Fungal And Bacterial Relative Contributuions To Soil N₂O Production Processesas Affected By Soil Water Contents And Organic Carbon Sources For A Plantation Of Cunninghamia Lanceolata In Mid-subtropical China

The study that combining the substrate induced respiration inhibition method and depression15N isotope tracer method has been carry out to explore the rule of N2O release from the soil of Cunninghamia lanceolata plantation in humid subtropical and main influencing factors of it, in addition to research the possible N cycle pathway and dominating microbe species to better understand soil N2O emissions from forest of the area and provide some theory accumulation. The major resulits are summarized as follows:l)Soil water content is an important factor that affect soil N2O emission. When soil water content is lower than the saturated moisture content, the N2O fluxs are positively correlation to soil water content.2)Soil water content is an important factor that affect soil fungal growth. Lower water content or relatively aerobic conditions are more suitable for fungal growth.3)The study used substrate induced respiration inhibition method (SIRIN) to estimate soil fungi and bacterial biomass proportion, the results show that, the fungi:bacteria biomass proportion ratio is0.86-0.91, fungi biomass comparable with bacteria biomass.4)The results show that, the contribution ratio of fungi and bacteria to soil N2O fluxs is0.92-1.30, it shows that fungi has great potential contribution on the soil N2O emission.5) The results of15N isotope tracer study shows that denitrification is the main source of soil N2O both under60%WHC and90%WHC, followed by heterotrophic nitrification and autotrophic nitrification contribute least to soil N2O emission, less than<10%.6)The N2O that root in15NO3--N is mainly composed of two types of molecules,46[N2O] and45[N2O]. the higher the water content, a higher percentage of45[N2O] are find in90%WHC trement and45[N2O] mainly comes from the "Co-denitrification" of fungi. It is an important phenomenon as co-denitrification might lead to a huge N2O estimates.7) The study shows that, the types of organic carbon influence soil microbial metabolism, thus affecting N2O and CO2emissions. Citrate promotes CO2emissions in the soil, and has the possible inhibitory effect on N2O emission.Under the condition of60% WHC, the soil that add formate has a greater N2O emissions than add glucose, while under the condition of90%WHC, add glucose lead to a greater N2O emissions than add formate, the amount of CO2is less than add formate meanwhile.