灰胡杨(Populus pruinosa)是塔里木荒漠河岸林的关键种, 研究其生态化学计量特征及内稳性的变异格局, 对科学认识荒漠河岸林养分循环规律、植被健康状况及物种适应策略具有重要意义。该研究对塔里木河干流上游地下水埋深(GWD)梯度下灰胡杨种群进行野外调查与室内化验, 比较分析了不同GWD生境灰胡杨叶片与土壤碳(C)、氮(N)、磷(P)生态化学计量学及内稳态特征。结果表明: (1)随GWD增加, 灰胡杨叶片N、P含量降低, C含量与C:N、C:P、N:P均升高; 各指标变异系数均较低且C含量最小, 但不同GWD间差异显著; N含量与C含量、C:P, P含量与C:P、N:P呈显著负相关关系。(2)土壤C、N、P含量及其化学计量比均随GWD增加呈降低趋势, 除P含量外其他指标变异系数较高且不同GWD间差异显著, P含量与C、N含量呈显著正相关关系。(3)浅、中GWD生境大部分叶片C、N、P含量与土壤C、N、P化学计量特征相关性均不显著, 深GWD生境仅叶片P含量、N:P与土壤化学计量特征显著相关且叶片C:N, C:P均高其他2种生境, 表明叶片化学计量特征并非由土壤养分含量特征直接决定, 灰胡杨通过提高养分利用率来适应干旱逆境。(4)干旱荒漠区灰胡杨叶片与林下土壤养分含量整体偏低, 叶片N、P化学计量内稳态指数(H)表现为H_N > H_N:P > H_P, 结合养分限制诊断指标(N:P)表明灰胡杨生长易受P限制。(5)灰胡杨通过内稳态调节来保持体内C、N含量及C:N、C:P的相对稳定状态, 以保守型防御策略适应日益旱化的贫瘠荒漠环境。(6)退化荒漠河岸林生态修复过程中应注意P的供应与活化。

Aims Populus pruinosa is a key species of desert riparian forest playing an irreplaceable role in eco-environmental protection in Tarim extremely arid region, China. Studies on variation pattern of ecological stoichiometric characteristics and homeostasis of plant and soil were helpful to understand the health status of desert vegetation and also provide insights into ecosystem nutrient cycling, and ecological strategies of organisms to environmental changes. The aim of the present study was to explore the variations of ecological stoichiometry of plant and soil carbon (C), nitrogen (N), phosphorus (P) and their stoichiometric homeostasis of P. pruinosa leaves along groundwater depth (GWD) in Tarim basin.

Methods Through field investigation, we measured C, N, P contents in leaves of P. pruinosa and in soils. The differences between C, N, P contents and their stoichiometric ratios of leaves and soils as well as in stoichiometric homoeostasis were examined among sites with different groundwater depths.

Important findings With the increase of GWD, the N, P contents of leaves decreased and C content, C:N, C:P, N:P increased. The variation coefficient of all stoichiometric indices was basically low and that of C content was the lowest, but the difference among different GWD was significant. Leaf C content and C:P were significantly negative correlated with leaf N content, and leaf C:P and N:P were significantly negative correlated with leaf P content. Soil C, N, P contents and their stoichiometric ratios all decreased with the increase of GWD, and the variation coefficients of other indices except P content were high and significantly different among different GWDs. Soil P content was positively correlated with soil C and N contents. Moreover, the correlation of C, N, P stoichiometry between leaf and soil in shallow and middle GWD habitats were non-significant, while there were significant correlations between leaf P content, leaf N:P and soil stoichiometry indices in deep GWD habitats, and leaf C:N, C:P were higher in deep GWD habitats than that of other two habitats. It indicated that leaf stoichiometric characteristics were not directly determined by soil nutrient conditions, P. pruinoseimproved nutrient utilization to adapt arid adversity. The N and P stoichiometric homeostasis index (H) of P. pruinosa were ranked in the order of H_N > H_N:P > H_P. Combined with nutrient restriction diagnostic index (N:P), evidence suggested the growth of P. pruinosa was limited by P. Populus pruinosa maintained a relatively stable state of C content, N content, C:N, C:P with homeostasis regulation, adopting the conservative defense strategy to adapt to the increasingly arid environment. Therefore, adequate P supply should be considered during the restoration process in degraded desert riparian forests.