Five-year fertilization alters soil microbial composition and functionality in sandy grassland

The impacts of reclamation and fertilization of sandy grassland on soil microbial communities and functional groups related to carbon (C) and nitrogen (N) cycling are not well understood. To fill this gap, three types of fertilizers, namely, chemical fertilizer (CF), manure (M), and chemical fertilizer plus manure (CF_M), were applied annually for five years to reclaimed sandy cropland planted to maize. Nearby sandy grassland without fertilizer and maize was included as a control. Soil microbial communities and processes, soil properties, and aboveground biomass (AGB) were determined. Soil microbial Chao richness was lowest in soil without fertilizer and maize. Fungal Shannon diversity was lowest with chemical fertilizer plus manure, while soil microbial Chao richness and bacterial Shannon diversity were not influenced by fertilization. Reclamation and fertilization increased AGB, which was greatest with chemical fertilizer plus manure and was more than seven times greater than that of sandy grassland. Soil extracellular enzyme activities increased with chemical fertilizer plus manure. Fertilization enhanced C cycle functional groups by decreasing soil bulk density and elevating soil total N, total carbon, Firmicutes abundance, and bacterial Chao richness, but lessened N cycle functional groups by decreasing Nitrospirota abundance. Microbial functional category groups associated with C and N cycles responded differently to reclamation and fertilization of sandy soil, which, in turn, affected soil carbon sequestration and nutrient availability. IMPORTANCE: Reclamation and fertilization of sandy grassland altered biogeochemical functions by influencing microbial communities and functional category groups related to carbon (C) and nitrogen (N) cycling. Reclamation and fertilization could lead to the reduction of soil C content and insufficient soil N by altering functional category groups, which would be a potential risk leading to sandy grassland degradation. These findings not only improve our understanding of the consequences of sandy grassland reclamation and fertilization on ecosystem processes, but are also important for predicting soil C sequestration and nutrient cycling and for developing strategies to prevent degradation of sandy grassland.