Variation in nitrogen-use efficiency among and within subarctic graminoids and herbs

Abstract

• This study addresses the question of whether a trade-off between the annual nitrogen (N) productivity (aNP) and the mean residence time (MRT), an index of N conservation, occurs both among and within species. We hypothesized that a trade-off between aNP and MRT observed among species might not hold within species. • Seven perennial graminoids and herbs (including one evergreen) were subjected to two fertilizer concentrations and light intensities. The effect of these treatments was examined on plant traits determining aNP and MRT. • Except for the evergreen Tofieldia pusilla, fertilization had an overriding effect on most variables related to the species' nitrogen use and the response to fertilization among and within species closely matched. By contrast, shade had minor effects on plant nitrogen use. Across all species, aNP varied inversely with MRT, but within species aNP and MRT were not related. • We suggest that there might not be a trade-off between aNP and MRT within species because small intraspecific changes in leaf life span may not involve significant consequences for leaf morphology, photosynthesis and growth.