落羽杉根系有机酸与NSC代谢对三峡消落带水位变化的响应

为探究三峡库区消落带水位变化下落羽杉根系有机酸和非结构性碳水化合物(NSC)的响应特征,以适生木本植物落羽杉为对象,在消落带原位环境中设置对照-SS(海拔175 m,试验期间无水淹)、MS(海拔170 m,中度水淹胁迫)和DS(海拔165 m,深度水淹胁迫)3个处理,分别于海拔170 m和165 m退水时采集样品,测定并分析根系有机酸和NSC的变化。结果表明:(1)库区水淹对落羽杉基径无显著影响,仅有DS组明显抑制了高生长,落羽杉生长能较积极地响应库区水淹。(2)库区水淹对落羽杉侧根和总根有机酸的影响一致,侧根有机酸代谢作用优于主根。与SS组相比,MS组根系有机酸含量增高,DS组根系有机酸含量降低,除部分根系酒石酸、苹果酸、柠檬酸变化达到显著水平外,其余有机酸均无显著变化。(3)库区不同强度水淹对落羽杉根系NSC有不同程度的影响。与SS组相比,MS组可溶性糖无显著变化,淀粉、NSC含量显著增加,但总根NSC在水淹前与水淹后无明显差异;形成鲜明对比的是,DS组显著降低了可溶性糖、NSC含量,对淀粉无显著影响,且水淹后总根NSC显著低于水淹前。(4)相关分析表明,主根、总根草酸、苹果酸、柠檬酸及侧根、总根莽草酸分别与淀粉、NSC间表现出显著相关性(P0.05)。研究结果表明,在三峡库区消落带水淹胁迫下,落羽杉根系有机酸与NSC代谢联系紧密。通过维持一定的根系淀粉含量,保持植株正常的有机酸代谢水平,较好地适应三峡库区消落带生境。

Responses of root organic acids and nonstructural carbohydrates of Taxodium distichum to water-level changes in the hydro-fluctuation belt of the Three Gorges Reservoir

Along the Three Gorges Dam reservoir on the Yangtze River in China, water levels fluctuate between 145-175 m annually, which has resulted in severe ecological problems, such as the degradation of vegetation and a decrease in biodiversity. In recent years, many efforts have been made to restore the vegetation in water-level-fluctuating zones. Some flood-tolerant species have been selected through pot experiments; however, only a few of these flood-tolerant plants survived after being planted in the hydro-fluctuation zones, bringing new challenges to rebuild vegetation in these areas. Chronic submergence is one of the major factors limiting the survival of plant species in the Three Gorges Reservoir. Previous studies showed that the root metabolism of organic acids and nonstructural carbohydrates (NSC) played an important role in the plant''s response to flooding. However, it is still unclear how the root metabolism of organic acids and NSC in adaptable plants responds to water-level changes in the hydro-fluctuation belt of the Three Gorges Reservoir. In this study, Taxodium distichum, a flood-tolerant plant, was planted at three elevations:the control-SS (175 m above sea level, abbreviates as ASL), prolonged moderate submergence-MS (170 m ASL) and prolonged deep submergence-DS (165 m ASL) in the reservoir riparian region of Zhong County, Chongqing. Organic acid and NSC content was measured and analyzed after collection during de-submergence of MS and DS. The results showed that:(1) There was no significant difference in the base diameter of T. distichum and the height was inhibited only by DS, indicating that the height and the base diameter of T. distichum could positively respond to water-level changes in the riparian zone. (2) The organic acids in lateral roots showed a trend consistent with that of the total root. The root organic acid content was higher in MS and lower in DS than that in SS. Except for tartaric acid, malic acid, and citric acid in some roots, there were no significant differences in the remaining organic acids. (3) Soluble sugar did not significantly change, whereas starch and NSC content was significantly higher in MS than in SS. However, the NSC content of the total root did not change after being flooded. In contrast, the content of soluble sugars and NSC was significantly lower, while starch content did not differ significantly in DS from that in SS. On the other hand, the NSC in total roots reduced to some extent after flooding. (4) Correlation analysis showed that the content of starch and NSC was negatively correlated with the oxalic acid content of taproots and total roots, whereas the NSC displayed a strong and positive correlation with the concentration of malic acid, citric acid of the taproot and total root, and shikimic acid of the lateral and total root. The results indicated that there was a close relationship in root metabolism between organic acids and NSC of T. distichum. With a sufficient amount of starch and the organic acid metabolic levels similar to those in the control, T. distichum could adapt well to the water-level-fluctuating zones of the Three Gorges Reservoir.