Growth and nutrient retranslocation in needles of radiata pine in relation to nitrogen supply

Abstract

The effects of N application on tree growth and the retranslocation of N, P, and K from young needles to new growth were examined in young radiata pine (Pinus radiata D. Don) trees.Nitrogen fertilization increased the number and size of needles, rates of shoot production, stem volume growth and tree biomass. Foliar N and P contents (μg per needle) fluctuated in a cyclic fashion with prominent phases of accumulation, retranslocation and replenishment. The patterns of these fluctuations in control and N-fertilized trees were similar, although the fluxes of N, P and K in and out of needles were increased by N fertilization. Greater translocation (g per tree) of N and K from needles of N fertilized trees occurred because fertilization increased the needle weight and the proportion of N and K retranslocated from individual needles. Nitrogen fertilization increased the retranslocation of P largely as a result of higher needle mass. Trees supplied with more than adequate amounts of P in the soil retranslocated up to 58 per cent of the initial pool of P from young needles. The periods of high retranslocation coincided with periods of high concentrations of soil mineral N and with shoot production. Conversely, the periods of rapid replenishment of N and P into the needles coincided with the time of slow shoot growth and low concentration of soil mineral N. The growth rate of trees, rather than the availability of nutrients in the soil was the main factor controlling retranslocation.For radiata pine, retranslocation from needles is not a mechanism specific for coping with low soil fertility. It seems to be a mechanism which enhances the nutrient supply to apical growing points, especially during periods of flushing. © 1987 Annals of Botany Company.