Photochemical responses to abrupt and gradual chilling treatments in eucalyptus species

Eucalyptus plant is one of the most economic important forest species explored worldwide and in some countries its cultivation is expanding to regions with lower temperatures, including Brazil. This study aimed to compare the photochemical response of 18 Eucalyptus species, one Corimbia and one hybrid subjected to low temperature using two chilling treatments. Six-month-old plants were exposed to (1) gradual chilling (20-0 degrees C in four steps of 5 degrees C for 10 min) and abrupt chilling (20-5 degrees C in one step). Based on chlorophyll fluorescence parameters, eucalyptus species responded differently depending on how chilling was applied. E. tereticornis presented the best performance under chilling, regardless how it was imposed. The effective quantum yield of photosystem II was the best parameter to identify variation in photochemical responses of eucalyptus species to chilling. It was also observed that E. brassiana, C. citriodora, E. grandis, E. gunni, and E. resinifera were sensitive to the way chilling was applied, leading to differential photochemical response.