Nitrogen-Induced Changes in Soil Environmental Factors Are More Important Than Nitrification and Denitrification Gene Abundance in Regulating N2O Emissions in Subtropical Forest Soils

Qingyan Qiu; Abubakari Said Mgelwa; Shaofei Jin; Yalin Hu

doi:10.3389/fpls.2022.950367

Nitrogen-Induced Changes in Soil Environmental Factors Are More Important Than Nitrification and Denitrification Gene Abundance in Regulating N₂O Emissions in Subtropical Forest Soils

Front Plant Sci. 2022 Jul 12:13:950367. doi: 10.3389/fpls.2022.950367. eCollection 2022.

Authors

Qingyan Qiu¹, Abubakari Said Mgelwa², Shaofei Jin³, Yalin Hu¹

Affiliations

¹ Forest Ecology and Stable Isotope Center, College of Forestry, Fujian Agriculture and Forestry University, Fuzhou, China.
² College of Natural Resources Management and Tourism, Mwalimu Julius K. Nyerere University of Agriculture and Technology, Musoma, Tanzania.
³ Department of Geography, Minjiang University, Fuzhou, China.

Abstract

Subtropical regions are currently experiencing a dramatic increase in nitrogen (N) deposition; however, the contributions of nitrification and denitrification processes to soil N₂O emissions and the underlying mechanisms under increasing N deposition remain unclear. Therefore, a ¹⁵N-tracing laboratory experiment with four N application rates (0, 12.5, 25, and 50 μg ¹⁵N g^-1 soil) was conducted to investigate the response of nitrification- and denitrification-derived N₂O to N additions in an evergreen broad-leaved forest (BF) and a Pinus forest (PF) in the Wuyi Mountains in southeastern China. Moreover, the abundance of functional genes related to nitrification (amoA), denitrification (nirK, nirS, and nosZ), and soil properties were measured to clarify the underlying mechanisms. Results showed that nitrification-derived N₂O emissions were generally decreased with increasing N input. However, denitrification-derived N₂O emissions were a non-linear response to N additions, with maximum N₂O emissions at the middle N application rate. Denitrification-derived N₂O was the dominant pathway of N₂O production, accounting for 64 to 100% of the total N₂O fluxes. Soil NH₄ ⁺-N content and pH were the predominant factors in regulating nitrification-derived N₂O emissions in BF and PF, respectively. Soil pH and the nirS abundance contributed the most to the variations of denitrification-derived N₂O emissions in BF and PF, respectively. Our results suggest that N application has the potential to increase the contribution of denitrification to N₂O production in subtropical forest soils. Changes in soil chemical properties induced by N addition are more important than the abundance of nitrification and denitrification functional genes in regulating soil nitrification- and denitrification-derived N₂O emissions.

Keywords: N application; N2O emissions; denitrification; microbial functional genes; nitrification.