Effects Of Organic, Low Input And Conventional Management Practices On Soil Biota Community Structure And Soil Food Web Under Greenhouse Conditions

Solar greenhouse is a typical intensive production model in north China. Compared with natural habitat and opened farmland system, the greenhouse is often in a semiclosed state with high input and high disturbance. Conventional management practices bring in high yield but induced serious environmental pollution. Low input and organic management practices improved soil condition, and affected soil organism and food web. Based on the Quzhou Experimental Station of China Agricultural University, A comparative study of organic (ORG), low input (LOW) and conventional (CON) vegetable greenhouse systems was conducted to assess the effect of management practices on the biomass of soil organism, community structure, diversity and food web characteristic. The mean results list below:All three greenhouse systems showed a bacterial-based decomposition pathway and flagellate was the most popular protozoa group. The soil fungal biomass carbon, bacterial biomass carbon, microbial biomass carbon, flagellate abundance, ciliate abundance, amoeba abundance and total protozoa abundance were significantly affected by management practices, while no significant effect was found on the fungal to bacterial ratio (FB) and the relative abundance of flagellate and amoeba. Generally, all soil bacterial, fungal and microbial biomass carbon among three systems presented a decreasing sequence of ORG>LOW>CON. The abundances of flagellate, amoeba and total protozoa under organic management practices were higher than that under low input and conventional management practices. The abundances of the above protozoa were closed in low input and conventional systems.Bacterivores were the most dominant trophic group in all three systems with a mean proportion of over80%, followed by omnivore-carnivores. In general, organic management practices increased the abundance of total nematodes, bacterivores, fungivores and omnivore-carnivores in comparison with low input and conventional management practices. Though inhibitory effects of plant feeders were found in organic and low input systems, these effects were more evident in organic systems. However, small differences were observed in the composition of trophic groups and fauna analysis. All three systems displayed enriched soil conditions and structured food webs. The Shannon index (H’) and genus dominance (λ) suggested that in greenhouse conditions, excessive manure input would cause a decrease in nematode diversity but increase the dominance, particularly for enrichment opportunists.No significant management practices effect was found on the abundance of soil mites, the relative abundance of various suborder and the relative abundance of fungivorous cryptostigmatic and predaceous mites. Significant management practices effects were only found on the relative abundance of fungivorous non-cryptostigmatic and nematophagous mites. The abundance of total mites and various trophic groups fluctuated at different degrees during the sampling times, and they differed in different greenhouses. Acaridae was the most abundant family (meanly38.7%). No significant management practices effect was found on the Shannon index (H1) and dominance (λ) indices.The soil food web structure under organic management practices was better than that under low input and conventional management practices. Higher values of the number of functional groups, connectance, food chain length and food web diversity were obtained in organic greenhouse than in the other two greenhouses. The total biomass among three systems presented a decreasing sequence of ORG>LOW>CON. The biomass of most functional groups were higher in organic system compared with the other two systems, which exhibited similar levels to each other. Organic management practices was more effective in promoting the biomass of high trophic level. The analysis of interaction strengths of food webs showed that both the effect on prey and the effect on predator of various trophic levels were appeared at trophic level2. At0-10cm soil depth, the prey effects and food regulation effects of total organism and various trophic levels among three systems presented a decreasing sequence of ORG>LOW>CON, indicating an increased effect of both bottom-up and top-down effects in organic system than in low input and conventional systems. The energy flow pathway was mainly occurred at the process of microbe feeding on detritus. Higher C and N (only in the0-10cm depth) mineralization rates were found in organic greenhouse than in low input and conventional greenhouses. The contributions of soil fauna to C and N mineralization rates were11.1%and48.3%, respectively, and largest contribution was observed on bacterivore nematodes. Organic management practices improved the contributions of soil fauna to C and N mineralization rates compared with the other two management practices.Management practices were more influential on microorganism biomass than community structure (or functional groups structure). For mesofauna (micro-arthropodes), no evident difference was found on biomass and community structure among three greenhouses. Organic management practices did not show advantage on diversity index, although more taxon were found in this greenhouse. However, food web diversity, which the diversity is based on the functional groups level, presented a higher value than that in the other two greenhouses.We concluded that organic agriculture promoted the optimization of belowground food web structure, and improved the soil organism biomass and function of C and N mineralization. The advantage of biomass can be further reflected on the ecosystem function, such as nutrient mineralization.