Enzyme patterns in topsoil and subsoil horizons along a latitudinal transect in Western Siberia

Wien

2014

S. 12

Artikel aus einer ZeitschriftUnselbständiges Werk

200189772

Soil horizons below 30 cm contain up to 60 % of the carbon stored in soils. Although we gain more and more insight into physical and chemical stabilisation mechanisms and into microbial community composition in these horizons, we lack information on functions of subsoil microbial communities and consequently on microbial processes. We investigated activities of six extracellular enzymes (cellobiohydrolase, leucine-amino-peptidase, N-acetylglucosaminidase, chitotriosidase, phosphatase and phenoloxidase), and the resulting enzyme patterns. We sampled soils from organic topsoil horizons (0 - 10 cm), mineral topsoil horizons (6 - 28 cm) and mineral subsoil horizons (23 - 75 cm) from seven biomes along a 1,500 km long latitudinal transect in Western Siberia. To identify controls on enzyme patterns, we correlated enzyme patterns with biotic and abiotic soil parameters, as well as with microbial community composition (estimated using phospholipid fatty acid analysis). We found that hydrolytic enzyme activities decreased rapidly with depth, whereas oxidative enzyme activities in mineral horizons were as high as, or higher than in organic topsoil horizons. To our surprise, enzyme patterns varied stronger between ecosystems in mineral subsoils than in organic topsoil horizons. This might have been caused by a diverging chemical composition of soil organic matter with ongoing decomposition, or by a higher variability in microbial community composition in mineral horizons. The enzyme patterns in topsoil horizons were mainly correlated with SOM content (C and N) and microbial community composition. The enzyme patterns in mineral subsoil horizons, in contrast, were related to water content, pH and microbial community composition. The consistent correlations of enzyme patterns with microbial community composition in all three horizons suggest that enzyme patterns reflect the functional capacity of the microbial community. The lack of correlations of enzyme patterns and SOM quantity in the mineral subsoil indicates that SOM chemistry, spatial separation or physical stabilization of SOM rather than SOM content might determine substrate availability for enzymatic breakdown and calls for caution when considering subsoils in ecosystem models and in upscaling exercises.