天然沙冬青器官生态化学计量特征对异质生境的响应

Responses of ecological stoichiometric characteristics in organs of Ammopiptanthus mongolicus to heterogeneous habitats

以我国重点保护的珍稀濒危植物且是西北荒漠地区唯一常绿阔叶灌木沙冬青(Ammopiptanthus mongolicus)为研究对象,分析异质性荒漠生境(固定沙地、半固定沙地、石质沙地、洪积砾石坡地和盐碱滩地)对沙冬青叶、茎、根、花和种子生态化学计量学特征的影响,了解其生长的适应机制和生存策略。结果表明:沙冬青各器官碳(C)含量表现为叶>茎>根>种子>花,而氮(N)、磷(P)、钾(K)营养元素含量均表现为种子>花>叶>根>茎,N、P、K三大营养元素在繁殖器官中的富集,可以促进沙冬青由营养生长向生殖生长的转变,反映了资源分配模式和植物生长策略。沙冬青各器官的碳氮磷钾含量和各元素化学计量比在不同生境条件下变化较复杂,其中在沙质土壤(固定和半固定沙地)具有更高的C、N、P储存能力,而K在砾质土壤(石质沙地和洪积砾石坡地)含量较高,且砾质荒漠沙冬青的C∶N、C∶P及N∶P均显著高于沙质土壤,表明沙冬青在石质沙地和洪积砾石坡地有更高的养分利用效率。各器官元素含量相关分析表明器官间的养分协同性远高于器官内部。化学计量比C∶N、C∶P、C∶K均表现为:茎>根>叶>花>种子,N∶P为根>叶>茎>花>种子,N∶K为茎>根>叶>种子>花,K∶P为叶>根>种子>茎>花,各器官中的C∶N和N∶P比在各生境间相对较稳定,而K∶P比变化巨大,N∶P与P含量呈显著的负相关(P<0.05),与N含量的相关性不显著(P>0.05),说明P作为敏感性元素决定了沙冬青体内N∶P比值的变化,且不同生境叶片N∶P比值均大于16,说明沙冬青生长主要受P限制。器官与生境对沙冬青化学计量特征都有影响,生境对C含量和N∶K、K∶P的影响较大,器官对N、P、K含量及C∶N、C∶P、C∶K、N∶P的影响较大。除P元素外,各元素含量及其化学计量比均受器官和生境交互作用影响。了解植物根-茎-叶-花-种子的整体资源权衡和协变策略,为沙冬青物种资源的保护和开发提供理论依据。

Ammopiptanthus mongolicus is a rare and endangered plant in China and is the only evergreen broad-leaved shrub in desert areas.To understand the growth mechanism and survival strategy of A.mongolicus and the effects of habitats and organs on its ecological stoichiometric characteristics,we analyzed the ecological stoichiometric characteristics of leaves,stems,roots,flowers,and seeds of A.mongolicus in five habitats,namely the fixed sand,semi-fixed sand,stony sand,alluvial gravel slope land,and saline-alkali flat land.The results showed that the C content was in the order of leaf>stem>root>seed>flower,while the nutrient contents of N,P,and K were in the order of seed>flower>leaf>root>stem.The enrichment of the N,P,and K in the reproductive organs promoted the transition from vegetative growth to reproductive growth,indicating the resource allocation pattern and plant growth strategy.Additionally,the contents of C,N,P,K and their stoichiometric ratios in different organs varied among different habitat types.The storage capacity of C,N,and P was higher in sandy soil(fixed and semi-fixed sandy land),whereas the content of K was higher in gravelly soil(stony-sandy land and alluvial gravel slope),and the C∶N,C∶P,and N∶P were significantly higher in gravelly soil than those in sandy soil.A.mongolicus had higher nutrient use efficiency in stony-sandy land and alluvial gravel slope.Furthermore,the correlation analysis of element content in different organs showed that the nutrient synergy between different organs was much higher than that in the same organ.The stoichiometric ratios of C∶N,C∶P,and C∶K followed the order of stem>root>leaf>flower>seed,N∶P followed the order of root>leaf>stem>flower>seed,N∶K followed the order of stem>root>leaf>seed>flower,and K∶P followed the order of leaf>root>seed>stem>flower.The C∶N and N∶P ratios in each organ were relatively stable among different habitats,whereas the K∶P ratio varied greatly.There was a significantly negative correlation between N∶P and P content(P<0.05),and the correlation with N content was not significant(P>0.05),indicating that the change of N∶P ratio in A.mongolicus was mainly determined by the change of P content.The N∶P ratios of leaves were all greater than 16 in different habitats,indicating that the growth was mainly limited by P.Moreover,both organs and habitats had impacts on the stoichiometric characteristics of A.mongolicus,with habitat having a greater impact on C content and organs having a greater influence on N,P,K content and C∶N,C∶P,C∶K and N∶P.Except for P element,the content of each element and its stoichiometric ratio were affected by the interaction between organs and habitat.Our study provides a theoretical basis for the protection and development of species resources of A.mongolicus,and helps to understand the overall resource trade-off and covariation strategy of plant root-stem-leaf-flower-seed.