EFFECT OF LOW TEMPERATURE DURING THE NIGHT IN YOUNG SWEET PEPPER PLANTS: STRESS AND RECOVERY

The optimization of heating in greenhouses should be an energy saving target in the cultivation of sweet pepper plants; from both an environmental and economical point of view. It is important to understand the effect of low temperatures on this crop. While the effect of low temperature has been studied in plants exposed to light, there are few studies on the effect of cold in the dark, which is a more realistic situation in greenhouses. The objective of this work was to study the effect of low temperatures during the night in sweet peppers and to assess the physiological consequences during the following day. Therefore, we subjected sweet pepper plants of two cultivars to 5 or 7 cycles of 12/12 h warm light (500 μmol m^-2 s^-1 PAR, 21°C) and cold dark (6°C). After the treatment, several measurements were performed on leaves (first in the dark and cold, and one hour after light was switched on): chlorophyll fluorescence (spot and imaging) and measurements of biomass. Our results showed a decrease in the efficiency of photochemistry in photosystem II (Y(II)) during the dark, cold period related to a stimulation of photoprotection mechanisms in the photosynthetic apparatus. However, 1 h after rewarming in light conditions, leaves had recovered high values of Y(II). In addition, fully expanded leaves increased their specific leaf area and fresh to dry weight ratio during this period. This may indicate that, during the recovery period, dry weight decreased due to redistribution of assimilates to expanding leaves and/or that leaf water content increased. The fast recovery of this crop after several cold nights opens possibilities for new strategies of energy saving in greenhouses. However, more studies should be carried out within this area.