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After dating the tree-ring samples of Pinus massoniana that were collected from Mt. GuShan, Fuzhou City, FuJian province, we measured the stable carbon isotope content (813C) of tree-ring a-cellulose along a time series of 35 years (1975-2010). Thereafter, by checking the correlationship between tree-ringδ13C and atmospheric CO2 concentration, atmoshperic temperature, precipitation, relative atmosphere humidity, sunshine duration, wind velocity, we aimed to find out the response ofδ13C in tree-ring a-cellulose to climate changes. The results are listed below:(1) From 1975 to 2009, the 813C in P. massoniana tree-ring a-cellulose ranged from-24.73‰to -23.28‰, with the mean value being -23.85%o. Basically, the sequence of 813C was going on a downward trend.(2) There was an extramarked negative correlation betweenδ13C low frequency sequence of P. massoniana tree-ring a-cellulose and atmospheric CO2 concentration (r=-0.997,P< 0.01), indicating thatδ13C in P. massoniana tree-ring a-cellulose was sensitive to the change of atmospheric CO2 concentration.(3) An extramarked positive correlation was found betweenδ13C high frequency sequence (A813C sequence) of P. massoniana tree-ring a-cellulose and annual mean temperature, annual mean maximum temperature, annual mean minimum temperature(r= 0.725,0.696,0.707,P<0.01). Likewise, an extramarked negative correlation betweenΔδ13C sequence and annual mean atmosphere relative humidity, a significant negative correlation betweenΔδ13C sequence and annual mean sunshine duration (r=-0.703, P<0.01; r=-0.362, P<0.05). AndΔδ13C sequence was positively, although not significant, correlated to annual precipitation and annual mean wind velocity. These observations indicate thatΔδ13C sequence of P. massoniana tree-ring a-cellulose responses, in different sensitivities, to different climatic factors.(4) By analyzing the autocorrelation ofΔδ13C serial, we found the first, second, third order autocorrelation coefficients being 0.840,0.717,0.582 (P<0.01), respectively. This suggests that there was an obvious "hysteresis effect" in the response, namely,Δδ13C sequence was affected by both the climatic factors, especially the atmosphere temperature and relative atmosphere humidity, in the very year and indirectly, that in the previous neighbouring years.(5) From the result of stepwise regression analysis, we conclude that previous annual mean temperature(X1), mean relative atmosphere humidity in spring(X2), the annual sunshine duration (X3) are the main climate factors. These three imposed greater impact on the value ofδ13C of P. massoniana, in the order of X1> X2> X3; they could contribute to the 77.5% changement ofΔδ13C within 35 years.(6) From the response equation of tree-ringδ13C (orΔδ13C) sequence to influence factors that set through regression analysis, we reconstructed atmospheric CO2 concentration and previous year mean temperature. These two are the main factors that can affect tree-ringδ13C (orΔδ13C) sequence. From the result, we can know that, the measured value and reconstructed value can match well (r=0.997 and 0.727, P<0.01).
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