Effects of Grazing Exclusion on Soil Carbon and Nitrogen Storage in Semi-arid Grassland in Inner Mongolia, China

The semi-arid grasslands in Inner Mongolia, China have been degraded by long-term grazing. A series of ecological restoration strategies have been implemented to improve grassland service. However, little is known about the effect of these ecological restoration practices on soil carbon and nitrogen storage. In this study, characteristics of vegetation and soil properties under continued grazing and exclusion of livestock for six years due to a nationwide conservation program—′Returning Grazing Lands to Grasslands(RGLG)′ were examined in semi-arid Hulun Buir grassland in Inner Mongolia, China. The results show that removal of grazing for six years resulted in a significant recovery in vegetation with higher above and below-ground biomass, but a lower soil bulk density and pH value. After six years of grazing exclusion, soil organic C and total N storage increased by 13.9% and 17.1%, respectively, which could be partly explained by decreased loss and increased input of C and N to soil. The effects of grazing exclusion on soil C and N concentration and storage primarily occurred in the upper soil depths. The results indicate that removal of grazing pressure within the RGLG program was an effective restoration approach to control grassland degradation in this region. However, more comprehensive studies are needed to evaluate the effectiveness of the RGLG program and to improve the management strategies for grassland restoration in this area.

Community structure and carbon and nitrogen storage of sagebrush desert under grazing exclusion in Northwest China

Overgrazing is regarded as one of the key factors of vegetation and soil degradation in the arid and semi-arid regions of Northwest China.Grazing exclusion(GE)is one of the most common pathways used to restore degraded grasslands and to improve their ecosystem services.Nevertheless,there are still significant controversies concerning GE’s effects on grassland diversity as well as carbon(C)and nitrogen(N)storage.It remains poorly understood in the arid desert regions,whilst being essential for the sustainable use of grassland resources.To assess the effects of GE on community characteristics and C and N storage of desert plant community in the arid desert regions,we investigated the community structure and plant biomass,as well as C and N storage of plants and soil(0-100 cm depth)in short-term GE(three years)plots and adjacent long-term freely grazing(FG)plots in the areas of sagebrush desert in Northwest China,which are important both for spring-autumn seasonal pasture and for ecological conservation.Our findings indicated that GE was beneficial to the average height,coverage and aboveground biomass(including stems,leaves and inflorescences,and litter)of desert plant community,to the species richness and importance values of subshrubs and perennial herbs,and to the biomass C and N storage of aboveground parts(P<0.05).However,GE was not beneficial to the importance values of annual herbs,root/shoot ratio and total N concentration in the 0-5 and 5-10 cm soil layers(P<0.05).Additionally,the plant density,belowground biomass,and soil organic C concentration and C storage in the 0-100 cm soil layer could not be significantly changed by short-term GE(three years).The results suggest that,although GE was not beneficial for C sequestration in the sagebrush desert ecosystem,it is an effective strategy for improving productivity,diversity,and C and N storage of plants.As a result,GE can be used to rehabilitate degraded grasslands in the arid desert regions of Northwest China.

Effects of long-term grazing exclusion on vegetation structure,soil water holding capacity,carbon and nitrogen sequestration capacity in an alpine meadow on the Tibetan Plateau

Grazing exclusion is one of the primary management practices used to restore degraded grasslands on the Tibetan Plateau.However,to date,the effects of long-term grazing exclusion measures on the process of restoring degraded alpine meadows have not been evaluated.In this study,moderately degraded plots,in which the vegetation coverage was approximately 65%and the dominant plant species was Potentilla anserina L,with grazing exclusion for 2 to 23 years,were selected in alpine meadows of Haibei in Qinghai-Tibet Plateau.Plant coverage,plant height,biomass,soil bulk density,saturated water content,soil organic carbon(SOC)and total nitrogen(TN)were evaluated.The results were as follows:(1)With aboveground biomass and total saturated water content at 0-40 cm depth,the average SOC and TN contents in moderately degraded alpine meadows increased as a power function,and the plant height increased as a log function.(2)The average soil bulk density at 0-40 cm depth first decreased and then increased with increasing grazing exclusion duration,and the minimum value of 0.90 g·cm^(-3) was reached at 15.23 years.The plant coverage,total belowground biomass at 0-40 cm depth,total aboveground and belowground biomass first increased and then decreased,their maximum values(80.49%,2452.92g·m^(-2),2891.06 g·m^(-2))were reached at 9.41,9.46 and 10.25 years,respectively.Long-term grazing exclusion is apparently harmful for the sustainable restoration of degraded alpine meadows.The optimal duration of grazing exclusion for the restoration of moderately degraded alpine meadows was 10 years.This research suggests that moderate disturbance should be allowed in moderately degraded alpine meadows after 10years of grazing exclusion.

Long-term grazing exclusion influences arbuscular mycorrhizal fungi and their association with vegetation in typical steppe of Inner Mongolia,China

It is not certain that long-term grazing exclusion influences arbuscular mycorrhizal （AM） fungi and their association with steppe vegetation. In this study, soil and plant samples were collected from two sites of grazing exclusion since 1983 （E83） and 1996 （E96）, and one site of free-grazing （FG） in the typical steppe of Xilinguole League, Inner Mongolia, China, and assayed for soil basic physicochemical properties, AM fungal parameters, aboveground biomass and shoot phosphorus （P） uptake as well. The results showed that long-term grazing exclusion of E83 and E96 led to less drastic seasonal changes and significant increases in spore density, hyphal length density and root colonization intensity of AM fungi and even soil alkaline phosphatase activity, by up to 300, 168, 110 and 102％, respectively, compared with those of FG site. In addition, the total aboveground biomass and shoot P uptake of E83 and E96 were 75-992％ and 58-645％, respectively, higher than those of FG. Generally, the root colonization intensity, spore density, and hyphal length density of AM fungi were all positively correlated with the aboveground biomass and even shoot P uptake of plant. These results may imply that grazing exclusion play a critical role in increasing the growth of AM fungi, and subsequently, may increase plant P uptake and aboveground biomass production. Moreover, the spore density could sensitively reflect the impacts of long-term grazing exclusion on AM fungi since survival strategy of spores in soil.

Species Richness and Diversity of Alpine Grasslands on the Northern Tibetan Plateau:Effects of Grazing Exclusion and Growing Season Precipitation

Species richness and diversity indices （Shannon-Wiener index, Simpson dominance index and Pielou evenness index） in alpine grassland ecosystems （alpine meadow, alpine steppe and desert steppe） under grazing-excluded and freely grazed sites were investigated along the Northern Tibetan Plateau Alpine Grassland Transect during summer 2009 and 2010. We found that species richness and diversity have not been significantly altered by short-term grazing exclusion since 2006 at vegetation and regional scales. Species richness and diversity were mainly driven by growing season precipitation （GSP）, which accounted for over 87 % of the total variation observed, Species richness and diversity at grazing- excluded and freely grazed sites appear to respond to growing season precipitation in parallel. Species richness exponentially increased with GSP while diversity indices showed positively linear relationships with GSP. This indicates that GSP on the Northern Tibetan Plateau is crucial in regulating species richness and diversity and should be taken into account in future studies on alpine grassland conservation.

封育对伊犁绢蒿荒漠草地土壤碳氮磷、酶活性及其化学计量特征的影响

明确土壤酶活性及其化学计量特征在封育恢复过程中的变化特征,对揭示土壤养分可利用性随着植被恢复的变化规律及阐明生态系统养分循环机制有重要意义。本研究通过对土壤碳氮磷、酶活性及其化学计量特征的测定,初步分析了封育6年的蒿类荒漠草地对封育措施响应的特征变化。结果表明:1)封育后蒿类荒漠草地0~20 cm土层土壤有机碳、全氮、全磷、C/P、N/P及土壤亮氨酸氨基肽酶、碱性磷酸酶,酶活性C/N均无显著变化,而4月各样地β-1,4-葡萄糖苷酶活性及7月玛纳斯样地β-1,4-N-乙酰氨基葡萄糖苷酶活性较对照呈增加趋势;2)封育显著增加了7月玛纳斯样地的C/N及4月各样地酶活性C/P,降低了7月玛纳斯样地酶活性N/P值,封育后4月各样地向量长度均显著增加,且各样地封育前后向量长度均大于45°,表明研究区土壤微生物主要受碳和磷的限制;3)冗余分析表明封育后土壤碳氮磷及其计量特征解释了土壤酶活性及化学计量特征、向量特征变异的56.03%,且结构方程模型显示封育后土壤有机碳极显著影响土壤酶活性及其化学计量特征,表明土壤有机碳可能是影响蒿类荒漠草地土壤酶活性及其化学计量特征的主要因子。

Reconsidering the efficiency of grazing exclusion using fences on the Tibetan Plateau

Grazing exclusion using fences is a key policy being applied by the Chinese government to rehabilitate degraded grasslands on the Tibetan Plateau(TP)and elsewhere.However,there is a limited understanding of the effects of grazing exclusion on alpine ecosystem functions and services and its impacts on herders’livelihoods.Our meta-analyses and questionnaire-based surveys revealed that grazing exclusion with fences was effective in promoting aboveground vegetation growth for up to four years in degraded alpine meadows and for up to eight years in the alpine steppes of the TP.Longer-term fencing did not bring any ecological and economic benefits.We also found that fencing hindered wildlife movement,increased grazing pressure in unfenced areas,lowered the satisfaction of herders,and rendered substantial financial costs to both regional and national governments.We recommend that traditional free grazing should be encouraged if applicable,short-term fencing(for 4-8 years)should be adopted in severely degraded grasslands,and fencing should be avoided in key wildlife habitat areas,especially the protected large mammal species.

围封和施肥对高寒草甸群落特征和植被碳氮库的影响

为探究不同恢复措施对退化高寒草甸的影响,研究了不同围封年限(0、4、13年)和长期施肥(N、P)下草甸群落特征和碳氮库的变化。结果表明:1)随着围封年限增加,物种丰富度指数和Shannon-Wiener指数显著降低,Simpson指数和Pielou指数呈先上升后下降的特征;长期N和P添加分别显著降低了物种丰富度指数和ShannonWiener指数。2)地上生物量和根系生物量在4和13年围封下均显著增加,且在4年围封时最高,而凋落物生物量则随围封年限增加而逐渐增加;长期施肥对生物量的影响不显著。3)围封后,植被碳和氮储量显著增加,其中地上生物量和根系碳、氮库均在4年围封时最高,凋落物碳、氮库则在13年围封时最高;长期施肥对植被碳储量无显著影响,仅长期N添加显著提高了地上生物量氮库。4)偏最小二乘(PLS)路径模型显示:围封和施肥导致环境因子发生变化,抑制了群落多样性,促进了植物生物量和植被碳库的积累,而植被氮库特征在施肥处理下发生变化。综上,围封整体上抑制了物种多样性,但能够促进群落生产力提高和植被碳氮库增汇;长期N添加对物种多样性和植被碳库无显著正效应,但促进了植被氮库增汇。

Impact of Grazing Exclusion on the Surface Heat Balance in North Tibet

The grazing exclusion program used by the Tibetan government to protect the ecological environment has changed the vegetation and impacted the surface heat balance in North Tibet. However, little information is available to describe the in?uences of the current grazing exclusion program on local surface heat balance. This study uses the records of fenced grassland patch locations to identify the impact of grazing exclusion on surface heat balance in North Tibet. The records of fenced grassland patch locations, including the longitude, latitude, and elevation of the vertices of each fenced patch(polygon shapes), were provided by the agriculture and animal husbandry bureaus of the counties where the patches were located. ArcGIS 10.2 was used to create polygon shapes based on patch location records. Based on satellite data and the surface heat balance system determined by the model, values for changes in land surface temperature(LST), albedo and evapotranspiration(ET) induced by grazing exclusion were obtained. All of these can influence surface heat balance and alter the fluctuation of LST in the northern Tibetan Plateau. The LST trends for day and night showed an asymmetric diurnal variation, with a larger magnitude of warming in the day than cooling at night. The maximum decrease in absorbed shortwave of LST(?0.5 ? ?0.4 ℃ per decade) occurred in the central region, while the minimum decrease(?0.2 ? ?0.1 ℃ per decade) occurred in the eastern region. The decreased latent heat lead to the LST increased maximum(>1 ℃ per decade) occurred in the central region, The eastern region increased at a rate of 0.2?0.5 ℃ per decade, while the minimum increase(0?0.1 ℃ per decade) occurred in the northwestern region.

长期封育对内蒙古羊草草地土壤有机碳组分的影响

封育是当前恢复和改良内蒙古草地的重要措施，也是实现草地固碳效应最有效的途径之一。本文利用内蒙古封育32年和自由放牧的羊草草地，分析了其土壤有机碳组分、土壤团聚体和土壤腐殖质组分碳含量的变化，并运用13 C核磁共振波普法对土壤腐殖质的有机碳组分进行波普分析，探讨了长期封育对羊草草地土壤有机碳组分和土壤有机质结构的影响，期望能为科学地评估长期封育状况下草地固碳效应及其稳定性提供理论依据。实验结果表明：长期封育显著提高了草地土壤有机碳含量；在土壤有机碳组分中，除土壤微生物碳（MBC ）含量降低外，其碳组分含量都相应增加。其中，易氧化有机碳（EOC）含量增加最为明显，长期封育草地是自由放牧草地土壤的4．53倍；长期封育显著提高了草地土壤0．25～2 mm 团聚体所占比例及其有机碳含量；长期封育提高了草地土壤腐殖质中的胡敏酸碳（HAC）、胡敏素碳（HUC）含量和胡敏酸／腐殖质碳，降低了富里酸碳（FAC）的含量，封育草地土壤的 H AC／FAC是自由放牧草地土壤的5．66倍。此外，长期封育草地土壤的脂族碳含量显著增加，芳香度相应增加，疏水碳／亲水碳增大。总之，长期封育不仅提高了草地土壤有机碳贮量，还能改善草地土壤结构、增强土壤有机碳的稳定性。

半干旱草地长期封育进程中针茅植物根系格局变化特征

以云雾山不同封育年限草地针茅植物根系和土壤为研究对象,对其根系特征、土壤特性及两者关系进行研究,以探讨分析封育对针茅根系格局的影响。结果表明:(1)针茅植物根系生物量、根长密度、根表面积和根体积在封育初期轻微下降,之后缓慢上升,并在封育30 a草地得到显著增加。(2)随封育年限增加,各根系指标在3种针茅物种间的组成格局具有类似变化规律,具体表现为:长芒草在放牧草地所占比例最高,之后逐渐降低,并在封育30 a草地消失;大针茅所占比例呈先升后降变化规律,并在封育22 a草地达到最大值;甘青针茅仅出现于封育30 a草地,且占据优势地位。(3)大针茅和甘青针茅0—0.6 mm径级根系比例高于大针茅,使其根系直径显著低于大针茅,比根长和比根面积显著高于大针茅;此外,长芒草根组织密度显著高于长芒草和甘青针茅。(4)长期封育在显著提高土壤水分、养分含量和土壤氮磷比的同时显著降低土壤碳氮比,但对微生物生物量碳、氮无明显影响。(5)针茅根系特征与土壤指标的关联性分析显示针茅根系受土壤氮资源的显著影响。

锡林郭勒退化草原不同禁牧恢复演替阶段土壤种子库比较

以冷蒿(Artemisia frigida)+糙隐子草(Cleistogenes squarrosa)退化草原经过长期围栏禁牧恢复演替(23a和10a)群落为研究对象,并对比围栏外退化的冷蒿+糙隐子草草原,揭示锡林郭勒退化草原长期围栏禁牧后的土壤种子库特征。随着群落的恢复演替,土壤总种子库物种组成和密度均增加,但持久性土壤种子库占土壤总种子库的比例下降。代表土壤总种子库的4月份取样,围栏禁牧23a、10a和围栏外退化样地土壤种子库密度平均值分别为4433、4756粒.m-2和856粒.m-2,在0.001水平上差异显著,基本代表持久土壤种子库(persistent soil seed bank)的6月底取样,3个样地土壤种子库密度在0.05水平上差异显著;多数植物土壤种子库主要分布在0～3cm层,各样地种子库密度随土壤深度的增加而减少;围栏禁牧23a、10a和围栏外重度退化样地的持久土壤种子库密度分别为土壤总种子库的52.6%、47.4%和90.9%,;各样地一年生植物,构成了草原土壤种子库密度的主要组成部分。结果表明,对于严重退化的冷蒿+糙隐子草群落,只要在恢复起点仍有零星分布的羊草和大针茅植株,经过长期围栏禁牧可恢复其土壤种子库物种组成和种子库规模。

围封禁牧对小叶锦鸡儿灌丛化草原群落组成和结构的影响

典型草原向灌丛化草原的转变是过度放牧引起的重要结果之一。为研究内蒙古地区小叶锦鸡儿灌丛化草原对围封禁牧的响应,在内蒙古锡林郭勒典型草原退化区选取小叶锦鸡儿成片分布的典型地段,自2003年,分别设置禁牧样区和放牧样区。于2008—2011年连续四年调查禁牧样区小叶锦鸡儿种群生长和生理生化指标及灌丛间群落基本特征,并将2011年禁牧样区与放牧样区小叶锦鸡儿种群与灌丛间群落进行比较。结果显示:(1)围封后小叶锦鸡儿种群开始衰退,主要体现在种群盖度的降低和叶片氮磷含量(特别是磷含量)有所降低,而个体构件生长状况无显著差异;(2)灌丛间群落的物种组成随围封年限增加发生显著变化:禁牧后1年生植物逐渐退出群落,多年生丛生禾草重要值随围封年限增加而显著增加,即围封禁牧对小叶锦鸡儿灌丛化草原的群落恢复有积极作用;(3)小叶锦鸡儿种群盖度与多年生丛生禾草的重要值显著负相关,说明两者之间存在竞争关系,推测多年生丛生禾草的竞争是禁牧后小叶锦鸡儿衰退的重要原因。

火烧对长期封育草地土壤碳固持效应的影响

火烧是内蒙古典型草原的自然现象,对长期封育草地碳固持效应具有潜在的重要影响。基于野外控制火烧实验(未火烧、1a火烧1次、2a火烧1次、4a火烧1次),采用土壤和土壤粒级组分相结合的指标体系,分析了火烧以及火烧频率对长期封育草地土壤碳贮量的影响。结果表明:火烧会降低长期封育草地0—30 cm土壤碳贮量;其中,频繁火烧将显著降低草地土壤碳贮量,而4a 1次的火烧对土壤碳贮量影响较小。火烧对0—10 cm土壤碳贮量影响明显,而对10—30 cm土层影响较小。此外,火烧对长期封育草地土壤砂粒和粉粒碳氮贮量影响较大、对粘粒碳氮贮量影响较小。火烧后表层土壤砂粒和粉粒C∶N比下降,表层土壤有机质的稳定性有所提高。与自由放牧草地相比,连续遭受火烧处理的长期封育草地仍具有较高的碳贮量。总之,火烧会一定程度降低长期封育草地的碳贮量,但并不会彻底改变其显著的碳固持效应。

土壤种子库在黄土高原本氏针茅草地群落长期封禁演替过程中的作用

地上植被与土壤种子库的耦合研究对于探索退化草地在长期封禁过程中的演替过程及其机理具有重要意义。采用除趋势对应分析(DCA)对黄土高原典型草原本氏针茅群落进行地上/地下演替梯度分析;利用非加权组平均(UPGMA)聚类分析对土壤种子库与地上植被的相似性进行数量生态学分析。结果表明,随着封禁年限的延长,本氏针茅群落经历了以下几个演替阶段:杂草群聚生长阶段→本氏针茅大量出现→本氏针茅稳定发展阶段。在整个演替过程中,地上植被有明显的顺向演替趋势,但是土壤种子库之间未能表现出明显差异。地上植被演替阶段影响土壤种子库与地上植被的关系,演替初期地上植被与土壤种子库的相似性高于演替后期的二者相似性,说明土壤种子库在演替初期对地上植被的贡献比较大。因此,推动地上植被演替的内部驱动力不是土壤种子库,而是繁殖体散布和无性繁殖。

短期休牧对昭苏草甸草原地下生物量及其分布特征的影响

【目的】研究短期休牧对昭苏草甸草原地下生物量的影响。【方法】在不同放牧强度（0.38、0.64和0.90头牛/hm2）下设置了3个休牧期（6-7月、7-8月、8-9月）,采用挖掘法测定地下生物量。【结果】短期放牧条件下,放牧强度及休牧对草地地下生物量影响不显著（P〉0.05）,0-30cm土层地下生物量介于763.33-2 123.08 g/m2;同一放牧强度不同休牧期间0-10 cm、10-20 cm及20-30 cm土层地下生物量差异不显著（P〉0.05）,但轻度放牧及中度放牧在6-7月或8-9月休牧、重度放牧在8-9月休牧有利于草地地下生物量的积累;随土层深度的增加,地下生物量逐渐减少,且0-10 cm地下生物量占0-30 cm地下生物量总重的69%以上。【结论】短期放牧条件下,休牧及放牧强度对草甸草原地下生物量的影响不显著。

封育年限对伊犁绢蒿荒漠土壤有机氮组分的影响

为探究荒漠土壤有机氮组分对封育年限的响应规律,研究了不同封育年限(封育时间为0、1、4和11a)对中度退化伊犁绢蒿(Seriphidium transiliense)荒漠草地土壤全氮(total nitrogen,TN)、轻组氮(light fraction organic nitrogen,LFON)、颗粒氮(particulate organic nitrogen,PON)、微生物量氮(soil microbial biomass nitrogen,SMBN)及其分配比例的影响。结果表明,与封育0a相比,其它封育年限5-10、10-20、30-50cm土层的TN含量均显著降低(P<0.05),且0-50cm土层TN含量随封育年限延长呈"降-升"趋势;封育11a,0-5cm土层PON含量达到最高,而封育4a,5-10和20-30cm土层PON分配比例显著增加;0-20cm土层LFON含量增加显著,且0-5cm土层含量最高。0-50cm土层SMBN随封育年限增加呈"降-升"趋势,而封育4a,5-10和20-30cm土层SMBN分配比例显著高于封育0a和封育1a(P<0.05);0-10cm土层LFON和0-50cm土层LFONR与封育年限呈显著正相关。总之,短期封育(1~11a)下,中度退化伊犁绢蒿荒漠土壤全氮含量仍未得到恢复,但促进了LFON、PON、SMBN及其分配比例的增加。

禁牧对退化山地草甸植物多样性及土壤有机碳储量的影响

为明确轻度退化山地草甸植物群落特征和土壤养分对禁牧的响应规律,采用野外实地调查取样与室内分析相结合的方法,对禁牧区10年和自由放牧区(载畜量1.5~2.0羊单位/hm^(2))赛里木湖山地草甸植物数量特征、植物多样性和土壤有机碳碳储量等进行测定分析。结果表明,禁牧后退化山地草甸植物平均高度显著增加41.36%(P<0.05),而植物群落盖度、密度、地上生物量及植物多样性增降不显著(P>0.05);禁牧后土壤有机碳在土层0~30 cm显著降低70.03%~76.05%(P<0.05),且有机碳储量在30~50 cm土层显著降低59.75%(P<0.05)。禁牧对退化山地草甸植物群落特征和土壤物理性质的效果不明显,10年的禁牧年限对土壤有机碳固持效果不明显,仍需更长的禁牧年限来观测土壤有机碳储量的变化。

禁牧封育对黑土滩人工草地群落特征的影响

对三江源区"黑土滩"四龄垂穗披碱草人工草地进行围栏禁牧封育,封育期为一年,8月中旬进行群落调查,以冷季放牧利用的四龄人工草地作为对照,分析围栏内外样地的群落特征。结果表明:禁牧封育使"黑土滩"四龄垂穗披碱草人工草地物种丰富度,多样性指数,均匀度指数显著降低,生态优势度和优势种的重要值显著提高,禁牧封育与放牧利用的群落相似性系数为0.5。

禁牧对中度退化伊犁绢蒿荒漠植被特征的影响

为探究草地植物群落和植物生态经济类群对禁牧的响应,研究了不同禁牧年限(禁牧时间为0年、1年、4年、11年)对伊犁绢蒿荒漠草地群落特征、物种多样性以及生态经济类群演变特征的影响。结果表明,随着禁牧年限的增加,伊犁绢蒿种群的高度、盖度、生物量呈增加趋势,种群密度呈先升后降再升的波动变化;群落的高度、生物量呈增加趋势,密度呈先减后增再减的波动变化;Simpson指数、Shannon-Wiener指数、Pielou指数呈先降后增再降的波动变化,而Patrick指数总体呈下降趋势;半灌木的优势度呈先增后降再升的波动变化。总之,适当的禁牧有利于中度退化伊犁绢蒿荒漠草地恢复。