Determination of respiration and photosynthesis fractionation factors for atmospheric dioxygen inferred from a vegetation–soil–atmosphere analogue of the terrestrial biosphere in closed chambers

[摘要] The isotopic composition of dioxygen in the atmosphere is a global tracerwhich depends on the biosphere flux of dioxygen toward and from theatmosphere (photosynthesis and respiration) as well as exchanges with thestratosphere. When measured in fossil air trapped in ice cores, the relativeconcentration of 16 O, 17 O, and 18 O of O 2 can be used forseveral applications such as ice core dating and past global productivityreconstruction. However, there are still uncertainties about the accuracy ofthese tracers as they depend on the integrated isotopic discrimination ofdifferent biological processes of dioxygen production and uptake, for whichwe currently have very few independent estimates. Here we determined therespiration and photosynthesis fractionation factors for atmosphericdioxygen from experiments carried out in a replicatedvegetation–soil–atmosphere analogue of the terrestrial biosphere in closedchambers with growing Festuca arundinacea . The values for 18 O discrimination during soilrespiration and dark respiration in leaves are equal to - 12.3 ± 1.7  ‰ and - 19.1 ± 2.4  ‰,respectively. In these closed biological chambers, we also found a valueattributed to terrestrial photosynthetic isotopic discrimination equal to + 3.7 ± 1.3  ‰. This last estimate suggests thatthe contribution of terrestrial productivity in the Dole effect may havebeen underestimated in previous studies.

[学科分类] 大气科学