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Resistance of soil protein depolymerization rates to eight years of elevated CO2, warming, and summer drought in a temperate heathland

Wild, Birgit, Ambus, Per, Reinsch, Sabine, Richter, Andreas
Biogeochemistry 2018 v.140 no.3 pp. 255-267
amino acids, ammonium, autumn, carbon dioxide, carbon dioxide enrichment, climate change, climatic factors, depolymerization, drought, extracellular enzymes, heathlands, microorganisms, mineralization, nitrogen, plants (botany), polymers, proteins, soil, stable isotopes, summer, temperature
Soil N availability for plants and microorganisms depends on the breakdown of soil polymers such as proteins into smaller, assimilable units by microbial extracellular enzymes. Changing climatic conditions are expected to alter protein depolymerization rates over the next decades, and thereby affect the potential for plant productivity. We here tested the effect of increased CO₂ concentration, temperature, and drought frequency on gross rates of protein depolymerization, N mineralization, microbial amino acid and ammonium uptake using ¹⁵N pool dilution assays. Soils were sampled in fall 2013 from the multifactorial climate change experiment CLIMAITE that simulates increased CO₂ concentration, temperature, and drought frequency in a fully factorial design in a temperate heathland. Eight years after treatment initiation, we found no significant effect of any climate manipulation treatment, alone or in combination, on protein depolymerization rates. Nitrogen mineralization, amino acid and ammonium uptake showed no significant individual treatment effects, but significant interactive effects of warming and drought. Combined effects of all three treatments were not significant for any of the measured parameters. Our findings therefore do not suggest an accelerated release of amino acids from soil proteins in a future climate at this site that could sustain higher plant productivity.