Ecostoichiometric characteristics of Tithonia diversifolia with different invasion degrees

【Objective】In this paper,the stoichiometric characteristics of different organs and rhizosphere soil of Tithonia diversifolia plants with different invasion degrees were investigated,and the resource utilization and allocation strategies of T. diversifolia were analyzed,which provided theoretical reference for the prevention and control of T. diversifolia invasion. 【Method】A study site with at least 4 years of T. diversifolia invasion was selected along the suburban highway in Simao District,Pu’er City,Yunnan Province. Fifteen experimental areas were set up, including five severely invaded areas（T. diversifolia coverage＞70%）, five moderately invaded areas（T. diversifolia coverage 30%-70%）,and five mildly invaded areas（T. diversifolia coverage＜30%）. Samples of roots, stems and leaves of T. diversifolia and its rhizosphere soil were collected to detect the contents of the total phosphorus（TP）, total nitrogen（TN）,and soil organic carbon（SOC）,and to analyze the stoichiometric characteristics. 【Result】With the increase of invasion degree,the contents of TN and SOC in soil of T. diversifolia habitat decreased significantly（P＜0.05,the same below）, while the content of TP did not change significantly（P＞0.05,the same below）. From mild to severe invasion, the content of TN decreased by 54.2%, and the content of SOC decreased by 53.1%, indicating that the soil in the invaded areas was poor in SOC and TN. The contents of TN and TP in different organs of T. diversifolia with three degrees of invasion were leaf＞root＞stem,and the content of SOC was root＞leaf＞stem,indicating that severe invasion was beneficial to the accumulation of TP content in the plants of T. diversifolia,and mild invasion was beneficial to the accumulation of TN content in the stems of T. diversifolia.As the degree of invasion increased,the C∶N value of root and stem increased significantly,the C∶P value of root and stem decreased significantly,and the N∶P value of stem decreased significantly. The C∶N,C∶P values of T. diversifolia were stem＞root＞leaf;N∶P value in mild invasion was leaf＞stem＞root,in moderate and severe invasion was leaf＞root＞stem. The degree of invasion had significant or extremely significant（P＜0.01,the same below） influence on the contents of TN and TP and C∶N and N∶P values, and different organs had extremely significant influence on the contents of SOC, TN and TP and C∶N, C∶P and N∶P values.The interaction between the organs and the degree of invasion only had extremely significant influence on N∶P, and had no significant influence on other indicators. There were significant or extremely significant correlations between the contents of TP, TN and SOC and stoichiometric ratios of roots, stems, leaves and soil of T. diversifolia. 【Conclusion】The invasion of T. diversifolia has certain influence on the study of local soil, and the change of soil also gives feedback to T. diversifolia. The N and P elements are more allocated to the leaves, and the C element is more allocated to the roots, and the growth is limited by the N element. The roots and leaves of T. diversifolia have relatively rapid growth ability to expand the population and increase the invasiveness.