Different temperature sensitivity and kinetics of soil enzymes indicate seasonal shifts in C, N and P nutrient stoichiometry in acid forest soil
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Acid forest soils in the Bohemian Forest in Central Europe are biogeochemically imbalanced in organic C, N and P processing. We hypothesized that these imbalances can be due to different temperature sensitivities of soil enzyme activities and their affinities to substrate in litter and organic soil horizons. We measured potential activities of five main soil enzymes (β-glucosidase, cellobiohydrolase, Leu-aminopeptidase, Ala-aminopeptidase, and phosphatase) responsible for organic carbon, nitrogen and phosphorus acquisition. We also modeled potential in situ enzyme activities and nutrient release based on continuous in situ temperature measurements. We determined basic kinetic parameters (Km, Vmax), enzyme efficiencies (kcat) and temperature sensitivities (Ea and Q10) according to Michaelis–Menten kinetic and modified Arrhenius models. Our results showed significant differences in substrate affinities between the litter and organic soil horizons. Higher aminopeptidase affinity (lower Km) in the litter soil horizon can lead to leaching of peptidic compounds to lower soil horizons. β-Glucosidase and phosphatase showed high temperature response following the Arrhenius model. However, both aminopeptidases showed no or even decreased activity with increasing temperature. The aminopeptidase temperature insensitivity means that peptidic compounds are degraded at the same or even lower rate in warmer and colder periods of the year in acid forest soils. This imbalance results in different release of available nutrients from plant litter and soil organic matter which may affect bacterial and fungal community composition and nutrient leaching from these ecosystems.
KeywordsAcid forest soil Enzyme kinetics Potential enzyme activity modeling Q10 Soil enzymes Temperature sensitivity
This study was supported by the Czech Science Foundation, project 526/08/0751 and project GAJU 143/2010/P. We acknowledge the laboratory and field assistance provided by our colleagues and students. We also thank the authorities of the National Park Bohemian Forest for giving their permission to study the lake ecosystems. We thank Dr. Keith Edwards for language correction.
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