<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors></contributors><titles><title><style face="normal" font="default" size="100%">Evaporation and carbonic anhydrase activity recorded in oxygen isotope signatures of net CO2 fluxes from a Mediterranean soil</style></title><secondary-title><style face="normal" font="default" size="100%">Global Change Biology</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2008</style></year></dates><publisher><style face="normal" font="default" size="100%">Blackwell Publishing Ltd</style></publisher><volume><style face="normal" font="default" size="100%">14</style></volume><pages><style face="normal" font="default" size="100%">2178-2193</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The oxygen stable isotope composition (δ18O) of CO2 is a valuable tool for studying the gas exchange between terrestrial ecosystems and the atmosphere. In the soil, it records the isotopic signal of water pools subjected to precipitation and evaporation events. The δ18O of the surface soil net CO2 flux is dominated by the physical processes of diffusion of CO2 into and out of the soil and the chemical reactions during CO2–H2O equilibration. Catalytic reactions by the enzyme carbonic anhydrase, reducing CO2 hydration times, have been proposed recently to explain field observations of the δ18O signatures of net soil CO2 fluxes. How important these catalytic reactions are for accurately predicting large-scale biosphere fluxes and partitioning net ecosystem fluxes is currently uncertain because of the lack of field data. In this study, we determined the δ18O signatures of net soil CO2 fluxes from soil chamber measurements in a Mediterranean forest. Over the 3 days of measurements, the observed δ18O signatures of net soil CO2 fluxes became progressively enriched with a well-characterized diurnal cycle. Model simulations indicated that the δ18O signatures recorded the interplay of two effects: (1) progressive enrichment of water in the upper soil by evaporation, and (2) catalytic acceleration of the isotopic exchange between CO2 and soil water, amplifying the contributions of ‘atmospheric invasion’ to net signatures. We conclude that there is a need for better understanding of the role of enzymatic reactions, and hence soil biology, in determining the contributions of soil fluxes to oxygen isotope signals in atmospheric CO2.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Wingate, Lisa</style></author><author><style face="normal" font="default" size="100%">SEIBT, ULLI</style></author><author><style face="normal" font="default" size="100%">MASEYK, KADMIEL</style></author><author><style face="normal" font="default" size="100%">OGÉE, JÉRÔME</style></author><author><style face="normal" font="default" size="100%">Almeida, Pedro</style></author><author><style face="normal" font="default" size="100%">YAKIR, D. A. N.</style></author><author><style face="normal" font="default" size="100%">Pereira, João S.</style></author><author><style face="normal" font="default" size="100%">MENCUCCINI, MAURIZIO</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Evaporation and carbonic anhydrase activity recorded in oxygen isotope signatures of net CO2 fluxes from a Mediterranean soil</style></title><secondary-title><style face="normal" font="default" size="100%">Global Change Biology</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">atmospheric invasion</style></keyword><keyword><style  face="normal" font="default" size="100%">carbonic anhydrase</style></keyword><keyword><style  face="normal" font="default" size="100%">Drought</style></keyword><keyword><style  face="normal" font="default" size="100%">Mediterranean forests</style></keyword><keyword><style  face="normal" font="default" size="100%">oxygen isotopes</style></keyword><keyword><style  face="normal" font="default" size="100%">Quercus suber</style></keyword><keyword><style  face="normal" font="default" size="100%">Soil CO2 efflux</style></keyword><keyword><style  face="normal" font="default" size="100%">soil evaporation</style></keyword><keyword><style  face="normal" font="default" size="100%">soil water δ18O composition</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2008</style></year><pub-dates><date><style  face="normal" font="default" size="100%">2008///</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://dx.doi.org/10.1111/j.1365-2486.2008.01635.x</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">14</style></volume><pages><style face="normal" font="default" size="100%">2178 - 2193</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The oxygen stable isotope composition (δ18O) of CO2 is a valuable tool for studying the gas exchange between terrestrial ecosystems and the atmosphere. In the soil, it records the isotopic signal of water pools subjected to precipitation and evaporation events. The δ18O of the surface soil net CO2 flux is dominated by the physical processes of diffusion of CO2 into and out of the soil and the chemical reactions during CO2–H2O equilibration. Catalytic reactions by the enzyme carbonic anhydrase, reducing CO2 hydration times, have been proposed recently to explain field observations of the δ18O signatures of net soil CO2 fluxes. How important these catalytic reactions are for accurately predicting large-scale biosphere fluxes and partitioning net ecosystem fluxes is currently uncertain because of the lack of field data. In this study, we determined the δ18O signatures of net soil CO2 fluxes from soil chamber measurements in a Mediterranean forest. Over the 3 days of measurements, the observed δ18O signatures of net soil CO2 fluxes became progressively enriched with a well-characterized diurnal cycle. Model simulations indicated that the δ18O signatures recorded the interplay of two effects: (1) progressive enrichment of water in the upper soil by evaporation, and (2) catalytic acceleration of the isotopic exchange between CO2 and soil water, amplifying the contributions of ‘atmospheric invasion’ to net signatures. We conclude that there is a need for better understanding of the role of enzymatic reactions, and hence soil biology, in determining the contributions of soil fluxes to oxygen isotope signals in atmospheric CO2.</style></abstract><issue><style face="normal" font="default" size="100%">9</style></issue><notes><style face="normal" font="default" size="100%">The following values have no corresponding Zotero field:&lt;br/&gt;publisher: Blackwell Publishing Ltd</style></notes></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors></contributors><titles><title><style face="normal" font="default" size="100%">Large daily variation in 13C-enrichment of leaf-respired CO2 in two Quercus forest canopies</style></title><secondary-title><style face="normal" font="default" size="100%">New Phytologist</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2005</style></year></dates><publisher><style face="normal" font="default" size="100%">Blackwell Science Ltd</style></publisher><volume><style face="normal" font="default" size="100%">167</style></volume><pages><style face="normal" font="default" size="100%">377-384</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">* • The use of the 13C : 12C isotopic ratio (δ13C) of leaf-respired CO2 to trace carbon fluxes in plants and ecosystems is limited by little information on temporal variations in δ13C of leaf dark-respired CO2 (δ13Cr) under field conditions. * • Here, we explored variability in δ13Cr and its relationship to key respiratory substrates from collections of leaf dark-respired CO2, carbohydrate extractions and gas exchange measurements over 24-h periods in two Quercus canopies. * • Throughout both canopies, δ13Cr became progressively 13C-enriched during the photoperiod, by up to 7, then 13C-depleted at night relative to the photoperiod. This cycle could not be reconciled with δ13C of soluble sugars (δ13Css), starch (δ13Cst), lipids (δ13Cl), cellulose (δ13Cc) or with calculated photosynthetic discrimination (Δ). However, photoperiod progressive enrichment in δ13Cr was correlated with cumulative carbon assimilation (r2 = 0.91). * • We concluded that there is considerable short-term variation in δ13Cr in forest canopies, that it is consistent with current hypotheses for 13C fractionation during leaf respiration, that leaf carbohydrates cannot be used as surrogates for δ13Cr, and that diel changes in leaf carbohydrate status could be used to predict changes in δ13Cr empirically.</style></abstract></record></records></xml>