DO PALM WATER USE CHARACTERISTICS EXPLAIN THE SPATIAL DISTRIBUTION OF PALMS IN THE CENTRAL AMAZON?

Abstract

We studied plant water use characteristics of the tree Theobroma grandiflorum (Cupuacu, (Willd. ex Spreng.) Schum., Malvaceae) and the palm Euterpe precatoria (Acai, Mart., Arecaceae) both native to the Amazon and commonly occurring in the region. The tree species is occurring mainly in the terra firme forest whereas the palm species is restricted to the extreme habitats in stream valleys. This study was conducted in a small fruit plantation close to the city of Manaus, in the Central Amazon, Brazil. The main objective of this study was to compare water use characteristics in relation to plant structural traits. Three representative individuals of each species were equipped with Granier-type thermal dissipation probes to measure sap flux density. Water use scaled independent of species with the size of the conductive xylem area (r2=0.85). Furthermore, we found a clear species-specific scaling of water use with plant-size. Overall, palms had a 3.5-fold higher water consumption compared to trees with similar stem diameter and/or plant height. Palms transpired a mean of 1.67 mm m-2 of water per unit crown projection area per day, whereas trees transpired only 0.30 mm m-2 per day, resulting in a 5.6 times lower transpiration rate. We assume that especially the unbalanced plant height/water use ratio of the palms might be limiting the height growth due to increasing hydraulic limitations. Hence, palms are restricted to extreme habitats with higher water availability and usually do not co-occur with more efficient and taller broad leaved tree species in the terra firme forest.