Are the soil microbial biomass and basal respiration governed by the climatic regime?

Abstract

Soils in C equilibrium from various climatic regions were sampled to assess the influence of macroclimate on soil microbial biomass (C mic) and basal respiration (CO 2-evolution). C mic was measured using the substrate-induced respiration technique. C mic (μg C mic g −1 soil d.m.) was significantly correlated with several climatic variables, among them mean annual temperature (TEMP). At 20° and 5°C TEMP. 50 and 500 μg C mic g −1 soil were found, respectively. When C mic was calculated based on organic C (C mic-to-C org ratio), a very high correlation with precipitation/evaporation as the climatic variable was found. Of the variance 73% could be explained with the quadratic function y = 64.1− 109.5 x + 55.7 x 2, where y = C mic-to-C org ratio (mg C mic g −1 C org) and x = precipitation/evaporation. Soils from arid climates exhibited a high C mic-to-C org ratio (up to 50 mg C mic g −1 C org). in soils from climates with balanced precipitation and evaporation (P/E = 1), the C mic-to-C org ratio was lowest (15mg C mic g −1 C org). As P/E exceeds this, the C mic-to-C org ratio increased. Any deviation of the C mic-to-C org ratio from this regression line would indicate that a certain soil is not in C equilibrium but is losing or accumulating organic matter. In this study, for soils from a wide climatic range, the effects of pH, N or clay content on C mic and the C mic-to-C org ratio were small. For basal respiration, too, a significant relationship with climatic variables was found. Soils from warmer climates exhibited a basal respiration of 0.3 mg CO 2 g −1 soil h −1 compared to 0.1 mg for cooler climates. The metabolic quotient qCO 2 (μg respiratory CO 2-C g −1 C mic h −1) increased with temperature.