Relationship between nitrogen resorption and leaf size in the aroid vine Rhodospatha oblongata (Araceae)

Abstract

Nitrogen resorption (NR) from senescing leaves enhances nutrient conservation in plants. Leaf area in lianescent aroid vines increases dramatically as the plant ascends vertically on its host. In Rhodospatha oblongata Schott, the largest leaves have up to 35 times the area and 50 times the N content of the smallest. We hypothesised that despite the costs of reallocating nitrogen within the plant, the huge increase in nitrogen cost to produce larger new leaves in R. oblongata should lead to increased NR from large leaves, mitigating the high demands on N acquisition from primary sources. The amount of veins available per unit leaf area may however constrain the ability to reutilise nitrogen within the plant. It was found that N concentration was 2–3% in green and 1–2% in senescent leaves, independent of leaf area, whereas vein density increased with leaf area. N use efficiency, resorption efficiency, and proficiency were not affected by leaf area; however, results indicate that R. oblongata does not have a conservative use of N despite occurring in oligotrophic soils. The absence of increased N resorption indicates that R. oblongata may have the capacity to acquire large amounts of soil and aerial N to produce new larger leaves, which after leaf fall may positively affect litter decomposition.