PS 85-206 - Dissolved [CO2] in xylem sap of C3 annuals, shrubs, vines, and bamboo

Thursday, August 9, 2012
Exhibit Hall, Oregon Convention Center
Cody M. Luedtke1, Doug P. Aubrey2, Mary Anne McGuire1 and Robert O. Teskey1, (1)Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, (2)Department of Biology, Georgia Southern University, Statesboro, GA
Background/Question/Methods

A portion of the carbon dioxide (CO2) released during respiration remains within the stem and can be transported internally through the xylem stream.  Photosynthetic cells in stems and leaves may fix this CO2, or it may diffuse from the plant into the atmosphere. High xylem CO2 concentrations ([CO2]) have been observed in many tree species, with measurements in the range of <1% to 26.3%. While most investigations of xylem [CO2] have focused on trees, high xylem [CO2] has been measured in two shrub species, suggesting that internal CO2 may play an important role in the carbon dynamics of shrubs and other plant functional groups. The objective of this study was to survey xylem [CO2] in C3 annuals (3 species), shrubs (8 species), vines (2 species), and bamboo (1 species). One to seven individuals were selected from plant species growing in the Athens, GA area and CO2 microelectrodes were used to measure xylem gaseous [CO2]. Stem diameter and height of microelectrode insertion were recorded to examine any possible effects on xylem [CO2]. Xylem temperature and xylem sap pH were measured and used to calculate dissolved xylem carbon dioxide concentration ([CO2*]) using gaseous [CO2] measurements and Henry’s law.

Results/Conclusions

Mean xylem [CO2*] ranged among species from 0.231-3.251 mmol L-1, which is within the range of concentrations observed in trees. The overall mean [CO2] of xylem sap was 2.69% gas by volume, which is about 70 times higher than current atmospheric [CO2]. Differences in mean [CO2*] were observed between functional groups.  Annuals had a mean (±SE) [CO2*] of 0.956 (±0.557), shrubs 0.814 (±0.462), and vines 0.300 (±0.142) mmol L-1. Only bamboo (Phyllostachys aurea) was significantly different (P<0.0001), with a mean [CO2*] of 3.251 (±2.131) mmol L-1. In a comparison of species, only Phyllostachys aurea (bamboo) and Lonicera japonica (vine) were significantly different, with mean xylem [CO2*] of 3.251 (±2.131) and 0.231 (±0.059) respectively. Stem diameter, height of microelectrode insertion, xylem temperature, and xylem sap pH did not have a significant effect on xylem [CO2*] when examined across all species. Stem xylem [CO2*] may also be affected by factors not measured in this study, such as climate, soil, herbivory, or community composition.  Future studies should incorporate a larger sample size and additional measurements to gain a better understanding of xylem CO2 in understudied functional groups.