Thermal Limits and Sensitivity of Brosimum rubescens Taub. (Moraceae): Implications for Monodominance in a Warming Climate

• Understanding temperature tolerance is key to predicting tropical trees' responses to global warming. However, the thermal limits of monodominant tropical forests remain understudied, leaving their vulnerability to climate change unclear.
• This study examined the thermal safety margin, tolerance parameters of PSII (T₅, T₅₀, T₉₅), leaf traits (e.g., leaf water mass content, leaf thickness, stomatal conductance), and temperatures of Brosimum rubescens Taub. (Moraceae) seedlings during the dry season in southern Amazonia, a rapidly warming and drying region.
• We analyzed 60 seedlings and found that open-canopy conditions reduced thermal tolerance, with leaf temperatures surpassing T₅₀ in over 40% of seedlings under a 3°C warming scenario. The closed-canopy area exhibited more effective leaf cooling driven by trait plasticity; however, this cooling was not sufficient to maintain leaves within safe thermal limits. When temperatures exceeded 40°C, PSII performance declined sharply, particularly in the open-canopy area, resulting in reduced thermal safety margins.
• Overall, our findings suggest that these effects may hinder the natural regeneration of B. rubescens, potentially affecting its role as a monodominant species and gradually influencing local dynamics and biodiversity in the long term, in response to warming and prolonged dry seasons in southern Amazonia.