Abstract
Previous investigations on photosynthesis have been performed on leaves irradiated from the adaxial surface. However, leaves usually sway because of wind. This action results in the alternating exposure of both the adaxial and abaxial surfaces to bright sunlight. To simulate adaxial and abaxial surfaces alternant irradiation (ad-ab-alt irradiation), the adaxial or abaxial surface of leaves were exposed to light regimes that fluctuated between 100 and 1,000 μmol m−2 s−1. Compared with constant adaxial irradiation, simulated ad-ab-alt irradiation suppressed net photosynthetic rate (Pn) and transpiration (E) but not water use efficiency. These suppressions were aggravated by an increase in alternant frequency of the light intensity. When leaves were transferred from constant light to simulated ad-ab-alt irradiation, the maximum Pn and E during the high light period decreased, but the rate of photosynthetic induction during this period remained constant. The sensitivity of photosynthetic gas exchange to simulated ad-ab-alt irradiation was lower on abaxial surface than adaxial surface. Under simulated ad-ab-alt irradiation, higher Pn and E were measured on abaxial surface compared with adaxial surface. Therefore, bifacial leaves can fix more carbon than leaves with two “sun-leaf-like” surfaces under ad-ab-alt irradiation. Photosynthetic research should be conducted under dynamic conditions that better mimic nature.
Highlights
Irradiation conditions[9,18], and no attention has been given to investigating the photosynthetic gas exchange of leaves under ad-ab-alt irradiation
This finding suggests that the differences in photosynthetic gas exchange under adaxial or abaxial surface irradiation were independent of the absorptance
Some recent reports have investigated dynamic photosynthesis under fluctuating irradiance[22], the majority of studies were performed on leaves that were irradiated on the adaxial surface[12,13,14,15,16,17]
Summary
Irradiation conditions[9,18], and no attention has been given to investigating the photosynthetic gas exchange of leaves under ad-ab-alt irradiation. Due to the different protein and pigment distributions between the adaxial and abaxial surfaces[5,8], we expect differential responses to ad-ab-alt irradiation between the adaxial and abaxial surfaces of an individual leaf. To test these hypotheses, we examined dynamic gas exchange in the leaves of two trees (Platanus orientalis L. and Melia azedarach L.) and one herb (Solanum lycopersicum L.) under simulated ad-ab-alt irradiation or constant irradiation
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