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Abstract:
Management intensity modifies soil properties, e.g., organic carbon (Corg) concentrations and
soil pH with potential feedbacks on plant diversity. These changes might influence microbial P
concentrations (Pmic) in soil representing an important component of the P cycle. Our objectives
were to elucidate whether abiotic and biotic variables controlling Pmic concentrations in soil are
the same for forests and grasslands, and to assess the effect of region and management on Pmic
concentrations in forest and grassland soils as mediated by the controlling variables. In three
regions of Germany, Schwa¨bische Alb, Hanich-Du¨ n, and Schorfheide-Chorin, we studied forest
and grassland plots (each n = 150) differing in plant diversity and land-use intensity. In contrast to
controls of microbial biomass carbon (Cmic), Pmic was strongly influenced by soil pH, which in
turn affected phosphorus (P) availability and thus microbial P uptake in forest and grassland
soils. Furthermore, Pmic concentrations in forest and grassland soils increased with increasing
plant diversity. Using structural equation models, we could show that soil Corg is the profound
driver of plant diversity effects on Pmic in grasslands. For both forest and grassland, we found
regional differences in Pmic attributable to differing environmental conditions (pH, soil moisture).
Forest management and tree species showed no effect on Pmic due to a lack of effects on controlling
variables (e.g., Corg). We also did not find management effects in grassland soils which
might be caused by either compensation of differently directed effects across sites or by legacy
effects of former fertilization constraining the relevance of actual practices. We conclude that variables
controlling Pmic or Cmic in soil differ in part and that regional differences in controlling variables
are more important for Pmic in soil than those induced by management.
