Tree water uptake enhances nitrogen acquisition in a fertilized boreal forest – but not under nitrogen poor conditions

Henriksson, N., Lim, H., Marshall, J., Franklin, O. ORCID: https://orcid.org/0000-0002-0376-4140, McMurtrie, R.E., Lutter, R., Magh, R., Lundmark, T., & Näsholm, T. (2021). Tree water uptake enhances nitrogen acquisition in a fertilized boreal forest – but not under nitrogen poor conditions. New Phytologist 232 113-122. 10.1111/nph.17578.

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Abstract

Understanding how plant water uptake interacts with acquisition of soil nitrogen (N) and other nutrients is fundamental for predicting plant responses to a changing environment, but it is an area where models disagree. We present a novel isotopic labelling approach which reveals spatial patterns of water and N uptake, and their interaction, by trees. The stable isotopes 15 N and 2 H were applied to a small area of the forest floor in stands with high and low soil N availability. Uptake by surrounding trees was measured. The sensitivity of N acquisition to water uptake was quantified by statistical modelling. Trees in the high-N stand acquired twice as much 15 N as in the low-N stand and around half of their N uptake was dependent on water uptake (2 H enrichment). In contrast, in the low-N stand there was no positive effect of water uptake on N uptake. We conclude that tree N acquisition was only marginally dependent on water flux toward the root surface under low N conditions but under high-N conditions, the water-associated N uptake was substantial. The results suggest a fundamental shift in N acquisition strategy under high-N conditions.

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