The Regulation Of Algae Crusts On Soil Nitrogen Gross Transformation Rates And N₂O Fluxes Under Global Warming In Mid-subtropical China

The soil covered by algae crusts and bare soil of young Cunninghamia lanceolata plantation in mid-subtropical region were collected intactly from the top soil of 0-5 cm depth.A short-term lab simulation experiment of warming and illuminance using 15N-labeling method was conducted to explore the response of nitrogen transformation rates and N2O fluxes to warming(22? and 26 ?),algae crusts and light.The major conclusions as following:(1)Warming promoted the soil gross mineralization rates and gross nitrification rates.The soil gross mineralization rates were negatively correlated with mineral nitrogen,especially significantly and negatively correlated with mineral nitrogen of the soil covered by algae crusts between warming and non-warming treatments.The soil gross mineralization rates and gross nitrification rates respectely showed positive correlation to organic matter and SOC and showed significantly positive correlation to that in the soil covered by algae crusts.There was a significant relationships between soil gross mineralization rates and NAG activity.Soil nitrification rates were significantly positively correlated with abundance of amoA genes and gross mineralization rates.Which purports that warming increased the total mineralization rates and total nitrification rates by decreasing soil mineral nitrogen,increasing the organic matter,NAG activity,SOC,amoA gene abundance and total mineralization rates.(2)Algae crusts increased the soil gross mineralization rates,while decreased the soil gross nitrification rates of control treatment obviously.Soil gross mineralization rates has a significant and positive linear correlation with organic matter in the soil below algae crusts and bare soil of warming treatment.Algae crusts notably reduced soil gross nitrification rates.Soil gross nitrification rates increase was positively correlated with organic matter,pH and negativeliy correlated with DOC in the soil with and whithout algae crusts,indicating that the algae crusts could not provide energy,substrate and suitable living environment for the reproduction of soil nitrifying microorganisms.(3)The soil NH4+-N immobilization rates of warming and the soil covered by algae crusts were respectively lower than that of control treatment and bare soil.However,the results from the effects of warming and algae crusts on NO3--N immobilization rates were inconsistent with that of NH4+-N immobilization rates:warming increased NO3--N immobilization rates,while algae crusts decreased.Between warming and non-warming treatment,NO3--N immobilization rates correlated remarkably positively with soil gross nitrification rates,meanwhile NO3--N immobilization rates correlated remarkably positively with C/N between the soil covered by algae crusts and bare soil,which suggests that increasing soil nitrification rates and C/N could increased the NO3--N immobilization rates.(4)Warming enhanced soil inorganic nitrogen fixation capacity because of lower decreased NH4+-N immobilization rates than increased NO3--N immobilization rates.on the contrary,algae crusts weaken nitrogen retention capacity.However,because of the ecological functions of algae crusts and the unique climate characteristics of subtropics,warming increases the potential risk of soil inorganic nitrogen leaching,while algae crusts reduce.(5)Overall,warming inhibited N2O fluxes but not significantly;Algal crusts significantly inhibited the fluxes of N2O,and N2O mean fluxes caused by alternation of dark and light showed positively correlated with NO3--N,SOC,C/N and pH.Light has a great impact on N2O fluxes;algae crusts inhibited N20 fluxes by carrying on photosynthesis in light,while when photosynthesis were weaken and even stopped in dark,N2O fluxes were improved.(6)N2O from NO3--N mainly consists of two types of homozygous 46[N2O]and heterozygous 45[N2O]molecules.In this experiment although the molecular of heterozygous 45[N2O]accounted for the smaller proportion,the contribution to the denitrification cannot be ignored.