Stomatal Dynamics Multilevel Regulation and Physiological Response of Prunus mira Koehne under Extreme CO2 Toxicity Stress.

Rising atmospheric CO2 levels not only drive global warming but also exert toxic effects on plant photosynthesis and physiology under extreme exposure, however the adaptive responses of stress tolerant species such as Prunus mira Koehne remain poorly understood. In this study, we investigated the physiological and stomatal response mechanisms of P. mira under 5% CO2 conditions. The results of our physiological and biochemical analyses revealed that 5% CO2 concentrations reduced chlorophyll content and impaired photosynthetic efficiency. Concurrently, high CO2 stimulated alternative respiration, disrupted membrane integrity, elevated ROS (reactive oxygen species) levels, and increased antioxidant enzyme activities. In guard cells, high CO2 triggered accumulations of ROS and NO (nitric oxide), leading to stomatal closure, reduced stomatal conductance, while transpiration rates fluctuated during the treatment period. Moreover, pharmacological analyses suggested the involvement of Ca2+ in regulating ROS and NO accumulation, while ASA (ascorbic acid) promoted scavenging of excess H2O2. Our results suggest that ROS accumulation and Ca2⁺ signaling are involved in stomatal regulation under extreme CO2 toxicity stress. In summary, these findings provide mechanistic insights into plant responses under acute extreme CO2 toxicity and lay a foundation for understanding stress signaling robustness in woody species.