ARE THE SOIL MICROBIAL BIOMASS AND BASAL RESPIRATION GOVERNED BY THE CLIMATIC REGIME

Soils in C equilibrium from various climatic regions were sampled to assess the influence of macroclimate on soil microbial biomass (Cmic) and basal respiration (CO2-evolution). Cmic was measured using the substrate-induced respiration technique. Cmic (μg Cmic 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 Cmic g-1 soil were found, respectively. When Cmic was calculated based on organic C (Cmic-to-Corg 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 x2, where y = Cmic-to-Corg ratio (mg Cmic g-1 Corg) and x = precipitation/evaporation. Soils from arid climates exhibited a high Cmic-to-Corg ratio (up to 50 mg Cmic g-1 Corg). in soils from climates with balanced precipitation and evaporation (P/E = 1), the Cmic-to-Corg ratio was lowest (15mg Cmic g-1 Corg). As P/E exceeds this, the Cmic-to-Corg ratio increased. Any deviation of the Cmic-to-Corg 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 Cmic and the Cmic-to-Corg 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 CO2 g-1 soil h-1 compared to 0.1 mg for cooler climates. The metabolic quotient qCO2 (μg respiratory CO2-C g-1 Cmic h-1) increased with temperature. © 1990.