Resistance to photodamage in evergreen conifers

Conifers in the temperate zone are subject to extremes in climatic conditions, such as low temperatures and water deficits. Under such conditions chloroplast antenna pigments can absorb more light energy than can be utilized in photosynthesis. If the plant is unable to dissipate this excess energy by combined radiationless decay (heat), fluorescence emission and carotenoid quenching, photodamage can result. Potentially damaging conditions exist during winter when low temperatures often occur simultaneously with intense light levels and desiccation. Photodamage is caused when regulatory controls on the production of toxic oxygen species produced in the chjoroplast and the capacity of scavenging systems to dispose of them are exceeded. By becoming cold‐hardened and dormant, conifer species can resist all but the most severe effects of the winter climates to which they are adapted. Mechanisms which protect chloroplasts from photodamage appear to be among the essential adaptations enabling temperate conifers to resist the effects of drought and low winter temperatures, especially when light levels are high.