Fire increases the risk of hydraulic failure of woody species: Evidence from an experiment and a meta-analysis

Fire-induced damage to plant tissues can affect the capacities for water transport, carbon fixation, and carbon utilization, potentially resulting in immediate or delayed post-fire tree mortality. In this study, we measured leaf and stem hydraulic (pressure-volume traits, hydraulic conductivity, and embolism resistance) and economic (photosynthesis, non-structural carbohydrates, and nutrients) traits of Larix gmelinii following fire events in northeastern China. To obtain a comprehensive understanding of fire effects on tree hydraulics and economics, we also conducted a meta-analysis to explore the global universal responses of tree carbon-water physiological traits to fire. Our experimental study showed that fire led to reductions in stem embolism resistance, hydraulic safety margin, vulnerability segmentation margin, and leaf non-structural carbohydrates, implying that fire would increase the vulnerability to drought and diminish the ability to repair embolism. Our global meta-analysis further validated the reduction in stem embolism resistance, while the hydraulic traits of angiosperms were more sensitive to fire than those of gymnosperms. Furthermore, angiosperms and gymnosperms also showed opposite responses to fire in photosynthetic rate and stomatal conductance, with positive responses in angiosperms and negative responses in gymnosperms. Therefore, angiosperms typically up-regulate photosynthetic rates and stomatal conductance to enhance carbon assimilation, even at the risk of hydraulic failure after fire. In contrast, gymnosperms, including Larix gmelinii, tend to close stomata to compensate the increased stem embolism vulnerability and preserve hydraulic safety following fire. Overall, by combining an experimental study with a meta-analysis, we suggest that fire increases the risk of hydraulic failure in woody species.