Ageing in Woody Plants

Abstract

The shoot systems of trees undergo characteristic changes with time, as they increase in size and complexity. Certain of these changes, such as reduced annual growth increment, loss of apical dominance, and changes in the geotropic responses, are easily reversible, by pruning or by grafting shoots from older trees on to young stocks. These changes are referred to as ‘ageing’. This paper describes the changes occurring in Pinus sylvestris and Larix leptolepis during ageing and reports an investigation into the possible mechanisms controlling these changes. Pruning experiments suggest that ageing is due to increased competition for nutrients between the various constituent shoots as the branch systems increase in complexity, but the distribution of available nutrients is modified by apical dominance. These conclusions were supported by the results of experiments involving the injection of radioactive phosphorus (²²P), in association with the pruning treatments.