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United States Department of Agriculture

Agricultural Research Service

Title: Carbon and Nutrient Flow Through Multiple Trophic Levels in a Co2-Enriched Southern Pine Forest Community

Authors
item Rogers Jr, Hugo
item Davis, Micheal - UNIV. OF SOUTH. MISS.
item Pritchard, Seth - AUBURN UNIVERSITY
item Schlesinger, William - DUKE UNIVERSITY
item Runion, George
item Prior, Stephen
item Gjerstad, Deam - AUBURN UNIVERSITY

Submitted to: Technical Report
Publication Type: Other
Publication Acceptance Date: May 1, 2003
Publication Date: May 1, 2003
Citation: Rogers Jr, H.H., Davis, M., Pritchard, S., Schlesinger, W., Runion, G.B., Prior, S.A., Gjerstad, D. 2003. Carbon and nutrient flow through multiple trophic levels in a co2-enriched southern pine forest community. Southeastern Regional Center, National Institute for Global Environmental Change, Annual Report for Fiscal year 2002. The University of Alabama, Tuscaloosa, AL. 10 pp.

Interpretive Summary: We are investigating the effects of elevated atmospheric CO2 on forest litter and how this impacts soil fauna in a southeastern pine forest. Changes in litter quality and microhabitat can alter detritivore communities and carbon flow between the litter and soil. Early results suggest that the litter microhabitat at Duke forest is largely unaffected by changing CO2 level. Litter chemistry or quality were also relatively unaffected by CO2. But, feeding trials indicated that climate-induced changes in litter chemistry may exist in terms of shifts in defensive compounds. Initial results on soil fauna abundance and diversity suggest that diversity is not impact by CO2, however, shifts in species composition occurred within these communities. This research focuses on an aspect of the carbon cycle that has been neglected, thus allowing for more accurate estimates of soil carbon fluxes.

Technical Abstract: The ability to predict the consequences of global change is predicated on our understanding of controls of energy and material flows through ecosystems. Research was conducted at the Forest Atmosphere CO2 Transfer and Storage-1 (FACTS-1) site at Duke University. This is a flagship experiment of the Terrestrial Carbon Processes (TCP) research program of the US Department of Energy, a core project of the International Geosphere-Biosphere Program (IGBP), and a contributes to the US Global Change Research Program. The FACTS-1 experiment consists of six experimental rings (30 m diameter). Gaseous CO2 is delivered through a series of perforated vertical pipes that extend to the top of the canopy. Starting in 1996, three fully instrumented plots receive ambient air (control), and three are enriched with CO2 (ambient +200 ppm). To date, 384 forest floor samples and 288 pitfall samples have been collected from Duke Forest. Processing and taxonomic sorting of current samples should be complete by May 2004. Both types of samples will contribute species richness data and the forest floor samples will provide arthropod density data. The final survey is scheduled for September 2003. Dry weight of litter samples did not differ between CO2 treatments in September 2001 nor in May 2002. The first set of samples (September 2001) has been taxonomically sorted. Arthropods were sorted by class into Chilopoda, Diplopoda, Pauropoda, Symphala, Insecta and Arachnida. Insecta and Arachnida were sorted to family. Thirty-six insect families were identified from twelve orders and fourteen arachnid families were identified from four orders. In addition, three non-arthropod phyla were included (Mollusca, Annellida, and Nematoda). Initial analyses indicate that there are no differences in overall diversity between treatments, however, species composition of the soil fauna communities differs. Several taxa were exclusive to either elevated or ambient plots. Litter enriched by CO2 did not affect the growth of millipedes over the duration of the feeding experiment, although there was a trend towards decreased weight gain for millipedes fed CO2-enriched Pinus taeda litter. Overall, however, millipedes performed better on a diet of P. taeda litter than on a diet of either (Liquidambar styraciflua or Cersis canadensis litter. Although, C. canadensis litter had the highest N content of any other type of litter, detritivores performed poorest on a diet of this litter. Litter from ten different tree species representing different structural and functional guilds was analyzed for C:N, total phenolics, and condensed tannins. Exposure to elevated CO2 did not significantly affect total phenolics condensed tannin contents of litter for any species. Carbon-nitrogen ratios of litter were unaffected for all species except C. florida, for C:N was significantly higher in CO2-enriched litter. Interspecific differences were present for total phenolics, condensed tannins, and C:N. Of the three species used in the millipede feeding study (P. taeda, L. styraciflua, and C. canadensis), P. taeda litter appeared to be the poorest quality diet based on chemical analysis (high values for phenolics, condensed tannins and C:N). Yet, as stated previously, millipedes performed better on P. taeda litter than on L. styraciflua or C. canadensis litter, likely due to the presence of alkaloids in C. canadensis litter. Preliminary finding suggest the following: 1) long-term changes in litter microhabitat may be a factor in determining arthropod community composition; 2) overall density of arthropods seems to be unaffected by CO2 enrichment, however, shifts in relative importance of certain species occurred; 3) in most instances, the quantitative defensive chemistry (tannins, etc.) of litter from individual species did not respond to CO2 enrichment, however, additive effects can alter overall litter quality; 4) C:N and polyphenolic compounds are not always the most important criteria for determining dietary quality; 5) qualitative defensive chemistry (e.g. alkaloids) also plays an important role; 6) taxonomic patterns exist for litter quality responses; 7) 'negative' detritivore responses do not always result in decreased carbon and nutrient flow through soil food webs suggesting that compensatory feeding on low quality litter may actually increase decomposition.

Last Modified: 4/21/2014
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