Leymus chinensis is a perennial rhizomatous clone plant. It exhibits strong rhizomatous tillering and clonal growth through asexual reproduction. The root system is interdependent with aboveground growth and root growth can regulate aboveground growth and photosynthesis. Melatonin has been shown to regulate root growth and promote photosynthesis. However, it remains unclear whether melatonin affects aboveground growth and photosynthesis by regulating rhizome growth. To address this gap, we studied nine Leymus chinensis from different geographical locations, all grown under the same conditions. We selected two materials with strong (LC19) and weak (LC2) rhizome growth abilities from nine materials and treated them with exogenous melatonin. We found there were significant positive correlations between stem length, plant height, leaf number and rhizome traits. Additionally, rhizome traits showed significant positive correlations with photosynthetic indices and chlorophyll content. Specifically, for LC2, treatment with 200 μmol/L melatonin significantly increased root length, the number of extravaginal ramets and rhizome clonal growth rate by 88.72%, 43.75% and 43.70%, respectively, resulting in significant increases in aboveground traits. Similarly, for LC19, 200 μmol/L melatonin treatment led to significant increases of 74.66%, 23.02%, 62.71% and 62.72% in four traits, respectively, along with aboveground trait improvements. Furthermore, around 300 μmol/L melatonin treatment promoted photosynthetic efficiency in LC2, while around 100 μmol/L melatonin treatment had the same effect in LC19. In conclusion, our study highlights the relationship between rhizome growth ability, aboveground growth and photosynthesis in Leymus chinensis. Additionally, it suggests that exogenous melatonin can enhance aboveground growth and photosynthesis by regulating rhizome growth.

Climate change related abiotic stress has been potentially impacting the quantity and quality of forage grass. Melatonin, a multifunctional molecule that has been found to be present in all plants examined to date, plays a crucial role in improving forage grass tolerance to both biotic and abiotic stresses. However, research on melatonin’s role in forage grass is still developing. In this review, the effects of melatonin application on abiotic stress are the primary topic, and we try to find relative mechanisms. In order to determine whether melatonin has a good effect on forage grass, we compared and summarized the adapting ability of different forage grasses under abiotic stress after melatonin application in aspects of growth and development, photosynthesis, antioxidant systems, plant hormone interactions, and ion homeostasis. According to part of the data, we found that different forage grasses exhibited varying responses to endogenous melatonin content and exogenous melatonin dose applications. Meanwhile, the regulatory mechanisms of melatonin application include the expression of chlorophyll synthesis and degradation genes, electron transport and phosphorylation genes, stress regulation pathway genes, and plant hormone synthesis genes. We propose possible future studies that can further explore the metabolic pathways of melatonin and the molecular mechanisms of melatonin regulation of abiotic stress in forage grass. Specifically, research can focus on elucidating the signaling pathways, gene expression of regulatory networks, and interactions with other plant hormones. This will provide valuable theoretical and practical guidance for adapting to climate change and forage grass development.