Leaf wetting mitigates midday depression of photosynthesis in tomato plants

We studied the effects of leaf wetting on midday depression of photosynthesis regarding plant water balance and leaf morphological traits. The plants without leaf wetting showed a significant reduction in midday photosynthesis with a concomitant decrease with leaf conductance, because of lower leaf water potential (-1.3 MPa) due to excessive transpiration water loss. However, midday depression was not observed in the plants with leaf wetting. Lower contact angle between leaf surface and water droplet showed that tomato leaves have lower water repellency. However, water on the leaf surface completely dried within 20 min indicating that effect of water coverage on stomata for CO2 uptake was small. In addition, leaf wetting significantly decreased evaporative demands, which contributed to maintaining appropriate water balance and avoided midday stomatal closure, and it contributed to mitigation of midday depression of photosynthesis.