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.