The Niche Mechanism of Weeds in Cotton Field Under Drip-Irrigated in North Xinjiang, China

The aim of this study was to investigate the niche mechanism and diversity of weeds in drip-irrigated and machine-harvested cotton fields in north Xinjiang, China. The dominant classes of weeds in 25 cotton fields under drip-irrigated and machine-harvested in 5 regions of north Xinjiang were investigated by seven-grade visual method, and converted to important value data, the 20 main weeds niche breadth and niche overlap were caculated on the basis of the data above. The ecological similiarity revealed by DCA sorting and minimum spanning tree of graph theory cluster analysis is drawed on the basis of the niche overlap value. The results show that Convolvulus arvensis L., Chenopodium album L., Amaranthus retroflexus L., Solanum nigrum L., Phragmites australis (Cav.) Trin. ex Steud., Setria viridis (L.) Beauv., Abutilon theophrasti Medicus., Hibiscus trionum L., Echinochloa crusgalli (L.) Beauv., nine species of weeds, which are the dominant species (malignant weeds) in drip-irrigated and machine-harvested cotton fields in North Xinjiang, have wide niche. The niche overlap values of S. nigrum L. and C. album L., A. theophrasti Medicus. and A. retroflexus L., H. trionum L. and E. crusgall (L.) Beauv., A. retroflexus L. and E. crusgalli (L.) Beauv. are higher. The minimal spanning tree method based on niche overlap value to reflect similar degree of the ecological needs of the weeds, 20 main weeds will be divided into 4 groups. DCA ordination of 20 main weeds comprehensive ecological needs of 25 sampling sites: the vicious weeds all gathered at the central sorting chart, the distinction is obvious with the general weed and the corresponding of DCA ordination chart with minimal spanning tree is better. The minimal spanning tree by its focus on the results of which show that weeds are the most similar to the ecological requirements, but not be used for the no adjacent species, and no clear that the ecological relationship between them, the DCA sorting can reflect the ecology similar relations between all weeds wholely, though this method will lose a small amount of ecological information through the data conversion. Therefore, the two methods will be combined, complementary advantages, the superiority is obvious. Along with drip irrigation age years increase, S. nigrum L., C. arvensis L., C. album L. and so on, between dominant value of nine species of malignant weeds and the drip irrigation age years has the remarkable regression relations.