SYMP 1-3: Soil invertebrate composition and ecosystem processes: Comparing agricultural ecosystems with natural ecosystems
Deborah Neher, University of Vermont
In soil, the basic food web structure is similar to other food webs by containing primary producers, consumers and detritivores. In contrast, soil food webs tend to have longer food chains, greater incidences of omnivory, and possibly greater complexity than other food webs. Plant roots, organic debris, soil aggregates, and soil pore structure provide habitats for soil organisms.
As interest in reducing fossil-fuel-based inputs increases, reliance on natural cycles and processes will increase. Perhaps it is more important to mimic the diversity of ecosystem function observed in natural systems than to mimic diversity of community composition. For example, an index of trophic diversity may serve as a measure of functional diversity in soil communities. Use of a trophic diversity index assumes that greater diversity of trophic groups in soil food webs and longer food chains correspond with improved ecosystem function. To test the validity of such assumptions, it is important to identify ecological functions of soil and how soil organisms are involved in those functions. Soil organisms play principal roles in several ecosystem functions, i.e., promoting plant productivity, enhancing water relations, regulating mineralization, permitting decomposition, and acting as an environmental buffer.
Rates of nutrient release and decomposition are sensitive to physical disturbances such as cultivation and the presence of plant roots. Soil fumigation with general biocides has short and/or long-term impacts on soil community composition and abundance. Soil community composition with perennial crops resembles that of natural ecosystem soils more closely than is the case with annual crops. Although it is difficult to separate their individual effects, concurrent additions of organic matter and elimination of general biocides have the benefit of allowing omnivores and predaceous species to increase in prevalence, which promotes natural disease suppression. Agricultural soils would more closely resemble soils of natural ecosystems if management practices would reduce or eliminate cultivation, heavy machinery, and general biocides; incorporate perennial crops and organic material; and synchronize nutrient release and water availability with plant demand.