Responses of root exudation and nutrient cycling to grazing intensities and recovery practices in an alpine meadow: An implication for pasture management
Background and aims
The rhizosphere priming effect is caused by root carbon (C) exudation into the rhizosphere; the role of this effect in nutrient cycling and ecosystem recovery of natural grasslands as affected by different grazing intensities is still unknown. The objective of the present study was to investigate the relationships among root C exudation, rhizospheric microbial activity, and their influences on plant nutrient uptake during grazing and recovery periods.
Field experiments were conducted in the Hongyuan Alpine Meadow to measure root exudation rate and nutrient cycling processes of the dominant species Elymus nutans. Three grazing intensities (an ungrazed control, moderate grazing and heavy grazing) were introduced for two months, following which all treatments received a recovery practice (no grazing for 21 days).
Heavy grazing significantly decreased root exudation rate, soil nitrogen (N) mineralization rate, β-1,4-glucosidase (BG) activity, and foliar C concentration, while moderate grazing had no influence on these parameters compared to the control. After the 21 days of recovery, all these parameters, except N mineralization rate and foliar C concentrations in the heavy grazing treatment, returned to similar levels as in the control, whereas root exudation rate and BG activity rose to even higher levels. Meanwhile, moderate grazing significantly promoted root exudation rate, soil inorganic N concentration, net soil N mineralization rate, and β-N-acetylglucosaminidase (NAG) activity during the recovery stage as compared to the control. Foliar quality was also improved by the recovery practice, indicating that the high availability of N and P is a consequence of the positive root–microbe feedback and will ultimately benefit grazers.
The flush of labile C released to the rhizosphere by grazed plants stimulated extracellular enzyme activities, enhanced soil N mineralization, and increased plant nutrient uptake. These results imply that reasonable (i.e. moderate) grazing followed by a recovery practice can effectively restore and strengthen grassland vegetation, and contribute to the sustainable use of alpine meadows such as Hongyuan.
KeywordsGrazing intensities Microbial activity Nitrogen mineralization Recovery Root exudation
We thank Timothy A. Doane, anonymous reviewers and Accdon/Let Pub Experts for their thoughtful comments, which helped in improving the manuscript. This work was supported by the National Science Foundation of China (Nos. 31350110328, 31500346 and 41361076), the Ministry of Science and Technology of the People’s Republic of China (2016YFC0501803), the Chinese Academy of Sciences (KFJ-SW-STS-177, Western Light Program), the Sichuan Science & Technology Bureau (2015HH0025, 2015JY0231, 2016HH0082 and 2016JY0117) and the Youth Professor Program of Chengdu Institute of Biology.
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