Chin J Plan Ecolo ›› 2014, Vol. 38 ›› Issue (10): 1099-1109.doi: 10.3724/SP.J.1258.2014.00104

• Research Articles • Previous Articles     Next Articles

Photosynthetic responses of the heteromorphic leaves in Populus euphratica to light intensity and CO2 concentration

WANG Hai-Zhen*, HAN Lu, XU Ya-Li, and NIU Jian-Long   

  1. College of Plant Science, Tarim University, Key Laboratory of Protection and Utilization of Biological Resource in Tarim Basin, Xinjiang Production & Construction Groups, Alar, Xinjiang 843300, China
  • Received:2014-05-30 Revised:2014-07-13 Online:2014-10-22 Published:2014-10-01
  • Contact: WANG Hai-Zhen E-mail:whzzky@163.com
  • Supported by:

    Adaptation mechanism and water use strategy of constructive species of desert riparian forest to soil water deficit in Tarim;Leaf shape plasticity and eco-physiological adaptation mechanism of Populus euphratica

Abstract:

Aims Populus euphratica is an important tree species and its leaf shape changes along the growth stages. Adult trees commonly comprise polymorphic leaves, including lanceolate, oval and serrated broad-oval leaves. Our objective were to elucidate the ecophysiological mechanisms of P. euphratica adapting to high temperature and strong light environment and its survival strategy by comparing photosynthetic efficiency and chlorophyll fluorescence parameters in heteromorphic leaves in an extremely arid desert area, and to explore the causes of changes in leaf shape in P. euphratica, in order to provide a scientific basis for the protection of desert P. euphratica forests.
Methods Individuals with 10 cm diameter at breast height from a planted P. euphratica forest were selected. Measurements were made on the parameters of gas changes and chlorophyll fluorescence of three different leaf shapes on branches at the similar height using a LI-6400 Portable Photosynthesis System and a PAM-2100 chlorophyll fluorometer. The light/CO2 response curves of net photosynthetic rate (Pn) and rapid light curves of chlorophyll fluorescence in heteromorphic leaves were fitted and analyzed.
Important findings The light and CO2 response curves, rapid light curves of the three different leaf shapes in P. euphratica were better fitted by the modified rectangular hyperbola models, and the model values of key photosynthetic parameters were very close to the measured data. There were significant differences in the light responses, biochemical parameters and the parameters of rapid light curves among the oval, serrated broad-oval leaves and lanceolate leaves, but the heteromorphic leaves did not significantly differ in carbon assimilation efficiency. The maximum net photosynthetic rate (Pnmax) of the heteromorphic leaves under saturated intercellular CO2 concentration was higher than under saturated irradiance, indicating that photosynthetic efficiency was limited to the great extent by CO2 supply and regeneration rate of ribulose biphosphate (RuBP). Initial quantum yield (α), initial carboxylation efficiency (CE), Pnmax, photosynthetic capacity (Amax), maximum carboxylation rate (Vcmax) were greater in the oval and serrated broad-oval leaves than in the lanceolate leaves; the serrated broad-oval leaves had the highest light saturation point (LSP), photosynthetic electron transportation rate (ETRmax) and rate of photorespiration (Rp), whereas the lanceolate leaves had the lowest light compensation point (LCP), LSP, α and CE. All the results above indicate that the serrated broad-oval leaves having greater resistance to strong light and higher Rp may be an important mechanism for dissipating excessive light energy and protecting the photosynthetic apparatus from light damage. In contrast, the oval leaves had higher values in α, CE, triose-phosphate utilization efficiency (TPU), PSII actual photochemical efficiency (ΦPSII), leaf nitrogen allocation strategy and low LCP and therefore could maintain high photosynthetic rate in extremely arid areas. The lanceolate leaves had the lowest values in Pn, ΦPSII, and ETR, which would be difficult to meet the individual growth demand because of the low production of photosynthate, and their number declined with growth and distributed mainly toward the lower tree crowns.

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