Influence Of Drying-wetting And Freezing-thawing Processes On Greenhouse Gases Fluxes From Temperate Forest Soils

Studies have shown that both drying-wetting and freezing-thawing processes haveprofound impacts on soil greenhouse gases (GHG) fluxes and transformation processes of soilcarbon and nitrogen. The current increasingly severe global climate change is expected toincrease the frequency of soil drying-wetting and freezing-thawing processes, which probablylead to great influences on Changbai Mountain areas due to its geographic location andclimate conditions. Whether those influences will significantly change the annual fluxes of theGHG and how they, which are brought about by climate change, feed back to the globalclimate are still unclear. Hence, it is particularly important and urgent for us to study soilGHG fluxes and transformation processes of soil carbon and nitrogen during drying-wettingand freezing-thawing and the mechanisms involved. This study will be beneficial to providescientific support for reasonably asssing the changing trends of regional soil carbonsequestration and GHG fluxes and for the buildup of related models.Packed soil-core incubation experiments were done to study1) the singular andinteractive effects of carbon (glucose,6.4g C m-2) and nitrogen (NH4Cl and KNO3,4.5g Nm-2) addition on soil GHG fluxes and soil properties from a mature broadleaf and Korean pinemixed forest (BKPF) and adjacent white birch forest (WBF) under two wetting intensities(55%and80%WFPS) duing drying-wetting and freezing-thawing processes;2) the mainmechanisms of soil GHG fluxes during drying-wetting and freezing-thawing processescombining with the varation of main soil properties. The results show that:1) With the exception of the WBF soils added with NH4Cl under a high wetting intensity,increased wetting intensity and addition of carbon(C) and nitrogen(N)could significantlyenhance N2O fluxes from both soils singly and interactively (P<0.05). There is a greatdifference between WBF and BKPF soils concerning the responses of N2O fluxes to differentwetting intensities and addition of carbon and nitrogen. Under the experimental conditions,N2O fluxes during drying-wetting process from both soils could be related to the wettingintensity, microbial biomass and available N pools of the soils. 2) Without carbon and nitrogen addition, compared with BKPF soils, CO2fluxes fromWBF soils are significantly higher and they decreased with the increasing wettingintensity (P<0.05). Glucose addition significantly increased CO2fluxes from both soilsand soil microbial biomass C (MBC), microbial biomass C:N ratio and microbialmetabolic quotient(qCO2)(P<0.05). Adding N with two types could significantly inhibitCO2fluxes from both soils during drying-wetting process. Under the experimentalconditions, CO2fluxes from the both forest soils during drying-wetting process wereprofoundly influenced by the soil MBC and negatively correlated to the soil available Npools.3) Increasing wetting intensity and addition of C and N could both significantly increasedN2O fluxes from both forest soils during freezing-thawing process(P<0.05). For the both soilsafter soil thawing process, the stimulation of glucose addition on N2O fluxes could besignificantly weakened with the increasing wetting intensity (P<0.05). Under theexperimental conditions, N2O flux from WBF soil during freezing-drying process wassignificantly influenced by soil pH and MBC; while for BKPF soils, it was only influencedby WFPS.4) With the increasing wetting intensity, CO2fluxes during freezing-thawing processwere significantly decreased for the WBF soil, but significantly increased for the BKPF soil（P<0.05）. Glucose addition could significantly increased CO2fluxes during freezing andthawing process from both soils（P<0.05）. Increasing wetting intensity and glucose additioncould interactively influence CO2fluxes during freezing-thawing process from both soils（P<0.05）. CO2fluxes from WBF soils during freezing-thawing process were significantlyinfluenced by soil MBC, MBN and K2SO4-extractable DON concentrations, and the fluxeswere influencd by K2SO4-extractable mineral N and DOC concentrations of the BKPFsoil.5) During freezing-thawing process, under the low wetting intensity conditions, the bothforest soils absorbed CH4. Adding C and N singually and combinedly could both inhibit theabsorption of CH4by the both forest soils, and the inhibition intensity in all treaments at twosoil wetting intensities was increased in the order of Glu <Glu+KNO3<KNO3<NH4Cl <Glu+NH4Cl. However, under a high wetting intensity, both soils alternately absorbed or emited CH4with small amount, with no significant differences among all the treatments.