Leaf carbon management in slow-growing plants exposed to elevated CO

摘要

Two slow-growing plant species (Chamaerops humilis, L. and Cycas revoluta Thunb.) were exposed to elevated CO conditions over a 20-month period in order to study the CO effect on growth, photosynthetic capacity and leaf carbon (C) management. The ambient isotopic p#pdC/p#poC composition (tp#pdC) of the greenhouse module corresponding to elevated CO (800 omol molp# CO) conditions was changed from tp#pdC ca. -12.8pl0.3[per thousand] to ca. -19.2pl0.2[per thousand]. Exposure of these plants to elevated CO enhanced dry mass (DM) by 82% and 152% in Chamerops and Cycas, respectively, mainly as a consequence of increases in plant level photosynthetic rates. However, analyses of A-Ci curve parameters revealed that elevated CO diminished leaf photosynthetic rates of Chamaerops whereas in Cycas, no photosynthetic acclimation was detected. The fact that Chamaerops plants had a lower DM increase, together with a longer leaf C residence time and a diminished capacity to respire recently fixed C, suggests thatthis species was unable to increase C sink strength. Furthermore, the consequent C source/sink imbalance in Chamaerops might have induced the downregulation of Rubisco. Cycas plants were capable of avoiding photosynthetic downregulation due to a greaterability to increase C sink strength, as was confirmed by DM values, and p#poC-enriched CO labeling data. Cycas developed the ability to respire a larger proportion of recently fixed C and to reallocate the recently fixed C away from leaves to other plant tissues. These findings suggest that leaf C management is a key factor in the responsiveness of slow-growing plants to future CO scenarios.