Leaf morpho-anatomical traits in Vigna radiata L. affect plant photosynthetic acclimation to changing vapor pressure deficit.

Vapor Pressure Deficit (VPD) influences plant photosynthesis and the hydraulic behaviour associated with stomata regulation. However, it is not clear whether and how changes in leaf morpho-anatomical traits drive photosynthetic acclimation to VPD. Here, we examined the role of leaf anatomy in the eco-physiological responses of Vigna radiata L. to VPD changes in controlled environment. Plants were grown under two VPD levels (high-VPD, HV; low-VPD, LV) and then transferred to the opposite conditions (high-to-low, HLV; low-to-high, LHV). We hypothesised that growth under different VPDs may determine anatomical changes that could affect plant physiological plasticity to VPD variations. HV plant growth (height, leaf area, number of leaves) and gas-exchange (net-photosynthesis, stomatal conductance, water use efficiency) were reduced in a range of 16–47 % compared to LV. This was mostly attributed to reduction in stomatal and vein density and lower stomatal conductance. After transferring these plants to a more favourable environment (HLV), they showed unchanged photosynthesis and conductance while LHV plants reduced their gas-exchange rates to control water loss under high evaporative demand. Morpho-anatomical traits (high density and smaller stomata, higher vein density) in LHV plants showed higher physiological plasticity. Therefore, physiological plasticity induced by anatomical traits should be considered when evaluating how plants would cope with environmental changes in a climate change scenario.