胡杨叶功能性状特征及其对地下水埋深的响应

叶片性状反映了植物对环境的适应能力及其自我调控能力。以塔里木干旱荒漠区建群种胡杨（Populus euphratica）为研究对象，通过分析自然生长状况下胡杨叶功能性状对地下水埋深（GWD）的响应及功能性状间的权衡关系，揭示胡杨对极端干旱荒漠环境的生态适应策略。结果表明：胡杨7个叶功能性状种内变异程度不同（9.20%-40.02%），叶面积（LA）变异程度最大，叶干物质含量（LDMC）与叶片含水量（LWC）变异程度较低，GWD梯度上表现出较大的分化变异特征。叶性状在不同GWD之间差异显著（P<0.05），与GWD呈极显著相关（P<0.01）。比叶面积（SLA）、LA、LWC与叶干重（LDM）呈极显著正相关（P<0.01），与叶厚度（LT）、叶组织密度（LTD）、LDMC呈极显著的负相关（P<0.01）；LDMC与LT、LTD，LWC与LA、SLA呈极显著正相关（P<0.01），反映胡杨通过叶性状间的相互调节与权衡来适应干旱荒漠环境。逐步回归分析表明LA、LT对GWD变化最敏感，可间接借助这2个性状来预测干旱荒漠区地下水埋深变化。随GWD降低，胡杨SLA、LA、LDM、LWC减小，而LT、LTD、LDMC增大，其由高生长速率、资源利用能力的开拓型策略转变为以增强自身养分储存、防御能力的保守型策略，拓宽了生态幅和增强其在干旱逆境的适合度。可见，极端干旱荒漠区胡杨形成了小的LA、SLA、LDM，大的LT、LDMC、LTD等一系列有利于减少水分散失、储存养分和增强耐旱能力的干旱性状组合，这可能是其适应干旱贫瘠环境的生态策略。

Leaf functional traits of Populus euphratica and its response to groundwater depths in Tarim extremely arid area

Plant functional traits, defined as morpho-physio-phenological traits, reflect the response and adaptation of plants to the environment, and function as a bridge between the plant and environmental factors. In this study, we explored how leaf functional traits responded to groundwater depth (GWD) and their interactions of P. euphratica growing in different arid habitats, and examined the relationship between leaf functional traits and groundwater depths in Tarim extremely arid area, in order to reveal the potential ways of P. euphratica in adapting arid desert environment. The experiments were carried out at eight sampling points (50 m×50 m) with different GWD in the upper reaches of Tarim river, Xinjiang Province, northwestern China in the summer 2019. Seven leaf functional traits of ten P. euphratica individuals in each plot with stem base diameter (BDH)>10 cm were measured, and the GWD and soil moisture of each plot were measured. We then carried out one-way ANOVA and Duncan tests to assess differences in leaf functional traits (specific leaf area, SLA; leaf area, LA; individual lamina mass, LDM; leaf water content, LWC; leaf thickness, LT; leaf dry mass content, LDMC; and leaf tissue density, LTD) under eight GWD. Pearson correlation and the stepwise regression were conducted to determine the quantitative relationships between leaf functional traits and GWD. The results showed that seven leaf traits varied in varying degrees from 9.02% to 40.02%, while the maximum and minimum coefficient of intraspecific variation were LA and LWC, LDMC, respectively. The leaf traits showed large variation along groundwater depth gradient. The leaf functional traits had significant difference in the eight groundwater depths, and were extremely significant correlation with GWD (P<0.01). LA, SLA, and LWC were positively correlated with LDM (P<0.01), but negatively correlated with LT, LTD and LDMC (P<0.01). LDMCs were positively correlated with LT and LTD, and LWCs were positively correlated with LA and SLA (P<0.01), which indicated that P. euphratica adapted to the harsh desert environment through mutual adjustment and trade-off with leaf functional traits. Stepwise regression analysis showed that LA and LT were the most sensitive to the change of GWD, and they could be used to indirectly diagnose the change of GWD in arid desert area. The SLA, LA, LDM, and LWC of P. euphratica declined, on the contrary, the LT, LTD and LDMC increased with GWD decreasing, which indicated that P. euphratica had changed from development strategy with high growth rate and resource utilization to conservative strategy with enhancing nutrient storage and defense ability, broadening its ecological amplitude and enhancing its fitness in desert adversity. In brief, P. euphratica formed trait combination with series of functional traits in extremely arid area, such as smaller LA, SLA, LDM and larger LDMC, LTD, LT, which were beneficial to reduce water loss, store nutrient and enhance drought tolerance. This may be its main ecological strategy for adapting to arid and barren environments.