Defoliation and fertiliser influences on the soil microbial community associated with two contrasting Lolium perenne cultivars

The influence of repeated defoliation on soil microbial community (SMC) structure and root turnover was assessed in two contrasting Lolium perenne cultivars (AberDove and S23) grown in fertilised (+F) and non-fertilised (NF) soil. BiOLOG sole carbon source utilisation profiles (SCSUPs) indicated consistently greater potential carbon utilisation in defoliated (+D) compared to non-defoliated (ND) soils regardless of cultivar and fertiliser, and was accounted for in a variety of substrate groups (sugars, carboxylic, amino and phenolic acids). Potential carbon utilisation was also stimulated in +F compared to NF soils, primarily through increased potential utilisation of carboxylic acids. PLFA indicators for the bacterial biomass did not significantly differ between cultivar, soil fertilisation, or defoliation. Defoliated swards grown in fertilised soil (+F+D) had a higher fungal:bacterial ratio and a greater bacterial stress index (cy19:0/18:1w7c), compared to that of +F ND, NF ND and NF+D, and regardless of cultivar. Overall SMC structure (canonical variate (CV) analysis of PLFAs) discriminated based on cultivar, defoliation and soil fertilisation. Primary discrimination of the SMCs could be related to differences in root density and total plant biomass, and in the case of NF soils, secondary community shifts, evident with defoliation, related to root disappearance over the growing season. Despite the strong common effects of defoliation, and to a lesser extent soil fertilisation, cultivar specific drivers of the soil microbial community were maintained, resulting in consistent, but subtle, discrimination of the SMC associated with the contrasting L. perenne cultivars.