A Study On The Differences In The Radial Growth And Stable Carbon And Oxygen Isotope Ratios Of Trees And Shrubs In The Loess Hilly Area Of Northern Shaanxi In Response To Climate

Loess hilly region of northern shaanxi was selected as the study area of this paper.The samples of Pinus tabulaeformis,Sophora viciifolia and Rosa xanthina were collected at Wazijie Forest Farm in Huanglong County and Renjiatai Forest Farm in Fuxian County of Yan'an City,respectively.These samples were used to measure the tree ring width,stable carbon and oxygen isotope ratios(?13C and ?18O).Tree ring standard chronology(STD),Basal Area Increment(BAI),and stable carbon and oxygen isotope ratio chronologies were established.The intercellular carbon dioxide concentration(Ci),the difference between atmospheric carbon dioxide concentration and intercellular carbon dioxide concentration(Ca-Ci),and the ratio of intercellular carbon dioxide concentration to atmospheric carbon dioxide concentration(Ci/Ca)were calculated.By using correlation analysis and linear regression analysis,the responses of Pinus tabulaeformis and different shrubs to climate change were compared and analyzed.Finally,the radial growth,stable carbon isotope and intrinsic water-use efficiency of trees were analyzed.The change trend of intrinsic water-use efficiency(iWUE)and their relationship with climate change were discussed.The responses and physiological mechanism of the growth of Pinus tabulaeformis,Sophora viciifolia and Rosa xanthina to climate change were discussed.The main conclusions are as follows:(1)The tree ring samples of Pinus tabulaeformis collected in wazijie forest farm showed that:the radial growth of Pinus tabulaeformis was significantly negatively correlated with the temperature and vapor pressure deficit(VPD)in May and July.The radial growth of Pinus tabulaeformis was significantly negatively correlated with the sunshine hours in May.The radial growth of Pinus tabulaeformis was significantly positively correlated with precipitation and relative humidity in March and May.The radial growth of Pinus tabulaeformis was significantly positively related to the Palmer Drought Severity Index(PDSI)from April to July.Tree-ring samples collected in renjiatai forest farm showed that:the radial growth of Pinus tabulaeformis was significantly negatively related to the temperature in September of the previous year and May of this year.The radial growth of Pinus tabulaeformis was significantly positively correlated with the temperature in September.The radial growth of Pinus tabulaeformiswas significantly positively related to the precipitation in November of the previous year.The radial growth of Pinus tabulaeformis was significantly positively correlated with the relative humidity in April and July.The radial growth of Pinus tabulaeformis was significantly positively correlated with PDSI from April to July.The radial growth of Sophora viciifolia was significantly negatively related to the temperature in September of the previous year and July to August of this year.The radial growth of Sophora viciifolia was significantly negatively correlated with the October precipitation.The radial growth of Sophora viciifolia was significantly negatively correlated with the relative humidity in January.The radial growth of Sophora viciifolia was significantly positively correlated with VPD in September.The radial growth of Sophora viciifolia was significantly positively correlated with PDSI in July-August,December of the previous year and March-July of this year.Radial growth of Rosa xanthina was significantly negatively correlated with the temperature in July.Radial growth of Rosa xanthina was significantly positively correlated with sunshine hours in March.Radial growth of Rosa xanthina was significantly positively correlated with VPD in March.Radial growth of Rosa xanthina was significantly positively correlated with PDSI in July.The increase of drought degree reduced the drought resistance of trees,and weakened the resistance(RT)and resilience(RS)of Pinus tabulaeformis and Sophora viciifolia.The differences among tree species were as follows:resistance(RT):Sophora viciifolia>Pinus tabulaeformis,recovery(RC):Pinus tabulaeformis>Sophora viciifolia>Rosa xanthina,resilience(RT):Rosa xanthina>Sophora viciifolia.(2)The ?13C sequence of Pinus tabulaeformisin wazijie forest farm,Pinus tabulaeformis and Sophora viciifoliain renjiatai forest farm showed a significant upward trend,while the ?13C sequence of Rosa xanthina in renjiatai forest farm showed a slight downward trend.The ?18O sequences of Pinus tabulaeformisin wazijie forest farm,Pinus tabulaeformis and Sophora viciifolia in renjiatai forest farm showed a slight downward trend,and Rosa xanthina in renjiatai forest farm showed a significant upward trend.Climatic-responses of tree rings ?13C and ?18O revealed that ?13C of Pinus tabulaeformis in wazijie forest farm was mainly affected positively by the temperature of the previous year,while the three tree species at renjiatai forest farm were significantly affected by the temperature of both the previous and current year.The three tree species ?13C were all affected by precipitation and relative humidity during the growing season,and all of which are positively correlated with VPD and negatively correlated with PDSI.The tree ring ?18O is restricted by the temperature of the previous year and the growing season of current year,and the relative humidity of June and May of the previous year.The tree ring ?18O is positively correlated with VPD,and negatively correlated with PDSI.(3)The changes in Ci and iWUE were estimated bytree-ring ?13C of Pinus tabulaeformis,Sophora viciifolia and Rosa xanthina in theLoess hilly region of northern shaanxi.The changes in Ci and iWUE were continuously increasing;the trend of Ci was decreasing and Ca-Ci was increasing,but Ci/Ca was in a relatively stable state.The physiological responses in three different scenarios were calculated.The physiological responses of different tree species to elevated CO2 concentrations were shown to be essentially constant(active response).The increase of iWUE was affected by the atmospheric CO2 concentration,and the atmospheric CO2 concentration had a significant positive correlation with iWUE of different tree species.IWUE of Pinus tabulaeformis was negatively correlated with PDSI,but did not reach a significant level;while both iWUE of Sophora viciifolia and Rosa xanthina were significantly positively correlated with PDSI.By analyzing the change trends of BAI and iWUE over time,it was revealed that iWUE of different tree species were significantly positively correlated with BAI.The first-order difference(high-frequency variation)showed that BAI and iWUE of Pinus tabulaeformis in wazijie forest farm were significantly negatively correlated,while in renjiatai forest farm,the correlation between BAI and iWUE of the three tree species was not significant.