Nematode response to nitrogen and phosphorus in grasslands, assessed by microscopy and molecular methods
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Although nematode community analysis is considered to be a useful environmental indicator, a major impediment to its wider adoption is the need for detailed morphological identification. Molecular techniques offer an alternative to this time-consuming traditional way. With both directed molecular T-RFLP approach and traditional microscopy for nematode analysis, this study characterized the responses of belowground nematode diversity and other associated soil processes to P fertilization in a long-term grassland trial and to inorganic N and cattle slurry application in short-term grassland plot. P fertilization (> 40 years) increased the proportion of bacterial-feeding nematodes, while decreased that of fungal-feeding nematodes, indicating a shift from fungal to bacterial pathways in more intensively managed systems. In addition, the microbial PLFA profiles confirmed fungal biomass and fungal-bacterial ratio decreased, but soil microbial biomass C, N and P increased, with P fertilization. Over the short-term period trial (< 2 years), nematode abundance increased significantly with slurry application, but not with inorganic N application. Inorganic N significantly increased bacterial-feeding nematodes, and decreased omnivorous ones, while slurry had no effects. Compared with slurry, higher inorganic N increased the herbage production and enhanced N uptake, indicating a faster N flux following inorganic N fertilization. The traditional and molecular techniques yielded comparable results on profiling nematode community. The rapid, easy and replicable T-RFLP approach was suitable for the routine monitoring of the soil nematode community, which helped to advance the characterization of soil biodiversity and monitoring the soil quality. Further, real-time PCR assessment was used to determine the correlation between SSU rDNA copy number and body size of four free-living nematode species. No correlation was found for Caenorhabditis elegans, showing it is eutelic. The three other species (Panagrolaimus detritophagus, Anatonchus tridentatus and Aporcelaimellus obtusicaudatu, however, are non-eutelic, showing that rDNA copy number increased significantly with body size.