4.6 Article

Canopy processing of N deposition increases short-term leaf N uptake and photosynthesis, but not long-term N retention for aspen seedlings

Journal

NEW PHYTOLOGIST
Volume 229, Issue 5, Pages 2601-2610

Publisher

WILEY
DOI: 10.1111/nph.17041

Keywords

N-15 labeling; canopy nitrogen uptake; leaf photosynthesis; nitrogen allocation; nitrogen deposition; soil nitrogen addition; stable isotope

Categories

Funding

  1. National Natural Science Foundation of China [31670478, 31600389, 31988102, 31522011]
  2. Youth Innovation Promotion Association of the Chinese Academy of Science [2020082]
  3. Strategic Priority Research Program of the Chinese Academy of Science [XDA23080301]

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The processing of nitrogen in forest canopies can impact short-term leaf nitrogen supply and photosynthesis, but not long-term nitrogen retention. There were no significant differences in plant biomass, nitrogen concentration, and leaf nitrogen resorption between canopy and soil nitrogen applications. This highlights the importance of considering canopy nitrogen processing for accurately predicting the impact of nitrogen deposition.
Forest canopies can retain nitrogen (N) from atmospheric deposition. However, most empirical and modeling studies do not consider the processing of the N deposited in the canopy. To assess whether N deposition through canopy will alter the plant's N uptake and retention, we conducted a 3-yr mesocosm experiment by applying ((NH4)-N-15)(2)SO4 solution to aspen sapling canopies or directly to the soil. We found that N-15-NH4+ applied to the canopy was directly taken up by leaves. Compared with the soil N application, the canopy N application resulted in higher photosynthesis but lower N retention of the plant-soil system in the first growing season. Plant biomass, N concentration, and leaf N resorption were not significantly different between the canopy and soil N applications. The partitioning of retained N-15 among plant components and soil layers was similar between the two treatments 3 yr after the N application. Our findings indicated that the canopy N processing could alter leaf N supply and photosynthesis in the short term but not N retention in the long term. Under natural conditions, the chronic N deposition could continuously refill the canopy N pool, causing a sustained increase in canopy carbon uptake. Canopy N processing needs to be considered for accurately predicting the impact of N deposition.

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