1、Excluding carbonate in carbonaceous chondrite,the terrestrial range of d13C values exceed 100 46.1*102322COCOHCOpaK35.6*110323COHHHCOaaaK33.10210323HCOHCOaaaKpH02468101214log ai-8-7-6-5-4-3-26.3510.33H2CO3*HCO3-CO32-H+OH-Common pHrange in natureBjerrum plot showing the activities of inorganic carbon
2、 species as a function of pH for a value of total inorganic carbon of 10-3 mol L-1.In most natural waters,bicarbonate ion is the dominant charged carbonate species in the alkalinity definitionnIn equilibrium with atmospheric CO2,ClosedOpen13D=a+(b-a)Ci/Caa:Fractionation of diffusionb:Fractionation o
3、f RubiscoCi:Substomatal CO2Ca:Atmospheric CO2When Ci=0(not realistic for plants),13D=a,diffusion onlyWhen Ci=Ca(infinite conductance),13D=bFarquhar et al.(1982)Aust.J.Plant Physiol.9,121-1376.1)/1()()(aiaaiwiacPPPeegPPgEAGc:Conductance to diffusion of CO2Gw:Conductance to diffusion of H2O.In the air
4、,Gw/Gc=1.6:Difference in intercellular and atmospheric vapor pressure of water,ei-ea6.1)/1()1(aiaPPPwW is proportionate to Pi/Pa,which can be conveniently determined for large number of plants from analyses of carbon isotope ratiosKranz Anatomy,most common,but not required(Voznesenskaya et al.,Natur
5、e 414,543-546,2001)3-phosphoglyceric acid(PGA):a C3 compoundoxaloacetic Acid:a C4 compoundMost CAM plants have similar d13C values as C4 plants,but some CAM plants can switch to C3 pathway when conditions allowC4 plant:Zea Mays(corn),Poaceae,Gramineae of warm regions(by Peter v.Sengbusch)C4 plant:Sa
6、ccharum officinarum(sugar cane),Poaceae(by Peter v.Sengbusch)A salt marsh C4 plantsFarquhar,1983,Aust.J.Plant Physiol.9,121-137.C4 plants tend to occur in hot,intense sunlight ecosystemsDecreased carbon accumulationIncreased stomatal conductanceFrom Maherali et al.,2000 ESALeafCO2H2O200400pCO2Today:Closed Canopy200400pCO2LGM:Open CanopyGasp!Gasp!Most CAM plants have similar d13C values as C4 plants,but some CAM plants can switch to C3 pathway when conditions allowThese plants only use CAM pathway when under water stressReversed TCA cycleLess fractionation
