Land cover change effects on soil chemical and biological properties after planting Mongolian pine (Pinus sylvestris var. mongolica) in sandy lands in Keerqin, northeastern China

We compared soil moisture content, pH, total organic carbon (C (org)), total nitrogen (TN), total phosphorus (TP) and inorganic N (NH4 (+)-N, NO3 (-)-N) concentrations, soil potential C and N mineralization rates, soil microbial biomass C (C (mic)), soil metabolic quotient (qCO(2)), soil microbial quotient (C (mic)/C (org)) and soil enzyme (urease and invertase) activities in semiarid sandy soils under three types of land cover: grassland, Mongolian pine (Pinus sylvestris var. mongolica) plantation, and elm (Ulmus punila)-grass savanna in southeastern Keerqin, in northeast China. Soil C (org), TN and TP concentrations (0-10, 10-20, 20-40 and 40-60 cm) were lower while soil C/N and C/P ratios were higher in the plantation than in grassland and savanna. The effects of land cover change on NH4 (+)-N and NO3 (-)-N concentrations, soil potential nitrification and C mineralization rates in the surface soil (0-10 cm) were dependent on sampling season; but soil potential N mineralization rates were not affected by land cover type and sampling season. The effects of land cover change on C (mic) and qCO(2) of surface soil were not significant; but C (mic)/C (org) were significantly affected by land cover change and sampling season. We also found that land cover change, sampling season and land cover type x sampling season interaction significantly influenced soil enzyme (urease and invertase) activities. Usually soil enzyme activities were lower in the pine plantations than in grassland and savanna. Our results suggest that land cover change markedly influenced soil chemical and biological properties in sandy soils in the semiarid region, and these effects vary with sampling season.