Canopy storage capacity and wettability of leaves and needles: The effect of water temperature changes

The canopy storage capacity (S) is a major component of the surface water balance. We analysed the relationship between the tree canopy water storage capacity and leaf wettability under changing simulated rainfall temperature. We estimated the effect of the rain temperature change on the canopy storage capacity and contact angle of leave and needle surfaces based on two scenarios. Six dominant forest trees were analysed: English oak (Quercus roburL.), common beech (Fagus sylvatica L.), small-leaved lime (Tilia cordata Mill), silver fir (Abies alba), Scots pine (Pinus sylvestris L.),and Norway spruce (Picea abies L.). Twigs of these species were collected from Krynica Zdrój, that is, the Experimental Forestry unit of the University of Agriculture in Cracow (southern Poland). Experimental analyses (simulations of precipitation) were performed in a laboratory under controlled conditions. The canopy storage capacity and leaf wettability classification were determined at 12 water temperatures and a practical calculator to compute changes of S and contact angles of droplets was developed. Among all species, an increase of the rainfall temperature by 0.7 °C decreases the contact angle between leave and needle surfaces by 2.41° and increases the canopy storage capacity by 0.74 g g−1; an increase of the rain temperature by 2.7 °C decreases the contact angle by 9.29° and increases the canopy storage capacity by 2.85 g g−1. A decreased contact angle between a water droplet and leaf surface indicates increased wettability. Thus, our results show that an increased temperature increases the leaf wettability in all examined species. The comparison of different species implies that the water temperature has the strongest effect on spruce and the weakest effect on oak. These data indicate that the rainfall temperature influences the canopy storage capacity.