Grantee Research Project Results
1999 Progress Report: Diversity and Abundance of Forest Soil Arthropods Under Elevated Carbon Dioxide
EPA Grant Number: R825861Title: 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 Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $332,902
RFA: Terrestrial Ecology and Global Change (1997) RFA Text | Recipients Lists
Research Category: Climate Change , Ecological Indicators/Assessment/Restoration , Aquatic Ecosystems
Objective:
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 carbon dioxide (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. Thus, the quality of the food supply for litter decomposing biota is very likely to be changed by the projected increase in atmospheric CO2. The greatest reservoir of animal diversity in temperate systems is in the litter and soil: a single m2 may contain several hundred arthropod species. This complex fauna plays a significant role in litter decomposition and nutrient cycling and contributes to the metabolism of up to 90 percent of NPP. The present study experimentally examines the response of the litter-dwelling arthropods, their trophic structure, species diversity, and functional impact, to elevated atmospheric CO2 and the concomitant changes in their resource base.Progress Summary:
This study is being conducted over a 3-year period in two plantation forests, an 8-year old sweetgum forest and a 14-year old loblolly pine forest, using 25 m and 30 m diameter plots, respectively, which receive supplemental CO2 raising the concentration in the canopy by +200 ppm over ambient, or which remain at ambient CO2 . The project has two primary elements: a biannual census of the microarthropod assemblages in the full litter layer (including pretreatment litter) and a litterbag experiment to examine the microarthropod response to treatment litter and their effect on its decomposition. In the census, we are monitoring the diversity and abundance of four taxonomic groups (prostigmatid, mesostigmatid, and oribatid mites, and collembola). Litter quality, in terms of carbon, nitrogen, and lignin contents, are being measured as controlling factors for decomposition that are likely to change under elevated CO2 conditions.At the Duke forest site, we have sampled the assemblage each fall and spring for the 2 years since the fall of 1996 when the elevated CO2 treatment began. Because loblolly pine needles take 18 months to mature and senesce, we did not anticipate any treatment effects until fall 1998. Even 2 years after the initiation of the elevated CO2 treatments, as treatment litter is beginning to accumulate, pretreatment litter still makes up a substantial portion of the assemblages' habitat and resource base. Despite the pretreatment carryover and seemingly limited potential for litter-mediated effects, a trend has emerged, consistent among the four groups, of lower microarthro- pod abundances in the elevated CO2 rings. The divergence was most marked in the spring 1998 sampling when overall abundances were high. Mean total microarthropod abundance in the elevated CO2 rings was 30 percent lower than in the ambient rings (F1,3=30.58, p=0.012). Of the four groups, the adult oribatid mites had the strongest divergence, with abundance in elevated rings 35 percent lower. The significant trend also was consistent in the remaining three groups, collembola, prostigmatid mites, and mesostigmatid mites. The dominant oribatid species, Oppiella nova, comprising 30 percent of the oribatid abundance, showed a particularly strong response to the elevated CO2 treatment. O. nova abundance was 63 percent lower in the elevated rings (F1,3=20.16, p=0.021). Since these responses precede any shift in litter quality, they indicate responses to plant- induced effects in the soil that are being transmitted to the litter layer.
At the Oak Ridge site, the CO2 elevation treatment and our sampling began in spring 1998. Our samples to date show a much lower abundance of animals compared to the Duke sites, but already have revealed a change in litter quality (i.e., increased C:N ratio) of the fall 1999 litter. Spring 2000 samples should be informative regarding possible responses of the microarthropods.
We also examined the extent to which stable isotope of carbon associated with the isotopic signature of the CO2 added in the elevated CO2 treatments could be used to trace trophic relationships. In the summer of 1999, we examined the 12/13C signature of the litter profile and of an arthropod food chain in ambient and elevated rings. The elevated CO2 12/13C signature was present in the upper litter horizons (fall 1998 litter) and in fine roots compared to the ambient rings (39.4 versus 28.1 delta ppt, respectively). There was not a significant elevated treatment carbon signature, though, in either the lower litter horizons originating from fall 1997 litter or in the bulk mineral soil at the surface. The 12/13C signature was readily detectable in collembola (fungal feeders) and in spiders (primary predators on microarthropods). Both collembola and spiders from the elevated rings were nearly 10 ppt greater than those from ambient rings, 25.9 versus 16.2 ppt, respectively, indicating that the food webs had been saturated with signal despite the retention of pretreatment litter in the lower litter profile layers.
The progression toward lower microarthropod numbers in elevated CO2 rings was reversed following the arrival of litter with significant treatment influences. By the fall of 1999, abundances of most groups had become equivalent in the two treatments and the abundances of collembola, a microarthropod group co-dominant with the oribatid mites, were higher in the elevated rings. This may be attributable to greater litterfall in elevated rings providing a thicker litter layer that buffers the effects of drying or to other litter effects not associated with changes in quality.
Future Activities:
The assessment of soil arthropod abundances at Duke and Oak Ridge will continue using both organic profile characterization and litterbag studies. In addition, we instituted an additional experiment at the loblolly pine site to distinguish above ground (litter quality) effects from the apparent below ground effects observed during the first 18 months of the experiment. This new litterbag experiment transplants litter from the two treatments into the opposing treatment and by comparison with litterbags using within treatment litter, we should be able to partition the effects on decomposition and the influence of microarthropods. The diversity and composition of the microarthropod assemblage colonizing the bags will be analyzed with the same resolution as in the census sampling. Litterbags will be compared with respect to their mass-loss, C:N ratio, and lignin contents.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 5 publications | 1 publications in selected types | All 1 journal articles |
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Hansen RA, Williams RS, Degenhardt DC, Lincoln DE. Non-litter effects of elevated CO2 on forest floor microarthropod abundances. Plant and Soil 2001;236(2):139-144. |
R825861 (1999) R825861 (Final) |
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Supplemental Keywords:
global change, biodiversity, elevated carbon dioxide, litter quality, decomposition, soil arthropods, Collembola, Oribatida., RFA, Scientific Discipline, Air, Waste, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Environmental Chemistry, climate change, Forestry, Monitoring/Modeling, Atmospheric Sciences, plantation forests, environmental monitoring, biodiversity, forest soil arthopods, carbon dioxide, CO2 concentrations, elevated carbon dioxide, environmental stressors, habitat diversity, harmful environmental agents, litter bags, climate variability, arthropodsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.