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

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 N-15, while converting from natural to semi-natural the influence may be small. So, this study assesses the impact of LUC on N2O emission and N-15 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 mu g m(-2) h(-1)), intermediate (8.2 N2O-N mu g m(-2) h(-1)) from the Tamarix and the lowest (4.0 N2O-N mu g m(-2) h(-1)) from the grassland ecosystem. The N-15 isotopic signatures in N2O emitted from the soil were also significantly affected by the LUC with more depleted from cropland (- 25.3 parts per thousand) and less depleted from grassland (- 0.18 parts per thousand). 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 N-15 in atmospheric N2O, and the contribution of anthropogenic N addition was found more significant than any other processes.