Distribution of Extracellular Enzymes in Soils: Spatial Heterogeneity and Determining Factors at Various Scales

Decomposition of organic matter in soil is mediated by a complex set of extracellular enzymes that are produced by soil fungi and bacteria. Therefore, enzyme activity measurements can suitably represent the turnover of nutrients in soils and litter and can be widely used to explore soil functioning. Previous studies that have been performed at different scales have indicated that enzyme distribution in space is highly heterogeneous. This review summarizes the current knowledge regarding the extent of this spatial variability and the factors that contribute to its establishment. The distribution of enzymes is spatially heterogeneous at various scales. Spatial autocorrelation has been recorded for the activity of hydrolytic and oxidative enzymes in the range of 10s of centimeters to a scale of meters when considering areas ranging from square meters to hectares; however, enzyme molecules are unevenly distributed even across areas of several centimeters, exhibiting spatial autocorrelation in the range of 10s of millimeters. At these scales, patches of nutrients and microbial biomass, plant roots, or colonies of specific microorganisms seem to induce high enzyme activity. In such areas, the activity of multiple enzymes is often increased. At larger scales, variation in microbial biomass, effect of individual trees, and actual soil moisture may shape enzyme distribution. Additionally, when studying a range of several square kilometers, the dominant vegetation, land use type, and soil physicochemical properties affect enzyme distribution. Because these factors change with time (soil moisture content, in particular), the distribution of soil enzymes and decomposition rates are probably highly dynamic.