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

Night chilling (5-degrees-C) subsequently lowered photosynthetic inten sity in the leaves of maize seedlings at 20-degrees-C through an incre ase in leaf diffusive resistance brought on by lower tissue water cont ent in morning hours. A more significant increase in leaf diffusion re sistance was observed when soil temperature was lowered than in the ca se of lower air temperature. The unfavorable effect of soil and air co oling temperature on photosynthesis was limited by air saturated with water vapour. However, as a result of lowering the night temperature f rom 5-degrees-C to 1-degrees-C, the efficiency of the protective influ ence of higher atmospheric humidity was decreased. This demonstrates t hat the participation of factors unrelated to plant water status in in hibiting photosynthesis increases with lower night temperatures. An ad ditional reason for inhibited photosynthesis following cool nights was a decrease in chlorophyll accumulation, below 50 mug per 1 cm2 of lea f area.