Owing to overexploitation, wild resources of Astragalus mongolica, a Chinese herbal plant that is widely distributed in the arid and semi-arid areas of Northern China, have gradually become exhausted, and therefore, commercial cultivation is increasingly important to meet the growing demand for astragalus and reduce the pressure on wild populations. Nitrogen level is an important factor that affects the yield and quality of A. mongolica. However, uniform standards for fertilization among production areas have not yet been determined. In this study, the effect of nitrogen fertilizer treatment on the yield and quality of A. mongolica in the Qinghai-Tibet Plateau was explored using a control treatment (no added nitrogen, N0) and five different nutrient levels: 37.5 kg/ha (N1), 75 kg/ha (N2), 112.5 kg/ha (N3), 150 kg/ha (N4), and 187.5 kg/ha (N5). According to grey relational analysis, the optimal nitrogen fertilizer treatment was the N4 level followed by the N5 and N2 levels. Nitrogen fertilizer significantly increased the root biomass, plant height, root length, and root diameter. However, nitrogen fertilization had no significant effect on the content of Astragaloside IV and mullein isoflavone glucoside. The content of ononin and calycosin continually accumulated throughout the growing period. The results showed that the ononin and calycosin content under N4 and N2 is higher than other levels and there is not significantly different between different nitrogen fertilizer levels about them. The content of formononetin decreased gradually with the progression of the growing season. The optimal nitrogen fertilizer treatment for A. mongolica is recommended to be 150 kg/ha and the content of active compounds and yield were observed to reach the maximum in October.

Although the soils in the Tibetan Plateau shrublands store large amounts of total nitrogen (N), the estimated values remain uncertain because of spatial heterogeneity and a lack of field observations. In this study, we quantified the regional soil N storage, spatial and vertical density distributions, and related climatic controls using 183 soil profiles sampled from 61 sites across the Northeast Tibetan Plateau shrublands during the period of 2011–2013. Our analysis revealed a soil N storage value of 132.40 Tg at a depth of 100 cm, with an average density of 1.21 kg m⁻². Soil N density was distributed at greater levels in alpine shrublands, compared with desert shrublands. Spatially, soil N densities decreased from south to north and from east to west, and, vertically, the soil N in the upper 30 and 50 cm accounted for 42% and 64% of the total soil N stocks in the Tibetan Plateau. However, compared with desert shrublands, the surface layers in alpine shrublands exhibited a larger distribution of soil N stocks. Overall, the soil N density in the top 30 cm increased significantly with the mean annual precipitation (MAP) and tended to decrease with the mean annual temperature (MAT), although the dominant climatic controls differed among shrubland types. Specifically, MAP in alpine shrublands, and MAT in desert shrubland, had a weak effect on N density. Soil pH can significant affect soil N density in the Tibetan Plateau shrublands. In conclusion, changes in soil N density should be monitored over the long term to provide accurate information about the effects of climatic factors.

The degradation of alpine meadows on the Qinghai–Tibet Plateau has seriously affected the structure and productivity of grassland communities. In this experiment, a sample area was set up in Keqihetan of Zexiong Village, Youganning Town, Henan County, Mongolian Autonomous Prefecture. The degraded alpine meadow was divided into three plaque types, bare patches (BP), short-term recovered patches (SRP), and long-term recovered patches (LRP), and Native alpine meadows (NM) as controls, in order to reveal the effects of grassland degradation on community structure and aboveground/belowground biomass allocation in alpine meadow. Here, we measured total biomass (TCB), aboveground biomass (AGB), belowground biomass (BGB), and root/shoot ratio (R/S) of alpine meadows on the Qinghai–Tibetan Plateau and investigated plant community cover and height. The results showed that with the restoration of the patchy alpine meadow, the height decreased first and then increased, the amount of AGB increased first and then decreased, while the coverage and BGB increased in turn, and BGB decreased with the deepening of soil depth. We also found that R/S decreased first and then increased with the patch recovery of the alpine meadow. The overall distribution of AGB and BGB belongs to allometric growth distribution, but the native meadow belongs to isometric growth distribution, while other recovery stages belong to allometric growth distribution. By studying the biomass and its distribution of degraded grassland, we can understand the impact of grassland degradation on the community structure and productivity of the alpine meadow.