Organic management practices enhance soil food web biomass and complexity under greenhouse conditions

Abstract Conventional agriculture has induced serious environmental problems that are severe under greenhouse conditions because of the large chemical inputs and high levels of disturbance. Organic and low input management practices with the application of organic amendments, and elimination or reduction of synthetic fertilizer inputs and pesticides, were proposed to alleviate these problems. Existing studies have assessed the effect of different management practices on the communities of one or several types of soil organisms, but the effects on the whole soil food web are unknown. Therefore, we analyzed the impact of three management practices—organic (ORG), low input (LOW) and conventional (CON)—on the structure and biomass of soil food webs under greenhouse conditions in northern China. A range of soil biota including microorganisms, protozoa, nematodes, microarthropods, and annelids, were collected to construct the soil food web. Sampling events were carried out monthly from August to December for 0–10 and 10–20 cm soil depths. The results showed that the number of functional groups, connectance, maximum and mean of food chain length, and food web diversity were highest in ORG, indicating that the soil food web was more complex under organic management practices than the other practices tested. The total food web biomass presented a decreasing sequence of ORG > LOW > CON in both soil layers. For each trophic level, the biomass was greater in ORG than in LOW and CON, and this advantage for ORG increased with increasing trophic level, indicating that organic management practices were more beneficial to biota at higher trophic levels. The principal component analysis based on functional groups showed that the soil food web composition of LOW was between that of ORG and CON, and that of LOW and CON were more similar at 0–10 cm depth. The Bray-Curtis similarity index showed lower variability in ORG than in LOW and CON, indicating a relatively stable soil food web in the organic greenhouse. In summary, organic management practices under greenhouse conditions enhanced soil food web biomass and complexity, which was likely driven by supply of manure and the elimination of chemical inputs.