Cold-induced photoinhibition and foliar pigment dynamics of Eucalyptus nitens seedlings during establishment

The effects of cold-induced photoinhibition on chlorophyll and carotenoid dynamics and xanthophyll cycling in Eucalyptus nitens (Deane and Maiden) Maiden were assessed between planting and 32 weeks after planting. The seedlings were fertilised or nutrient-deprived (non-fertilised) before planting and shaded or not shaded after planting. The experimental site was 700 m a.s.l., which is considered marginal for establishment of E. nitens plantations in Tasmania due to low mean annual minimum temperatures. Low temperature - high light conditions caused a reduction in variable to maximal chlorophyll fluorescence ratio (Fv/Fm), which was more pronounced in non-fertilised than in fertilised seedlings. Shadecloth shelters alleviated this depression. Except in shaded fertilised seedlings, Fv/Fm did not recover to the level before planting until after 20 weeks. Total chlorophyll content was initially reduced in shaded treatments but subsequently increased with increasing temperatures and Fv/Fm. Total xanthophyll content and xanthophylls per unit chlorophyll remained relatively constant in fertilised seedlings but decreased in non-fertilised seedlings within 2 weeks after planting. Total xanthophyll and xanthophylls per unit chlorophyll subsequently recovered in non-shaded, non-fertilised seedlings with increasing temperatures and Fv/Fm. Diurnal [yield and non-photochemical quenching (NPQ] and seasonal (Fv/Fm) variation in chlorophyll fluorescence parameters were not reflected in xanthophyll cycling during the period of most severe photoinhibition. This result may indicate that chlorophyll - xanthophylls protein complexes form in winter-acclimated E. nitens foliage as have been demonstrated to occur in Eucalyptus pauciflora Sieb. ex Spreng.