Maturation and related aspects in clonal forestry – Part II: reinvigoration, rejuvenation and juvenility maintenance

Several techniques have been developed for reinvigorating, rejuvenating or maintaining the juvenility of plants. None of these techniques is as effective as natural rejuvenation whereby the most mature plant parts, the reproductive organs, produce the most juvenile plant parts, the embryos, through gametogenesis and sexual reproduction. The most common criteria for identifying reinvigoration or rejuvenation are based on morphology, morphogenic capacity and the ability to produce cones or flowers. Doubts remain over whether true rejuvenation (reduced ontogenetic age) can be achieved by artificial methods such as serial vegetative propagation, or whether these methods merely provide reinvigoration (reduced physiological age) by temporarily removing environmental and physiological constraints to growth. Rejuvenation and reinvigoration are difficult to distinguish from each other but there is some evidence that artificial methods provide at least partial rejuvenation of plants. This review examines methods for delaying the maturation of juvenile plants and for reducing the ontogenetic or physiological age of more-mature plants. The review discusses theoretical and practical aspects of juvenility, rejuvenation and reinvigoration in clonal forestry, and identifies research areas in maturation that could lead to more-effective methods for establishing high-productivity plantations