Effects of Grazing Regimes on Plant Traits and Soil Nutrients in an Alpine Steppe, Northern Tibetan Plateau
Northern Tibetan
Plateau. PLoS ONE 9(9): e108821. doi:10.1371/journal.pone.0108821
Effects of Grazing Regimes on Plant Traits and Soil Nutrients in an Alpine Steppe, Northern Tibetan Plateau
Jian Sun 0
Xiaodan Wang 0
Genwei Cheng 0
Jianbo Wu 0
Jiangtao Hong 0
Shuli Niu 0
Cheng-Sen Li, Institute of Botany, China
0 1 Synthesis Research Centre of Chinese Ecosystem Research Network, Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences , Beijing , China , 2 The key laboratory of mountain surface processes and eco-regulation, Institute of Mountain Hazard and Environment, Chinese Academy of Sciences , Chengdu , China
Understanding the impact of grazing intensity on grassland production and soil fertility is of fundamental importance for grassland conservation and management. We thus compared three types of alpine steppe management by studying vegetation traits and soil properties in response to three levels of grazing pressure: permanent grazing (M1), seasonal grazing (M2), and grazing exclusion (M3) in the alpine steppe in Xainza County, Tibetan Plateau. The results showed that community biomass allocation did not support the isometric hypothesis under different grassland management types. Plants in M1 had less aboveground biomass but more belowground biomass in the top soil layer than those in M2 and M3, which was largely due to that root/shoot ratios of dominant plants in M1 were far greater than those in M2 and M3. The interramet distance and the tiller size of the dominant clonal plants were greater in M3 than in M1 and M2, while the resprouting from rhizome buds did not differ significantly among the three greezing regimes. Both soil bulk density and soil available nitrogen in M3 were greater than in M1 at the 15-30 cm soil depth (P = 0.05). Soil organic carbon and soil total nitrogen were greater in M3 than in M1 and M2 (P = 0.05). We conclude that the isometric hypothesis is not supported in this study and fencing is a helpful grassland management in terms of plant growth and soil nutrient retention in alpine steppe. The extreme cold, scarce precipitation and short growing period may be the causation of the unique plant and soil responses to different management regimes.
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Funding: This research was jointly funded by the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-XB3-08), CAS Strategic Priority
Research Program (XDA05050602), and the Open Fund of Key Laboratory of Ecosystem Network Observation and Modelling (110301A1PA). The funders had no
role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Alpine grasslands make up the dominant ecosystem occupying
approximately 94% of Northern Tibet [1]. The natural
environment of the region is extremely harsh, and the alpine steppe, a
fragile ecosystem, is extremely susceptible to the impacts of human
activities [2]. It suffers from overgrazing, deforestation, and the
harvesting of numerous herbs commonly used in traditional
medicines [35]. Studies examining the response of above- and
belowground biomass, the root/shoot ratio, the morphological
characteristics of dominant plants, and the soil properties to
human disturbance offer important insights that can contribute to
adopting the most effective approach to grassland management in
an alpine steppe, in which it is particularly difficult to recover from
ecosystem degradation due to the regions long period of frost and
relatively short growing season [3,6].
Although grazing and fencing, both of which have a substantial
affect on vegetation traits and soil properties [79], are the most
prevalent management regimes for grasslands worldwide, and
although the effects of herbivores on soil properties in (sub)alpine
ecosystems have recently been reported [10,11], knowledge about
plants and soils in response to grassland management regimes (i.e.,
fencing and grazing) in the Tibetan Plateau remains limited due to
an extremely difficult geographic situation [9,12]. With regard to
soil properties, it has been documented that grazing depresses soil
carbon storage by changing the plant biomass and composition of
a Tibetan alpine meadow [13]. In contrast, Shi et al. [14] found
grazing exclusion to decrease soil organic carbon storage in an
alpine grassland of the Tibetan Plateau, while another report
suggested that seasonal grazing might enrich soil nutrients [15].
Such conflicting results indicate that different grazing intensities
may have varying impacts on soil properties.
Understanding the influence of different management types on
grassland production is essential for improving grassland
conservation and management [16]. Previous studies have yielded
varying results for aboveground biomass changes. Grazing thus
increased [17] or decreased [18] aboveground (...truncated)