三峡水库消落带植物叶片光合与营养性状特征

自2007年三峡大坝试运行以来,其独特的人工水位调度节律给当地的水库消落带生态系统带来了巨大的负面影响。植物功能性状可以反映某一特殊生境植物的生理生态过程特殊性,是指示生态系统结构与功能的有效指标。因此,在三峡水库消落带形成2a后,于2009年调查了消落带的42种适生植物以及对照带33种植物的6个叶片功能性状:最大净光合速率(Amax)、叶片气孔导度(Gs)、比叶重(LMA)、叶片全氮含量(Nmass)、全磷含量(Pmass)和全钾含量(Kmass)。运用标准化主轴回归分析对消落带植物叶片各功能性状之间关系进行分析,并对照全球尺度叶片功能性状数据库,旨在说明反季节淹水对消落带植物叶片功能性状之间关系与全球尺度对比发生了哪些变化。同时,运用成对方差t检验的分析方法,对比了在消落带和对照带都存在的33个种的叶片光合与营养性状之间的差异,以阐明消落带植物对消落带特殊生境的生理响应。结果表明:(1)消落带植物叶片各性状关系呈现出与全球尺度基本一致的格局,表现出植物叶性状之间关系的趋同性;(2)消落带植物Amass、Nmass、Pmass和Kmass显著高于全球尺度,而LMA则显著低于全球尺度。处于驯化阶段的消落带植物各叶片性状处在全球叶片经济型谱"低投入-快速回收"的一端。(3)消落带植物叶片Amass与对照带相比,有显著提高。表明三峡水库消落带植物叶片光合能力得到显著提高,这可能是其适应消落带特殊生境的关键生理生态对策之一。

Features of leaf photosynthesis and leaf nutrient traits in reservoir riparian region of Three Gorges Reservoir, China

Since 2007, the unique anthropogenic hydrological regime of the Three Gorges Dam has had significant negative impacts on the reservoir riparian ecosystem. These include changes in the local climate pattern, habitat fragmentation, generation of methane gas, loss of biodiversity, and inundation of cities and highly productive agricultural land. The functional traits of plants in a particular area can reflect the eco-physiological processes that are specific to that environment, and can serve as crucial indicators of the structure and function of the local ecosystem. These functional traits play a key role in adaptation to anti-seasonal flooding, and might reveal clues about the adaptation mechanisms of plants in this area. Therefore, two years after the formation of the reservoir riparian region (RRR) in the Three Gorges Area, we investigated six leaf functional traits of 42 species growing in the RRR in 2009. As a reference, we also investigated these functional traits in 33 species in an upland non-flooding belt (CKB), to determine variations in physiological processes associated with anti-seasonal flooding. The six leaf functional traits were leaf mass per area (LMA), maximum net photosynthesis rate (Amax), leaf stomata conductance (Gs), leaf nitrogen content per mass (Nmass), leaf phosphorus content per mass (Pmass) and leaf potassium content per mass (Kmass). A standardized major axis (SMA) analysis method was used to determine the relationships among these traits. We compared these results with data in the global plant trait network (GLO) to determine how the leaf traits relationships for plants in the RRR compare with those in the worldwide leaf spectrum. For species that coexist in RRR and CKB, we used paired-sample T-tests to compare differences in leaf functional traits between the two areas, to determine which physiological processes are important for growth in the RRR environment. The results showed that: 1) although there were slight differences in the SMA slopes/elevation of some paired traits, there were similar patterns of leaf functional trait relationships between RRR and GLO, indicating convergence of leaf traits in the RRR ecosystem. 2) Amass, Nmass, Pmass, and Kmass of RRR species were significantly higher than their corresponding values in GLO, but the LMAs of RRR species were statistically lower than LMA values in GLO. The traits of RRR species were constrained to the lower-investment and faster-return end of the global leaf spectrum, and were consistent with typical fast-growing species. 3) When the 33 species common to both RRR and CKB were compared, we found that those in the RRR showed significantly higher Amax. The results of the present study suggest that enhanced photosynthetic capacity is one of the key physiological strategies for growth in the RRR environment. However, there are many uncertainties that remain after this study, because the RRR area is only two years old and plants are likely to be in the response or acclimation stages rather than the adaptation stage. Therefore, long-term investigations and observations should be continued in this area to identify and monitor adaptive changes in plant species.