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.