Adaptive changes in chlorophyll content and photosynthetic features to low light in Physocarpus amurensis Maxim and Physocarpus opulifolius “Diabolo”

Abstract

The present study aims to investigate the differences in leaf pigment content and the photosynthetic characteristics under natural and low light intensities between the Chinese nativePhysocarpus amurensis Maximand the importedPhysocarpus opulifolius“Diabolo” from North America. We aim to discuss the responses and the adaptive mechanism of these two cultivars ofPhysocarpusto a low light environment. The results show that the specific leaf area (SLA) and the chlorophyll content were significantly increased in the leaves of bothPhysocarpuscultivars in response to a low light intensity, and the SLA and chlorophyll content were higher in the leaves of low light-treatedP. opulifolius“Diabolo” compared with the leaves of low light-treatedP. amurensis Maxim. Moreover, the content of anthocyanin was markedly reduced in the leaves ofP. opulifolius“Diabolo” under low light intensity, which allowed for a greater capacity of photon capture under the low light condition. Under natural light, the photosynthetic carbon assimilation capacity was greater in the leaves ofP. amurensis Maximcompared with the leaves ofP. opulifolius“Diabolo” that were rich with anthocyanin. However, in response to low light, AQY,Pmax, LCP and LSP decreased to a lesser extent in the leaves ofP. opulifolius“Diabolo” compared with the leaves ofP. amurensis Maxim. These results suggest thatP. opulifolius“Diabolo” exhibits a greater ability in adaption to low light, and it is probably related to the relatively higher chlorophyll content and the smaller SLA in the leaves ofP. opulifolius“Diabolo.” In addition, the low light intensity resulted in a reduced photochemical activity of photosystem (PS) II in the leaves of bothPhysocarpus, as evidenced by increased values of the relative variable fluorescence at point J and point I on the OJIP curve. This result suggests that the electron acceptor in PS II was the major responsive site to the low light stress in the leaves of bothPhysocarpuscultivars, and that the low light intensity significantly inhibited electron transfer on the acceptor side of PS II and reduced the activity of the oxygen-evolving complex (OEC) in the leaves of bothPhysocarpuscultivars. The PS II function inP. opulifolius“Diabolo” was higher than that inP. amurensis Maximin response to low light. Under low light, the composition of photosynthetic pigments was altered in the leaves ofP. opulifolius“Diabolo” in order to maintain a relatively high activity of primary photochemical reactions, and this is the basis of the greater photosynthetic carbon assimilation capacity and one of the main reasons for the better shade-tolerance inP. opulifolius“Diabolo.”