环境胁迫对海草非结构性碳水化合物储存和转移的影响

非结构性碳水化合物在海草体内的代谢对植株的生长有重要影响。为更好地跟踪非结构性碳水化合物在海草响应环境胁迫中所起的作用,根据国内外最新文献,重点综述了光强、营养盐、盐度、海洋酸化、温度、硫化物和动物摄食等环境胁迫对海草非结构性碳水化合物储存和转移的影响。光限制和富营养化均降低非结构性碳水化合物的合成,并使之从地下根茎转移到叶;而海洋酸化却促进非结构性碳水化合物合成并向地下组织转移;盐度变化改变海草体内渗透压,需要非结构性碳水化合物的新陈代谢来维持;温度通过影响光合作用、呼吸作用、氮代谢来影响非结构性碳水化合物的合成与储存;而硫化物和动物摄食则分别通过抑制海草酶的活性和啃食海草光合组织,减少非结构性碳水化合物的合成和储存。同时指出了一些今后关于海草非结构性碳水化合物的重点研究方向:(1)海草不同生命阶段(种子休眠和萌发,发育,繁殖等)非结构性与结构性碳水化合物之间,以及可溶糖与淀粉之间的转化分配机制;(2)双环境因子或者多环境因子对海草非结构性碳水化合物的耦合作用;(3)非结构性碳水化合物作为海草床生态系统健康评价指标的研究与应用。

Effect of environmental stress on non-structural carbohydrates reserves and transfer in seagrasses

The seagrass bed is one of the most productive wetland ecosystems, providing valuable ecological goods and services. About 2%-5% of seagarss populations disappeared each year on Earth, which has been due to a wide variety of human and natural disturbances in recent years. The dynamics of non-structural carbohydrates (NSC) reserves play an important role in determining seagrass growth and its response to environmental disturbances. In order to improve our understanding of the NSC in seagrasses, the information on the NSC responses to environmental stresses, such as light, nutrient, salinity, ocean acidification, temperature, sulfide and animal grazing were summarized. Seagrasses are particularly sensitive to reductions in light availability, where small decreases can cause significant declines in growth and distribution. During periods of reduced photosynthesis caused by light limitation, the stored NSC in belowground tissue can be reallocated to meet the C (Carbon) demand of seagrasses. Thus, seagrass species with higher belowground biomass and carbohydrate storage capacity can tolerate longer period of light limitation. Nitrogen assimilation requires carbon skeletons for the respiratory pathway and reserves. Under excessive nitrogen conditions, carbon requirements for synthesizing amino acids may exceed carbon fixation capacity, leading to a decrease in NSC concentration and NSC reserves reallocation. Under hypo- and hypersaline conditions, a number of organic compounds in seagrass including soluble sugar can be produced in response to salinity stress. Furthermore, carbon skeletons are also important for the synthesis and accumulation of proline (and other nitrogen containing osmotica such as glycine betaine or ectoine) during elevated salinities. Ocean acidification may promote seagrass photosynthesis, resulting in an increase of NSC synthesis in aboveground tissue and transfer to belowground tissue. And the belowground tissues of seagrass became a sink for fixed carbon. The effect of temperature on the NSC accumulation was significant by means of altering seagrass photosynthesis, respiration and nitrogen metabolism. Additionally, the decrease of NSC biosynthesis and reserves was resulted from both sulfide and animal grazing by inhibiting the enzyme activity and grazing seagrass photosynthetic tissue, respectively. Finally, research fields in the future are pointed out including: (1) the transformation mechanism between NSC and structural carbohydrates, and between soluble sugar and starch of seagrass in different life stage (seed dormancy and germination, development and reproduction); (2) the coupling impact of dual and/or more environmental factors on seagrass NSC; (3) the application of NSC as an ecological indicator for evaluating the seagrass ecosystem health evaluation.