Substrate quality affects microbial‐ and enzyme activities in rooted soil |
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| Authors: | Sebastian Loeppmann Mikhail Semenov Evgenia Blagodatskaya Yakov Kuzyakov |
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| Affiliation: | 1. Dept. of Soil Science of Temperate Ecosystems, University of G?ttingen, Büsgenweg 2, 37077 G?ttingen, Germany;2. Lomonosov Moscow State University, Department of Soil Science, Leninskie Gory 1–12, 119991 Moscow, Russian Federation;3. V.V. Dokuchaev Soil Science Institute, Pyzhevskiy pereulok 7, 119017 Moscow, Russian Federation;4. Institute of Physicochemical and Biological Problems in Soil Science, 142290 Pushchino, Moscow Region, Russian Federation;5. Dept. of Agricultural Soil Science, University of G?ttingen, Büsgenweg 2, 37077 G?ttingen, Germany |
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| Abstract: | The rhizosphere reflects a sphere of high substrate input by means of rhizodeposits. Active microorganisms and extracellular enzymes are known to be responsible for substrate utilization in soil, especially in rooted soil. We tested for microbial‐ and enzyme activities in arable soil, in order to investigate the effects of continuous input of easily available organics (e.g., root‐exudates) to the microbial community. In a field experiment with maize, rooted and root‐free soil were analyzed and rhizosphere processes were linked to microbial activity indicators such as specific microbial growth rates and kinetics of six hydrolytic extracellular enzymes: β‐glucosidase, β‐cellobiohydrolase, β‐xylosidase, acid phosphatase, leucine‐ and tyrosine‐aminopeptidase. Higher potential activities of leucine‐aminopeptidase (2‐fold) for rooted vs. root‐free soil suggested increased costs of enzyme production, which retarded the specific microbial growth rates. Total microbial biomass determined by the substrate‐induced respiration technique and dsDNA extraction method was 23% and 42% higher in the rooted surface‐layer (0–10 cm) compared to the root‐free soil, respectively. For the rooted soil, potential enzyme activities of β‐glucosidase were reduced by 23% and acid phosphatase by 25%, and increased by 300% for β‐cellobiohydrolase at 10–20 cm depth compared to the surface‐layer. The actively growing microbial biomass increased by the 17‐fold in rooted soil in the 10–20 cm layer compared to the upper 10 cm. Despite the specific microbial growth rates showing no changes in the presence of roots, these rates decreased by 42% at 10–20 cm depth compared to the surface‐layer. This suggests the dominance in abundances of highly active but slower growing microbes with depth, reflecting also their slower turnover. Shifts in microbial growth strategy, upregulation of enzyme production and increased microbial respiration indicate strong root effects in maize planted soil. |
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| Keywords: | microbial activity microbial biomass specific enzyme activity specific microbial growth rates dsDNA |
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