Effects of grazing exclusion on soil carbon dynamics in alpine grasslands of the Tibetan Plateau

Abstract Globally, excessive grazing is identified as one of the key disturbances leading to grassland degradation and soil carbon (C) loss. Grazing exclusion has been proposed as an effective practice to restore degraded grasslands and to promote C sequestration. However, there is still little knowledge about how soil C changes with grazing exclusion in high-altitude alpine ecosystems with very cold climates. We synthesized data from 63 sites in the literature and 15 sites in a field sampling and investigated the dynamics of soil C stocks following grazing exclusion in alpine grasslands of the Tibetan Plateau. The results showed that the soil C stock increased with grazing exclusion at most sites, with average C sequestration rates of 0.84, 0.58, and 0.49 Mg ha−1 yr−1 in the soil layers of 0–10, 10–20, and 20–30 cm, respectively. Based on these results, if 60 million ha of the grasslands on Tibetan Plateau were excluded from grazing livestock by 2020 according to the national plan, then approximately 0.11 Pg C yr−1 would be sequestered in the soil which equates to about 4.4% of fossil fuel and cement CO2 emissions in China in 2013. Generally, the rates of soil C increase exhibited a declining pattern with increasing years of grazing exclusion, with a significant decrease occurring after ten years of grazing exclusion. Of the factors examined, the rates of absolute and relative soil C change were both positively related to mean annual precipitation but negatively related to the year of grazing exclusion and initial soil C stock, respectively. The rates of soil C changes increased linearly with those of N change, and no matter how soil C changed (whether it increased or decreased), soil C:N ratios remained stable over the years of grazing exclusion. Our results implied that grazing exclusion is beneficial for soil C sequestration in degraded alpine grassland, especially in humid areas. Moreover, the intrinsic increase in N could keep up with the pace of soil C changes and would sustain soil C sequestration during the recovery process.

[1]  D. O. Hall,et al.  The global carbon sink: a grassland perspective , 1998 .

[2]  W. Parton,et al.  Progressive Nitrogen Limitation of Ecosystem Responses to Rising Atmospheric Carbon Dioxide , 2004 .

[3]  S. Niu,et al.  A synthesis of the effect of grazing exclusion on carbon dynamics in grasslands in China , 2016, Global change biology.

[4]  E. Veldkamp,et al.  Effectiveness of exclosures to restore degraded soils as a result of overgrazing in Tigray, Ethiopia , 2007 .

[5]  R. Beeton,et al.  Carbon sequestration and biodiversity restoration potential of semi-arid mulga lands of Australia interpreted from long-term grazing exclosures , 2011 .

[6]  J. Brandle,et al.  Temporal progress in improving carbon and nitrogen storage by grazing exclosure practice in a degraded land area of China's Horqin Sandy Grassland , 2012 .

[7]  Jingyun Fang,et al.  Above- and belowground biomass allocation in Tibetan grasslands. , 2009 .

[8]  Zhenxi Shen,et al.  Effects of livestock exclusion and climate change on aboveground biomass accumulation in alpine pastures across the Northern Tibetan Plateau , 2014 .

[9]  L. Mann,et al.  CHANGES IN SOIL CARBON STORAGE AFTER CULTIVATION , 1986 .

[10]  C. Wan,et al.  Changes in soil properties and vegetation following exclosure and grazing in degraded Alxa desert steppe of Inner Mongolia, China , 2008 .

[11]  Changhui Peng,et al.  Distribution and storage of soil organic carbon in China , 2003 .

[12]  Colin J. Yates,et al.  Grazing effects on plant cover, soil and microclimate in fragmented woodlands in south‐western Australia: implications for restoration , 2000 .

[13]  J. Derner,et al.  CARBON SEQUESTRATION AND RANGELANDS: A SYNTHESIS OF LAND MANAGEMENT AND PRECIPITATION EFFECTS , 2007 .

[14]  R. van der Wal,et al.  Combination of herbivore removal and nitrogen deposition increases upland carbon storage , 2015, Global change biology.

[15]  K. Paustian,et al.  GRASSLAND MANAGEMENT AND CONVERSION INTO GRASSLAND: EFFECTS ON SOIL CARBON , 2001 .

[16]  J. Leeuw,et al.  Long-term livestock exclosure did not affect soil carbon in southern Ethiopian rangelands , 2017 .

[17]  Richard H. Hart,et al.  IMPACT OF GRAZING MANAGEMENT ON THE CARBON AND NITROGEN BALANCE OF A MIXED-GRASS RANGELAND , 1999 .

[18]  Markus Steffens,et al.  Carbon storage capacity of semi‐arid grassland soils and sequestration potentials in northern China , 2015, Global change biology.

[19]  Jianshuang Wu,et al.  Effects of grazing exclusion on plant productivity and soil carbon, nitrogen storage in alpine meadows in northern Tibet, China , 2014, Chinese Geographical Science.

[20]  M. Kirschbaum,et al.  The temperature dependence of soil organic matter decomposition, and the effect of global warming on soil organic C storage , 1995 .

[21]  Yongqiang Yu,et al.  Differential Effects of Conservational Management on SOC Accumulation in the Grasslands of China , 2015, PloS one.

[22]  F. Raiesi,et al.  The influence of grazing exclosure on soil C stocks and dynamics, and ecological indicators in upland arid and semi-arid rangelands , 2014 .

[23]  J. Paruelo,et al.  Pathways of Grazing Effects on Soil Organic Carbon and Nitrogen , 2010 .

[24]  C. Kummerow,et al.  The Tropical Rainfall Measuring Mission (TRMM) Sensor Package , 1998 .

[25]  N. Batjes,et al.  Total carbon and nitrogen in the soils of the world , 1996 .

[26]  K. Paustian,et al.  Soil carbon saturation : evaluation and corroboration by long-term incubations , 2008 .

[27]  Wenming Bai,et al.  Rangeland degradation and restoration management in China , 2008 .

[28]  P. Shi,et al.  Effects of grazing exclusion on carbon sequestration and plant diversity in grasslands of China—A meta-analysis , 2016 .

[29]  J. Paz-Ferreiro,et al.  Grazing exclusion affects soil and plant communities, but has no impact on soil carbon storage in an upland grassland , 2012 .

[30]  J. Leeuw,et al.  Effects of enclosure management on carbon sequestration, soil properties and vegetation attributes in East African rangelands , 2017 .

[31]  Linghao Li,et al.  Soil carbon and nitrogen stores and storage potential as affected by land-use in an agro-pastoral ecotone of northern China , 2007 .

[32]  Thomas H. Painter,et al.  Climatic, edaphic, and biotic controls over storage and turnover of carbon in soils , 1994 .

[33]  J. Hassink.  Preservation of Plant Residues in Soils Differing in Unsaturated Protective Capacity , 1996 .

[34]  R. Harris.  Rangeland degradation on the Qinghai-Tibetan plateau: A review of the evidence of its magnitude and causes , 2010 .

[35]  David Tilman,et al.  DYNAMICS OF SOIL NITROGEN AND CARBON ACCUMULATION FOR 61 YEARS AFTER AGRICULTURAL ABANDONMENT , 2000 .

[36]  D. Coomes,et al.  Carbon storage in terrestrial ecosystems: do browsing and grazing herbivores matter? , 2012, Biological reviews of the Cambridge Philosophical Society.

[37]  Peter D. Stahl,et al.  Carbon accumulation and storage in semi-arid sagebrush steppe: Effects of long-term grazing exclusion , 2008 .

[38]  G. Du,et al.  Effect of fencing and grazing on a Kobresia-dominated meadow in the Qinghai-Tibetan Plateau , 2009, Plant and Soil.

[39]  Yanhong Tang,et al.  Storage, patterns and controls of soil organic carbon in the Tibetan grasslands , 2008 .

[40]  Z. Shang,et al.  Grazing exclusion decreases soil organic C storage at an alpine grassland of the Qinghai–Tibetan Plateau , 2013 .

[41]  Y. Hong,et al.  The TRMM Multisatellite Precipitation Analysis (TMPA): Quasi-Global, Multiyear, Combined-Sensor Precipitation Estimates at Fine Scales , 2007 .

[42]  Houyuan Lu,et al.  Distribution of carbon isotope composition of modern soils on the Qinghai-Tibetan Plateau , 2004 .

[43]  Xiaorong Wei,et al.  Ecosystem Carbon and Nitrogen Accumulation after Grazing Exclusion in Semiarid Grassland , 2013, PloS one.

[44]  Zhicai Zhang,et al.  Management and land use change effects on soil carbon in northern China's grasslands: a synthesis , 2011 .

[45]  Effects of Soil Development Time and Litter Quality on Soil Carbon Sequestration: Assessing Soil Carbon Saturation with a Field Transplant Experiment along a Post‐mining Chronosequence , 2017 .

[46]  Lei Deng,et al.  Long-term fencing effects on plant diversity and soil properties in China , 2014 .

[47]  Yuesi Wang,et al.  Carbon and nitrogen store and storage potential as affected by land-use in a Leymus chinensis grassland of northern China , 2008 .

[48]  S. Schnabel,et al.  The Impact of Heavy Grazing on Soil Quality and Pasture Production in Rangelands of SW Spain , 2018 .

[49]  J. Morgan,et al.  Response of Organic and Inorganic Carbon and Nitrogen to Long-Term Grazing of the Shortgrass Steppe , 2004, Environmental management.

[50]  R. B. Jackson,et al.  THE VERTICAL DISTRIBUTION OF SOIL ORGANIC CARBON AND ITS RELATION TO CLIMATE AND VEGETATION , 2000 .

[51]  P. Ciais,et al.  Reduced carbon emission estimates from fossil fuel combustion and cement production in China , 2015, Nature.

[52]  Christopher B. Field,et al.  Nitrogen and Climate Change , 2003, Science.

[53]  R. Lal.  Carbon Sequestration in Dryland Ecosystems , 2004, Environmental management.

[54]  M. Wiesmeier,et al.  Aggregate stability and physical protection of soil organic carbon in semi‐arid steppe soils , 2012 .

[55]  Guiyao Zhou,et al.  Grazing intensity significantly affects belowground carbon and nitrogen cycling in grassland ecosystems: a meta‐analysis , 2017, Global change biology.

[56]  R. Lal,et al.  Soil carbon sequestration in China through agricultural intensification, and restoration of degraded and desertified ecosystems , 2002 .

[57]  X. Chang,et al.  Effects of grazing exclusion on carbon sequestration in China's grassland. , 2017 .

[58]  K. Siddique,et al.  Grazing exclusion—An effective approach for naturally restoring degraded grasslands in Northern China , 2018, Land Degradation & Development.

[59]  Keith Paustian,et al.  Potential soil carbon sequestration in overgrazed grassland ecosystems , 2002 .