Leaf gas exchange and growth of two papaya (Carica papaya L.) genotypes are affected by elevated electrical conductivity of the nutrient solution

- Papaya growth is reduced by elevated solute concentrations in the substrate.
- Nutrient imbalances do not account for plant growth reductions.
- Papaya genotypes are very sensitive to stomatal effects.
- Papaya's photochemical capacity is not affected by high solute concentrations.

Papaya (Carica papaya L.) nutrient requirements can be supplied through fertigation. However, this application method can increase solute concentrations, thereby increasing salinity and raising the electrical conductivity (EC) of the substrate when the nutrients are applied at supra-optimal levels. This can profoundly affect plant photosynthetic capacity and growth. We undertook an investigation to determine: (i) if reduced papaya growth due to salinity is caused by a possible decrease in osmotic potential, a nutrient imbalance, or both, (ii) the sensitivity of stomata of two papaya genotypes to increased EC, and (iii) if increased EC is detrimental to papaya photochemical capacity. Two different papaya genotypes (Sunrise Golden and Uenf-Caliman 01 hybrid) were fertilized with a nutrient solution with different EC: 1.0, 1.6, 2.2, 2.8 or 3.4 deciSiemens per meter (dS m−1). We found that (i) reduced growth was likely caused by a decrease in osmotic potential of the substrate. Nutrient imbalances were not present and did not account for growth reductions of either genotype under elevated EC, (ii) both genotypes are very sensitive to stomatal effects in response to increased EC, and (iii) an increase in EC up to 3.4 dS m−1 did not negatively affect the photochemical capacity of either genotype. However, there may have been non-stomatal effects at the Calvin cycle enzyme level. The results of this study show the importance of considering salinity as a relevant abiotic condition for papaya plantations and provide a basis for further field experiments to evaluate effects of high solute concentrations on yield and quality of papaya fruit.