Effects Of Water Stress On Three Kinds Of Landscape Tree Seedlings

Trees are the skeleton of the plant landscape,which play an important role in increasing the diversity of the landscape and improving the ecological environment.The South China region is affected by the monsoon climate,so heavy rain often occurs in summer season and drought often occurs in autumn season.Such special urban site conditions seriously restricted the growth of landscape trees.Researching on the water stress resistance of landscape tree and selecting plants with both drought and waterlogging resistance will have great significance to the selection of urban greening,reduction of the landscape greening conservation cost construction of sponge city system and the reduction of landscape conservation cost.One-year-old seedlings of Cinnamomum burmannii,Elaeocarpus sylvestris and Ilex rotunda,which were commonly used in the south China landscape,were selected as the experimental materials in this paper.Four kinds of water treatment groups were set up,they are control group,continuous drought group,continuous flooding group,and drought and flooding alternating group.The growth indexes,leaf functional traits,physiological indexes and photosynthetic characteristics were measured after 45 days of water stress experiment.In addition,the response of three kinds of tree seedlings to different water conditions was analyzed by mathematical statistics in this paper.The importance of each index was judged by principal component analysis,and the drought tolerance and waterlogging capacity of three kinds of tree seedlings were evaluated by fuzzy membership function.The main research results are as follows:(1)Under the continuous drought stress,the stem and leaves of the three trees showed different symptoms.Compared with the control group,the plant height,ground diameter,total root length,root surface area and root volume of the three kinds of trees were significantly decreased(P<0.05),and the specific leaf area had different degrees of decline.There was different degrees of increase in leaf dry matter content,leaf thickness.and leaf(2)tissue density increased.The root / shoot ratio of Elaeocarpus sylvestris and Cinnamomum burmannii increased significantly(P<0.05).Drought stress didn’t inhibit the photosynthesis of Elaeocarpus sylvestris,and its net photosynthetic rate increased significantly(P<0.05).On the contrary,the net photosynthetic rate of Ilex rotunda and Cinnamomum burmannii decreased significantly(P<0.05).With the prolongation of stress time,the content of malondialdehyde(MDA)in Elaeocarpus sylvestris and Ilex rotunda increased,the activities of superoxide dismutase(SOD)of Cinnamomum burmannii and Ilex rotunda increased first and then decreased,and the soluble protein of the three trees showed an increasing trend.The total chlorophyll content of Elaeocarpus sylvestris and Ilex rotunda also showed an increasing trend.(3)Under the continuous flooding stress,the leaf color of the three kinds of trees turned yellow,and some enlarged lenticels appeared in stem base.Additionally,the root surface appeared different degrees of black rot.Compared with the control group,the net increase of height and root diameter were significantly decreased(P<0.05).There were decreased in different degrees in total root length,root surface area,root average diameter,root / shoot ratio,specific leaf area and water use efficiency.Leaf thickness,leaf dry matter content and leaf tissue density had different degrees of increase.The net photosynthetic rate of Cinnamomum burmannii and Ilex rotunda was significantly decreased(P<0.05).With the prolongation of stress time,the MDA content of Cinnamomum burmannii and Elaeocarpus sylvestris increased,and always higher than the control.The SOD activity of the three kinds of trees showed a decreasing trend,but their soluble protein content showed an increasing trend.In addition,the chlorophyll content of three kinds of trees were lower than control.(3)Under the stress of drought and water alternating,a small part of root surface turned to black,and some were rotteny.Compared with the control group,the net growth of height and diameter,the total root length,the root surface area and the root / shoot ratio of the three kinds of trees decreased in different degrees.Leaf dry matter content and leaf tissue density of three trees increased in different ranges,while the specific leaf area and net photosynthetic rate of the three trees decreased significantly(P<0.05).With the prolongation of the experiment time,the MDA content of Elaeocarpus sylvestris and Ilex rotunda increased first and then decreased,and the activity of SOD decreased first and then decreased.The soluble protein content of Cinnamomum burmannii and Ilex rotunda showed an increasing trend.(4)21 indicators of three kinds of landscape tree which were treated by four kinds of water treatments were analyzed by principal component analysis.It founds that the five principal components can reflect more than 87% of the original data information.The water resistance of three kinds of tree landscape seedlings was evaluated by membership function method.The results showed that the drought tolerance of the three plants from high to low is:Elaeocarpus sylvestris(0.53),Cinnamomum burmannii(0.45),Ilex rotunda(0.42),the waterlogging resistance from high to low is: Ilex rotunda(0.58),Elaeocarpus sylvestris(0.45),Cinnamomum burmannii(0.42),the drought and flooding alternating resistance from high to low is: Ilex rotunda(0.62),Elaeocarpus sylvestris(0.48),Cinnamomum burmannii(0.42).Elaeocarpus sylvestris and Cinnamomum burmannii is more suitable for planting in the extensive management of green space and in the construction of water-saving garden green space.Ilex rotunda is more suitable for planting in waterfront green,rainwater garden or other alternating environment of drought and flood.