Forest canopy nitrogen uptake can supply entire foliar demand

作者：Daniele Ferraretto, Richard Nair, Nadeem Shah, David Reay, Maurizio Mencuccini, Michael Spencer, Kate V. Heal · 发表于：Functional Ecology · 年份：2022 · DOI：10.1111/1365-2435.14005 · 被引用次数：35 · 研究领域：Soil Carbon and Nitrogen Dynamics、Plant Water Relations and Carbon Dynamics、Plant responses to elevated CO2

Abstract Plant canopies intercept, process and potentially assimilate atmospheric nitrogen (N) additions, but the forest‐scale effects of canopy processes on N cycling and plant nutrition are not clear. Substantial method artefacts and scaling issues exist in previous experimental studies which measure relevant N fluxes either at (a) natural abundance, (b) via a 15 N tracer or (c) by incorporation of additional 15 N into measured biomass, meaning these processes are often overlooked or discounted. Here, working in a mature Sitka spruce plantation and under ambient conditions, we used all three of these methods independently at stand, tree and branch scale to assess the effects of canopy interception on capture, assimilation and incorporation of inorganic N deposition by canopy biomass. We consistently found that above 70% of N deposition was unaccounted for (i.e. assimilated, processed beyond detectability, volatilised or retained) when passing through the canopy, independent of the assessment method. Using short‐term 15 N tracers, we found that this unaccounted N was retained in canopy tissues. Apparent uptake from monitoring of ecohydrological fluxes was sustained and consistent, suggesting that the tree canopies were a sink for N deposition. Seasonal variation in recovery also suggested biological activities influenced fluxes and transformations of this ion within the canopy. The total amount of this canopy N uptake was greater than the mean annual N in litterfall, implyin...