Grazing is the basic way of grassland utilization, and reasonable grazing is an important way to maintain the health of the grassland ecosystem. However, the traditional grazing time in warming seasons is negative for sustainable desert steppe ecosystem. Determining reasonable grassland grazing methods is to remain a critical issue for the ecological conservation and rational utilization of desert steppe. Therefore, our objectives were to explore the effects of warming seasonal rotation grazing on the species diversity and functional diversity of grassland plants and to reveal controlling factors of plant community diversity. The warm-season rotational grazing modes included traditional time of grazing (FG), delayed start of grazing (YG), early end of grazing (TG), delayed start early end of grazing (YT), and enclosed steppe (CK). The results showed that the important value of Agropyron mongolicum of the gramineae and Lespedeza potaninii of the leguminosae in YG increased by 12.10%-120.66% and 23.57%-34.25% than other treatments (CK, FG, TG, and YT), respectively. Therefore, the YG treatment has more advantages on the IV of A. mongolicum of the gramineae and L. potaninii of the leguminosae. Warming seasonal rotational grazing (FG, YG, TG, and YT) significantly increased the important value of Leymus secalinus by 51.43%-79.64% compared with CK (p < .05). Compared with CK, FG and YG promoted the growth of gramineae and appropriately reduced the proportion of forbs. There was no significant difference in the Shannon-Wiener index between grazing treatments and CK, while the Shannon-Wiener index in YT increased by 21.43% and 15.71% compared with FG and YG (p < .05). The functional richness index in FG and YG significantly decreased by 19.05%-23.81% compared with CK and TG (p < .05). The results of the redundancy analysis showed that the diversity of plant communities was mainly affected by soil-available nitrogen. These observations indicated that delayed start of grazing can improve the diversity of plant communities by increasing the important value of dominant plants in the community and promoting the growth of gramineous and leguminous plants, thereby optimizing the composition of community structure. Our findings can provide a theoretical basis for formulating a reasonable and scientific grazing period in desert steppe.

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