Effect of Simulated Tibetan Sheep and Yak Trampling at Different Periods on the Reproductive Characteristics, Underground Morphology, and Carbohydrate Content of Kobresia humilis

Abstract

Studying the effects of trampling at different stages on plant reproduction is necessary to provide the basis for grassland management. However, the changes in forage growth characteristics are still unclear under the action of livestock trampling from soil thawing to regreening stage of alpine meadows.We studied the changes of growth, reproduction, and storage characteristics of Kobresia humilis in the alpine meadow of Tianzhu, Gansu Province, after 2 yr of simulated Tibetan sheep and yak trampling at five periods (prophase, initial, and middle period of thawing, initial regreening, and regreening period).Trampling period had the highest influence on K. humilis phenotypic traits, followed by livestock species. Considering the same trampling period, the negative effects of Tibetan sheep trampling on the sexual reproduction, different modular biomass, and root growth of K. humilis were lower than those of yak trampling. Sexual reproduction effort and storage growth effort were higher in Tibetan sheep trampling conditions, and vegetative reproductive effort was lower in sheep compared with yak trampling treatment conditions.There was a trade-off of resource allocation between K. humilis reproductive organs and storage organs. For the average of each indicator under different combination treatments, the vegetative reproductive effort was 11.1 times that of sexual reproduction effort. The comprehensive evaluation of K. humilis phenotypic traits showed that the trampling treatments could be divided into excellent (prophase period of thawing), good (middle period of thawing), general (initial period of thawing), and inferior (initial regreening to regreening period) grades of Tibetan sheep and yak trampling.We suggest that the actual grazing process in the cold-season pastures of this alpine meadow should be fully used at the prophase of soil thawing, implement rest-grazing for grassland and confinement from initial period of soil thawing to the forage regreening period, and appropriately increase the proportion of Tibetan sheep and reduce the number of yaks to avoid the high-intensity trampling of grassland. This will not only make optimum use of the limited grassland resources but also promote their recuperation.