【作者】 王楠；

【导师】 王根轩；

【作者基本信息】 浙江大学 ， 生态学， 2013， 博士

【摘要】 气候变化尤其是其导致的干旱胁迫对生态系统的影响及生态系统对这些胁迫因子的响应方式是当前生态学界研究的热点问题之一。由于人类活动造成的全球变暖及水资源匮乏对植物个体,群落结构乃至整个生态系统的稳定性都起到了深远的影响。所以研究长期水分亏缺对群落结构、种群分布及个体代谢造成的影响及其机理有着重要意义。本文中,我们通过分析水分利用效率、个体形态特征及化学计量比等性状研究不同植物功能群及群落特征是如何适应干旱梯度变化的。首先,我们分析了叶片稳定性碳同位素(δ13C)与植物地上密度-生物量关系(α)间的相关规律。越来越多的研究证明α不是一个恒定的值。争论依旧存在于到底是什么在改变α值中起着关键作用。通过研究叶片δ13C、植物根冠比、高茎异速比等形态特征和α值沿着东南到西北的自然干旱梯度变化的动态,我们发现α值随干旱胁迫的增大而增加,且与植物水分利用效率协变。这种协变主要是由植物根冠比、高茎异速比等形态变化驱动的,这种变化是植物在干旱胁迫下为提高水分利用效率而采用的一种适应性策略。这一信息将为理解和预测群落及生态系统过程提供理论支持。其次,我们研究了稳定碳同位素值(δ13C)在植物功能群间的变化形式及其与干旱梯度相关因子的互作方式。我们发现,由生活型划分的功能群间的δ13C在统计学上表现出显著性差异,但是在数值上的差距较小(<1‰)。乔木(-26.78‰)和灌木(-26.89‰)具有相似的δ13C,均显著的高于草本(-27.49‰)。常绿灌木(-25.82‰)的δ13C显著的高于落叶灌木(-26.92‰)。多年生草本(-26.83‰)的δ13C显著的高于一年生草本(-27.10‰)。禾草类(-26.46‰)的δ13C显著的高于非禾草类(-26.96‰)。综合数据显示,δ13C显著的负相关于年平均降水量(MAP)和年平均温度(MAT),而显著的正相关于纬度和海拔。在尺度的变化上MAP存在一个阈值,如果高于这个值δ13C将不会有显著的变化。功能群间沿海拔的变化不是一致的。功能群间δ13C的变化很小只在1‰的范围内波动,而环境因子,如：MAP和MAT对δ13C的影响较剧烈(尺度上超过了4‰)。大多数功能群的δ13c响应环境变化的方式是一致的,但是它们为响应梯度变化而产生的自身变化的速率是不同的。此类信息能够帮助我们预测不同功能群应对未来环境变化而产生的分布变化。第三,我们分析了白刺(Nitraria tangutorum)叶片与根部的氮(N)、磷(P)及N：P沿干旱胁迫变化的规律。我们发现在本研究进行的区域里,四月份叶片N和P均高于全球及中国本地物种的值,而在八月又均低于这些值。白刺在四月表现出来的是N限制(平均叶片N：P=11.13),而在八月表现出来P限制(平均叶片N：P=38.78)。叶片与根部中的N和P均是高度自相关的。四月份,随着干旱胁迫的增加,叶片和根部的N和P均增加。叶片N：P沿干旱胁迫的增加而不变,根部N：P随干旱的增加而增加。我们认为叶片N：P能揭示不同生长阶段的养分供应情况,而根部N：P则能说明土壤养分是否亏缺。以上结果分别从水分利用效率和氮磷化学计量方面阐释了植物群落密度调控指数α值干旱胁迫变化的内在原因。功能群水分利用效率随干旱相关因子改变会潜在影响群落结构特征这一结果也在侧面支持了α值的变化与水分利用效率相关这一假说。个体特征及其水分利用效率和氮磷化学计量随干旱胁迫定量变化证明群落结构和功能直接或间接的被体型和功能及其相互作用所控制。更多还原

【Abstract】 The effects of global changes such as drought stress on ecosystem and the responses of ecosystem are high research priorities. Anthropogenic factors that cause global warming and water shortage have strong influence on community structure and stability of ecosystem. The effects of long-term water shortage on community structure, population distribution and individual metabolism need further research. In this study, our objectives were to interpret the variability of the traits of plant functional groups and community responses to aridity gradients based on variations in water use efficiency, individual traits and stoichiometry.First, we analyzed the relationship between foliar stable carbon isotopes (δ13C) and scaling exponent (a). Accumulating evidence has shown that a is not a constant. Debate continues over what determines the variation in a. We found that a changes with aridity gradients and co-varies with water use efficiency. By measuring foliar stable carbon isotope, plant morphological traits (root-shoot and height-radius ratios) and a along an aridity gradient from eastern to western China, we confirmed that the variation in a was accounted for by changes in plant morphological traits which are adaptive strategies for enhancing water use efficiency during drought stress. This information can be crucial for understanding and predicting community and ecosystem processes.Second, the variation in foliar stable carbon isotope signature (δ13C) of different plant functional groups (PFGs) and its relationship with environmental factors in China were investigated in this study. There were some significant, but small differences in813C among PFGs categorized by life-form (<1‰). The trees (-26.78%o) and shrubs (-26.89‰) had similar mean δ13C, both significantly higher than herbs (-27.49‰). The evergreen shrubs (-25.82‰) had significantly higher mean δ13C than deciduous shrubs (-26.92‰). The perennial herbs (-26.83%o) had significantly higher mean δ13C than annual herbs (-27.10‰). The grasses (-26.46‰) had significantly higher mean δ13C than forbs (-26.96‰). For pooled data,δ13C was significantly and negatively correlated with the mean annual precipitation (MAP) and the mean annual temperature (MAT), while significantly and positively correlated with the latitude and the altitude. There was a threshold value of MAP along the gradients, and813C had no significant change with higher values. The δ13C of PFGs changed with altitude differently, suggesting that increases in δ13C with altitude cannot be generalized. Differences in δ13C between PFGs were generally much smaller than1‰and therefore insignificant. In contrast, MAP and MAT had relatively large effects on δI3C (more than4%o between extremes). The δ13C of some PFGs responded to environmental gradients in the same manner, while their ’rates’of change were significantly different in some cases. This kind of information could help predict potential changes in the distribution of PFGs in response to future climate changes.At the end, nitrogen (N) and phosphorus (P) concentrations and N:P ratios between leaf and root of Nitraria tangutorum along aridity gradients were studied. Our analysis indicated that the means of both leaf N and P in April were higher than the global and Chinese average values, while in August being lower than these reported average values. N. tangutorum was relatively limited by N in April (mean leaf N:P ratios=11.13) and by P in August (mean leaf N:P ratios=38.78). N and P in both leaf and root were highly correlated across sampling sites. Increase in leaf N and P was accompanied by increases in the N and P of root in April along aridity gradients. Leaf N:P ratios were invariant along aridity gradients, while root N:P ratios increased with increasing aridity gradients in April. We suggested that leaf N:P ratios could indicate nutrient status of different plant growth stages, while root N:P ratios could show us whether the soil nutrient become deficient.Our research explained the mechanism of varied a along aridity gradients, which related to WUE and stoichiometry. The fact that variations in WUE of different plant functional groups will change community structure support the hypothesis that a changes with WUE. Individual traits, WUE and stoichiometry changed with aridity gradients, which showed that community structure is controlled by individual behavior and function indirectly or directly due to changing with drought stress.更多还原