Foliar uptake of atmospheric nitrate by two dominant subalpine plants: insights from in situ triple-isotope analysis.

The significance of foliar uptake of nitrogen (N) compounds in natural conditions is not well understood, despite growing evidence of its importance to plant nutrition. In subalpine meadows, N-limitation fosters the dominance of specific subalpine plant species, which in turn ensures the provision of essential ecosystems services. Understanding how these plants absorb N and from which sources is important in predicting ecological consequences of increasing N deposition. Here, we investigate the sources of N to plants from subalpine meadows with distinct land-use history in the French Alps, using the triple isotopes (Δ O, δ O, and δ N) of plant tissue nitrate (NO ). We use this approach to evaluate the significance of foliar uptake of atmospheric NO (NO ). The foliar uptake of NO accounted for 4-16% of the leaf NO content, and contributed more to the leaf NO pool after peak biomass. Additionally, the gradual N enrichment of NO from the soil to the leaves reflected the contribution of NO assimilation to plants' metabolism. The present study confirms that foliar uptake is a potentially important pathway for NO into subalpine plants. This is of major significance as N emissions (and deposition) are predicted to increase globally in the future.