The strong control of temperature on the timing of plant phenology is expected to cause substantial shifts in flowering times under climate change. Yet, the sensitivity of flowering phenology in dryland regions to climate change, and the potential implications for community composition, remain largely unexplored. Here, we investigate the effects of climate warming and nitrogen addition on flowering phenology of four C3 plants and two C4 plants and explore cascading effects on shifts in C3 vs C4 plant dominance in a 17-year field experiment in a desert steppe. Across the last 10 years of the experiment (2013–2022), we found that warming had a greater effect on phenological shifts in C3 than in C4 plants. Warming significantly advanced the flowering time of C3 plants by 4.3 ± 0.1 days and of C4 plants by 2.8 ± 0.1 days. Warming also reduced the duration of flowering by 1.8 ± 0.1 days and decreased the dominance of C3 plants compared to C4 plants (P＜0.05). Nitrogen addition extended the duration of flowering of C4 plants by 3.4 ± 0.2 days and increased their relative dominance, while having no effect on C3 plants. Structural equation models highlighted that these phenological responses were influenced by soil temperature and soil water availability. Our results show the divergent phenological responses between C3 and C4 plants under global changes, predicting shifts in dominance between these plant types in temperate dryland ecosystems.

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).

1.Overgrazing-induced grassland degradation has become a severe ecological problem worldwide. The diversity and composition of soil microbial communities are responsive to grazing disturbance. Yet, our understanding is limited with respect to the effects of grazing intensity on bacterial and fungal communities, especially in plant rhizosphere. 2.Using a long-term (15 years) grazing experiment, we evaluated the richness and composition of microbial communities in both rhizosphere and non-rhizosphere regions, under light, moderate, and heavy intensities of grazing, in a semiarid grassland. We also examined the relative roles of grazing-induced changes in some abiotic and biotic factors in affecting the richness and composition of microbial communities. 3.Our results showed that the responses of soil bacteria to grazing intensity differed greatly between rhizosphere and non-rhizosphere, and so did soil fungi. Specifically, the bacterial richness decreased markedly under moderate and heavy grazing in rhizosphere soil, whereas little impact on the fungal richness was observed. For microbial composition, with the increase in grazing intensity, an increase in dissimilarity among bacterial communities was observed, and this trend also held true for the fungal communities. Hierarchical partitioning analyses indicated that the bacterial composition in rhizosphere was primarily driven by root nitrogen and soil nitrogen concentrations while that in non-rhizosphere by soil available phosphorus. In addition, soil available phosphorus played an important role in affecting the fungal composition in both rhizosphere and non-rhizosphere regions. 4.Synthesis: This study provides direct experimental evidence that the richness and composition of microbial communities were severely altered by heavy grazing in a semiarid grassland. Thus, to restore the grazing-induced, degraded grasslands, we should pay more attention to the conservation of soil microbe in addition to vegetation recovery.

Livestock grazing strongly affects biodiversity and ecosystem functioning in grasslands. However, it remains unclear how different grazing impact multiple biodiversity, ecosystem multifunctionality (EMF), and their relationship with the interactions of grazing duration, livestock type and climatic factors. Here, we conducted a global synthesis from 104 published studies. Our results showed that light and moderate grazing improved multi-diversity, but heavy grazing significantly decreased multi-diversity and EMF. The grazing-induced decrease of EMF intensified with grazing duration, and the reduction of multi-diversity and EMF under intensive grazing was stronger in more arid climates. The response of EMF increased linearly with that of multi-diversity under all grazing intensities. Moreover, grazing intensity reduced EMF largely via decreasing multi-diversity, whereas a shift of livestock type from small to large size promoted EMF by increasing multi-diversity. This study provides first empirical evidence and new insights into the relationship between multi-diversity and EMF under grazing in global grasslands.