The responses of soil organisms to the addition of crop residue and aboveground herbivory under conventional tillage and no-till agroecosystems

In agroecosystems, tillage is the major disturbance to soil, causing the redistribution of plant residue and soil organic matter, and subsequently changing the structure of soil communities. Apart from plant residues, the plant roots and root-associated materials are also major resources for soil organisms in agroecosystems. What is the relative importance of plant residues and plant roots to soil organisms under different tillage regimes? Bearing this in mind, I conducted a pair of studies (laboratory vs field) to monitor the responses of soil organisms to the addition of plant residues and another field study to monitor the responses of soil organisms to the aboveground herbivory. The overall objective of these studies was to investigate the factors organize belowground food webs in agroecosystems. 14C labeling techniques were used to trace the carbon flow from aboveground to belowground components. 14C distribution in different soil compartments was estimated, and the dynamics of soil organic matter and soil food webs were modeled for conventional tillage (CT) and no-till (NT) agroecosystems.; Our results illustrated that most 14C input to soil from plant residues was released into air through soil respiration in both CT and NT treatments, with only a small portion bound in microbial biomass and nematodes. However, more 14C was respired and less retained in biomass under NT than under CT, in another word, carbon utilization efficiency was higher under CT than under NT regime. We also observed that residue-derived carbon contributed more to different soil compartments under CT than under NT, and 14C specific activity of different soil compartments were significantly higher under CT than under NT. Therefore, we concluded that plant residues might be a more important resource to soil organisms under CT than under NT.; The sensitivity analysis of C model showed that the population of soil microorganisms were sensitive to the change of decomposition rate of crop residue but not to any change of other groups of soil animals at higher hierarchical levels, indicating that soil microorganisms were controlled by resources rather than predators. However, the populations of soil protozoa, nematodes and microarthropods were sensitive to both the change of microbial activity and earthworm biomass, suggesting these soil organisms were controlled by both resources and predators.; In the herbivory study, we found that the aboveground herbivory had a significant impact on trophic groups of soil nematodes, particularly to the fungivorous and bactrivorous nematodes under NT regime, however, it did not affect the soil nematodes under CT regime. We hypothesized that plant roots and root associated materials might be more important to soil organisms under NT than under CT.