Coupled response of soil carbon and nitrogen pools and enzyme activities to nitrogen and water addition in a semi-arid grassland of Inner Mongolia |
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Authors: | Ruzhen Wang Timothy R Filley Zhuwen Xu Xue Wang Mai-He Li Yuge Zhang Wentao Luo Yong Jiang |
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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 5. University of Chinese Academy of Sciences, Beijing, 100049, China 2. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, 47907, USA 3. Forest dynamics, Swiss Federal Research Institute WSL, Zuercherstrasse 111, CH-8903, Birmensdorf, Switzerland 4. College of Environmental Science, Shenyang University, Shenyang, 110044, China
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Abstract: | Background and aims Previous studies have demonstrated positive net primary production effects with increased nitrogen (N) and water availability in Inner Mongolian semi-arid grasslands. However, the responses of soil carbon (C) and N concentrations and soil enzyme activities as indicators of impacts of long-term N (urea) and water addition are still unclear. We tested the effect of 7 years of a N and water addition experiment on soil C, N, and specific soil-bound enzymes in a semi-arid grassland of Inner Mongolia. Methods We determined concentrations of soil organic carbon (SOC) and soil total nitrogen (TN) in both the 0–10 and 10–20 cm soil layers. Concentrations of labile carbon (LC) and inorganic nitrogen (nitrate and ammonium), and soil pH were measured. Additionally, soil dehydrogenase (DHA), β-glucosidase (BG) and acid and alkaline phosphomonoesterase (PME) enzyme activities were determined in the 0–10 cm soil layer. Results SOC concentration in the 0–10 cm soil layer showed no response to N addition or N plus water addition, but increased with water addition alone by 0.3–15.7 %. N addition significantly increased nitrate by 46.0–138.4 % and ammonium by 19.0–73.3 % in the 0–10 cm soil layer, whereas water addition did not affect them. The activities of DHA and alkaline PME enzymes, as well as soil pH, in the 0–10 cm layer decreased with N addition, however water addition alone caused these enzyme activities to increase. Unlike the surface soil (0–10 cm), the lower soil layer (10–20 cm), was responsive to N and water addition in that SOC and TN concentrations decreased with N addition and increased with water addition. Conclusions The accumulation of SOC and TN in N and water addition plots may be caused by the input of plant biomass exceeding SOC decomposition. Decrease in microbial activity, derived from decreased DHA and alkaline PME activities might result from suppression effects of lower pH and decreased microbial N supply. Water availability is proved to be more important than N availability for soil C and N accumulation in this semi-arid grassland. |
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