Does Root-Zone Heating Mitigate the Cold Injury in Coffee Tree (Coffea arabica)?

Cold winter injury is a significant challenge in cultivating tropical trees in temperate regions. The conventional solution involves heating the entire greenhouse to protect the plants; however, this approach is fuel-intensive and costly. This study investigated whether root-zone heating can mitigate cold injury in coffee trees. In the Control, non-heated treatments, leaf relative water content dropped to approximately 70%, leading to wilting, whereas in the Heat treatment, it remained above 90%. In the Control treatment, defoliation progressed, ultimately resulting in more than 50% leaf loss. In contrast, defoliation was reduced by approximately 20% with the Heat treatment. During the cold-treatment period, photosynthesis declined sharply in both the Control and Heat treatments, with CO₂ assimilation dropping to nearly zero. However, one week after the complete of cold treatment, F_v/F_m recovered to pre-treatment levels, while CO₂ assimilation and electron transport rates improved to more than 50% of pre-treatment levels in the Heat treatment. These findings indicate that root-zone heating helps prevent leaf wilting and defoliation by maintaining high leaf water content. The surviving leaves recovered their photosynthetic function and were crucial in subsequent biomass production. Thus, root-zone heating is a cost-effective and efficient strategy for cultivating tropical trees in temperate regions.