Comparative study on the adaptability of four submerged macrophytes to low light environment in Lake Erhai

Abstract

水下弱光环境是水生态系统沉水植被恢复面临的常见问题，因此研究沉水植物在弱光胁迫下的适应性是必要的.本研究以云南大理州洱海南部重度退化的湖区（惯称湖心平台，曾分布有大面积沉水植物）作为实验地点，选取4种沉水植物——苦草（Vallisneria natans）、轮叶黑藻（Hydrilla verticillata）、穗花狐尾藻（Myriophyllum spicatum）、竹叶眼子菜（Potamogeton wrightii）作为研究对象，开展原位盆栽实验，通过比较4种沉水植物的生长情况来选取潜在的目标物种，为洱海湖心平台沉水植被恢复提供科学依据.结果表明：1）水下弱光环境对4种沉水植物生长均造成胁迫，生物量和株高显著性降低，物种间的相对生物量差异表现为：苦草和竹叶眼子菜>轮叶黑藻和穗花狐尾藻，相对株高差异表现为：苦草>竹叶眼子菜>穗花狐尾藻>轮叶黑藻；2）生理特征方面，苦草、穗花狐尾藻和竹叶眼子菜有相似的胁迫反应，均表现为：氮（N）和游离氨基酸含量均升高，碳氮比（C∶N比）、可溶性糖含量与淀粉含量均下降，仅苦草的叶绿素含量升高，而轮叶黑藻的生理胁迫反应表现为：氨基酸含量下降，可溶性糖和淀粉含量升高；3）四者最终存活率为：苦草>竹叶眼子菜>穗花狐尾藻>轮叶黑藻，且苦草相对生物量和相对株高高于其他3种植物.以上原位实验结果表明，与其他3种植物相比，苦草更能适应湖心平台的水下弱光环境，可考虑作为湖心平台沉水植被恢复的目标物种.;Low light environment under water is a common problem in the revegetation of submerged macrophytes. Therefore, it is necessary to study their adaptability to low light stress. The central part of the southern Lake Erhai (a mesotrophic lake in Yunnan Province, China) is flat, with an average annual water depth of about 6.3 m, which was called the “lake center platform” (LCP). Large areas of aquatic vegetation were once existed in the LCP, which had important roles in the lake ecological function but completely disappeared since 2003. Therefore, we chose the LCP as our experimental site, and select four common submerged macrophytes (Vallisneria natans, Hydrilla verticillata, Myriophyllum spicatum, and Potamogeton wrightii) as the research objects for the in-situ pot experiment, then select the potential species for revegetation by comparing their growth and final survival rates. Our results showed that: 1) the growth of the four species was stressed under the low light environment, and the biomass and plant height significantly reduced. The relative differences in biomass among species were as follows: V. natans and P. wrightii>M. spicatum and H. verticillata, and the relative differences in plant height were as follows: V. natans>P. wrightii>M. spicatum>H. verticillate; 2) In terms of physiological characteristics, V. natans, P. wrightii and M. spicatum had similar physiological response to low light stress-the contents of N and free amino acids increased, the ratio of C∶N, soluble carbohydrate and starch content decreased. Only the chlorophyll content of V. natans increased. The physiological response of H. verticillata to low light stress was as follows: the content of free amino acids decreased, and those of soluble carbohydrate and starch increased; 3) the final survival rates of four species were as follows: V. natans>P. wrightii>M. spicatum>H. verticillata. In summary, the relative biomass and plant height and final survial rate of V. natans were highest, therefore it was more suitable for underwater low light environment and could be considered as a pioneer species for revegetation in LCP.