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.