CO₂, H₂O exchange and stomatal regulation of regenerated Camptotheca acuminata plantlets during ex vitro acclimatization

Abstract

For finding the changes in CO₂, H₂O exchange and their stomatal regulation during ex vitro acclimatization of regenerated Camptotheca acuminata plantlets, the net photosynthesis rate (P_n), respiration rate (R_d), light compensation point (L_c) and light saturation point (L_s), transpiration rate (Tr), stomatal conductance (g_s) and water use efficiency(WUE) were measured during 37 days of ex vitro acclimatization. The results showed that P_n sharply increased until 29 days, then slightly decreased. A substantial decrease in L _c and a substantial increase of L _s in the former two weeks were observed, indicating the light regime enlargement for effective leaf photosynthesis. Tr and g_s abruptly decreased during the first week then linearly increased until 29days ex vitro acclimatization, reflecting the strong regulation effect of stomata on water changes of ex vitro acclimating plantlets. Stomatal regulation effect on CO₂ exchange was different from that on water exchange, i.e. P_n was almost independent of g_s during the first week, while P_n was significantly correlated with g_s thereafter (i.e. dual patterns). Different from dual patterns of g_s-P_n relation, the Tr monotonously linearly increased with g_s. Furthermore, WUE was almost independent on g_s during the first week, while a marked decreasing tendency with g_s was found thereafter. At the beginning of the acclimatization, WUE was mainly determined by photosynthetic capacity, while transpiration becomes a main determinant factor for WUE from 7 to 37 days’ acclimatization.

Keywords

Camptotheca acuminate / Acclimatization / Photosynthesis / Transpiration / Water use efficiency / Relation between stomatal conductance (g_s) and net photosynthesis rate (P_n) / g_s-WUE relation