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

• DOI: 10.1111/nph.17041
• Publication Date: 2020-10-28T16:05:38Z
• Authors: Xin Wang; Bin Wang; Chengzhang Wang; Zhenhua Wang; Jing Li; Zhou Jia; Sen Yang; Ping Li; Yuntao Wu; Shengnan Pan; Lingli Liu
• Keywords: 550; Nitrogen; Ecology and Evolutionary Biology; Plant Sciences; Agriculture; Genetics and Genomics; nitrogen allocation; Forests; 15. Life on land; 01 natural sciences; nitrogen deposition; Plant Leaves; leaf photosynthesis; soil nitrogen addition; Seedlings; stable isotope; Photosynthesis; canopy nitrogen uptake; Forest Sciences; 15N labeling; 0105 earth and related environmental sciences

Summary

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 (15NH4)2SO4 solution to aspen sapling canopies or directly to the soil. We found that 15N‐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 15N 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.