LEAF GAS EXCHANGE OF 20 PALM SPECIES UNDER FIELD CONDITIONS

Abstract

Leaf gas exchange variables of 20 palm species were determined under field conditions in Miami, Florida during June 1994 in order to establish a comparison among the six palm subfamilies. Diurnal variation in net CO₂ assimilation (A) and stomatal conductance to H₂O (g_s) was measured on leaves of Sabal causiarum on a representative mostly sunny day for the season. Pinnae A and g_s rapidly increased following sunrise to a maximum by 0900 h, followed by a slow decline throughout the day. Moderate recovery of A occurred during late afternoon, but g_s did not follow this pattern. Dark respiration of S. causiarum was 5.3% of maximum A. Based on these data, measurements on the 20 species were made during the morning hours when gas exchange was maximal. Net CO₂ assimilation ranged from 5.5 µmol m^-2s^-1 for Ravenea rivularis to 16.9 µmol m^-2s^-1 for Bismarckia nobilis. The range of gs was 121 mmol m^-2s^-1 for Phytelephas macrocarpato 582 mmol m^-2s^-1 for B. nobilis. Mean transpiration (E) ranged from 1.9 to 6.2 mmol m^-2s^-1. Values of A, g , and E were lowest for Calamoidae and Phytelephantoidae species, lowest to mid-range for Arecoidae and Ceroxyloidae species, mid-range for the only Nypoidae species, and mid-range to highest for the Coryphoidae species. Values for gas exchange variables of these palm species were within the range to be expected for evergreen woody plants.