【作者】 杨红；

【导师】 孙宗玖；

【作者基本信息】 新疆农业大学 ， 草学， 2025， 博士

【摘要】 青藏高原作为全球气候变化的敏感区和调节器,据统计,高寒草地土壤有机碳储量约占全球土壤有机碳库储量的2.5%,是维持全球碳平衡的关键。土壤有机碳(SOC)主要来源于植物根系分泌物输出、衰老组织脱落、枯落物分解、微生物代谢及残体的输入。草地利用方式的改变将引起SOC来源及其固存机制的变化。然而,季节休牧后植被特征、土壤理化性质与SOC累积及其稳定性之间的关系尚不明确,生物来源碳和有机碳官能团在土壤中的分布及其对SOC贡献的研究较为匮乏,这将极大地限制对季节休牧高寒草地SOC变化的准确预测。因此,本论文以藏北不同海拔季节休牧5年的高寒草地为对象,通过对季节休牧与传统放牧条件下草地植被特征、土壤理化性质、有机碳官能团、生物来源碳及总有机碳等指标的测定,解析高寒草地SOC积累及其稳定性对季节休牧的响应机制,为理解季节休牧对高寒草地SOC的调控提供理论依据。主要结果如下:(1)季节休牧显著提高了高寒草地植被地上、地下生物量、凋落物量、平均高度及总盖度(P<0.05),增加了植被群落多样性,提高了高寒草地豆科、禾本科和莎草科植物功能群的重要值,显著降低了杂类草的重要值(P<0.05)。季节休牧后SOC、全氮(TN)、全磷(TP)、全钾(TK)、速效氮(AN)、速效磷(AP)、速效钾(AK)、容重(BD)均有所降低,而土壤含水量(SW)、土壤温度(ST)和孔隙度有所增加。随海拔增加,2种草地利用方式的植被特征、物种多样性及土壤理化指标均呈降低趋势。相关分析表明,季节休牧增加了植被特征与SOC、AN、SW之间的相关性,减弱了海拔、BD、ST、微团聚体和粘粉粒对植被特征的影响。可见,季节休牧后高寒草地向着植被群落稳定的方向演替。(2)季节休牧区土壤大团聚体有机碳含量较传统放牧增加了3.38%～10.75%,而微团聚体及黏粉粒有机碳含量依次降低了1.15%～18.28%、4.35%～7.03%;季节休牧后土壤团聚体稳定性(MWD和MGD)增加,这主要与大团聚体占比增加、微团聚体和黏粉粒占比降低相关。随海拔增加,土壤大团聚体所占比例降低和微团聚体所占比例增加,导致高海拔土壤团聚体稳定性下降。与传统放牧相比,季节休牧降低了海拔和土壤化学性质对团聚体稳定性及其有机碳含量的影响效应,提高了植被特征对团聚体稳定性及其有机碳含量的影响效应。总体而言,季节休牧提高了土壤团聚体稳定性及其有机碳含量,有利于维持高寒草地土壤碳汇功能。(3)季节休牧提高了土壤颗粒有机碳(POC)、微生物有机碳(MOC)、可溶性有机碳(DOC)和氨基糖(AS)含量,木质素酚(LP)含量仅4308 m有所提高。季节休牧和传统放牧区土壤氨基葡萄糖/胞壁酸的比值均大于1,且季节休牧大于传统放牧,表明真菌群落在高寒草地土壤微生物群落中占主导地位,且季节休牧区更明显。丁香基/香兰基和肉桂基/香兰基比值均大于传统放牧,可见,季节休牧降低了土壤木质素酚的降解程度,有利于SOC的固存。季节休牧区土壤微生物残体碳对SOC的贡献大于传统放牧,木质素酚对SOC的贡献仅4308 m和4402 m海拔表现为季节休牧大于传统放牧。2种放牧模式下土壤碳官能团含量由高到低依次为芳香碳、羰基碳、烷氧碳、烷基碳。季节休牧区土壤烷基碳/烷氧碳值高于传统放牧区,说明季节休牧提高了土壤有机碳的烷基化程度,增加了有机碳稳定性。相关分析表明,季节休牧对土壤氨基糖和木质素酚组分含量的影响作用更显著,而土壤碳官能团并未积极响应于季节休牧。从有机碳累积分析,季节休牧增加了氨基糖、木质素酚、活性碳及植被特征对SOC的调节效应。以上发现表明,季节休牧整体上增加了生物来源碳对土壤有机碳的贡献,促进了土壤有机碳的累积及其稳定性。(4)传统放牧区土壤碳库活度(A)、碳库活度指数(AI)、碳库指数(CPI)、碳素有效性(ACC)均依次显著高于季节休牧区37.89%～128.95%、111.06%～314.12%、19.18%～31.38%、19.89%～80.31%(P<0.05),而季节休牧区土壤碳库管理指数(CPMI)和有机碳空间稳定性(SOCS)均显著高于传统放牧区84.05%～242.92%、2.33%～20.29%(P<0.05)。表明季节休牧降低了土壤有机碳库活性,增加了土壤有机碳稳定性,同时,季节休牧区土壤OC-Fe含量的增加对维持土壤有机碳稳定具有积极作用。冗余分析表明,季节休牧降低了SOC、ROC、TN、BD对土壤碳稳定性的贡献,增加了TP、TK、ACC的贡献。结构模型表明,季节休牧后土壤理化性质、植被特征与土壤碳库稳定性的关系更加密切,更能反映土壤碳库稳定性的变化。(5)影响季节休牧高寒草地土壤有机碳累积的关键因子为生物来源碳,其次为土壤有机碳组分,植被特征主要通过影响生物来源碳的变化对土壤有机碳的累积产生影响;传统放牧高寒草地土壤有机碳累积的关键控制因子为土壤有机碳组分,其次为生物来源碳,植被特征对土壤有机碳累积的影响效应小于季节休牧。土壤理化性质对土壤有机碳累积的影响表现为季节休牧大于传统放牧。海拔对高寒草地土壤有机碳累积产生负效应,且对传统放牧的影响更加明显。季节休牧高寒草地土壤有机碳稳定性的关键控制因子为有机碳组分,其次为生物来源碳,植被特征间接的对土壤有机碳稳定性产生显著的正效应,海拔对土壤有机碳稳定性产生负效应;传统放牧区土壤有机碳稳定性关键控制因子为有机碳组分,其次是土壤理化性质。整体而言,季节休牧增加了土壤有机碳组分、生物来源碳及植被特征对土壤有机碳累积及其稳定性的影响效应,降低了海拔和土壤理化性质对土壤有机碳累积及其稳定性的影响效应。综上所述,5年的季节性休牧提高了土壤团聚体稳定性及SOC含量、真菌残体碳、木质素酚及植被特征在SOC累积中的作用,降低了高寒草地土壤木质素酚降解程度和碳库活度,增加了土壤有机碳的烷基化程度和空间稳定性,从而验证了季节休牧策略在提升草地生态系统土壤“碳汇”功能和助力实现国家“双碳”目标方面的科学性。因此,在藏北高寒草地施行季节休牧不仅有利于草地恢复和维持土壤“碳汇”功能,更是高寒牧场健康可持续发展的有效措施。更多还原

【Abstract】 The Qinghai-Tibetan Plateau,as a sensitive region and regulator of global climate change,contains alpine grassland soils that store approximately 2.5%of the global soil organic carbon(SOC)pool,serving as a crucial carbon sink in terrestrial ecosystems and playing a pivotal role in global carbon balance.SOC primarily originates from plant root exudates,senescent tissue shedding,litter decomposition,microbial metabolism,and residual inputs.Alterations in grassland management practices can induce changes in SOC sources and sequestration mechanisms.However,the relationships between vegetation characteristics,soil physicochemical properties,and SOC accumulation/stability following seasonal rest grazing remain unclear.Furthermore,research on the distribution of biogenic carbon and organic carbon functional groups in soils,along with their contributions to SOC,remains insufficient.This knowledge gap significantly hinders accurate predictions of SOC dynamics in seasonally rested alpine grasslands.This study investigates northern Xizang alpine grasslands subjected to five years of seasonal rest grazing across different altitude,comparing vegetation characteristics,soil physicochemical properties,organic carbon functional groups,biogenic carbon,and total organic carbon between seasonal rest grazing and traditional grazing systems.The research aims to elucidate the response mechanisms of SOC accumulation and stability to seasonal rest grazing,providing theoretical support for understanding SOC regulation in managed alpine grasslands.Key findings include:(1)Seasonal rest grazing significantly increased(P<0.05)the above-ground and below-ground biomass,apoplastic volume,average height and total cover of alpine grassland vegetation,increased the diversity of vegetation communities,increased the importance values of the functional groups of alpine grassland plants in the families Leguminosae,Graminae and Salicaceae,and significantly decreased the importance values of miscellaneous grasses(P<0.05).SOC,total nitrogen,total phosphorus,total potassium,quick-acting nitrogen,quick-acting phosphorus,quick-acting potassium,and bulk weight decreased after the seasonal rest grazing,while soil water content,soil temperature,and porosity increased.The vegetation characteristics,species diversity and soil physicochemical indexes of the two grassland utilization modes showed a decreasing trend with increasing altitude.Correlation analyses showed that seasonal rest increased the correlation between vegetation characteristics and SOC,AN,and soil moisture,and attenuated the effects of elevation,BD,soil temperature,micro-agglomerates,and clay dust particles on vegetation characteristics.It can be seen that the alpine meadows are evolving in the direction of stabilization of vegetation communities after the seasonal grazing break.(2)The organic carbon content of soil macro-aggregates in the seasonal fallow area increased by 3.38%～10.75%compared with traditional grazing,while the organic carbon content of micro-aggregates and sticky powder particles decreased by 1.15%～18.28%and4.35%～7.03%,respectively;the stability of soil aggregates(MWD and MGD)increased after the seasonal fallow,which was mainly related to the increase in the proportion of macro-aggregates and the decrease in the proportion of micro-aggregates and sticky powder particles.decreased.The decrease in the proportion of soil macro-aggregates and the increase in the proportion of micro-aggregates with increasing altitude led to a decrease in the stability of soil aggregates at high altitude.Compared with traditional grazing,seasonal rest grazing reduced the effects of altitude and soil chemical properties on aggregate stability and its organic carbon content,and increased the effects of vegetation characteristics on aggregate stability and its organic carbon content.Overall,seasonal grazing rest improved soil aggregate stability and its organic carbon content,which was conducive to maintaining the carbon sink function of alpine grassland soils.(3)Seasonal rest grazing increased soil particulate organic carbon,microbial organic carbon,soluble organic carbon,and amino sugar content,and lignin phenol content was increased only in 4308 m.The ratio of soil Glu N/Mur N was greater than 1 in both seasonal rest and traditional grazing areas,and was greater in seasonally rested than in traditional grazing areas,indicating that the fungal community dominated the soil microbial community in the alpine grassland,and was more pronounced in seasonal rest grazing areas.The Sp/Vp and Cp/Vp ratios were greater than those of traditional grazing,indicating that seasonal rest grazing reduced soil lignin phenol degradation and favored SOC sequestration.The contribution of soil microbial residue carbon to SOC was greater than that of traditional grazing in the seasonal rest grazing area,and the contribution of lignin phenol to SOC was only 4308 m and 4402 m altitude showed greater seasonal rest grazing than traditional grazing.The content of soil carbon functional groups under the 2 grazing patterns was,in descending order,Aromatic-C、Carbonyl-C、O-alkyl-C、Alkyl-C.Soil Alkyl-C/O-alkyl-C values were higher in the seasonal rest grazing area than in the traditional grazing area,indicating that seasonal fallow improved soil organic carbon alkylation and increased organic carbon stability.Correlation analysis showed that seasonal rest grazing had a more significant effect on the content of soil amino sugars and lignin phenol fractions,while soil carbon functional groups did not respond positively to seasonal rest.From the analysis of organic carbon accumulation,seasonal rest grazing increased the regulating effects of amino sugars,lignin phenols,active carbon and vegetation characteristics on SOC.The above findings indicate that seasonal grazing rest overall increased the contribution of biogenic carbon to soil organic carbon and promoted soil organic carbon accumulation and its stability.(4)Soil carbon pool activity,carbon pool activity index,carbon pool index,and carbon validity were all significantly higher in the traditional grazing area than in the seasonal rest grazing area from 37.89%～128.95%,111.06%～314.12%,19.18%～31.38%,and 19.89%～80.31%,in that order(P<0.05),whereas the seasonal rest grazing area soil carbon pool management index and organic carbon spatial stability were both significantly higher than those of traditional grazing areas,84.05%～242.92%and 2.33%～20.29%(P<0.05).It can be seen that seasonal rest grazing decreased soil organic carbon pool activity and increased soil organic carbon stability,and meanwhile,the increase of soil OC-Fe content in seasonal rest grazing areas had a positive effect on maintaining soil organic carbon stability.Redundancy analysis showed that seasonal rest grazing decreased the contributions of SOC,ROC,TN,and BD to soil carbon stability and increased the contributions of TP,TK,and ACC.The structural model showed that the relationship between soil physicochemical properties,vegetation characteristics and soil carbon pool stability after seasonal rest grazing was closer and better reflected the changes in soil carbon pool stability.(5)The key factor affecting the accumulation of soil organic carbon in alpine grassland with seasonal rest grazing is biogenic carbon,followed by soil organic carbon fractions,and the vegetation characteristics mainly affect the accumulation of soil organic carbon by influencing the changes of biogenic carbon;the key controlling factor for the accumulation of soil organic carbon in alpine grassland with traditional grazing is soil organic carbon fractions,followed by biogenic carbon,and the effect of the vegetation characteristics on the soil organic carbon accumulation is The effect of vegetation characteristics on soil organic carbon accumulation is smaller than that of seasonal rest grazing.The effect of soil physical and chemical properties on soil organic carbon accumulation was greater in seasonal rest grazing than in traditional grazing.Altitude had a negative effect on soil organic carbon accumulation in alpine grassland,and the effect on traditional grazing was more obvious.The key controlling factor of soil organic carbon stability in seasonal rest grazing alpine grassland is organic carbon fraction,followed by biogenic carbon,vegetation characteristics indirectly have a significant positive effect on soil organic carbon stability,and altitude has a negative effect on soil organic carbon stability;the key controlling factor of soil organic carbon stability in traditional grazing area is organic carbon fraction,followed by soil physicochemical properties.Overall,seasonal rest grazing increased the effects of soil organic carbon fractions,biogenic carbon and vegetation characteristics on soil organic carbon accumulation and its stability,and decreased the effects of altitude and soil physical and chemical properties on soil organic carbon accumulation and its stability.In summary,the 5-year seasonal grazing rest increased the soil macroaggregates and their SOC content,the role of fungal residue carbon,lignin phenol and vegetation characteristics in SOC accumulation,reduced the degree of lignin phenol degradation and carbon pool activity in alpine grassland soil,and increased the degree of alkylation and spatial stability of soil organic carbon.These findings collectively validate the scientific rationale underlying seasonal rest grazing strategies for enhancing soil carbon sequestration capacity in grassland ecosystems,thereby providing an effective approach to support the achievement of China’s national"Dual Carbon"goals.Therefore,the implementation of seasonal grazing rest in the alpine grassland in northern Xizang is not only conducive to grassland restoration and maintenance of soil“carbon sink”function,but also an effective measure for the healthy and sustainable development of alpine pastures.更多还原