EFFECT OF LOW NIGHT TEMPERATURES ON PHOTOSYNTHETIC ACTIVITY OF THE MAIZE SEEDLINGS (ZEA-MAYS L)

Night chilling (5-degrees-C) subsequently lowered photosynthetic intensity in the leaves of maize seedlings at 20-degrees-C through an increase in leaf diffusive resistance brought on by lower tissue water content in morning hours. A more significant increase in leaf diffusion resistance was observed when soil temperature was lowered than in the case of lower air temperature. The unfavorable effect of soil and air cooling temperature on photosynthesis was limited by air saturated with water vapour. However, as a result of lowering the night temperature from 5-degrees-C to 1-degrees-C, the efficiency of the protective influence of higher atmospheric humidity was decreased. This demonstrates that the participation of factors unrelated to plant water status in inhibiting photosynthesis increases with lower night temperatures. An additional reason for inhibited photosynthesis following cool nights was a decrease in chlorophyll accumulation, below 50 mug per 1 cm2 of leaf area.