C-4 plants use fluctuating light less efficiently than do C-3 plants: a study of growth, photosynthesis and carbon isotope discrimination

摘要

Plants in the field are commonly exposed to fluctuating light intensity, caused by variable cloud cover, self-shading of leaves in the canopy and/or leaf movement due to turbulence. In contrast to C-3 plant species, only little is known about the effects of dynamic light (DL) on photosynthesis and growth in C-4 plants. Two C-4 and two C-3 monocot and eudicot species were grown under steady light or DL conditions with equal sum of daily incident photon flux. We measured leaf gas exchange, plant growth and dry matter carbon isotope discrimination to infer CO2 bundle sheath leakiness in C-4 plants. The growth of all species was reduced by DL, despite only small changes in steady-state gas exchange characteristics, and this effect was more pronounced in C-4 than C-3 species due to lower assimilation at light transitions. This was partially attributed to increased bundle sheath leakiness in C-4 plants under the simulated lightfleck conditions. We hypothesize that DL leads to imbalances in the coordination of C-4 and C-3 cycles and increasing leakiness, thereby decreasing the quantum efficiency of photosynthesis. In addition to their other constraints, the inability of C-4 plants to efficiently utilize fluctuating light likely contributes to their absence in such environments as forest understoreys.