Effects of simulated precipitation gradients on nutrient resorption in the desert steppe of northern China

Grazing period management affects the accumulation of plant functional groups, and soil nutrient pools and regulates stoichiometry in the desert steppe of Northwest China

To understand how nutrient cycling and sequestration are influenced by different grazing periods, the C:N:P stoichiometry features of the plant-soil interface in the desert steppe were measured and evaluated. The 5-year seasonal grazing experiment employed four grazing period treatments: traditional time of grazing (TG), early termination of grazing (EG), delayed start of grazing (DG), and delayed start and early termination of grazing (DEG). Additionally, fenced off desert steppe served as the control. The grazing periods each had a differing impact on the C:N:P stoichiometry in both plant functional group and soil depth comparisons. Compared to the EG, DG, and DEG treatments, the TG treatment had a more significant impact on the C, N, and P pools of grass, as well as the C:P and N:P ratios of forbs, but had a reduced effect on the C:P and N:P ratios of legumes. In contrast to plants, the DG treatment exhibited greater advantages in increasing C pools within the 0-40 cm soil layer. Furthermore, in the 10-20 cm soil layer, the C:P and N:P ratios under the EG treatment were significantly higher, ranging from 8.88% to 53.41% and 72.34%-121.79%, respectively, compared to the other treatments (TG, DG, and DGE). The primary drivers of the C, N, and P pools during different grazing periods were above-ground biomass (AGB) and litter biomass (LB). Both lowering the plant C:P and N:P ratios and considerably raising the plant P pool during different grazing periods greatly weakened the P limitation of the desert steppe environment. It is predicted that delayed start grazing might be a management strategy for long-term ecosystem sustainability, as it regulates above-ground nutrient allocation and has a positive effect on soil C and N pools.

Short-term robust plant overcompensatory growth was observed in a degraded alpine meadow on the southeastern Qinghai-Tibetan Plateau

Plant overcompensatory growth (OCG) is an important mechanism by which plant communities adapt to environmental disturbance. However, it is not clear whether plant OCG can occur in degraded alpine meadows. Here, we conducted a mowing experiment in an alpine meadow at three degradation levels (i.e., severe degradation, SD; moderate degradation, MD; and light degradation, LD) on the southeastern Qinghai-Tibetan Plateau from 2018 to 2020 to investigate plant OCG and its relationships with soil available nutrients, plant nutrient use efficiency (i.e., nitrogen use efficiency, NUE; and phosphorus use efficiency, PUE), and precipitation. The results showed that 1) the OCG of the plant community generally occurred across all degradation levels, and the OCG strength of the plant community decreased with mowing duration. Moreover, the OCG strength of the plant community in the SD treatment was significantly greater than that in the MD and LD treatments after two years of mowing (p < 0.05). 2) In LD and MD, the soil nitrate nitrogen (NO3-) and available phosphorus (AP) concentrations exhibited a decreasing trend (p < 0.05), while the soil ammonium nitrogen (NH4+) concentration did not change from 2018 to 2020 (p > 0.05). In the SD treatment, the soil NO3- concentration tended to decrease (p < 0.05), the NH4+ concentration tended to increase (p < 0.05), and the AP concentration exhibited an inverse parabolic trend (p < 0.05) from 2018 to 2020. 3) From 2018 to 2020, plant NUE and PUE exhibited decreasing trends at all degradation levels. 4) Plant nutrient use efficiency, which is regulated by complex plant-soil interactions, strongly controlled the OCG of the plant community along each degradation gradient. Moreover, precipitation not only directly promoted the OCG of the plant community but also indirectly affected it by regulating the structure of the plant community and plant nutrient use efficiency. These results suggest that the OCG of the plant community in degraded alpine meadows may benefit not only from the strong self-regulating capacity of the plant-soil system but also from humid climatic conditions.