Stomatal and Non-stomatal Control of Photosynthesis in Poplar Genotypes in Response to Water Stress

摘要

The effects of water stress on photosynthesis and chlorophyll a (Chl a) fluorescence were investigated in a pot experiment using 1-year-old cuttings of four poplar genotypes, Populus x euramericana cv.I-214 (Italica), P. x euramericana Guinir cv. Robusta (Robusta), P. berolinensis (Berolinensis) and P. Popularis 35-44 (Popularis). Constant fluorescence was not affected by increasing water stress while the ratio of variable to constant fluorescence increased by 20%-50%, implying there was no injury tophotosystem II reaction center, as photoinhibition is characterized by a progressive decline in variable fluorescence. Net photosynthetic rates(Pn) of Italica and Robusta, which are more sensitive to water stress, were drastically reduced due to non-stomatal factors; their ribulose bisphosphate carboxylase-oxygenase (Rubisco) activity was also severely inhibited. For Berolinensis and Popularis, the two more drought-tolerant poplar genotypes, stomatal and non-stomatal components played equally importantroles in their photosynthseis, and only a moderate decrease of photosynthetic rate was detected in response to water stress, with no significant effect in Berolinensis. The reported relationship between M-peak in Chl a fluorescence kinetics and the darkreaction of photosynthesis was confirmed via the effect of temperature on Rubisco activity, resulting in the M-peak disappearing in response to water stress and ABA treatment.