The effect of reproduction on nitrogen use‐efficiency of three species of the carnivorous genus Pinguicula

Abstract

Summary Life history theory predicts that reproduction incurs costs in terms of future growth and survival. In infertile environments reproductive events may accelerate nutrient turnover such that losses of limiting nutrients cannot be replenished by uptake from the soil. We compared the effect of reproduction on nitrogen (N) turnover and N use‐efficiency, i.e. the annual dry matter produced per unit N lost, of three carnivorous species of the genus Pinguicula on an infertile subarctic heath. We hypothesized that reproduction should increase N turnover, unless a larger N pool or improved N resorption can compensate for the losses associated with reproduction. These carnivorous herbs showed a nitrogen use strategy similar to that of non‐carnivorous plants (herbs and grasses) with a relatively low mean residence time (MRT) of N and a large dry matter productivity per unit N in the plant (annual N productivity). N pool size and the efficiency of N resorption from senescent leaves were similar in reproductive and non‐reproductive individuals. Reproductive individuals had significantly larger annual N losses and thus a lower average MRT (0.8 vs. 1.8 years), with values < 1 indicating that the annual N losses are greater than the annual average N pool. Unless plants can enhance their nutrient acquisition, flowering may therefore impact on future growth and survival. This study presents evidence for a direct link between reproduction, reflected in a higher relative allocation to inflorescences, turnover and N use‐efficiency; the latter being reduced because of increased N turnover. The ranking of species in terms of reproductive allocation was the reverse of their ranking in terms of their N use‐efficiency.