Responses Of Soil Nematode Community To Grazing By Herbivore Assemblages In Songnen Grassland

Soil nematodes play a leading role in decomposition of organic materials, mineralization of nutrient and serving as a bio-indicator of environment. Moreover, the composition and diversity of nematode is related to the function and stability of ecological system. In grassland ecosystems, grazing by large herbivores plays an important role in affecting the soil nematode, which exerts impacts on plant community, soil nutrient and micro-environment. Feedback mechanism among multi-trophic levels makes it possible that the change of community and function of nematode induced by grazing also influence above-ground plant and higher trophic levels. Finally, feedback regulation among multi-trophic levels has important significance in the maintenance of ecosystem stability, promoting ecosystem process and functions.A randomized blocks designed experiment was established in the Songnen meadow steppe, with plant diversity and herbivore assemblages as two factors. There were two levels of plant diversity (low, high) and four herbivore assemblages (no grazing, sheep grazing, cattle grazing and mixed grazing) were randomly assigned to the plots and subplots respectively. There were8replicates for each treatment combination. We performed the soil nematode diversity investigation in early August2013. The nematodes extracted by Baermann funnel method were counted and identified. Then the diversity of soil nematodes with herbivore assemblages were indicated by species type, density, diversity and function index, which further revealed the interactions between large herbivores and soil nematodes. The main results are present as follows:(1) There were59genera on northeastern Songnen meadow steppe. The advantage genera among different plots were Chiloplacus, Aporcelaimus, Acrobeles, Acrobeloides, Eucephalobus, Tylenchorhynchus, Discolaimus, Prismatolaimus, Diphtherophora, Tylencholaimus, Aphelenchus, Eumonhystera, Helicotylenchus, and Gracilacus.(2) Sheep grazing reduced soil nematode density and mix grazing increased its abundance in the low diversity plot of Leymus chinensis. Cow grazing and mix grazing, increased abundance of nematode in the plots of high diversity, but sheep grazing reduced the density. Grazing reduced the abundance of soil nematodes in the plots of low plant diversity in the Kalimeris integrifolia community, especially for single grazing and mixed grazing. Cattle grazing and sheep grazing increased the density of soil nematodes significantly at high level of plant diversity.(3) Grazing increased the richness at low level of plant diversity in the community of L. chinensis, but it reduced the richness at high level of plant diversity. In the community of K. integrifolia with high plant diversity, sheep and cattle grazing increased nematode richness, diversity index and evenness index significantly, while in the plots with low plant diversity mixed grazing had negative effects.(4) Grazing reduced maturity index of nematodes in the plots with low plant diversity and increased the index in the plots with high plant diversity. This suggested that grazing decreased the stability of soil system in the plant community of low diversity. In the plots with high plant diversity, grazing has great significance for maintaining and improving soil stability.(5) Mix grazing improved the Wasilewska index at low diversity of plant in the community of L. chinensis, while cow grazing and sheep grazing reduced Wasilewska index. The increase of Wasilewska index within sheep grazing and mix grazing plot indicated that the portion of plant nematode was least. That means that it can maintain the health of above-ground plant. Sheep grazing had lowest proportion of plant-eating nematodes groups in the community of K. integrifolia with lower diversity, which had the vital significance for the nutritional health of above-ground vegetation. So, compared with cattle grazing and mixed grazing, sheep grazing can be used as the more effective grassland management in the community with low plant diversity. However, in the community with high plant diversity, grazing reduced soil nematodes gas index significantly. This suggested that grazing had negative effects on the health of vegetation of grassland ecosystem.In the meadow steppe of L. chinensis herbivore assemblages have a significant impact on soil nematodes. The mixed grazing significantly increased soil nematode abundance, diversity, richness and Wasilewska index, which is not only conducive to the maintenance of biological diversity of underground but also to keep aboveground vegetation health. For the above reasons, in L. chinensis grassland mixed grazing can become one of the most economical and effective way of grassland management.