Effects of nitrogen sources and glucose on the con- sumption of ethylene and methane by temperate volcanic forest surface soils

There is limited knowledge with regard to the consumption of ethylene (C2H4) and methane (CH4) in volcanic forest soils containing low microbial carbon-to-organic carbon ratio, and to the responses of both consumptions to nitrogen and carbon additions. Temperate volcanic forest surface soils under three forest stands (e.g. Pinus sylvestris L., Cryptomeria japonica and Quercus serrata) were used to compare CH4 and C2H4 consumption by forest soils, and to study the effects of nitrogen sources and glucose on both consumptions. There was a good parallel between CH4 and C2H4 consumption by for- est soils, but mineralization reduced CH4 consumption rather than C2H4 consumption in forest soils, particularly in a Pinus forest soil. The stimulatory effect of glucose addition on both CH4 and C2H4 consumption by forest soils was increased by increasing the pre-incubation period after glucose addi- tion, and a largest stimulation occurred in the Pinus forest soil. The addition of KNO3-N at the rate of 100 μg·g1 significantly reduced the consumptions of both C2H4 and CH4 by forest soils (P≤0.05). In the presence of urea plus dicyandiamide, the consumption rates of C2H4 and CH4 by forest soils were higher than those in the KNO3-N and urea-N treated soils at the same N rate (P≤0.05), but were similar to those of the control. Hence, under experimental conditions, there was a strong inhibitory effect of NO3 rather than NH4+ addition on the CH4 and C2H4 consumption in these forest soils. When amount of the added NO3-N increased up to more than 2―3 times the soil initial NO3-N concentrations, both C2H4 and CH4 consumption rates were reduced to 10%―20% of the rates in soils without nitrate addition. By comparing the three forest stands, it was shown that there was a smallest effective concentration of the added nitrate that could inhibit C2H4 and CH4 consumption in the Pinus forest soil, which indicated that C2H4 and CH4 consumption of the soil was more sensitive to NO3-N addition.

Measurement of ethylene and methane production in a temperate forest soil using inhibition of acetylene and carbon monoxide

We studied in the laboratory the effects of acetylene (C2H2) concentrations on the accumulation and consumption of ethylene and methane in a temperate pine forest soil, and in situ ethylene and methane production and flush effects of nitrogen sources on both productions in the pine forest stand (Pinus sylvestris L.). The addition of C2H2 at concentrations more than 50 Pa C2H2 in the headspace caused a more than 95% reduction in rates of ethylene and methane consumption in forest soil compared to those with no C2H2. Furthermore, addition of acetylene within a range of 50 to 10, 000 Pa C2H2 induced a similar rate of methane accumulation in forest soil. Hence, it can be concluded that presence of more than 50 Pa C2H2 in the headspace is an effective method to measure methane production in forest soil. The addition of C2H2 at concentrations more than 50 Pa C2H2 induced an increasing concentration of ethylene in the headspace (P≤0.05), indicating the reduction of acetylene to ethylene in forest soil. Using inhibition of 0.5 kPa C2H2 in combination with 5 kPa carbon monoxide that inhibits the reduction of acetylene in a short term, it was observed that there was a larger in situ methane production rate (218 ± 26 μg C m-2 h-1 (μg C per square meter per hour, the same below)) than in situ ethylene produc-tion rate (92 ± 6 μg C m-2 h-1) in the pine forest soil. The addition of nitrogen sources such as urea, urea plus a nitrification inhibitor dicyandiamide, and potassium nitrate, could induce a 5-fold greater in-crease in rates of in situ ethylene and methane production compared to those in the control, particu-larly in the latter (P≤0.05). The results can promote in situ measurement of ethylene and methane production in forest soils at different sites.

Temperature effects on ethylene and methane production from temperate forest soils

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.