Microbial community size is a potential predictor of nematode functional group in limed grasslands

Agronomic management practices can impose structural change within soil biotic communities that may negatively impact soil processes including function and biodiversity. Thus, optimizing sustainable crop production that confers minimal impacts on the structure and function of soil biota is an imperative to deliver healthy, functional and resilient production systems. Liming is a management intervention to mitigate soil acidification with a generally positive effect on crop biomass. The application of lime changes soil pH, a known driver of microbial community composition, but it is unknown whether pH derived shifts in bacterial communities result in altered nematode communities. In this study we used qPCR, next generation sequencing and nematode directed T-RFLP to characterise microbial and nematode communities in a liming field trial with a control and three liming applications to incrementally increase pH by 0.5, 0.75 and 1 pH unit. We demonstrate over a 14-month experimental period an interaction between microbial and nematode communities in managed grasslands. Liming had a limited effect on nematode and microbial community structures. However bacterial and archaeal abundance as measured by 16S rRNA gene copy number was found to be a potential predictor of nematode functional group, based on recognized trophic strategies, with increased abundance of omnivorous and predatory nematodes, that are known to prey upon bacterivorous nematodes, with a concomitant increase of 16S rRNA gene copy number. Thus, indirectly suggesting suppression of the bacterial and archaeal community in the presence of bacterivorous nematodes. Where populations of bacterivorous nematodes were highest the relative abundance of both predatory and omnivorous nematodes was lowest. Thus, this study demonstrates clear connectivity between soil microbial and nematode communities in grassland soil.