Weed community composition and niche characteristics of different crop fields in Qilian County, Qinghai Province

To examine the weed community composition and niche characteristics in different crop habitats, the inverted “W” sampling method was used to investigate the weed community and analyze the niche in 495 plots in five different crop fields in Qilian County, Qinghai Province. The results have shown that there were 55 weed species in farmland in Qilian County, Qinghai Province, belonging to 19 families and 45 genera. Gramineae, Compositae, and Polygonaceae were dominant, and the six most dominant weed species were Bromus tectorum, Avena fatua, Elsholtzia densa, Chenopodium album, Lepyrodiclis holosteoides, and Hypecoum leptocarpum, which had a higher degree of ecological overlap with other weeds. The Shannon-Wiener index showed that there were significant differences in weed diversity in different crop fields. The Jaccard dissimilarity coefficient and Bray-Curtis distance coefficient showed that the composition of weed communities in wheat and Brassica napus fields and highland barley / oat / cabbage fields were similar. Non-metric multidimensional Shepard and fitting degree maps showed that Galium spurium, Lepyrodiclis holosteoide, Microula sikkimensis, Poa annua, Daucus carota, Bromus tectorum, Chenopodium album, Elsholtzia densa had a high degree of fit with each crop field. The dominant weed community was divided into three ecological groups by pole ordination and minimum spanning tree map. Bromus tectorum had the largest niche breadth and higher ecological overlap with other weed species. The ecological distribution and interspecific relationships of different dominant weeds were clarified. This has provided a theoretical basis for maintenance of weed biodiversity and sustainable farmland management.