Contrasting redox regulation is associated with drought resilience in Eragrostis

Drought is a major constraint on grassland productivity and ecosystem stability under ongoing climate change. Eragrostis species, widely distributed in arid and semi-arid regions, are considered promising forage resources due to their inherent drought tolerance. However, how oxidative stress is coordinated with physiological responses during drought remains poorly understood. Here, we investigated drought responses in two Eragrostis accessions under controlled conditions by integrating physiological, biochemical, and statistical modeling approaches. Antioxidant enzyme activities, including superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, together with hydrogen peroxide, malondialdehyde, osmotic adjustment substances, and chlorophyll content, were measured across multiple drought stages. Random forest and correlation analyses were applied to identify key physiological variables, followed by accession-leve analyses to examine divergent response patterns. Hydrogen peroxide consistently emerged as a key physiological feature of drought responses, closely tracking changes in redox status and other physiological traits. Rather than discrete stress states, physiological responses varied along a continuous redox gradient. Importantly, the two accessions displayed distinct drought-response patterns, with catalase activity increasing in E. nutans but decreasing in HZF. These findings highlight the importance of temporal patterns of antioxidant responses in understanding drought resilience beyond the magnitude of individual antioxidant activities. This work provides a physiological basis for understanding divergent drought responses between the two Eragrostis accessions and offers new insights into the role of regulatory timing, with implications for improving resilience in grassland systems under increasing drought frequency.