Response Of Salix Cavaleriei And Zizania Latifolia To Water Level Rise In Lake Erhai

Aquatic plants are very sensitive to water level fluctuation,and high water level is a several stress on the survival and reproduction of aquatic plants.The water level of the Lake Erhai is rising in recent years.Whether an aquatic plant can survive in the rising water level is determined by its survival strategy.Two dominant aquatic plants(a woody plant Salix cavaleriei and an emergent macrophyte Zizania latifolia)were selected in this study.The maximum height of adventitious roots and abundance of adventitious roots between dead and live willows along a flooding gradient from 0cm to 170cm in Lake Erhai were surveyed and compared to analyze the survival strategy of S.cavaleriei.In addition,the distribution and plant composition of the floating mats of Lake Erhai were studied in the summer and winter in 2017 to make sure the importance of floating mat for the survival of Z.latifolia water level rise.The main results are as follows:(1)The survival rate of S.cavaleriei at low flooding depth was higher than that of S.cavaleriei at high flooding depth.When the flooding depth exceeds 100 cm,the survival rate of S.cavaleriei dropped sharply.At different water levels,the maximum height of adventitious roots and adventitious root class of surviving S.cavaleriei were higher than those of dead S.cavaleriei.The mature S.cavaleriei are more flood tolerant than young S.cavaleriei.Therefore,the height,basal stem diameter and crown projection area of live S.cavaleriei were higher than those of dead S.cavaleriei.The maximum height of adventitious roots and adventitious root class of S.cavaleriei were significantly positively correlated with flooding depth.The deeper the flooding depth,the higher the maximum height of adventitious roots and the higher the abundance of adventitious roots at the trunk of S.cavaleriei.The results showed that S.cavaleriei actively responded to water level rise by forming a richer adventitious root and a higher adventitious root height on the trunk.The results indicated that producing adventitious roots higher on the trees might be more important than developing abundant adventitious roots lower on the trees when S.cavaleriei was subjected to high flooding levels.(2)Eighten floating mats and 22 floating mats were investigated in the summer and winter,respectively.The plants that formed the Lake Erhai floating mats had a total of 15 families,19genera,and 26 species.Among them,Z.latifolia had the highest frequency and relative biomass both in summer and winter.The occurrence frequency of Z.latifolia in the summer and winter were 73.33%and 66.67%,respectively.The relative biomass of Z.latifolia in the summer and winter were 41.91%and 43.38%.It was the higher frequency and relative biomass that might make Z.latifolia be the single dominant species in floating mats.(3)Most of the floating mats distributed in the region within an offshore distance less than 60 m and the water depth was less than 2 m.The area of the most floating mats was less than 600 m~2(87%for summer and 95%for winter),and the number of species in the floating mats was less than 10,the longest root in the floating mats ranged from 40 to 120 cm.(4)The results showed that both species richness and biomass of the floating mat were positively correlated with the area of floating mat,but the mean biomass of the floating mat was not significantly correlated with the area of floating mat.The longest root of the floating mat was significantly correlated with the area of floating mat in summer but not in winter.The concentrations of total nitrogen(TN),total phosphorus(TP)and total dissolved phosphorus(TDP)in the water under the floating mat were greater than those in the open water,while the concentration of dissolved oxygen(DO)was vice versa.When the water level was rising,two different life-type dominant aquatic plants adopted an active escape strategy.S.cavaleriei survived the rise of the water level by producing more abundant adventitious roots and growing adventitious roots at higher positions on the trunk.Z.latifolia could use more resources for the growth of the crown and reduce the growth of the root system quickly and activelyand form floating mat to avoid flooding.Accordingly,these two dominant macrophytes are more competitive and could become the dominant plant species in the rise of water level in Lake Erhai.