Long-term overgrazing (OG) is one of the key drivers of global grassland degradation with severe loss of productivity and ecosystem functions, which may result in stress memory such as smaller stature of grassland plants. However, how the OG-induced stress memory could be regulated by phytohormones is unknown. In this study, we investigated the changes of four phytohormones of cloned offspring of Leymus chinensis that were developed from no-grazing (NG) plants and OG plants with a grazing history of 30 years. The concentrations of auxin (IAA) and gibberellic acid (GA) in OG plant leaves were 45% and 20% lower than control, respectively. Meanwhile, the level of abscisic acid (ABA) in OG leaves nearly doubled compared with that in NG leaves. The situation was quite similar in roots. Unexpectedly, no significant changes in the jasmonic acid (JA) level were observed between OG and NG plants. The changes in gene expression patterns between OG and NG plants were also investigated by transcriptomic analysis. In total, 302 differentially expressed genes (DEGs) were identified between OG and NG plants, which were mainly classified into the functions of synthesis, receptor, and signal transduction processes of phytohormones. The expression of 24 key genes related to the biosynthesis and signal transduction of IAA and GA was downregulated in OG plants. Among them, OASA1 and AO1 (regulating the biosynthesis of IAA and ABA, respectively) were reduced significantly by 88 and 92%, respectively. In addition, the content of secondary metabolites related to plant defense such as flavonoids and phenols was also increased in leaves. Taken together, the decrease of positive plant growth-related hormones (IAA and GA) together with the increase of plant stress-related hormones or factors (ABA, flavonoids, and phenols) induced the growth-defense trade-offs for L. chinensis adaptation to long-term OG stress. The findings reported in this study shed new light on the mechanism of plant–animal interaction in the grassland ecosystem and provide a deeper insight into optimizing grazing management and sustainable utilization of grassland.

Understanding the process of changes in substrate physical, chemical, and biological properties is critical for vegetation ecosystem reconstruction of open‐pit coal mining dumps. However, the relationships of soil chemical, biological, bacterial, and fungal characteristics in open‐pit coal mining dumps in grassland area are still unclear. The purpose of this study is to understand the changes and relationships of soil physic‐chemical, bacterial, and fungal properties under the reclamation time series of open‐pit coal mining dumps. Soil samples were collected from the waste dump reclaimed after 2, 5, 10, and 15 years in Shengli West No. 2 open pit coal mine in Inner Mongolia, China, and the surrounding natural grassland was set as a control at 0–10 cm and 10–20 cm. Soil pH, electrical conductivity (EC), soil organic matter (SOM), nutrient properties, bacterial, and fungal community structures were measured in the waste dump reclaimed after 2, 5, 10, and 15 years. The results showed that soil pH was decreased at 0–20 cm in the waste dump while SOM was increased by 1.2 times in 0–10 cm reclaimed after 15 years than that after 2 years. Soil EC was decreased by 55.5% and 58.3%, respectively, in 0–10 cm and 10–20 cm, respectively, after 10 years than that after 2 years. Soil available nitrogen, available phosphorus, and available potassium were 97.8%, 13.2%, and 60.9% lower after 15 years' reclamation than those in control. The acid phosphatase in 0–10 cm and 10–20 cm was increased by 2.2 and 2.1 times, respectively, after 15 years compared with that after 2 years. Alkaline phosphatase was decreased by 16.8% reclaimed after 15 years than that after 2 years in 10–20 cm soil. The Shannon diversity index of fungi was increased by 42.0% and 43.8%, respectively, in 0–10 cm and 10–20 cm, in the waste dump reclaimed after 15 years than that after 2 years. Soil organic matter was positively correlated with soil urease activity. Soil pH, EC, and texture had different effects on bacterial and fungal communities. Therefore, appropriate measurements should be applied to the reclamation dumps to help the soil properties of reclamation areas to recover to the natural grassland.

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