Relationship of forest productivity to nutrient and carbon supply-a modeling analysis.

Abstract

A simple model of photosynthetic and nutritional controls over foliar dynamics is analyzed to compare the magnitude of the growth response of forest stands to increased rates of photosynthesis and nutrient supply. According to the model, productivity achieved at canopy closure is sensitive to nutrient supply, except where nutrient availability exceeds the plants' uptake capacity. Plants growing under nutrient-limited conditions can only respond positively to enhanced photosynthetic rates if they simultaneously increase their nutrient uptake, or reduce nutrient concentrations in stem, branch, root or senescing leaf tissue, or shift their carbon allocation in favor of biomass components with low nutrient concentrations. In particular, a response is more likely where considerable internal cycling of nitrogen occurs before leaf senescence, or where foliar allocation decreases with decreasing leaf nutrient concentration.