Kirschbaum, M.U.F., Ohlemacher, C. and
Küppers, M. (2004). Loss of quantum yield in extremely low light. Planta
218: 1046-1053.
Abstract. It has generally been assumed that the photosynthetic quantum yield of all C3 plants is essentially the same for all unstressed leaves at the same temperature and CO2 and O2 concentrations. However, some recent work by Timm et al. (Trees 16: 47-62) has shown that quantum yield can be reduced for some time after leaves have been exposed to darkness. To investigate under what light conditions quantum yield can be reduced, we carried out a number of experiments on leaves of a partial-shade (unlit greenhouse) grown Coleus blumei hybrid.
We found that after leaves had been exposed to complete darkness, quantum yield was reduced by about 60%. Only very low light levels were needed for quantum yield to be fully restored, with 5 µmol quanta m-2 s-1 being sufficient for 85% of the quantum yield of fully induced leaves to be achieved. Leaves regained higher quantum yields upon exposure to higher light levels with an estimated time constant of 130 s.
It was concluded that the loss
of quantum yield would be quantitatively important only for leaves growing in
very dense understoreys where maximum light levels might not exceed 5 µmol
quanta m-2 s-1 even in the middle of the day. Most leaves
even in understorey conditions, do, however, experience light levels in excess
of 5 µmol quanta m-2 s-1 over periods where they obtain
most of their carbon so that the loss of quantum yield would affect total
carbon gain of those leaves only marginally.
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