Differences in photosynthetic characteristics among northern and southern C4 plants.
Both responses to short-term changes of temp. and to chilling under high light were analysed in populations of Echinochloa crus-galli var. crus-galli from Quebec, North Carolina and Mississippi to improve the understanding of C4 photosynthesis at low temp. Comparison also included plants of Eleusine indica from Mississippi to provide for differences among species and populations. After transfer from cool (21/15°C) to warm (28/22°) growth conditions, E. crus-galli from Mississippi achieved the highest photosynthetic rates. Plants from Quebec maintained the highest rates of CO2 uptake upon transfer to cool conditions. Exposure to 7° for 3 days at a photon fluence rate of 1000 µmol/m2 s resulted in a reduction in the growth rates of all populations. This reduction was paralleled by a decrease in net photosynthesis and in stomatal conductance. Following chilling under high light, the reduction in growth parameters was less important for plants from Quebec than for the other populations. It suggests that, among other characteristics, northern plants had developed a certain tolerance to chilling under light.