Protozoan grazing affects estimates of carbon utilization efficiency of the soil microbial community |
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| Institution: | 1. Natural Resource Ecology Laboratory, Colorado State University, Ft. Collins, CO 80523, USA;2. CSIRO Land and Water, Glen Osmond, SA 5064, Australia;1. Max Planck Institute for Biogeochemistry, Jena, Germany;2. Aquatic Geomicrobiology, Institute of Biodiversity, Friedrich Schiller University Jena, Jena, Germany;3. German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Puschstr. 4, 04103, Leipzig, Germany;4. Institute of Biology, Leipzig University, Puschstr. 4, 04103, Leipzig, Germany;5. Institute of Biology, Ecology Group, Humboldt-Universität zu Berlin, Philippstraße 13, 10115, Berlin, Germany;1. Department of Agricultural Soil Science, Department of Soil Science of Temperate Ecosystems, University of Goettingen, Büsgenweg 2, 37077, Goettingen, Germany;2. Agro-Technology Institute, RUDN University, Moscow, Russia;3. Institute of Environmental Sciences, Kazan Federal University, 420049, Kazan, Russia;1. Thünen Institute of Climate-Smart Agriculture, Bundesallee 65, 38116, Braunschweig, Germany;2. Thünen Institute of Biodiversity, Bundesallee 65, 38116, Braunschweig, Germany;3. Saxony-Anhalt State Institute of Agriculture and Horticulture, Lindenstraße 18, 39606, Iden, Germany;4. Thuringian State Institute of Agriculture, Naumburger Straße 98, 07743, Jena, Germany;5. University of Hohenheim, Biobased Products and Energy Crops, Fruwirthstraße 23, 70599, Stuttgart, Germany;6. Wageningen University & Research, Agrosystems Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands;1. Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China;2. Sydney Institute of Agriculture, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW, 2570, Australia;3. Department of Microbiology and Ecosystem Science, University of Vienna, 1090, Wien, Austria;4. Environmental Studies Department, University of California, Santa Cruz, CA, 95064, USA;1. Key Laboratory of Geographical Processes and Ecological Security of Changbai Mountains, Ministry of Education, School of Geographical Sciences, Northeast Normal University, Changchun, 130024, China;2. Key Laboratory of Vegetation Ecology, Ministry of Education, Northeast Normal University, Changchun, 130024, China;3. CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China |
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| Abstract: | Reliable estimates of microbial growth yield efficiency (Y=microbial production/substrate utilization) are needed to quantify and predict soil carbon (C) dynamics. We examined patterns of C utilization in two soils, a Paleustoll (USA) and Rhodoxeralf (Australia), under two levels of protozoan grazing (low vs high) when substrate was not limiting. Soil, either amended with unlabeled or 14C-labeled glucose was incubated at 25°C and glucose-C concentration, CO2-C evolution, and microbial biomass-C were determined over a 12–20 h period. Three approaches were used for estimating Y: Ys=(dSC−ΣCO2-C)/dSC, Yb=dBC/(dBC+ΣCO2-C), and Yc=dBC/dSc where dSC is the change in substrate concentration (substrate utilization), ΣCO2-C the cumulative amount of CO2-C evolved, and dBC the change in microbial biomass (biomass production). Calculation of Ys assumes that all substrate-C utilized, minus that respired, is used for biomass and metabolite production. Calculation of Yb assumes that substrate use equals biomass-C plus respired-C and does not account for biomass production consumed by grazers. Under low grazing, the three estimates of Y were similar with an average value of 0.58 and 0.55 for the Paleustoll and Rhodoxeralf, respectively. Under high grazing, the value of Y varied depending on the calculation used, with values of Yb (0.44) and Yc (0.26) being significantly lower than Ys (0.67). The total amount of glucose utilized did not vary with protozoan grazing intensity, but a high level of grazing increased the rate of glucose use and significantly reduced the amount of measurable biomass C. Substrate-based yield (Ys) provided the most reliable C assimilation efficiency estimate under both grazing treatments. |
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