Effects of Spring Rest Grazing on Underground Bud Bank in Alpine Meadow of Tibetan Plateau Before Critical Period of Soil Thawing

The bud bank is the reproductive body bank of grassland plants, which plays a key role in population maintenance and renewal. To study the effects of rest grazing on underground bud bank density, the changes in bud bank density were clarified to provide reference for grassland grazing management. In this experiment, according to the soil thawing and forage grass regreening in spring, the time when the cold-season pasture began to rest was determined. The period of grass withering is the end time of rest grazing. Different grazing rest periods are as follows: critical period of soil thawing–plant withering (RP1), early period of grass revival–plant withering (RP2) and period of local traditional rest grazing–plant withering (RP3). We studied the effects of different periods of rest grazing on the density and composition of underground bud banks. The results showed that the total density of underground bud banks increased by 33%, and the density of tiller buds, rhizome buds and root tiller buds increased by 9~62% compared with RP3. The proportion of different buds in different plots was tiller bud > rhizome bud > root tiller bud > bulb bud. Compared with RP3, the tiller bud density in RP1 increased by 24%. In RP1, the aboveground biomass and branch density of plants in RP1 were significantly higher than those in RP3 (p < 0.05), which were 56% and 29% higher than those in RP3, respectively. Finally, it is concluded that grazing rest before soil thawing in spring alpine meadow can promote the increase in plant underground bud bank density and the accumulation of aboveground biomass.