Nitrite transformations under acidic conditions in temperate and subtropical forest ecosystems

Publication date: 1 May 2018
Source:Geoderma, Volume 317
Author(s): Fan Yang, Shenyan Dai, Jinbo Zhang, Christoph Müller, Zucong Cai
Nitrite (NO2 ⁻) is an intermediate in a number of soil N transformations, and is a precursor for NO and N2O emissions. Due to the transient nature of NO2 ⁻ it is often neglected in N cycling research. Thus, the full suite of production and consumption pathways of NO2 ⁻ in terrestrial ecosystems is poorly understood. The primary objectives of this study were to clarify the production and consumption pathways of NO2 ⁻ in the acidic forest soils and compare the NO2 ⁻ dynamics between temperate and subtropical forest soils. A series of ¹⁵N tracing studies were performed, where ¹⁵N was added as NH4 ⁺, NO3 ⁻, or NO2 ⁻ to temperate and subtropical forest soils, and NO2 ⁻ transformations were investigated in these acidic forest soils. The results showed that the average NO2 ⁻ production rates ranged from 4.42 to 5.90mgkg⁻¹d⁻¹ and from 1.29 to 2.77mgkg⁻¹d⁻¹ in the temperate and subtropical forest soils, respectively, within the 1–6h incubations. Oxidation of soil organic N was the dominant NO2 ⁻ production pathway in the acidic forest soils, which was negatively related to soil pH (p<0.01). The average consumption rates of NO2 ⁻ varied during the incubation period from 12.46 to 14.10mgkg⁻¹d⁻¹ and from 5.84 to 6.74mgkg⁻¹d⁻¹ in the temperate and subtropical forest soils, respectively. The NO3 ⁻ pool recovered 6–44% of added ¹⁵N-NO2 ⁻ in the studied forest soils, which was positively related to soil pH (p<0.05). The 32–36% of added ¹⁵N-NO2 ⁻ was incorporated into insoluble soil organic N pool (SON) associated with soil organic C concentration. Nitrite incorporation into DON was also important for soil N retention in the subtropical strongly acidic forest soils (pH4.7), however, in the temperate acidic forest soils, ¹⁵N was not detected in the DON pool. Self-decomposition of NO2 ⁻ to NO and NO2 was a main pathway under subtropical strongly acidic conditions. The NO2 ⁻ turnover was most likely the key driving force for N transformations in the acidic forest soils. Further work regarding the dynamics of NO2 ⁻ and their mechanisms in soils of the different terrestrial ecosystems is important to gain an improved understanding of the global N cycle.