Air warming and CO 2 enrichment cause more ammonia volatilization from rice paddies: An OTC field study.

Ammonia (NH ₃ ) volatilization in rice paddies may be affected by elevated atmospheric CO ₂ concentration ([CO ₂ ]) and temperature due to changes in plant and soil nitrogen (N) metabolism. At present, little is known about the individual and combined effects of CO ₂ enrichment and warming on NH ₃ volatilization under field conditions. An experiment was conducted in a rice paddy in Central China, after 4 years of warming and CO ₂ enrichment using open-top chamber (OTC) devices. Compared with ambient conditions, elevated [CO ₂ ] had no significant effects on NH ₃ volatilization, although increases in soil pH and urease activity were observed. The stimulation on plant N assimilation under CO ₂ enrichment might offset the possible enhancement on NH ₃ volatilization, as more soil N was absorbed by plant thus reducing NH ₃ loss potential. Elevated temperature increased NH ₃ volatilization significantly, which could be attributed to increased soil ammonium nitrogen (NH ₄ ⁺ -N) concentration, pH, and urease activity. Combination of CO ₂ enrichment and warming caused the highest cumulative NH ₃ loss, which increased by 26.5% compared with ambient conditions, but the interaction was not significant. Higher plant N uptake, soil NH ₄ ⁺ -N concentration, pH and urease activity were also observed with co-elevation of [CO ₂ ] and temperature, but the combined effects were variable and not synergistic. Our findings confirm that field warming and CO ₂ enrichment cause more NH ₃ volatilization in rice paddies, among which warming effects are dominant, and suggest that improved N management or field practices are required to reduce NH ₃ losses under future climate change.
Competing Interests: Declaration of competing interest The authors declare no competing financial interests.
(Copyright © 2020. Published by Elsevier B.V.)