over ambient (approximately 550 ppm) or remain at ambient CO2 (approximately 350 ppm). The FACE facilities at Duke University (loblolly pine) and Oak Ridge National Laboratory (sweetgum) are the most realistic approaches to date for examining the effects of CO2 enrichment on forests. The presence and abundance of forest soil arthropod detritivores and predators, as well as their activity in litter decomposition, will be assessed under the ambient and elevated CO2 conditions. Litter quality via altered nutritional and allelochemical characteristics will also be measured. This study provides a unique approach in that we are able to compare two intact forests, differing in tree species composition and soil characteristics, which are experimentally manipulated in essentially the same manner. The similar climate shared at the sites enables us to compare, under a common framework of abiotic factors such as temperature and moisture, how alterations in phytochemical constituents in leaf litter important to soil arthropods.
The proposed research will: 1) determine how CO2 enrichment alters the litter quality in a pine and a sweetgum forest through changes in important phytochemical constituents, e.g. nitrogen, lignin, non-structural carbohydrates, phenolics, and C:N and L:N ratios, 2) elucidate how altered leaf litter chemistry in elevated CO2 plots affects the trophic structure and activities of soil arthropods (i e. test for bottom-up effects), and 3) assess how alterations in trophic dynamics affect the biodiversity of the soil system as species are replaced or disappear, and as functional groups of organisms change in their abundance and activity.
SignificanceThe control of trophic food webs of soil biota is a fundamental feature of forest ecosystem function. The lack of experimental data from manipulated experiments within forests has up to this time precluded understanding how global change driven alterations in trophic structure could affect not only the activities of these systems, but the abundance and diversity of the organisms within them. These considerations become even more important as atmospheric CO2 concentration increases because of the effects CO2 enrichment has on plant physiological processes and phytochemical constituents, which are conveyed through trophic webs, can also affect soil dwelling organisms and decomposition processes.
This study will provide much needed data by examining the fundamental mechanisms underlying changes in trophic structure and function in forests, as well as the biodiversity of the abundant, complex assemblage of soil arthropods. Because we are comparing two different forest types manipulated under similar conditions, we are able to broaden our results to the responses of soil biota to changing leaf litter quality of different compositions. By focusing on the most speciose groups of organisms within these forest ecosystems (i.e. soil arthropods), this study will provide broadly applicable results about the relationship of biodiversity and ecosystem function. The data collected on soil arthropod abundances and diversity will be applicable on a much broader scale than has been possible before, increasing our understanding of how the diversity and trophic level function of soil biota may change in a future elevated CO2 atmosphere.