3.3 Leaf water uptake in Capparis odoratissima
The initial water content of detached leaves was approximately 9.5 mg cm-2. Weight loss of leaves exposed to lab conditions was used to understand epidermal evapotranspiration (Supplementary figure1). Leaf water content remained higher than 80% during the first 21 hours of exposure at low humidity, but then decreased sharply, with leaves becoming brittle 143 hours after the initial measurements. The epidermal water loss rate over the first 10 hours was 0.041 mg cm-2 h-1.
Leaves of Capparis odoratissima submerged for 15 minutes (wet cycle) absorbed water at a rate of 0.30 mg cm-2h-1. Rates of water loss during the dry cycle averaged 0.27 mg cm-2 h-1, approximately seven times larger than epidermal water loss rates of leaves allowed to dry over a period of many hours. The water retained following each dry cycle (i.e. not evaporated) increased at a rate of 0.013 mg cm-2 h-1 (Fig. 5a), suggesting that evaporative losses became smaller with each cycle (r 2=0.97).
The contribution of adaxial and abaxial leaf surfaces to water uptake was evaluated by loading each surface individually with water droplets (Figure 5b). Comparing the proportional weight variation over time revealed that even though only 30% of one surface was covered with water, the leaves significantly reduced their evaporative losses. However, there was a clear asymmetry: leaves loaded on the adaxial surface reduced their proportional water losses twofold with respect to the unloaded leaves, whereas leaves loaded on the abaxial surface reduced their evaporative losses almost six times. While this indicates that both surfaces can absorb water, water uptake by the abaxial surface is approximately three times larger (0.033 mg cm-2h-1, r 2=0.84) relative to water absorption by the adaxial surface. These data suggest that loading each surface with the same amount of water results in different absorption capacities, but water absorption depends on the capacity to uptake water by each surface, but also on the epidermal evaporation of each unloaded surface, likely higher in the abaxial side, although this needs further testing.