Canopy processing of N deposition increases short‐term leaf N uptake and photosynthesis, but not long‐term N retention for aspen seedlings. Issue 5 (3rd December 2020)

• Record Type: Journal Article
• Authors: Wang, Xin; Wang, Bin; Wang, Chengzhang; Wang, Zhenhua; Li, Jing; Jia, Zhou; Yang, Sen; Li, Ping; Wu, Yuntao; Pan, Shengnan; Liu, Lingli
• Is Part Of: New phytologist. Volume 229:Issue 5(2021)
• Page Start: 2601
• Page End: 2610
• Publication Date: 2020-12-03
• Subjects: 15N labeling -- canopy nitrogen uptake -- leaf photosynthesis -- nitrogen allocation -- nitrogen deposition -- soil nitrogen addition -- stable isotope; Botany -- Periodicals; 580
• DOI: 10.1111/nph.17041
• Languages: English
• ISSNs: 0028-646X

Abstract

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