Effects of nitrogen sources and glucose on the consumption 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 forest 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 addition, and a largest stimulation occurred in the Pinus forest soil. The addition of KNO3-N at the rate of 100 mu g center dot g(-1) 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.