Variations of Forage Yield and Nutrients with Altitude Gradients and Their Influencing Factors in Alpine Meadow of Sanjiangyuan, China

This study aimed to investigate the forage yield and quality and extract factors affecting them and provide scientific support for ecological protection of alpine grassland and sustainable development of animal husbandry in the Qinghai-Tibetan Plateau. Samples were collected in late August (peak of the growing season) 2014 in two mountain transects (Laji mountain, 36 degrees 21 ' N, 101 degrees 27 ' E, 3389-3876 m a.s.l. and Heitu mountain, 34 degrees 22 ' N, 100 degrees 30 ' E, 4121-4268 m a.s.l.) of Sanjiangyuan. Forage biomass and nutrients were measured by the national standard method, and influencing factors were extracted by RDA. Results showed that the forage yield decreased significantly with the increasing altitude, no matter in the mountain > 4000 m a.s.l. or < 4000 m a.s.l. Forage yield was more affected by environmental factors in low altitude areas, but less in high-altitude areas. Forage nutrients were mainly affected by altitude and soil organic carbon (SOC) (p < 0.01) on the mountain < 4000 m a.s.l., while on the mountain > 4000 m a.s.l., fiber and lignin were mainly affected by soil pH and SOC and crude protein (CP) by soil pH (p < 0.05) and total phosphorus (TP). Overall, with the increasing altitude, forage CP and fat (CF) increased, while neutral detergent fiber and acid detergent fiber decreased, implying that warming may lead to the decline of forage quality and then affect the safety of animal husbandry. Moreover, forage CP and CF were also affected by soil inorganic nitrogen and TP rather than SOC and soil total nitrogen.