Comparison of gas exchanges between in situ and abscised leaves of high arbor trees: a case study of Cylobalanopsis glauca under three habitats

Abstract

It has been difficult to monitor the gas exchanges of tall arbor trees using portable equipment, e.g. Li-6400, as it is hard to reach to the leaf samples in situ. Due to the tree heights, we aimed to compare the gas exchange between in situ and abscised leaves of Cylobalanopsis glauca under three habitats, with the purpose of identifying a possible methodology with which we might be able to use abscised rather than in situ leaves. The results showed that after the samples were abscised, the leaf stomatal conductance (g_s) immediately increased before dropping gradually later. The extent of this change was found to be temperature-dependent. The linear relationships either between g_s and transpiration (E), or between g_s and net photosynthesis (P_n) were significant but the former had a higher correlation, indicating that the opening of the stomata has a more intensive effect on E than on P_n. Temperature is a key factor affecting the variation of gas exchanges of the abscised leaves, with higher temperature in the karst area resulting in a rapid E loss and leading to the fact that water stress occurs earlier to the part stomatal closure, which in turn decreases P_n. A reliable duration for measuring the gas exchanges from the abscised leaves is determined by leaf temperature. In the karst area where the leaf temperature is frequently over 32°C in the summer, the reliable duration can last only 3―6 min after abscission, while in the Guilin Botanical Garden (non-karst area) with leaf temperatures of about 32°C, the reliable duration can last 10 min; in the green house, it is at around 20°C, and the reliable duration will possibly last 20 min.

Keywords

in situ / abscised leaves / gas exchange / Cylobalanopsis glauca / habitat / reliable duration