Micro-scale distribution of microorganisms and microbial enzyme activities in a soil with long-term organic amendment

Microbial ecology is the key to understanding the function of biodiversity for organic matter cycling in the soil. We have investigated the impacts of farmyard manure added over 120 years on organic matter content, enzyme activities, total microbial biomass and structure of microbial populations in several particle‐size fractions of a Luvic Phaeozem a few kilometres northeast of Halle, Germany. We compared two treatments: no fertilization (control) and 12 t farmyard manure (FYM) ha^?1 year^?1 since 1878. The fine fractions contained most C and N, microbial biomass, total amount of phospholipid fatty acids (PLFAs) and greatest invertase activity. Xylanase activity as well as fungal biomass increased only gradually with diminishing particle size, whereas the relative abundance of fungi decreased with diminishing particle size. The least diversity of the soil microbial community, indicated by the smallest Shannon index based on the abundance and amount of different PLFAs and small number of terminal restriction fragments (T‐RFs) of 16S rRNA genes, was in the sand fractions. The results supported the hypothesis that this microhabitat is colonized by a less complex bacterial community than the silt and clay fractions. Addition of FYM had enhanced the amount of organic matter, total microbial biomass, and xylanase and invertase activity, and induced a shift of the microbial community towards a more bacteria‐dominated community in the coarse sand fraction. Microbial communities in finer fractions were less affected by addition of FYM.