Published by Copernicus Publications on behalf of the European Geosciences Union.L. Thieme et al.: Dissolved organic matter characteristics of deciduous and coniferous forests uous and coniferous forests. Forest management intensity, mainly determined by biomass extraction, contribution of species, which are not site-adapted, and deadwood mass, did not influence DOC concentrations, DOM composition and properties significantly.
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). Methods The potential enzyme activities (Vmax) and the apparent substrate affinities (Km) of βcellobiohydrolase (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. Results 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. Conclusions 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.
<p><strong>Abstract.</strong> Dissolved organic matter (DOM) is part of the biogeochemical cycles of carbon and nutrients, carries pollutants and drives soil formation. The DOM concentration and properties along the water flow path through forest ecosystems depend on its origin and transformation processes. To improve our understanding of the effects of forest management, especially tree species selection and management intensity, on DOM concentrations and properties of samples from different ecosystem fluxes, we studied throughfall, stemflow, litter leachate and mineral soil solution at 26 forest sites in the three regions of the German Biodiversity Exploratories. We covered forest stands with three management categories (coniferous and deciduous age-class, unmanaged beech forests). In water samples from these forests, we monitored DOC concentrations over four years and characterized the quality of DOM with UV-vis absorption, fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) and with Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). Additionally, we performed incubation-based biodegradation assays. Multivariate statistics revealed strong significant effects of origin of ecosystem fluxes and smaller effects of main tree species on DOM quality. Coniferous forests differed from deciduous forests by showing larger DOC concentrations, more lignin- and protein-like molecules, and less tannin-like molecules in throughfall, stemflow, and litter leachate. Cluster analysis of FT-ICR-MS data indicated that DOM compositions, which varied in aboveground samples depending on tree species, become aligned in mineral soil. This alignment of DOM composition along the water flow path in mineral soil is likely caused by microbial production and consumption of DOM in combination with its interaction with the solid phase, producing a characteristic pattern of organic compounds in forest mineral soils. We found similarly pronounced effects of ecosystem fluxes on the biodegradability of DOM, but surprisingly no differences between deciduous and coniferous forests. Forest management intensity, mainly determined by biomass extraction, contribution of species, which are not site-adapted, and deadwood mass, did not influence DOC concentrations, DOM composition and properties.</p>
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