The Response To Climate Change Of Intrinsic Water Use Efficiency In Trees

Intrinsic water use efficiency(iWUE)can represent the characteristics of water use efficiency of different species plants for a long and stable period of time.The stable carbon isotope(δ13C)is an effective means to reconstruct the historical variation of water use efficiency in treering,but the differences in historical changes of water use efficiency between different tree species and their driving factors are still unclear.To address this problem,this study used the stable carbon isotope in global tree-ring data(including 18 genus such as Quercus spp.,Pinus spp.,Larix spp.;113 tree-ring δ13C time series chronology),combined with the changes of atmospheric carbon dioxide concentration(Ca),temperature(TMP),annual precipitation(Annual PPT),Vapor Pressure Deficit(VPD),Palmer Drought Index(PDSI)and other environmental factors,using linear regression,difference analysis,relative importance analysis and mixed effect model,the historical variation law of the intrinsic water use efficiency of trees of different genus from 1901 to 2015 was first explored.The differences in the intrinsic water use efficiency of trees in different genus before and after the climate abrupt point(1963 year)were compared.Secondly,the influence of geographical conditions such as latitude and altitude on the water use efficiency of trees was explored.Finally,the influence of environmental factors on the internal water use efficiency of trees of different genus was analyzed,and its relative importance was quantified,and the driving factors of the spatial and temporal differences in water use efficiency of trees of different genus were revealed.This study can provide a basis for predicting the future response of terrestrial forest ecosystems to climate change,and the main results of the study are as follows:(1)The temporal trends of intrinsic water use efficiency of trees in different genera were different.There were significant differences in the internal water use efficiency of trees of different genus(Juniperus spp.)with the highest(106.93±10.33μmol CO2·mol-1H2O(average value ± SD,the same below)),and Pericopsis spp.was the lowest(59.74±0.00 μmolCO2·mol-1H2O).From 1901 to 2015,the change trend of water use efficiency of trees in different genus varied significantly,and most of them(16/18)showed a significant growth trend(n=110,p<0.001),with an average increase of 0.26 μmol CO2·mol-1 H2O·yr-1,and only Juniperus spp.(n=2,p=0.22)and Callitris spp.(n=1,p=0.39)did not increase significantly.After 1963,except for Callitris sp.,which showed a downward trend(n=1,slope=-0.09,p=0.36),the increase trend of water use efficiency in trees was more significant,with an average increase of 0.42 μmnol CO2·mol-1 H2O·yr-1.(2)There were significant differences in the intrinsic water use efficiency of trees at different latitudes and altitudes(n=113,p<0.001).The water use efficiency of trees in the low latitude region was the highest,84.76±13.37 μmolCO2·mol-1H2O,and the lowest water use efficiency of trees in the high latitude region was 68.41±10.18μmol CO2·mol-1H2O,and the middle latitude was 80.06±16.03 μmol CO2·mol-1H2O.The intrinsic water use efficiency of trees increased with the increase of altitude,and the intrinsic water use efficiency of trees was the highest in the ultra-high altitude area(>2000m),which was 96.34±10.82 μmolCO2·mol-1H2O,and in the low altitude area(<1500m)trees had the lowest intrinsic water use efficiency,with an average value of 75.89±15.57 μmolCO2·mol-1H2O,and the middle of the high altitude area was 84.22±13.72 μmolCO2·mol-1H2O.(3)Atmospheric CO2 concentration was the most important influencing factor for the change of intrinsic water use efficiency in different genus,and the relative importance of atmospheric CO2 concentration accounted for more than 50%in 13 genus and annual precipitation and temperature were the main influencing factors in the remaining 5 genus.In addition,from 1901 to 2015,the correlation coefficient and partial correlation coefficient of tree intrinsic water use efficiency and atmospheric CO2 concentration,temperature,annual precipitation and drought index showed that the relationship between tree intrinsic water use efficiency and environmental factors was alternate.In summary,this study systematically analyzed the changes of tree’s intrinsic water use efficiency and the difference of tree’s intrinsic water use efficiency by using stable carbon isotope and climate data,then the influencing factors of intrinsic water use efficiency change.In order to understand the physiological adaptation mechanism and ecological model prediction of tree response to climate change,this study provides effective data support.