Leveraging Diversity in Environmental Driven Responses Reveals a Key Role for Mesophyll Conductance and Root Sink...

In future climates both CO₂ and temperature are predicted to rise. Using high-throughput phenotyping, the diversity of 31 different banana varieties and their associated traits were leveraged to understand the impact of potential future climatic conditions of combined elevated CO₂ (e[CO₂]) and temperature. Under ambient CO₂ (a[CO₂]) the adaxial/abaxial stomatal density ratio (rSD) was identified as a strong predictor of growth, but its importance diminished when CO₂ was highly abundant. When evaluated at 400 versus 800 ppm and 30°C versus 34°C, variation in mesophyll conductance (g_m) and root sink strength drove growth under both a[CO₂] and e[CO₂]. Significant positive correlations between the e[CO₂] response of stomatal conductance (g_s,c), transpiration (E), root to shoot ratio, net photosynthetic rate at saturating irradiance (A_sat), maximum rate of electron transport (J_max) and maximum triose phosphate utilisation rate (TPU_max) indicated a coupling between sink strength, photosynthetic capacity and stomatal regulation. Moreover, g_m and g_s,c concurrently reduced under e[CO₂]. Interactions between acclimation towards e[CO₂] and temperature were evident on gas exchange and photosynthetic capacity. Under the investigated conditions, e[CO₂] counteracted the negative effect of the supra-optimal temperature on growth. Varieties with high mesophyll conductance and root sink strength benefitted most from e[CO₂] driven growth and photosynthesis enhancement. Results were further validated in an ecotron facility. This study reveals rSD, g_m and root sink strength as potential traits for crop improvement and highlights the importance of evaluating the simultaneous impact of CO₂ and temperature in future climate studies.