Temperate forest surface soils at the varying distances from main trunks (e.g., Pinus koraiensis and Quercus mongolica) were used to study the effects of acetylene (C2H2) at low concentrations on nitrification, mineralization and microbial biomass N concentrations of the soils, and to assess the contribution of heterotrophic nitrification to nitrous oxide (N2O) emissions from soils. The use of acetylene at partial pressures within a range from 10 to 100 Pa C2H2 in headspace gas gave a significant decrease in N2O emission at soil moisture of c. 45% water-filled porosity space, and the decrease was almost the same in each soil after exposure of C2H2 at low concentrations. Heterotrophic nitrification could account for 21%―48% of total N2O emission from each soil; the contribution would increase with increasing distances from the Pinus koraiensis trunks rather than from the Quercus mongolica trunks. Under the experimental conditions, the use of C2H2 at low concentrations showed no significant influ- ence on soil microbial biomass N, net N mineralization and microbial respiration. However, 100 Pa C2H2 in headspace gas could reduce carbon dioxide (CO2) emissions from soils. According to the rapid consumption of 10 Pa C2H2 by forest soils and convenience for laboratory incubations, 50 Pa C2H2 in headspace gas can be used to study the origin of N2O emissions from forest soils under aerobic con- ditions and the key associated driving mechanisms. The N2O and CO2 emissions from the soils at the same distances from the Quercus mongolica trunks were larger than those from the Pinus koraiensis trunks, and both emissions decreased as the distances from trunks increased. The stepwise regression analysis showed that 95% of the variability in soil CO2 emissions could be accounted for by the concentrations of soil total C and water soluble organic C and soil pH, and that 72% of the variability in soil N2O emissions could be accounted for by the concentrations of soil total N, exchangeable NH+4-N and microbial biomass N and 25% of
Change in temperature affects the activity of soil microorganisms.However,there is limited knowledge about temperature effects on ethylene(C2H4) and methane(CH4) production from forest soils.Topsoil samples(0―5 cm) collected from different temperate forest stands(e.g.,Pinus sylvestris L.,Cryptomeria japonica,and Quercus serrata) were used to compare C2H4 and CH4 production from soils at temperature from 5 to 35℃ under oxic and anoxic conditions.The rates of C2H4 and CH4 production from soils under oxic conditions were measured by using inhibition of acetylene(C2H2) and carbon monoxide(CO).The consumption of C2H2 by soils at an initial concentration of c.250 Pa C2H2 was negligible at 5 and 15℃,but it was significantly increased at 25 and 35℃.The presence of 2 kPa CO in the headspace gases tended to decrease the consumption of C2H2 by soils at high temperature.The Q10 values for the soil C2H2 consumption ranged from 2.3 to 3.8,and there were no significant differences in Q10 values between these topsoil samples.The rate of CH4 production from each sample under oxic conditions was larger than the soil C2H4 production at 5―35℃,particularly at low temperature,and presented a smaller Q10 value.Ethylene production from soil after 1 week of anoxic incubation at 5―35℃ was larger than the soil CH4 production,and presented a larger Q10 value.However,CH4 produc-tion from Quercus serrata forest soil and its response to temperature increased significantly with in-cubation time.Long-term anoxic conditions of in situ upland forest soils are normally not prevalent,so it can be reasonably concluded that there is a larger C2H4 production rather than CH4 production under temperate forest stands due to heavy rainfall in summer.
