Grantee Research Project Results
1998 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, 1997 through September 30, 1998
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:
The extent and manner of effects on biodiversity resulting from globally changing conditions, such as elevated atmospheric carbon dioxide, are not understood, but may be of substantial magnitude. 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% 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. 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 structure and -function of the decomposer assemblage.
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 for litter decomposing biota is very likely to be changed by the elevated CO2 conditions that are projected to occur within 50-75 years.
Approach: This study is being conducted over a three-year period in two plantation forests, an eight 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 (approximately 550 ppm) or which 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 project has two primary elements: a biannual census of the microarthropod assemblages in the full litter layer (including pre-treatment 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) about which we can make generalizations regarding trophic level and life history and their relationship to the effects of elevated carbon dioxide. We are analyzing the assemblages of the two most abundant taxa, the oribatid mites and collembola, with species-level resolution. Litter quality, in terms of carbon, nitrogen and lignin contents are being measured as controlling factors for decomposition which are likely to change under elevated carbon dioxide conditions.
The litterbag experiment includes two treatments: bags from which microarthropods are excluded and bags that are open to colonization. Over a two-year period at Duke and a 1-year period at Oak Ridge, 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. By tracking the decomposition of litter in bags from which arthropods are included and excluded, we will assess effects of elevated CO2 conditions on the animal contribution to decomposition.
Progress Summary:
At the Duke forest site, we have sampled the assemblage each fall and spring for the two years since the fall of 1996 when the elevated CO2 treatment began. To date, we have identified 91 species in 61 genera of oribatid species and 43 species in 19 genera of collembola from the Duke sites. Abundances of each of the four groups have followed a similar seasonal pattern, with abundances higher in spring than in the fall. We interpret this as a response to summer drought, particularly as observed in the fall of 1997.
Because loblolly pine needles take 18 months to mature and senesce, we did not anticipate any treatment effects until fall 1998. Even two 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 microarthropod 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% lower, though this was marginally insignificant. The trend was consistent, though not strong, in 3 of the four groups, collembola, prostigmatid mites and mesostigmatid mites. Of the four groups, the adult oribatid mites had the strongest divergence with abundance in elevated rings 35% lower. The dominant oribatid species, Oppiella nova, comprising 30% of the oribatid abundance, showed a strong response to the elevated CO2 treatment. O. nova abundance was 63% lower in the elevated rings. 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 two sampling dates show a much lower abundance of animals, on average 20% of the abundance at Duke. Species richness is also substantially lower: we have identified 20 species of oribatid mite to date.
Significance:
Decomposer fauna are the gatekeepers of material cycling through ecosystems. As in most systems, the fauna of the temperate forest floor is a hyperdiverse assemblage of invertebrate species including the vast majority of the animal diversity of the system. The control of this complex biota is a fundamental feature of forest ecosystem function and dat on faunal diversity, function and the link between the two are limited. Understanding these issues becomes even more important as atmospheric OC2 concentration increases because of the effect CO2 enrichment has on plant physiological processes and phytochemical constituents which are conveyed through trophic webs and have strong potential to affect soil dwelling organisms and decomposition processes.
This study will provide a first assessment on the impact of an elevated CO2 atmosphere on assemblage structure and biodiversity of the decomposer fauna. Simultaneously, it will document how those alterations in the fauna translate into changes in its crucial role in decomposition processes. Because the study includes two different forest types manipulated under similar conditions, our results will be general, providing insight into the responses of soil biota to changing leaf litter quality in both coniferous and deciduous temperate forest.
Journal Articles:
No journal articles submitted with this report: View all 5 publications for this projectSupplemental Keywords:
global change, biodiversity, elevated carbon dioxide, litter quality, decomposition, Collembola, Mesostigmata, Oribatida, Prostigmata, 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.