Research On The Effect Of Burrowing Poisonous Weed Residues Allelochemicals On Tibetan Plateau

The expansion of poisonous weeds in Alpine Meadow on the Tibetan Plateau, accelerated the degradation process of grassland, also affected the restoration of degraded grassland. How to control Poisonous weeds is an important scientific problem in the management of grassland degradation. The study found, allelopathy is an important factor for poisonous weeds diffusion, inhibiting the growth of edible forage and hindering the grassland restoration. Poisonous weed residues in the soil secreted substances may produce allelopathy. This study selected four common poisonous weeds in alpine grassland, simulated plants decomposition process in soil under natural conditions, and Study on the change of soil physical and chemical properties and organic chemical substances, in order to provide information of the allelopathy mechanism of poisonous weed in soil. Selected flowering Ajania tenuifolia, Artemisia nanschanica, Ligularia virgaurea and Morina kokonorica Hao whole plant on alpine meadow as donor materials, tested the effect of poisonous weed residues decomposing over time on soil moisture, pH, soil organic carbon, total nitrogen, detected the type and the content of chemicals in the soil. Combined with previous studies, looking for compounds with allelopathic potential, and analysed the evolution law of the compounds in the soil according to its content change. The main conclusions are as follows:(1) Along with the raising level of plant burrowing concentration in soil, moisture of Morina kokonorica Hao and Ajania tenuifolia buried soil decreased accordingly. Artemisia nanschanica buried soil moisture content showed increasing trend with increasing concentration, but in the middle of a concentration gradient20g/m2, soil moisture content become the minimum level. The soil pH value showed an upward trend overall, and pH values of four kinds poisonous weeds buried soil are all less than the undisturbed soil. The pH value of Morina kokonorica Hao buried soil increased with the improved concentration of burial, pH value of Ligularia virgaurea and Ajania tenuifolia decreased and reached the low concentration of three three levels in the middle concentration gradient, Artemisia nanschanica exactly the opposite, the pH value reached to the maximum in the middle concentration gradient. With the increased of the concentration of plant burial, Soil organic carbon of four plant showed increasing trend, the total nitrogen content reached the highest value in the middle concentration gradient, the available nitrogen content of Ajania tenuifolia burial soil reached a maximum at the intermediate concentration gradient.(2) Compared with the undisturbed soil, soil organic carbon, total nitrogen, available nitrogen content increased to a certain extent after four kinds of poisonous weed residues buried in soil, soil organic carbon, total nitrogen, available nitrogen content of Morina kokonorica Hao buried soil is the biggest, Artemisia nanschanica buried soil content is the minimum. With the burial time increases, soil moisture content of Ajania tenuifolia buried soil is greater than the other three plants’, Morina kokonorica Hao in the second, Ligularia virgaurea is the smallest. Soil pH value has a certain extent increase with residues buried, but all lower than pH value of the undisturbed soil.(3) Compared the effects on the type, quantity and the content of the compounds in soils Artemisia nanschanica residue is the biggest, Ajania tenuifolia and Ligularia virgaurea times, Morina kokonorica Hao is the last one. Compared three concentration gradient, Artemisia nanschanica, Ajania tenuifolia and Ligularia virgaurea, three Compositae show biggest effect on soil allelochemicals, and Morina kokonorica Hao relatively small.It is concluded that Artemisia nanschanica buried process is the greatest impact on soil in the four poisonous weeds. The changes of soil physical and chemical properties and orgnic compounds in soil were some extent reflected that Artemisia nanschanica residue’s decomposition process in soil may be one of the most important way of allelochemicals release, while Ligularia virgaurea and Artemisia nanschanica allelochemicals release maybe mainly by natural volatilization, rain leaching or root exudation.