Variations in Carbon Dioxide Efflux by Stem Height in Six Arborescent Palm Species

Abstract Background Stem respiration is influenced by elevation, but this phenomenon has not been adequately studied for palms. Therefore, the influence of stem height on carbon dioxide efflux ( E s ) was determined for 6 palm species. Methods Gas exchange protocols were employed to determine E s . The lowest height was 35 cm above the root collar, and the greatest height was 20 cm below the oldest living leaf in the crown. Results A consistent baseline flux was observed for the midlength of the stems, a moderate increase in E s occurred at the lowest elevation, and a substantial increase in E s occurred at the highest elevation. The midheight flux ranged from 0.9 µmol·m −2 ·s −1 for Corypha utan to 2.3 µmol·m −2 ·s −1 for Carpentaria acuminata . The basal increase in E s averaged 63% and was greatest for C. utan and least for Phoenix sylvestris . The apical increase in E s averaged 157% and was greatest for Wodyetia bifurcata and least for C. acuminata . A quadratic model described the influence of stem height on stem E s . Conclusion The moderate increase of E s at the lowest stem height was consistent with the influence of root-respired carbon dioxide entering the stem in xylem mass flow then conducting radially to the stem surface. The substantial increase in E s at the highest stem height was consistent with proximity to the growth respiration of the large primary thickening meristem of the pachycaulous palm stem. These findings confirm that the elevation of the stem influences palm E s , and the elevation pattern is consistent among every species.