Rest grazing from the critical period of soil thawing promotes the propagation of Kobresia humilis in alpine meadow

Abstract

Determining the optimal rest grazing period can provide a scientific basis for rest grazing during spring in alpine meadows. Kobresia humilis is one of the main construction species of alpine meadow that is of ecological and economic value. We studied the effects of rest grazing on the reproduction of K. humilis during different periods of spring. The five different rest grazing periods were set based on soil thawing depth and plant re-greening, which included the following: the critical period of soil thawing-plant withering period (P1), the late period of soil thawing-plant withering period (P2), the early period of grass regreening-plant withering period (P3), the late period of grass regreening-plant withering period (P4) and the period of local traditional rest grazing-plant withering period (P5). The biomass of each component of K. humilis in P1 was significantly higher than that in other plots, and the corresponding biomass of leaf and stalk + panicle in P1 were 239.6% and 207.1% higher than those of P5. The biomass of each component decreased with the delay of rest grazing time. The seed yield and its components (except the number of seeds per panicle) and seed quality of P1 were higher than those of the other plots. The stalk length and the seed yield of P1 was 416.3% and 142.5% higher than those of P5. The responses of vegetative reproduction indices to different rest grazing periods were varied. The number of leaves in P1 was 61.6% higher than that in P5, and the death leaf ratio in P1 was 233.3% lower than that in P5. Finally, rest grazing during the critical period of soil thawing-plant withering period (P1) was inferred to be beneficial to the growth and reproduction of K. humilis using the grey correlation analysis method. Therefore, spring rest grazing in alpine meadows should start from the critical period of soil thawing.