The variation in leaf mass per area in plants affectedby a daily short-term temperature drop
The effects of a daily short-term (2 h) temperature drop (DROP) to 12, 8, 4 or 1°C on leaf mass per area (LMA) in chilling-sensitive (cucumber, tomato, sweet pepper, eggplant) and chilling-tolerant (winter wheat, cauliflower) plants have been studied. The role of light (light intensity during DROP treatments, light intensity during plant cultivation and photoperiod duration) in the response of LMA to DROP treatments was revealed using several plant species. Despite the high level of interspecific variation in LMA (for chilling-sensitive species, LMA increased in the following order: cucumber–tomato–pepper–eggplant), no significant qualitative differences were found between the species in LMA response to DROP treatments. Intraspecific variation was related to light and temperature conditions of plant cultivation. Temperature shifts in the range of positive values affected LMA variability in chilling-sensitive, but not chilling-tolerant plants. Light had a significant effect on the variations in LMA in DROP-treated chilling-sensitive plants. When plants were treated by DROP in the dark, LMA remained unchanged or increased, but if DROP treatments were in the light, LMA decreased. The extent of its change increased with lowering temperature of DROP treatments. Higher light intensity contributed to a rise in LMA. At that, DROP treatments in the dark led to increasing while DROP treatments in the light to decreasing the extent of LMA as light intensity became higher. An extension of photoperiod from 16 to 24 h caused an increase in LMA, but the duration of photoperiod did not affect the response of LMA to DROP treatments. Thus, a daily short-term temperature drop to low positive values can cause significant changes in LMA in chilling-sensitive, but not in chilling-tolerant plants. Light conditions are an important modulating factor of these changes. The high degree of variation in LMA under intense DROP treatments reflects the ability of plants to significant structural transformations necessary for their growth and development under alternating temperature conditions.