Multidimensional synergistic adaptive mechanisms of Betula luminifera and its implications for ecological restoration in karst habitats

Karst ecosystems impose compound stresses of seasonal drought, calcium-rich substrates, and nutrient poverty, which severely constrain plant survival and ecological restoration. Betula luminifera , a native pioneer species of subtropical China, has emerged as a key candidate for restoring such degraded landscapes; however, research on its adaptation mechanisms remains fragmented, with individual physiological traits rarely integrated into a mechanistic framework. To address this gap, this review systematically synthesizes the existing evidence and proposes a carbon-driven synergistic adaptation framework, in which photosynthetic carbon serves as the universal currency, dynamically allocated among growth, resource acquisition, and defense to optimize fitness under compound stress. The framework integrates three interdependent systems: (1) an efficient photosynthetic-water system that manages the carbon-water trade-off and establishes a high-throughput carbon economy; (2) a rhizosphere nutrient-mobilization strategy for overcoming phosphorus limitation that is currently based on comparative rather than species-specific evidence and therefore requires exudate level validation, coupled with efficient internal nutrient cycling; and (3) a coordinated defense system combining antioxidant enzymes and osmotic adjustment to mitigate oxidative stress, with ion compartmentalization and calcium-management strategies (e.g., root sequestration, vacuolar storage) proposed as key components pending molecular validation. These systems are proposed to be coordinated through dynamic carbon allocation, although direct evidence for such allocation in B. luminifera is currently lacking. Under water limitation, a tentative priority hierarchy is proposed in which investment in photosynthetic tissues and hydraulic integrity outranks rhizosphere exudation and resource-intensive defense, with exudation activated mainly under phosphorus deficiency. The key contribution of this review is not the enumeration of individual adaptations but the construction of an integrative framework that explains how B. luminifera coordinates multiple strategies to overcome the karst stress triangle, explicitly separating direct evidence, comparative evidence, and proposed mechanisms. Because the rhizosphere phosphorus-mobilization pathway and calcium detoxification pathways currently rest on comparative rather than species-specific evidence, molecular validation of root exudation and Ca 2+ handling is a top priority. Future research should also prioritize long-term field trials, including direct comparisons of monoculture versus mixed-community restoration, to assess the predictive power of the framework for guiding precision restoration and developing stress-tolerant germplasm of B. luminifera .