The growth of three podocarp species under different nutrient regimes

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Abstract
An experiment was carried out to examine the growth of rimu (Dacrydium cupressinum Lamb.), kahikatea (Dacrycarpus dacrydioides (A. Rich.) DeLaub.), and totara (Podocarpus totara G. Benn. ex Don) at six levels of nutrient supply. The aim of this study was to identify species differences in growth response to nutrition. The nutrient treatments consisted of six, balanced nutrient solutions in which all macronutrients remained in constant proportion, but absolute levels varied. The solutions, referred to by their N concentration, ranged from a treatment nearly devoid of nutrients (10 ppm N) to one equivalent to rich potting soil (600 ppm N). Significant growth responses to nutrition occurred in all species. Nutrient treatment significantly affected net photosynthetic rate and allocation of carbon to leaves. All three species achieved maximum growth in the most nutrient-rich treatment (600 ppm N). In the lowest nutrient treatment (10 ppm N), the growth of all three species was very slow, and there were only small differences between species. With increasing nutrient supply, totara and kahikatea responded more rapidly than rimu. However, rimu absorbed more N and P per unit of root weight, and also contained a higher whole-plant concentration of these elements. It is suggested that those attributes enable rimu to compete on infertile sites.

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