Resource generation is critical to sustain moisture stress in Melia dubia Cav.

The present study is an effort to understand the role of photosynthesis in enduring moisture stress in Melia dubia. Five germplasm lines with the highest and lowest growth from a pool of forty-two lines were selected based on their growth performance under rainfed conditions. The carbon assimilation rate of germplasm lines with the highest and lowest growth ranged between 18.7 and 15.8 µmol m ^− 2 s ^− 1 and 15.63 and 12.30 µmol m ^− 2 s ^− 1 at field capacity, respectively. However, it reduced (14.47 to 9.87 µmol m ^− 2 s ^− 1 and 9.53 to 6.07 µmol m ^− 2 s ^− 1 , respectively) when subjected to 50% moisture stress. The mean reduction was 29.41% and 44.30%, respectively. Similarly, the germplasm lines with higher growth showed a lesser reduction in biomass when exposed to moisture stress, both in nursery and field experiments. The higher stomatal conductance in germplasm lines with higher growth, even under moisture stress, can be due to an anisohydric stomatal response. Both diffusive and carboxylation processes of photosynthesis were higher in the germplasm lines with the highest growth. The photosynthetic rates and growth of better-performing lines under moisture stress suggest that maintaining carbon assimilation during such conditions enhances stress tolerance. Furthermore, germplasm lines that perform better under moisture stress showed efficient partitioning of assimilated carbon among the shoot and root systems. These findings imply that increased carbon assimilation during moisture stress contributes to improved fitness for enduring such conditions, thereby indicating photosynthesis as a trait for early prediction of moisture stress tolerance at the seedling stage.