Effect of Organic Amendment Amount on Soil Nematode Community Structure and Metabolic Footprints in Soybean Phase of Soybean-Maize Rotation in Mollisols

Abstract In order to assess the effect of the amount of organic amendments on soil nematode community structure and metabolic activity, the community composition, abundance, and metabolic footprints of soil nematodes were determined in a long-term experiment field with various amounts of organic amendments in Northeast China. Fertilization treatments included (1) an unfertilized control (CK), (2) chemical fertilizer without manure amendment (OM 0 ), (3) manure applied at 7.5 Mg ha −1 plus chemical fertilizer (OM 1 ), and (4) manure applied at 22.5Mg ha −1 plus chemical fertilizer (OM 2 ). A total of 46 nematode genera were found in the present study. The treatments with higher organic amendments had the smallest number of genera of plant parasites (5), but larger number of dominant genera (7). Total soil nematodes, bacterivores and fungivores were most abundant in OM 2 , followed by OM 1 , and lowest in both OM 0 and CK. Organic amendments increased enrichment index (EI). High amount of organic amendments increased bacterivore metabolic footprint (Baf), fungivore metabolic footprint (Fuf), and enrichment footprint (Ef). The relationships between metabolic footprint of bacterivores or fungivores and increments of soil organic carbon (ΔSOC) or total soil nitrogen (ΔTN) were stronger than that between abundance of bacterivores or fungivores with exception of the relationship between bacterivores and ΔSOC. The EI and Ef were positively correlated with ΔSOC and ΔTN. These findings suggest that organic amendment amount affect activity or function of soil nematodes at entry levels in food web, and that metabolic footprints of soil nematodes may be better indicators than their abundances in assessing their relationships with nutrients.