【作者】 李娜；

【导师】 吴正方； 杜海波； 李迈和；

【作者基本信息】 东北师范大学 ， 自然地理学， 2025， 博士

【摘要】 高山苔原是典型的脆弱生态系统,因其低温和低养分有效性,对气候变化极为敏感。随着全球变暖和氮沉降增强,低海拔植物逐渐扩张至高海拔地区,改变了原生植物的生长环境与种间关系,影响了群落结构与生态功能。长白山苔原是我国为数不多的山地苔原系统之一,近几十年,来自低海拔岳桦林的大叶章(Deyeuxia angustifolia)持续上侵,威胁了该区域的典型灌木牛皮杜鹃(Rhododendron chrysanthum)的生长和生存,推动苔原植被草甸化进程,可能削弱生态系统的碳汇功能。本研究以长白山苔原为研究区,采用两个因子实验,系统探讨了大叶章上侵对灌木苔原土壤理化性质、微生物群落结构、牛皮杜鹃功能性状与径向生长的影响及其调控机制。实验一基于“海拔×大叶章上侵强度”野外梯度采样,分析不同海拔与大叶章上侵程度下,土壤理化性质、牛皮杜鹃功能性状及径向生长的响应特征;实验二通过在两个海拔点设置大叶章剔除与氮添加处理,探讨上侵与营养扰动对土壤微生物群落结构及其调控机制的影响。主要结果如下:(1)不同海拔下土壤养分对上侵的响应模式存在明显差异,比如总碳、氮、氮/磷比、碳/磷比、和铵态氮在低海拔表现为先促后抑,而在高海拔则整体抑制更强,表明高寒环境对入侵干扰更加敏感。总体来看,随海拔升高,土壤总氮、速效磷和可溶性有机碳含量下降,而总磷和硝态氮增加,揭示了海拔梯度在限制土壤养分供应和调控入侵效应中的重要作用。本研究强调了入侵与环境因子交互影响下土壤养分动态的复杂性,为理解高山生态系统中植物—土壤互作机制提供了理论支撑。(2)大叶章上侵、海拔升高和氮添加均对土壤微生物群落产生显著影响,但作用路径和主要影响指标不同。其中,大叶章上侵通过直接作用以及改变土壤速效磷和氮/磷比,显著降低了各类微生物的生物量,尤其对海拔2200米的放线菌和革兰氏阳性细菌影响最强;海拔升高主要通过改变土壤碳/氮比、全磷、铵态氮和p H等间接调控微生物组成,显著提升革兰氏阳性菌/阴性菌比;而氮添加则通过提升氮/磷比、铵态氮和p H,显著抑制真菌生物量和降低真菌/细菌比。总体来看,大叶章上侵对微生物总量影响最显著,海拔升高对革兰氏菌群结构影响最大,而氮添加则主要调节真菌的相对比例。(3)随着大叶章的持续侵入,牛皮杜鹃的生物量显著下降(约20.76%),种子质量减少近一半(约46.89%)。作为响应,牛皮杜鹃逐渐调整其性状策略,表现出由资源保守型向光资源获取型的转变,包括叶片变薄变大、截光能力增强、营养含量提升以及根部非结构性碳水化合物含量减少。与此同时,与水分利用和碳储能相关的性状表现出更高的环境变异性,而营养相关性状趋于稳定。随着上侵强度的增强,性状整合度明显提高,性状网络的边缘密度增加60%–100%,核心性状由根和芽相关性状转向叶功能性状,表现出性状协同格局的重构。此外,性状策略也由以性状均值主导向更强调可塑性与整合性转变。这些适应性调整主要受土壤温度、碳/氮比和养分可利用性变化的驱动,有助于牛皮杜鹃在大叶章上侵所造成的光竞争环境中提高生存能力。(4)牛皮杜鹃的径向生长总体呈上升趋势,且在大叶章侵占条件下增长更为显著。生长过程受发育阶段调控,尤其在海拔2200米处,植物在幼年期(≤15年)表现出显著的径向生长提升。大叶章侵入还显著改变了牛皮杜鹃对气候因子的敏感性:在2050米处,入侵缓解了冬季低温对生长的抑制作用,但在2200米处则加剧了这种负面效应;同时,入侵削弱了秋季降水对2050米生长的正向影响,却增强了该因子在2200米的促进作用。路径分析表明,海拔通过直接作用及其对植物性状和土壤性质的调节,显著影响牛皮杜鹃的生长表现;而大叶章通过改变植物功能性状间接调控其对温度的敏感性,积雪覆盖与土壤特性则主导了不同海拔下对降水的响应模式。这些结果揭示了植物—土壤—气候互作对灌木生长调控的复杂性,强调了入侵背景下不同海拔生态系统中气候适应机制的差异性。综上所述,大叶章的上侵通过改变土壤理化性质和微生物群落结构,诱导牛皮杜鹃的性状策略发生转变,并重构其性状整合模式,进而影响其生长表现及对气候因子的响应。海拔作为关键调控因子,增强了大叶章上侵对植物—土壤系统的干扰效应,尤以高海拔地区表现最为显著。本研究揭示了上侵植物在高寒苔原生态系统中通过多条路径影响苔原典型植物与土壤之间协同关系的作用机制,为预测长白山地区苔原植被的演替趋势以及制定科学合理的管理策略提供了理论支撑。更多还原

【Abstract】 Alpine tundra ecosystems are typically fragile due to their low temperatures and limited nutrient availability,making them highly sensitive to climate change.With ongoing global warming and increasing nitrogen deposition,low-elevation plant species are progressively expanding into higher elevations,altering the native plant environment and interspecific interactions,thereby affecting community structure and ecosystem functions.The alpine tundra of Changbai Mountain is one of the few remaining mountain tundra systems in China.Over recent decades,the continuous upward encroachment of Deyeuxia angustifolia,a grass species originating from lower-elevation Betula ermanii forests,has posed a serious threat to the growth and survival of the native alpine shrub Rhododendron chrysanthum,accelerating the meadowification of the tundra vegetation and potentially weakening the ecosystem’s carbon sink function.This study,conducted in the alpine tundra of Changbai Mountain,employed a two-factor experimental design to systematically investigate the effects and regulatory mechanisms of D.angustifolia encroachment on soil physicochemical properties,microbial community structure,functional traits,and radial growth of R.chrysanthum.The first experiment,based on a field sampling design along an“Elevation×Encroachment Intensity”gradient,analyzed how soil properties,R.chrysanthum traits,and its growth responded to varying levels of encroachment across different elevations.The second experiment used removal and nitrogen addition treatments at two elevations to assess how D.angustifolia encroachment and nutrient perturbation influence soil microbial community structure and its regulatory mechanisms.The main findings are as follows:(1)Soil nutrient responses to encroachment varied markedly across elevations:at2050 m a.s.l.,total carbon,total nitrogen,nitrogen:phosphorus ratio,carbon:phosphorus ratio,and ammonium nitrogen showed a pattern of initial increase followed by decline,while at 2200 m a.s.l.,the overall response was more strongly suppressive.This indicates that colder,high-elevation environments are more sensitive to encroachment-induced disturbances.In general,increasing elevation led to decreases in total nitrogen,available phosphorus,and dissolved organic carbon,but increases in total phosphorus and nitrate nitrogen,highlighting the critical role of elevation in constraining nutrient availability and modulating the ecological impacts of encroachment.These findings underscore the complexity of soil nutrient dynamics under interacting biotic and abiotic drivers and provide theoretical support for understanding plant–soil interactions in alpine ecosystems.(2)D.angustifolia encroachment,elevation,and nitrogen addition all significantly influenced soil microbial communities,though their pathways of influence and key microbial indicators differed.D.angustifolia encroachment reduced microbial biomass primarily through direct effects and by altering available phosphorus and the nitrogen-to-phosphorus ratio,with the strongest impacts observed on actinomycetes and Gram-positive bacteria at 2200 m a.s.l.Elevation affected microbial composition mainly through indirect changes in soil carbon:nitrogen ratio,total phosphorus,ammonium nitrogen,and p H,resulting in a marked increase in the Gram-positive to Gram-negative bacterial ratio.Nitrogen addition suppressed fungal biomass and reduced the fungal-to-bacterial ratio,primarily by increasing nitrogen:phosphorus ratio,ammonium nitrogen,and p H.Overall,D.angustifolia encroachment exerted the most pronounced effects on total microbial biomass,elevation had the greatest influence on Gram bacterial community,and nitrogen addition primarily regulated the relative abundance of fungi.(3)With the continued encroachment of D.angustifolia,the biomass of R.chrysanthum declined significantly by approximately 20.76%,and seed mass was reduced by nearly 46.89%.In response,R.chrysanthum progressively shifted its trait strategy from a resource-conservative to a light-acquisitive mode,characterized by thinner and larger leaves,enhanced light interception,increased nutrient concentrations,and reduced non-structural carbohydrate storage in roots.Meanwhile,traits related to water use and carbon storage exhibited greater environmental variability,while nutrient-related traits became more stable.As encroachment intensified,trait integration increased markedly,with network edge density rising by60%–100%,and core traits shifting from root-and shoot-associated traits to leaf functional traits,indicating a restructuring of trait coordination patterns.Additionally,trait strategies transitioned from being dominated by trait means to emphasizing plasticity and integration.These adaptive adjustments were primarily driven by changes in soil temperature,carbon:nitrogen ratio,and nutrient availability,helping R.chrysanthum improve its survival under light competition stress induced by D.angustifolia encroachment.(4)The radial growth of R.chrysanthum generally showed an upward trend,with more pronounced growth under D.angustifolia encroachment.Basal area increment was closely related to developmental stage,and at 2200 m a.s.l.,plants in juvenile stages(≤15 years)exhibited significantly increased radial growth.Moreover,encroachment altered the shrub’s sensitivity to climatic factors:at 2050 m a.s.l.,it reduced the negative impact of winter(February)temperatures on radial growth,whereas at 2200 m a.s.l.,it intensified this negative effect.Encroachment also weakened the positive influence of autumn precipitation on radial growth at 2050 m a.s.l.,while enhancing it at 2200 m a.s.l.Elevation affected radial growth both directly and indirectly by modulating plant traits and soil properties.Encroachment indirectly influenced the temperature sensitivity of radial growth by altering plant functional traits,while snow cover and soil properties primarily shaped the sensitivity to precipitation across different elevations.In summary,D.angustifolia encroachment altered soil physicochemical properties and microbial community structure,and induced shifts in the trait strategies of R.chrysanthum and restructured its trait integration patterns.These changes ultimately influenced the shrub’s growth performance and its responses to climatic factors.Elevation acted as a key regulatory factor,amplifying the disruptive effects of encroachment on the plant–soil system,with the strongest impacts observed at higher elevations.This study reveals the multi-pathway mechanisms through which an invasive species affects the coordination between native plants and soil in alpine tundra ecosystems,providing theoretical support for predicting vegetation succession trends in the Changbai Mountain tundra and for developing scientifically grounded management strategies.更多还原