Diurnal changes in photosynthesis in Sclerocarya birrea from South Africa and Israel after introduction and acclimatization in Wenshan, Yunnan Province, China

Abstract

Photosynthetic activity is one of the most important indicators for evaluating the introduction and acclimatization of trees to new geographies. The aim of this study was to investigate the photosynthetic characteristics of marula [Sclerocarya birrea (A. Rich.) Hochst. subsp. caffra (Sond.) Kokwaro (Anacardiaceae)] and the environmental conditions relevant to its growth in China. We analyzed the diurnal dynamics of photosynthesis in two S. birrea varieties, one from South Africa and one from Israel, after introduction into China using a portable photosynthesis measuring system. Our results showed that the diurnal net photosynthetic rate (Pn) exhibited an atypical double-peak pattern that was influenced mainly by stomatal factors. Moreover, the diurnal change in stomatal conductance (Gs) was consistent with that for Pn and showed an obvious double-peak curve, whereas the diurnal change in the transpiration rate (Tr) was opposite to that in intercellular CO2 concentration (Ci), which presented a single-peak curve. The extreme values of the environmental factors we monitored occurred at approximately the same time of day and influenced photosynthesis by affecting Ci, Tr, and leaf temperature (TL), with light intensity exerting an especially strong effect. The Pn of the S. birrea variety from Israel was higher than that of the S. birrea variety from South Africa, while South Africa S. birrea exhibited superior growth trait in southern China. We suggest that the photosynthetic performance of S. birrea can be acclimated to a new environment.