Intra-annual Oxygen Isotope Analysis And Climate Response Characteristics Of Coniferous Plants On The Southern Slope Of The Qinling Mountains

Compared to the tree ring width and other anatomical features,the stable oxygen isotope composition of tree ring α-cellulose(δ18Oα-cell)is less affected by the growth trend of trees,and has become a significant proxy in climatological and ecological research,such as reconstruction of paleoclimate,paleoenvironment and global change ecology.The oxygen isotopic composition of α-cellulose is determined by the isotope composition of source water,isotope enrichment effect associated with leaf evapotranspiration,and kinetic isotope effects associated with turning CO2 and H2O into soluble sugars(the CalvinBenson-Bassham cycle),and transport of sugars from leaf to the site of αcellulose biosynthesis and further isotope effect associated with incorporation of(recycled)sugars into α-cellulose.Thus,the oxygen,at each specific intramolecular position as governed by the biochemistries,has a distinct chemical history and carries the signal of an independent set of isotope effects.Unfortunately,compound-specific or bulk isotope analysis(CSIA or BSIA)of tree ring cellulose is inadequate to capture the environmental signal that is entangled with the metabolic signal.In this context,we conducted high-resolution oxygen isotope analysis of two coniferous species Larix gmelinii and Pinus tabuliformis,including BSIA,CSIA and PSIA(position specific isotope analysis of oxygen).The following conclusions were drawn:1.Intra-annual variation of oxygen isotope composition in α-cellulose of Larix gmelinii.Tree ring disic of Larix gmelinii(coniferous tree species)was collected on the south slope of the Qinling Mountains and was then cut into slices for high-resolution oxygen isotope analysis.The compound specific oxygen isotope(O-2～O-6 in glucose unit)and position specific oxygen isotope(O-2 and O-3～O-6)of α-cellulose were analyzed,combined with the field observation records of hourly tree radial growth dynamic recorder.Based on the rainfall isotope simulation results of daily-scale meteorological data,the following conclusions were obtained:(1)the correlations between δ18OPG and temperature and relative humidity are higher than the δ18Oα-cell(the R2 for PG-versus-T and αcellulose-versus-T are 0.736 and 0.481 respectively;the R2 for PG-versus-RH and α-cellulose-versus-RH are 0.488 and 0.097 respectively).(2)δ18OC-2 was only weakly(R2=0.378)correlated with the δ18OSW in growth season.It is proved that it is necessary to carry out PSIA-O experiment,and we can reconstruct the source water by measuring δ18OC-2.2.Intra-annual changes of oxygen isotope composition in a-cellulose glucose unit of cambium and leaves of P.tabuliformis.The cambium,leaves and soil of P.tabulaeformis were sampled from wild at regular intervals over a whole year.Then,we extracted soluble sugar,starch,α-cellulose and water from the collected samples.In addition,we derived the cellulose to phenylglucosazone,a compound which lacks the oxygen attached to the second carbon of the celluloseglucose moieties.Oxygen isotope analysis of phenylglucosazone allowed us to calculate the 18O content of the oxygen attached to the second carbon of the cellulose-glucose moieties.Combined with climate information,we found that:(1)sucrose accounts for the highest proportion in cambium,which was the result of cambium growth mechanism;(2)isotope distribution:δ18Oleaf-suc>δ18Oleaf-water>δ18Osoil-water;(3)there was a certain correlation between δ18Osoil-water and δ18OC-2 inα-cellulose moleculesfor carbonyl oxygen atom exchange;(4)δ18Osuc and δ18OPG of P.tabulaeformis were primarily controlled by relative humidity and rainfall amount,and the δ18Oleaf-suc was more correlative with climate information than that of cambium.