Avena sativa L. boosts Lolium perenne L. growth through root exudate reprogramming under extreme high temperature

Extreme climate events led to a reshuffling of plant ecological niches, potentially transforming competitive interactions into cooperative ones. This presents a great challenge for future species evolution and agricultural production. Yet, the drivers and mechanistic underpinnings of such interspecific relationship shifts remain poorly understood. Here, we used Lolium perenne L. and Avena sativa L. as a model system to explore how interactions vary under normal temperature (LT) and extreme high temperature (EHT) conditions. Avena sativa L. appeared to suppress Lolium perenne L. potentially via the secretion of inhibitory compounds under LT. In contrast, EHT was associated with a shift toward facilitation: Avena sativa L. root exudates became enriched in lipids and lipid-like molecules, while Lolium perenne L. roots accumulated flavonoids and likely coordinated systemic responses. This included enhanced the accumulation of meloside L in leaves and was linked to bolstered the plant's antioxidative and ROS-scavenging capacities, potentially contributing to the switch from competition to coordination. Additionally, EHT-induced mixed cropping reduced the abundance of Arthrobacter and MND1, which may lower octulosonic acid production and decrease flavonoids degradation. Collectively, these shifts are proposed to alleviate metabolic suppression of flavonoid biosynthesis, thereby potentially enhancing the thermotolerance of Lolium perenne L. Our findings reveal a potential ecophysiological mechanism of temperature-triggered metabolic reprogramming, informing agricultural management strategies that support food security and sustainability under climate change.