Land-use intensity shapes kinetics of extracellular enzymes in rhizosphere soil of agricultural grassland plant species

Abstract

The aim of this study was to identify how land-use intensity shapes the kinetic properties of extracellular hydrolytic enzymes (EHEs) in rhizosphere soil among and within plant species representing different i) resource acquisition strategies (exploitative (ex) vs. conservative (co) plant species) and ii) response types to land-use intensification (winner (Wi) vs. loser (Lo), i.e. species that increase in abundance due to land-use intensification vs. species that decrease in abundance). The potential enzyme activities (Vmax) and the apparent substrate affinities (Km) of β-cellobiohydrolase (CBH), β-glucosidase (BG), xylanase (XYL), N-acetylglucosaminidase (NAG), and phosphomonoesterase (PH) were determined in rhizosphere samples of Agrimonia eupatoria (co, Lo), Dactylis glomerata (ex, Wi), Lotus corniculatus (co, Lo), Taraxacum sect. Ruderalia (ex, Wi) and Trifolium repens (ex, Wi). Samples (n = 37) were taken on six permanent grasslands along a gradient in land-use intensity in central Germany. Plant species identity and performance of species to land-use intensity are less important for explaining enzyme kinetics than are land-use intensity and associated changes in soil properties (especially organic carbon, pH and C:N ratio) and composition of the surrounding plant community, i.e. the abundance of herbs and plant diversity. However, the rhizosphere of winner species of intensive land-use was characterized by higher Km of CBH and two out of the three winners were associated with lower Km of PH. Higher Vmax of XYL in the rhizosphere of winner species suggest higher production of hemicellulose-degrading enzymes in rhizospheres of higher land-use intensity. This study demonstrates that both land-use intensity and to a lower degree the type of plants’ resource acquisition strategy affect EHEs of C-, N-, and P-cycles in the rhizosphere. Rhizospheres of common grassland species are hotspots of hemicellulose, chitin, and organic P degradation but not of cellulose degradation. Further studies should consider variations in the kinetics of EHEs as a function of root orders and soil depths.