Global patterns of soil microbial nitrogen and phosphorus stoichiometry in forest ecosystems

Aim To investigate broad-scale patterns of soil microbial nitrogen (N) and phosphorus (P) stoichiometry and their environmental drivers. Location Global forests. Methods By synthesizing 652 observations of soil microbial biomass N and P derived from the published literature, we investigated global patterns of soil microbial N, P and N:P ratios and their relationships with climate, soil and vegetation types. Results Microbial N and P concentrations varied widely among forest types, with relatively low N and P concentrations but high N:P ratios in tropical forests. The N and P concentrations increased and the N:P ratio decreased with increasing latitude (or decreasing temperature). The N:P ratio showed a similar pattern along the precipitation gradient to that along the temperature gradient, whereas microbial N and P displayed weak trends along the precipitation gradient. Edaphic variables also regulated the patterns of microbial N and P stoichiometry: microbial N and P concentrations increased with soil N and P concentrations as well as with soil pH. Mixed-effects models revealed that edaphic factors explained the largest part of the variation in microbial N, P and the N:P ratio, suggesting their dominant role. Main conclusions Our findings highlight that there are broad-scale patterns in microbial N, P and the N:P ratio along the gradients of latitude, temperature and precipitation, which are similar to those reported in plants and soils. The consistency of these patterns in plant–soil–microbe ecosystems supports the hypothesis that P is more often the major limiting element at low latitudes than at high latitudes.