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

Spatial soil ecology is the key to understand the function of soil biodiversity for organic matter cycling. Therefore, we investigated the impacts of farmyard manure added over 120 years to organic matter content, enzyme activities, total microbial biomass and structure of microbial populations in different soil particle-size fractions of a Luvic Phaeozems a few km northeast of Halle, Germany. We compared two treatments: no fertilization (control) and 12 t FYM ha-1 year-1 (farmyard manure). Since 1878, the fine fractions contained most C and N, microbial biomass, total amount of phospholipid fatty acids (PLFAs) and highest 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 low number of terminal restriction fragments (T-RFs) of 16S rRNA genes - was found 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 farmyard manure had enhanced the amounts of organic matter, total microbial biomass, 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 .