Climate change and management intensity alter spatial distribution and abundance of P mineralizing bacteria and arbuscular mycorrhizal fungi in mountainous grassland soils

In mountainous grasslands management adaptations are required to maintain soil functions. We investigated climate change (CC) and management effects on the abundance and potential activity of microbiota catalyzing the major steps of P transformation which are still unknown in these grasslands. Soil samples were taken from intact plant-soil mesocosms managed extensively or intensively (two vs. five mowing and slurry applications, respectively). These mesocosms were previously translocated from high to lower altitudes to simulate two CC scenarios (CC1: +1 °C warming and mean annual precipitation (MAP) of 1347 mm and CC2: +3 °C warming and MAP of 956 mm), while control mesocosms (CC0) were relocated at their original site (6 °C and MAP of 1400 mm). Specific marker genes for P-solubilization (gcd), P-mineralization (phoN, phoD, phnX and appA), P-uptake (pitA and pstS), total bacteria and arbuscular mycorrhizal fungi (AMF) were quantified by quantitative real-time PCR. Spatial distributions of phosphatase activities were analyzed in situ by zymography analysis and total organic C, N and P contents were measured. Gene abundances and enzymatic activities were comparable for both managements under CC0, except for phytase-harboring (appA) microbiota which decreased under intensive management. The abundance of microbiota which catalyzes organic P (Po) mineralization (phoN and appA) and those harboring quinoprotein glucose dehydrogenase (gcd) for P solubilization significantly dropped by interacting effects of CC2 and extensive management. The same effect was found for microbes harboring specific P transporters (pitA and pstS). Under intensive management, microbiota catalyzing Po mineralization (phoN and appA), and alkaline phosphatase activities tended to increase in CC2. Noteworthy, the AMF abundance was reduced at 0–5 cm soil depth under CC. Our results suggest that CC and extensive management reduced microbial P solubilization, mineralization and uptake, while management intensification may increase P availability, which leads to shifts in nutrient stoichiometry and decreased AMF abundance.