Stipa breviflora (Stipa breviflora Griseb.) and Cleistogenes songorica (Cleistogenes songorica (Roshev.) Ohwi) are two dominant species in the critically important desert steppe of northern China. Under the interference of grazing, the two species will have the phenomenon of plant cluster fragmentation to varying degrees. Therefore, when the two plant populations appear in the same plant community, what changes will happen in the inter-specific relationship during grazing has important guiding significance for its regulation of plant community and function. To study this, we observed populations of wild S. breviflora and C. songorica in field under a suite of grazing intensities and at a variety of scales. The density changes of dominant species S. breviflora and C. songorica in desert steppe in Inner Mongolia were studied under four grazing intensities (no grazing, CK, 0 sheep·ha-1·half year-1, light grazing, LG, 0.93 sheep·ha-1·half year-1, moderate grazing, MG, 1.82 sheep·ha-1·half year-1, heavy grazing, HG, 2.71 sheep·ha-1·half year-1) and six scales (5 cm×5 cm, 10 cm×10 cm, 20 cm×20 cm, 25 cm×25 cm, 50 cm×50 cm and 100 cm×100 cm). Results showed that grazing changes the relationship between dominant species. With the increase of grazing intensity, the densities of S. breviflora and C. songorica increased, and the increase was more obvious with the increase of scale. Under heavy grazing conditions, the dominant populations of clustered grasses in Inner Mongolia desert steppe resisted the interference of high-intensity grazing by reducing inter-specific competition ability (increasing inter-specific affinity).

A high stocking rate can intensify wind erosion in grasslands, and strong wind can carry away soil surface particles and their nutrients, which leads to soil barrenness. In this research, the dust flux, total carbon (TC) and total nitrogen (TN) contents and fluxes of aeolian sediment were computed in the non-growing season (mid-October to mid-April of the following year) and growing season (mid-April to mid-October) from 2018 to 2020 at a long-term grazing gradient experiment platform and wind-erosion monitoring experiment in a desert steppe in Inner Mongolia, China. The results were as follows, 1) with the increasing of stocking rate, the fluxes of aeolian sediment at 10 cm (H10), 30 cm (H30), and 100 cm (H100) were greatly increased ( P<0.05). Aeolian sediment fluxes followed the order control (CK) < light stocking rate (LG) < moderate stocking rate (MG) < heavy stocking rate (HG). 2) TC and TN contents of aeolian sediment reflected stocking rates and followed the order CK>LG>MG>HG, and also reflected aeolian sediment collection height, as H10P>0.05). TC and TN contents in HG at different heights reduced by 31.1% and 25.9% on average in comparison to the CK in the non-growing season, and by 30.1% and 25.0% in the growing season. TC loss was higher than TN loss. Overall, as stocking rate increased, wind erosion increased, leading to the loss of soil nutrients and significant loss of the carbon pool in this desert steppe.

Root growth strategies are important to predict plant – soil interactions under nutrient-limited soil environments. A dominant species Stipa breviflora is found to develop cluster fragmentation in the arid and semi-arid areas of China, where water, nitrogen and phosphorus are the most important limiting factors to plant growth. Here, we aimed to assess how water, N, P additions and their interactions, and cluster fragmentation affect root growth traits in a greenhouse experiment to reveal the adaptation of S. breviflora under drought conditions. A standard Taguchi L8(27) arrays design was conducted with four factors such as nitrogen (N), phosphorus (P) and water (W) and cluster fragmentation (C) and three interactions (N × P, N × W and P × W). Each of four factors had two levels (N1 = 15 mg N / kg, N2 = 120 mg N / kg, P1 = 2 mg P2O5 / kg, P2 = 24 mg P2O5 / kg, W1 = 25 % ~ 30 % field moisture capacity of mixture (FMC), W2 = 75 % ~ 80 % FMC, C1 = individual with single ramet, C2= individual with three ramets).Water was the most important contributor to S. breviflora root system growth, while cluster fragmentation was the second contributor, followed by N and P in order. W2 and P2 both promoted root growth, whereas N2 significantly inhibited root growth. Moreover, under drought condition, N2 induced its roots developing an acquisition resource use strategy for escaping adverse environments compared to N1. While under sufficient P condition, W1 induced its roots developing an acquisition resource use strategy for acquiring more resource. And cluster fragmentation is beneficial to improving the adaptability of S. breviflora under low N condition.

Maintenance of a desirable mixture of shrubs and grasses is a key issue in sustainable grazing management. The aim of this study was to explore the effect of long-term sheep grazing on desert steppe shrubs. Based on a long-term controlled sheep stocking rate experiment in a desert steppe of north China, combined with long-term random sampling monitoring of above-ground vegetation standing crop (14 years) and short-term systematic sampling monitoring of vegetation cover and individual characteristics of shrubs (3 years), we analyzed plant community changes, the current situation of shrubs and the response of individual shrub characteristics to stocking rate. We found that low stocking rates have increased the cumulative above-ground standing crop of shrubs and herbaceous plants, but the cumulative above-ground standing crop of shrubs under high grazing rates tends to be flat. The cover and height of four shrub species generally showed a decrease with increasing stocking rate, while the response of the four shrubs to the stocking rate gradient varied. Among four shrub species, Artemisia frigida was the most sensitive to stocking rate, followed by Ceratoides latens and Caragana microphylla, while Kochia prostrata was relatively insensitive to stocking rate. These results suggest that grassland managers can use an appropriate stocking rate to maintain desirable plant community composition and configuration in the temperate grassland.