Responses of enzymatic activities within soil aggregates to 9-year nitrogen and water addition in a semi-arid grassland |
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| Institution: | 1. State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;2. Soil Science of Temperate Ecosystems, Büsgen-Institute, Georg August University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany;3. Key Laboratory of Regional Environment and Eco-remediation, College of Environment, Shenyang University, Shenyang 110044, China;4. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA;5. Department of Agronomy, Purdue University, West Lafayette, IN 47907, USA;6. University of Chinese Academy of Sciences, Beijing 100049, China;1. State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;2. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China;1. Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Inner Mongolia Prataculture Research Center, Chinese Academy of Science, Hohhot 010031, China;4. Institute of Agricultural Resources and Regional Planning, CAAS, Beijing 100081, China;5. Inner Mongolia Academy of Agricultural & Animal Husbandry Sciences, Hohhot 010031, China;6. School of Environment, Tsinghua University, Beijing 100084, China;1. CSIRO Agriculture Flagship, PMB No. 2, Glen Osmond, South Australia 5064, Australia;2. Department of Soil Science, University of Saskatchewan, Saskatoon S7N 5A2, Canada;1. Hebei College of Industry and Technology, Hongqi Street 626, Shijiazhuang 050091, China;2. Hebei Chemical and Pharmaceutical College, Fangxing Road 88, Shijiazhuang 050026, China;1. Environmental Sciences Research Institute, Ulster University, Coleraine BT52 1SA, UK;2. Agri-Food & Biosciences Institute, BT9 5PX Belfast, UK;3. School of Biomedical Sciences, Ulster University, Coleraine BT52 1SA, UK;4. Department of Life Sciences, Imperial College, Silwood Park, Ascot, Berkshire SL5 7PY, UK;5. Laboratoire d''Ecologie Alpine, UMR CNRS 5553, Université Grenoble Alpes BP53, 38041 Grenoble Cedex 9, France |
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| Abstract: | Soil microorganisms secrete enzymes used to metabolize carbon (C), nitrogen (N), and phosphorus (P) from the organic materials typically found in soil. Because of the connection with the active microbial biomass, soil enzyme activities can be used to investigate microbial nutrient cycling including the microbial response to environmental changes, transformation rates and to address the location of the most active biomass. In a 9-year field study on global change scenarios related to increasing N inputs (ambient to 15 g N m−2 yr−1) and precipitation (ambient to 180 mm yr−1), we tested the activities of soil β-glucosidase (BG), N-acetyl-glucosaminidase (NAG) and acid phosphomonoesterase (PME) for three soil aggregate classes: large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm) and microaggregates (<250 μm). Results showed higher BG and PME activities in micro-vs. small macroaggregates whereas the highest NAG activity was found in the large macroaggregates. This distribution of enzyme activity suggests a higher contribution of fast-growing microorganisms in the micro-compared with the macroaggregates size fractions. The responses of BG and PME were different from NAG activity under N addition, as BG and PME decreased as much as 47.1% and 36.3%, respectively, while the NAG increased by as much as 80.8%, which could imply better adaption of fungi than bacteria to lower soil pH conditions developed under increased N. Significant increases in BG and PME activities by as much as 103.4 and 75.4%, respectively, were found under water addition. Lower ratio of BG:NAG and higher NAG:PME underlined enhanced microbial N limitation relative to both C and P, suggesting the repression of microbial activity and the accompanied decline in their ability to compete for N with plants and/or the accelerated proliferation of soil fungi under elevated N inputs. We conclude that changes in microbial activities under increased N input and greater water availability in arid- and semi-arid grassland ecosystems where NPP is co-limited by N and water may result in substantial redistribution of microbial activity in different-sized soil particles. This shift will influence the stability of SOM in the soil aggregates and the nutrient limitation of soil biota. |
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| Keywords: | Global change Nitrogen deposition Precipitation regimes Extracellular enzymes Microbial nitrogen limitation Temperate grassland |
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