Quantification and assessment of growth-defense trade-offs in perennial ryegrass under varied light qualities

Light quality is widely recognized as a crucial environmental factor mediating the trade-off between plant growth and defense, with important implications for turfgrass production. However, the regulatory mechanism of the growth and physiology of perennial ryegrass to light quality, as well as its growth-defense trade-off remains unclear. Therefore, this study investigated how different light quality combinations affected turf quality, morphogenesis, photosynthetic characteristics, and metabolic processes in perennial ryegrass, using red-blue light (BR) as the control and red-blue light supplemented with far-red (BRFR), UV-A (BRUVA), and green (BRG) light as treatment conditions. The results showed that BRFR and BRG treatments could promote leaf expansion, aboveground biomass accumulation, and turf quality improvement, while increasing the IAA content and decreasing the ABA level, promoting a growth-oriented strategy in perennial ryegrass. In contrast, the BRUVA treatment suppressed belowground growth but increased leaf thickness, total nitrogen content, and ABA concentration, while reducing the C/N ratio and enhancing antioxidant responses, thereby inducing a stress-response-oriented physiological state in perennial ryegrass. Furthermore, carbohydrates were positively associated with growth, whereas hormones were negatively associated with defense-related physiological responses. Moreover, the fluctuations in hormonal levels and carbohydrate metabolism may be related to the carbon-nitrogen balance. In summary, our findings uncover the intrinsic processes that mediate how perennial ryegrass modulates its growth and physiological status under diverse light environments, thereby facilitating the precision application of light-quality regulation in modern turfgrass agronomic operations.