Responses Of The Distribution And Growth Of Submerged Plants To Different Environmental Factors And Hydrologic Regime In West Dongting Lake

Submerged plants are an important part of the wetland ecosystem,which plays a key role in maintaining the stability of the ecosystem.Its distribution and growth are determined by the environmental factors in the water and the hydrological situation.Dongting Lake is an important lake connecting the middle reaches of Yangtze River in China,it was affected by human disturbances and climate change in recent years,the hydrological rhythm and the environmental factors had changed,resulting in the decline of submerged plants,so scientific research is urgently needed.This study combines field surveys and control experiments to analyze the distribution and growth of submerged plants in the West Dongting Lake,as well as responses to environmental factors,hydrological conditions,and interspecies competition.Provide scientific basis for the protection and restoration of submerged plants in Lake connecting of Yangtze River in China.The field investigation of this study was conducted in the summer of 2018 and 2019.A total of 11 subsurface plants in different hydrological connectivity habitats in the West Dongting Lake and 11 environmental factors such as water depth and transparency were investigated,to study the response of submerged plant distribution to environmental factors and hydrological conditions;In the control experiment,we selected three common submerged plants in the middle reaches of the Yangtze River,namely Vallisneria spinulosa,Hydrilla verticillata,and Potamogeton malaianus.The experiment set up different water depths(30cm,80cm,130cm and 180cm)and planting methods(single species planting and two species mixed planting)to study the response of submerged plants to water depths and interspecies competition.The result shows(1)The distribution of submerged plants in West Dongting Lake is affected by environmental factors such as water depth,transparency,pH,and total phosphorus.Submerged plants are mainly distributed in semi-barrier lakes and the freely connected lake bay with shallow water depth(<3m),better water quality,and more stable water bodies.Hydrological connectivity and interannual hydrological rhythms have a comprehensive effect on the species and biomass of submerged plants.High-level hydrological conditions have an inhibitory effect on submerged plants.The semi-blocked seasonally connected lakes have a "refuge" effect on submerged plants(2)The results of control experiments show that water depth has a significant effect on the growth and reproduction of submerged plants.The biomass and plant height of the three submerged plants increase with the water depth.The suitable water depth for the growth of Vallisneria spinulosa is shallower than Hydrilla verticillata and Potamogeton malaianus.Under different water depths,the resource allocation of submerged plant vegetative propagules is different.In the shallow water,the asexual reproduction ability of Vallisneria spinulosa is more beneficial to the preservation of the population of wintering offspring;it is more favorable to the population expansion of the current generation in the deep water.The response of the asexual reproduction ability of Potamogeton malaianus and Hydrilla verticillata to water depth are not obvious(3)Interspecies competition has an impact on the growth of submerged plants.The analysis of the competition intensity index revealed that water depth changed the interspecies competition ability of submerged plants.In this experiment,the Hydrilla verticillata had the highest competition index at water depths of 30cm and 80cm,the Potamogeton malaianus had the highest competition at water depths of 130cm and 180cm,and the competition ability of Vallisneria spinulosa is the lowest at all water depthsMaintaining natural hydrological rhythms that are close to the multi-year average water level process,maintaining the heterogeneity of lake habitats with different connectivity,and healthy water quality are the keys to restoring submerged plants in lakes in the middle reaches of the Yangtze River.To carry out the restoration of submerged plants,we recommend choosing a lake bays or a semi-blocked lakes with a water depth of less than 3m,a moderate nutrient content,low velocity and wind waves,and considering the interspecific competition between plants under different water depths,and do a good job in restoring species.