Differences in the photosynthetic efficiency and photorespiration of co-occurring Euphorbiaceae liana and tree in a Chinese savanna

Abstract

Lianas perform better than co-occurring trees in secondary forests or disturbed areas. Lianas and trees differ strikingly in water use strategy, which may result in a significant difference in photosynthetic light use between both growth forms. However, the difference in the photosynthetic efficiency and light energy dissipation between these two growth forms is poorly understood. Moreover, photorespiration is an important mechanism of photoprotection under conditions of high light. In this study, we used Bridelia stipularis (Linn.) Bl. (liana) and Strophioblachia fimbricalyx Boerl. (tree) in order to measure the response curves of the gas exchange and photosynthetic electron flow to the incident light gradients and intercellular CO2 concentration, as well as the hydraulic conductivity. We tested whether the photochemical efficiency and photorespiration differed between both growth forms. Our results clearly demonstrated that B. stipularis possessed a significantly higher stem and leaf specific hydraulic conductivity, total electron flow, and maximum rate of ribulose-1,5-bisphosphate regeneration compared to the sympatric tree S. fimbricalyx. Correspondingly, B. stipularis exhibited a significantly higher photochemical quenching coefficient and electron flow to photorespiration relative to S. fimbricalyx under saturating light levels. We suggested that photorespiration might play an important role in photoprotection for both species under high light, but particularly for B. stipularis. These findings could enrich our knowledge of the superior photosynthetic and growth performance of lianas over the co-occurring trees.