Do soil properties with elevation affect alpine "grass-line"? Findings from Haibei, northern Tibetan Plateau

Many species showed that their richness and distribution shifts climate-driven towards higher elevation in Tibetan Plateau. However, vegetation and soil data from alpine grassland elevational gradients are rare (Huang et al., 2018). It is mostly unknown how the "grass-line" will respond to global warming and whether soils play a significant role in the vegetation pattern in high-altitude regions. At a local scale, the growth and distribution of vegetation at its upper limit may depend on nutrient limitation, as shown for treelines from the Himalayas. For example, the limited nutrient supply of soil N, K, Mg, and P becomes more intense with elevation, which declines in nutrient supply spatially coincides with abrupt changes in vegetation composition and growth parameters (Schwab et al., 2016). And low soil nutrient availability could affect tree growth in the Rolwaling Himal, Nepal treeline ecotone (Drollinger et al., 2017). To better understand the interrelationship between soil properties and grass growth at this upper limit, we took random soil samples in 3 altitudes, 3 geomorphic positions with 3 depth increments from Haibei grassland, northern Tibetan Plateau. Soil properties, like texture, bulk density, total C, N, and P fractions, were analyzed and compared to vegetation data.
Further, soil and vegetation data from open-top chambers (OTC) experiments to simulate global warming were analyzed better to understand the role of temperature for grass line-shift. The first results show that species composition change with altitude towards grassland plant communities with lower demands for P, which can be compared with the nutrient addition experiment that P addition alone significantly affects species diversity and biomass in the same area (Ren et al., 2016). We suppose that specific combinations of soil properties could limit grass growth and be even more marked than the warming, which controls biodiversity and biomass production in high mountain grassland ecosystems.