Study On Allelopathy Of Invasive Plant Alternanthera Philoxeroides On Turf Grass Zoysia Matrella Seedlings

Allelopathy is an adaptive strategy toward environment during biological evolution. It is also an important factor affecting interspecific relationship. As a common phenomenon, allelopathy widely exists among plants or between plant and microorganism by the mediation of allelochemicals. Exploring the mechanism of allelopathy of invasive plant and rational development and utilization of allelochemicals have become one of the important directions in this research field.According to field investigation, turf grass Zoysia matrella associated with invasive plant Alternanthera philoxeroides always presented withered, showing “tinea plaque”, then it was initially thought that Alternanthera philoxeroides may have strong allelopathic effects on green plants. Therefore, using invasive plant Alternanthera philoxeroides and turf grass Zoysia matrella as materials, the study took hydroponics and soil methods to test the dynamic changes of turf grass Zoysia matrella seedlings, which were disposed by extracts of Alternanthera philoxeroides and rhizosphere soil to definite the allelopathy of Alternanthera philoxeroides on Zoysia matrella. On this basis, compositions of Alternanthera philoxeroides were extracted with organic solvent, and analyzed with technology of GC-MS. According to the results of analysis, we select one kind of allelochemicals in a higher level to further explore its allelopathy effects on turf grass Zoysia matrella seedlings in order to providea scientific guidance for the maintenance of lawn ecosystem, and theoretical basis for the invasion mechanism and effects of Alternanthera philoxeroides. The main results were as follows:1.Results of hydroponic experiment showed: Zoysia matrella seedlings were treated by water extracts of Alternanthera philoxeroides and rhizosphere soil with different concentrations(5, 10, 20, 40, 80 g/L).With the increase of the concentration of extracts and processing time, theroot length, seedling height, fresh weight, chlorophyll content and antioxidant enzyme activity(CAT, POD, SOD) of Zoysia matrella seedlings were increased firstly, then decreased, while the MDA content was steadily increased, the peak of each index appeared at different time.When treated for 21~28d, concentration of extract was higher than or equal to 40 g/L, physiological and ecological index in all treatment groups were significantly different from those of control group(P< 0.05),the growth of Zoysia matrella seedlings were apparently inhibited. The allelopathic inhibition of water extracts of Alternanthera philoxeroides and rhizosphere soil on Zoysia matrella seedlings followed the order:root > leaf > rhizosphere soil> stem.2.The results of pot experiment showed that in early treatment(7~14d), extracts could promote the growth of the Zoysia matrella seedlings,showing the promotion of antioxidant enzyme activity, improvement of chlorophyll and osmotic adjustment substance contents. When the concentration of extracts was enhanced and stress period was prolonged,the growth of Zoysia matrella seedlings were inhibited, showing decrease of chlorophyll and soluble sugar contents, increase of membrane lipid peroxide level, the antioxidant enzyme system was out of balance. Zoysia matrella seedlings treated by extracts of Alternanthera philoxeroides roots and leaves at 80g/L were influenced mostly. The allelopathic inhibition of water extracts of Alternanthera philoxeroides and rhizosphere soil were as follows: root > leaf > rhizosphere soil> stem.The result was similar with that under hydroponic conditions.3.Analysis of extracts from different parts of Alternanthera philoxeroides and influence of main compounds on Zoysia matrella seedlings growth. Identification and analysis of compositions of extracts adopted the method of GC-MS. The result demonstrated that the compositions of extracts were more than 20 kinds, such as alcohols,esters, acids and other organic matters. Among them, the content of ethyl propionate was the most, the percentage of components from roots, stems and leaves extracts were 82.32%, 51.01%, 70.38% respectively, whichcorresponded to the degree of allelopathy of extractsfrom Alternanthera philoxeroides roots, stems and leaves(root > leaf > stem) in test 1and 2.Zoysia matrella were treated with ethyl propionate in different concentrations(0.1, 0.5, 1.0, 1.5, 2.0mmol/L). The result showed that with the increase of concentration, the osmotic adjustment substance of Zoysia matrella seedlings changed significantly. The content of soluble protein decreased, while contents of soluble sugar and proline increased consistently. When the concentration of ethyl propionate was low(≤1.0mmol/L), activities of CAT and SOD were enhanced, and reached the peak at 0.5 mmol/L, higher than that of control group 64.24%, 33.93%respectively. With increasing concentrations of ethyl propionate, the enzyme activity was inhibited, POD was the most sensitive, and extremely significant lower than that of control group(P<0.01), which was only 13.96% of control group, at 2 mmol/L concentration. In addition,MDA content and leaves electric conductivity increased, all physiological and ecological indexes of Zoysia matrella seedlings changed significantly.The study proved that ethyl propionate at high concentration could lead to oxidative stress, and had inhibitory allelopathic effect on Zoysia matrella seedlings, it might be a potential allelochemical.