Response Of Growth And Carbon And Nitrogen Isotope Content Of Larix Gmelinii To Environmental Changes

Our aims are to figure out the response differences of the radial growth of Larix gmelinii under different precipitation gradients in northern Daxing'an Mountains to climate,especially to recent warming.In this paper,three sampling sites,including Mordaoga(ME,annual total precipitation:363 mm),Tulihe(TLH,454 mm)and Alihe(ALH,525 mm),were selected along a precipitation gradient in the northern Daxing'an Mountains.Five sampling points along the temperature gradient-Mohe(MH),Mangui(MG),Tullihe(TLH),Wueqihan(WEQH)and Nanmu(NM)were selected for tree ring sampling.Under climate warming scenario,the spatial-temporal variations of radial growth of Larix gmelinii in different precipitation conditions and climate relationships was analyzed using the tree-ring climatology method,and the resistance,resilience and elasticity of Larix gmelinii to extreme climate were then discussed.The time series of tree radial growth,stable carbon isotope resolution(?13C)of tree rings and water use efficiency during 1959-2015 were established.The variation characteristics of these three factors and their relationship with main climatic factors were studied.Results showed that the effect of precipitation on the radial growth of Larix melinii was small under different precipitation conditions.Only in TLH site the growth of Larix gmelinii was positively related to precipitation in August and autumn.Temperature is the main factor limiting radial growth of Larix gmelinii,its effects significantly differs with site precipitation conditions.In low precipitation area(ME),minimum temperature in growing season is the main limiting factor for the growth of Larix gmelinii.In the middle precipitation area(TLH),minimum temperature in September of previous year had the strongest effect on Larix gmelinii growth.In the high precipitation area(ALH),mean and minimum temperature are the key climatic factors affecting arix gmelinii tree growth.The increase in temperature during autumn and winter of previous year is not conducive to the increase of Larix gmelinii growth.There is no significant relationship between ME chronology and PDSI.The TLH chronology was significant positively correlated with PDSI.The ALH chronology was significant negatively correlated with PDSI.After rapid warming since 1980s,the radial growth of Larix gmelinii at three sites showed an opposite trend with warming.Compared with the other two sampling sites,Larix gmelinii in ALH has higher resistance to extreme climate,but its resilience is weak.Under different temperature gradients,temperature is the main climate factor affecting tree growth,while precipitation has a weak impact.The growth of Larix gmelinii at MG sampling sites was positively correlated with temperature,the growth of Larix gmelinii at other sampling sites(MH,TLH,WEQII and NM)was negatively correlated with temperature.The growth of Larix gmelinii at MH and MG sampling sites was not significantly correlated with PDSI,but TLH,WEQH and NM were positively correlated with PDSI.The Delta 13C value in the study area ranged from 15(?)?19(?).There was a significant negative correlation between Delta 13C of Larix gmelinii ring and January precipitation at MG sampling site.The Delta 13C of Larix gmelinii ring at WEQH sampling site was positively correlated with precipitation in June and PDSI in June-October.The Delta 13C of Larix gmelinii ring at NM sampling site was negatively correlated with the average temperature from July to September and July to September of last year,and positively correlated with PDSI from May to October.The water use efficiency of Larix gmelinii was 66?138?mol·mol-1,which showed a very significant upward trend(P<0.01).With the increase of longitude,the content of delta 15N increased.With the decrease of latitude gradient and the increase of water use efficiency(WUE),Delta 15N first decreased and then increased.Our results show that water conditions will affect the response of Larix gmelinii to future climate warming,especially in the resistance and resilience of growth to extreme climate.The warming and drying envionment promoted the improvement of water use efficiency of trees.