Abstract
Overgrazing is a severe problem in several regions in Northwestern China and has caused serious land degradation. Secondary natural succession plays an important role in the accumulation of soil carbon and nitrogen contents. Estimating the effects of grazing exclusion on soil quality and plant diversity will improve our understanding of the succession process after overgrazing and promote judicious management of degraded pastures. This experiment was designed to measure soil properties and plant diversity following an age chronosequence of grasslands (ages ranged from one year, 12 years, 20 years, and 30 years) in Northwestern China. The results showed that continuous fencing resulted in a considerable increase in plant coverage, plant biomass (above- and below-ground biomass), and plant diversity, which can directly or indirectly improve the accumulation of soil organic carbon and total nitrogen content. The plant coverage and the above- and below-ground biomass linearly increased along the succession time, whereas soil organic C and N contents showed a significant decline in the first 12 years and, subsequently, a significant increase. The increased plant biomass caused an increase in soil organic carbon and soil total nitrogen. These results suggested that soil restoration and plant cover were an incongruous process. Generally, soil restoration is a slow process and falls behind vegetation recovery after grazing exclusion. Although the accumulation of soil C and N stocks needed a long term, vegetation restoration was a considerable option for the degraded grassland due to the significant increase of plant biomass, diversity, and soil C and N stocks. Therefore, fencing with natural succession should be considered in the design of future degraded pastures.
Highlights
Overgrazing has accelerated soil erosion and severe degradation in arid and semiarid grasslands over recent decades [1,2,3] as it has significantly reduced plant cover [4], declined plant height and biomass [5], decreased plant richness [6], and reduced soil organic carbon stocks reviewed by Dlamini [7]
We addressed the following three hypotheses: (1) plant diversity and above- and below-ground biomass should be enhanced across the succession; (2) soil carbon and nitrogen stocks increased with the increase of age duration as plant biomass was enhanced; and (3) the relationships between plant diversity and soil quality were significantly related along the succession age
Plant total biomass (TB), above-ground biomass (AGB), and BGB significantly increased with successional age after fencing
Summary
Overgrazing has accelerated soil erosion and severe degradation in arid and semiarid grasslands over recent decades [1,2,3] as it has significantly reduced plant cover [4], declined plant height and biomass [5], decreased plant richness [6], and reduced soil organic carbon stocks reviewed by Dlamini [7]. The installation of fencing and vegetation restoration have been implemented to reduce the risks of serious soil erosion and reverse degradation trends [2,8,10]. Observed that a nine-year fencing significantly enhanced the vegetation cover and the above-ground biomass [10]. The results from a meta-analysis on Chinese grasslands showed that the grazing exclusion had little effect on plant diversity recovery, but enhanced the soil carbon storage [11]. A short term grazing experiment showed that soil bulk density, soil organic carbon and above-ground net primary productivity were sensitive to grazing
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