An increase in livestock density increases forage nutritional value but decreases net primary production and annual forage nutritional yield in the alpine grassland of the Qinghai-Tibetan Plateau

Xixi Yao; Changhui Li; Anum Ali Ahmad; Akash Tariq; A Allan Degen; Yanfu Bai

doi:10.3389/fpls.2022.1020033

An increase in livestock density increases forage nutritional value but decreases net primary production and annual forage nutritional yield in the alpine grassland of the Qinghai-Tibetan Plateau

Front Plant Sci. 2022 Nov 24:13:1020033. doi: 10.3389/fpls.2022.1020033. eCollection 2022.

Authors

Xixi Yao¹, Changhui Li¹, Anum Ali Ahmad², Akash Tariq³, A Allan Degen⁴, Yanfu Bai⁵

Affiliations

¹ State Key Laboratory of Plateau Ecology and Agriculture, College of Agriculture and Animal Husbandry, Qinghai University, Xining, China.
² Lanzhou Institute of Husbandry and Pharmaceutical Sciences, Chinese Academy of Agricultural Sciences, Lanzhou, China.
³ Xinjiang Key Laboratory of Desert Plant Roots Ecology and Vegetation Restoration, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, China.
⁴ Desert Animal Adaptations and Husbandry, Wyler Department of Dryland Agriculture, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Beer Sheva, Israel.
⁵ College of Grassland Science and Technology, Sichuan Agriculture University, Chengdu, China.

Abstract

Pasture biomass and quality are dependent on herbivore grazing and precipitation, but the responses of vegetation to the interactive effects of climate and grazing regimes remain unclear. We conducted an eight-year sheep grazing experiment with 4 stocking rates (0, 3.5, 5.5, and 7.5 sheep/ha) in an alpine meadow of the northeastern Tibetan Plateau. The above-ground net primary productivity (ANPP) and forage nutritional value (FNV) of four dominant species (Poa annua, Kobresia humilis, Astragalus adsurgens and Potentilla fruticosa) were measured during a wet year (360 mm rainfall) and a drought year (216 mm rainfall). The FNV was used as indicator of forage quality and was calculated from the crude protein (CP) content, in vitro true dry matter digestibility (IVTD), metabolic energy (ME) yield, and neutral detergent fiber (NDF) content of the plant. The stocking rate explained a minimum of 76% of the variations of ANPP, and the precipitation sub-additive effect for ANPP ranged from 5% to 12%. The interaction of sheep stocking rate and precipitation affected ANPP of the 4 species, except for P. fruticosa. The FNV of the pasture increased with increasing grazing pressure, but ANPP and forage nutritional yield (FNY) decreased. In calculating FNY, the increase in FNV did not compensate for the decrease in ANPP. In non-grazed plots, the CP yield declined sharply (18%-55%) in response to drought, but there was no effect on ME yield. The interaction between stocking rate and precipitation affected forage quality of the 4 plant species differently. The grassland ANPP and FNY could be maintained at a grazing intensity of 3.5 sheep/ha in wet and dry years. Our results highlight that stocking density affects pasture ANPP and FNV, and is contingent on rainfall.

Keywords: alpine grasslands; climate change; dominant plant species; herbivore densities; pasture.