ON THE RELATIONSHIP BETWEEN NUTRIENT USE EFFICIENCY AND FERTILITY IN FOREST ECOSYSTEMS

The concept of nutrient use efficiency is central in understanding eco system functioning because it is the step in which plants call influen ce the return of the nutrients to the soil pool and the quality of the litter. There are several ways to define nutrient use efficiency, but a common way within ecosystem ecology is as the ratio of litterfall p roduction per unit nutrient to the litterfall nutrient content. Howeve r, this ratio is not a valid measurement to examine nutrient use effic iency in relationship to ecosystem fertility because there is a strong autocorrelation between litterfall dry mass per unit of nutrient and the amount of nutrients. More appropriate statistical analysis of the relationship between the fertility of ecosystems and the amount of nut rients in the litterfall are inconclusive, but indicate that, at least in some cases, there is (1) no pattern, (2) higher nutrient use effic iency at intermediate-fertility sites or (3) higher efficiency at high er-fertility sites. There is, however, no indication that nutrient use efficiency is greater in nutrient-poor ecosystems. This conclusion ha s important consequences for ecosystem nutrient cycling. Given the lac k of a clear? consistent relationship between site fertility and litte rfall nutrients, there is little likelihood that such a feedback mecha nism plays an important role in ecosystem nut-lent cycling.