Soil Microbial Biomass and Rhizosphere Effects in Natural Forest Stands : Root - Soil Interactions in Trees

2000

S. 83-90

16 Lit.Ang.

Unselbständiges Werk

200083825

In 12 natural forest stands of 6 different forest types, soil microbial biomass and microbial activity were assessed. In order to identify the readily available substrates for soil microbes, low molecular weight compounds in the soil organic matter were analysed. Across the forest stands studied, values of microbial biomass varied widely. Differences between microbial biomass measured by fumigation-extraction (FE) and by substrate-induced respiration (SIR) were attributed to the fact that both methods apply to different subset of the soil microbial biomass. While FE-biomass was mainly related to overall forest nutrient status, SIR-derived biomass was correlated to soil respiration and pH. In all forest types glucose and trehalose were the sugars ound in highest concentrations. Of the amino acids analysed, glutamine, alanine, valine and leucine were prevailing. Each forest stand showed a distinct pattern of individual amino acids, which reoccurred at all sampling dates. Absolute amounts varied depending on season. Among forest types, different limitations were found acting upon the growth of the microbial biomass. In the more acidic soils, microbial biomass was significantly correlated to soil pH. Positive correlations between microbial biomass and soil moisture and total soil N were found in soils of all forest types except the oak forests. By comparing soils from various forest types, effects of forest vegetation on the quantity and composition of low molecular weight compounds in the soil organic matter were shown. The forest stands selected for this study were widely unaffected by management practices and therefore were especially suited for ecosystem studies. We suggest that soil microbial biomass-characteristics of natural forests are valuable reference-data for studies in cultivated or stressed ecosystems.