Net N2O production from soil particle size fractions and its response to changing temperature.

Previous studies demonstrated that finer soil particles have smaller rates of CO2 emission but larger Q10 values (the proportionate increase in the rate for a warming of 10 °C) than coarser particles. However, it has not been tested whether there is a regular pattern for rates and Q10 for N2O emission (net production) across soil particle size fractions, considering the known positive correlation between soil CO2 and N2O emissions. A short-term incubation study with different soil particle fractions was conducted for soils from a grassland, a forest, an upland (including organic manure (OM) and chemical nitrogen, phosphorus, and potassium fertilizers (NPK) treatments), and a paddy (including manure plus chemical fertilizer (MNPK) and NPK treatments) under a series of increasing and decreasing temperatures between 5 °C and 30 °C with 5 °C intervals. For all the soils, net N2O production per unit mass of soil N was smaller from the silt (2-50 μm) fraction than from the sand (>50 μm) and clay (<2 μm) fractions. In paddy soils, Q10 for net N2O production was highest from the clay fraction. In contrast, Q10 was highest in the sand fraction for the grassland soil. In the upland and paddy soils, the rates of net N2O production were higher in OM or MNPK treatment than in their corresponding NPK treatment, but Q10 values were similar between the manure and NPK treatments. The net N2O production rates positively correlated with CO2 emission across all soil samples, and this was also the case for their Q10 values. Q10 values for net N2O production averaged 8% lower than those for CO2 emissions. In conclusion, the net N2O production rates appear to be the smallest from the silt fraction.