Experimental approaches to the study of the effects of nutrients and water on carbon assimilation by trees.

This paper outlines the experiemental approaches needed to provide detailed information about the effects of nutrients and water on carbon assimilation, and hence growth of trees. Data from a large multidisciplinary experiment being conducted in Australia illustrate important aspects of the approach advocated. The system model consists of a series of submodels describing the main physiological processes considered to govern the growth of trees. It is argued that field experiments designed to investigate physiological processes and their interactions should involve treatments that cause large differences in the growth rates of trees and in the condition of the trees at any time. The biomass of experimental stands should be defined. Measurements of stem and leaf growth, litterfall, leaf photosynthetic characteristics, plant water status and soil water content, plant nutrient status and nutrient mineralization rates in the soil provide the information needed to explain observed differences in growth and to refine the models underlying the research.