Agriculture Reference
In-Depth Information
increased with increasing growth temperature due mainly to
increasing activation energy of Vc max.
Canopy temperature and incident photosynthesis active
radiation were provided in mature plants of fi ve varieties of
rice exposed to a 3 day chilling treatment (21ºC day/10ºC night)
14 days after anthesis. Canopy photosynthesis was measured
before, during and after the chilling period. A Japonica like
cultivar Hungarian-1 from Central Europe, and an indica like
cultivar Lemonet from Texas were markedly less sensitive
to a chilling dependent reduction in photosynthesis than
were cultivars Guichao-2, Er. Bai Ai, and IR8 from South east
China and the philippines. The extent of chilling dependent
reduction in photosynthesis was greater if roots of plants were
allowed to be at air temperature in night. This led to a 5-7ºC
differential between root and air temperature in the morning
and associated with a midday depression of photosynthesis
in all varieties. If root temperature was kept at 20ºC during
the day and night and air temperature controlled at 21ºC day
and 10ºC night, the effects of chilling on photosynthesis were
much less pronounced.
Changes in canopy photosynthesis following treatments
were corelated with change, in leaf level perameters. The level
of sugars and starch levels was found to remain high during
the fi rst cool night and to increase further during the next day.
In cultivars which showed pronounced inhibition of canopy
photosynthesis throughout the chilling treatment (Guichao2,
IR8) soluble sugars remained at high levels until temperatures
were returned to control values. In the less sensitive cultivar
Hungarian-1 soluble sugars declined throughout the chilling
treatment. It is suggested that inhibition of photosynthesis
may be associated with sugar retention in leaves of rice at
low temperatures, and imply differences between cultivars
