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Studies on effects of burial depth are mainly focused on terrestrial plants,with little information on freshwater macrophytes.Burial depth could be an important environmental factor influencing the immature plant emergence and growth of freshwater macrophytes.However,most studies have paid their attention to burial-depth and water-level effects on germination and the immature plant emergence of seeds,with little focused on turions that are important "organ" of propagules.Furthermore,although studies choose water-level as one of the most important environmental factor influencing the distribution and growth of freshwater macrophytes are so many,the interactive effect of water level and burial depth on propagules emergence and early growth of freshwater plants is still poorly known.The plants of Myriophyllum oguraense subsp,yangtzense commonly occurs in the lower Yangtse river basin.It forms turions usually from late-October to December.After detachment from parents,turions stay dormant until they germinate in the next spring.In order to examine the effects of clay burial-depth and water-level on the immature plant emergence and early growth,we chose submersed plant Myriophyllum oguraense subsp,yangtzense which is one of the dominant aquatic macrophytes in the lower Yangtse river basin as our materials to conducted an outdoor pond experiment.The turions were buffed at 0,2,4,6 cm depths in plastic pots filled with unsterilized lake clay under 0,15,60 cm water-levels.In order to investigate the effects of burial-depth and water-level on the immature plant emergence and early growth of Myriophyllum oguraense subsp,yangtzense,We address two questions-what is the ultimate fate of Myriophyllum oguraense subsp. yangtzense turions planted at different depths in lake clay and water levels and is there any relationship between water level a圷?epth of burial in turion the immature plant emergence start our research.The result showed that:1.The percent emergence was significantly negatively correlated with burial depth (r=-0.926,p＜0.001),but was not significantly correlated with water-depth(r=-0.089, p＞0.05).The percentage of the immature plant emergence was highest at 0 cm burial depth(100%),but decreased with increasing burial depth in each water level(Figure 1). The immature plants percent emergence at 4 cm and 6 cm burial depth was rather low, especially at the 6 cm burial depth,there was only 1-2 the immature plants emerged.At 0; 4 and 6 cm burial depths,the percent emergence was not significantly different between water depth;but at 2 cm burial depth,percent emergence at 0 cm water depth were significantly higher than that at 15 and 60 cm water depths.2.The immature plant size was measured in terms of seedling biomass and seedling height.The immature plant height was significantly affected by both burial depth(F = 199.880,p＜0.001,Table 1) and water level(F = 311.896,p＜0.001),while the immature plant biomass was affected by water level(F = 81.870,p＜0.001) but not burial depth(F = 2.669,p＞0.05).Both the immature plant biomass and the immature plant height were highest at 0 cm water level(0.0653g and 7.95cm).The immature plant height decreased with increasing burial depth for all water-levels,but the immature plant biomass didn’t show such a tendency.The immature plant height was highest for deep buried turion and lowest for shallow buried turion at each water level and the immature plant biomass decreased with an increasing water level for all burial depth.However,the reciprocal effect of water level and burial-depth didn’t affect the immature plant biomass and the immature plant height(F = 1.711,p＞0.05;F=1.582,p＞0.05).3.Belowground stem-mass ratio,aboveground stem-mass ratio,roots-mass ratio and leaves-mass ratio were significantly affected by both burial depth(F = 99.565,p＜0.001; F= 21.631,p＜0.001;F= 18.890,p＜0.001;F=58.166,p＜0.001) and water level(F= 5.594,p＜0.01;F= 47.979,p＜0.001;F= 24.870,p＜0.001;F= 10.139,p＜0.001).In each water level,roots-mass ratio,aboveground stem-mass ratio and leaves-mass ratio decreased with increasing burial depth,while belowground stem-mass rati圷?creased.In each burial depth,with decreasing turion size,belowground stem-mass ratio increased, while roots-mass ratio,aboveground stem-mass ratio and leaves-mass ratio showed irregular changes.The results have the value as the reference for nematodes in the interactive effect of water level and burial depth on propagules emergence and early growth of freshwater plants,researching the mechanisms of responding under effects of environment factors. The results also have certain value for more research in bank dynamic.
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