1、Soil N2 and N2O emission from two temperate forests1Galloway et al 2004Global terrestrial N deposition BackgroundYear1860Natural processesFood production1990sNatural processesFood productionEnergy productionFossil fuel and biomass combustionUnit:mg N m-2 yr-12050(200 Tg N yr-1)Natural processesFood
2、productionEnergy productionFossil fuel and biomass combustion2BackgroundChina N deposition increasing Decadal average N deposition and change rate Spatial pattern of reduced and oxidized N deposition rate in China during the 1960s(a,b)and 2000s(c,d)1960s2000s Lu and Tian Atmospheric Environ.,2014 3B
3、ackgroundThe relative importance of storage versus denitrification production of N2 is arguably the largest uncertainty that exists for nitrogen budgets at most any scale(Galloway et al.,2004)Plant uptakeGas loss(N2,N2O,NOx,NH3)LeachingMicrobialuptake4(Fang et al.,2013)Where to go?N2O0.1 to 2 N20.1
4、to 2 Denitrification0.2 to 4 From Schlesinger,2009.PNASUnit:kg N ha-1 yr-15BackgroundN2O/(N2+N2O)ratio approachMethodsMethodsDenitrification Denitrification(kg N(kg N haha-1-1yr-yr-1 1Proportion Proportion of totalof total N N loss(%)loss(%)N N2 2 to to N N2 2O O ratioratioRef.Ref.Hawaii tropical fo
5、rests(5 forests)TDN-15N2 to 92 to 924 to 5324 to 53 3Houlton et al.,2006.PNASGlobal natural terrestrial ecosystemsSoil 15N3333Houlton and Bai,2009.PNASSouthern China and central Japan(6 forests)Nitrate 15N and 17O6 to6 to 30 3048 to 8648 to 864-190Fang et al.,2015.PNASPuerto Rico tropical forests15N
6、 tracer3.3 to 7.43.3 to 7.416 to 9516 to 955.4-48Yang et al.,2014 SBBDenitrification N emission underestimatedBackground6From Schlesinger,2009.PNAS7BackgroundN2O/(N2+N2O)ratio approachQuestion 1 N2 and N2O emissionSoil water content in the field?8Experiment SiteLat.4151 N,Long.12454 E,Alt.500 a.s.l.
7、MAP:811 mm;MAT:4.7 oCQingyuan Station(QY)Liaoning Province,Northeast China9larch forest,coniferousmixed forest,conifer and broadleaved 10Experiment SiteForesttypeSoil layer(cm)Soil bulk density (g cm-3)Water content (gH2O g-1 dry soil)pHTotal C(%)Total N(%)Mix forest0-100.620.475.95.00.4410-200.870.
8、335.82.10.2320-401.20.265.71.00.12Larch forest0-100.90.295.42.40.2310-201.20.246.01.00.1120-401.110.246.10.70.07Treatments:three natural water gradients,along a slopeTracer amounts:2.5 g 15N.m-2(Na15NO3 99.23 15N atom%),10 mm precipitation Chamber:30 cm x 30 cm x 20 cmDry Dry-Wet Wet Experiment desi
9、gn 1N=5N=4N=311FieldField 15 15N labellingN labelling156432Gas sampling time:0,4,7,24,30 hExperiment design 112Soil Soil layer(cm)layer(cm)soil moisture soil moisture(%,(%,water/fresh water/fresh soil)soil)NHNH4 4+(mg N/kg)mg N/kg)NONO3 3-(mg(mg N/kg)N/kg)Before incubation Dry0-20312.13.0Dry-wet 0-2
10、0555.92.4Wet0-20637.12.2After incubation of 30 hDry0-2037372.1 18.7Dry-wet 0-2060603.0 27.4Wet0-2070708.5 27.5Results 13Results15N2 and 15N2O emission rate140.20.08 Results15N2O/(15N2 +15N2O)ratio15At a forest ecosystem levelAreaArea(%)(%)N N2 2 (g/mg/m2 2.h).h)N N2 2O O(g/mg/m2 2.h).h)N N2 2O/(NO/(
11、N2 2+N+N2 2O)O)(%)(%)Dry80731920Dry-wet15587498Wet514741098Total100220220282811Soils under natural or recovering vegetation:49.5%(Schlesinger,2009 PANS)Results16u Co-denitrification15NO2-+14N compounds(e.g.,azide,ammonium NH4+,salicylhydroxamic acid,and hydroxylamine 45N2O 29N2u AnammoxAnammox (Anae
12、robic ammonia oxidationAnaerobic ammonia oxidation)14NH4+15NO2-29N2u Denitrification15NO3-+14NO3-29N215NO3-+15NO3-30N217Question 2Is anammox important in forest soil N2 production?18 Important in marine system and river sediments,and considerable in some wetland and paddy soils.No report for forest
13、soils,although forests cover 37%of the land.We expected that anammox exists in forest soils,due to the nature of coexistence of NH4+and NO3-,oxic and anoxic conditions.Anammox19larch forest,coniferousmixed forest,conifer and broadleaved Experiment design 2Qingyuan Station 0-10 cmSoil:10-20cm 20-40cm
14、20Laboratory 15N labellingExperiment design 2Procedures:Procedures:4g fresh soil to 20 mL VialsVacuum and flush with purity high N2(Pre-incubated in dark at 21 oC overnight)Add 15NO3-tracer solution (100 ug15N g fresh soil)Gas sampling after 24 hours Treatments:headspace N2 100%WFPS air：60%WFPS 100%
15、WFPS2129N230N229N229N2anammoxCo-denitrificationdenitrificationdenitrification29N2 production30N2 production15NO3-labellingFn=15NO3-/(14NO3-+15NO3-)Headspace,ultrapure N2ResultsMixed forestLarch forest23Mixed,60%of WFPSMixed,100%of WFPSLarch,60%of WFPSLarch,100%of WFPSHeadspace,airResults24ResultsAna
16、mmox and co-denitrification combined accounted for 2.6 to 13.5%of total N2 production over the entire 40 cm soil profile25Procedure:4 g fresh soil to 20 mL vialsVacuum and flush with ultrapure with ultrapure N N2 2 (Pre-incubated in dark at 21 oC overnight)Add different different 1515N tracer soluti
17、onN tracer solution(100 ug15N g fresh soil)(15NO3-,15NH4+,15NO2-)Gas sampling after 0,5,10,24 hours for isotope analysisCo-denitrification?(in the mixed forest)2630N2 production29N230N229N229N2anammoxCo-denitrificationdenitrificationdenitrification29N2 production15NO3-labelling15NH4+labelling27Fn=15
18、NO3-/(14NO3-+15NO3-)Results2829N2Results2929N2Results3029N2Results3129N2Co-denitrification,larger than anammox!32Anammox:2%of the total N2 production(in the 0-10 cm soil layer in the mixed forest)ResultsFunctional hzsB gene is under detected limitationanammox 16S rRNA genes10-20 cm soil layer0-10 cm soil layer33N2 2O accounted for about 10%of total N2 2O and N2 2 production,being much less than the mean of the literature for natural terrestrial soil(about 50%).ConclusionAnammox exists in the study forest soils,but is of minor importance in N2 2 production(2%).34
