Nitrogen isotopic signatures and fluxes of N2O in response to land-use change on naturally occurring saline–alkaline soil

Abstract

The conversion of natural grassland to semi-natural or artificial ecosystems is a large-scale land-use change (LUC) commonly occurring to saline–alkaline land. Conversion of natural to artificial ecosystems, with addition of anthropogenic nitrogen (N) fertilizer, influences N availability in the soil that may result in higher N₂O emission along with depletion of ¹⁵N, while converting from natural to semi-natural the influence may be small. So, this study assesses the impact of LUC on N₂O emission and ¹⁵N in N₂O emitted from naturally occurring saline–alkaline soil when changing from natural grassland (Phragmites australis) to semi-natural [Tamarix chinensis (Tamarix)] and to cropland (Gossypium spp.). The grassland and Tamarix ecosystems were not subject to any management practice, while the cropland received fertilizer and irrigation. Overall, median N₂O flux was significantly different among the ecosystems with the highest from the cropland (25.3 N₂O-N µg m⁻² h⁻¹), intermediate (8.2 N₂O-N µg m⁻² h⁻¹) from the Tamarix and the lowest (4.0 N₂O-N µg m⁻² h⁻¹) from the grassland ecosystem. The ¹⁵N isotopic signatures in N₂O emitted from the soil were also significantly affected by the LUC with more depleted from cropland (− 25.3 ‰) and less depleted from grassland (− 0.18 ‰). Our results suggested that the conversion of native saline–alkaline grassland with low N to Tamarix or cropland is likely to result in increased soil N₂O emission and also contributes significantly to the depletion of the ¹⁵N in atmospheric N₂O, and the contribution of anthropogenic N addition was found more significant than any other processes.