Response Of Eco-Stoichiometric Characteristics Of Leaf,Branch And Root In Larirx Gmelinii To Climate Warming

The carbon(C),nitrogen(N)and phosphorus(P)contents and their stoichiometric ratios of leaves,branches and roots,which are the main functional organs of trees,can reflect the nutrient absorption and utilization capacity of tree.Larix gmelinii is an important plantation tree species and the dominant tree species of boreal forest in China,and grows in the climate change sensitive area.Exploring the impact of climate warming on the eco–stoichiometric characteristics of different organs of Larix gmelinii can help us to understand the response mechanism of this tree species to climate change.In this study,we constructed a warming experiment by transplanting Larix gmelinii trees from four geographically distant sites(with the increase of latitude,the order is Dailing,Heihe,Songling,Tahe)to a common garden in Maoershan Ecological Station near the warm edge of this species’ range in China.We studied the effects of climate warming on contents of C、N、P and their stoichiometric ratios in leaves,branches and roots,and explored the differences in the effect among different seasons,warming amounts,organs,and elements.The main results are as following:Eco–stoichiometric characteristics of leaves,branches and roots of Larix gmelinii at three sites in 2013 showed that the eco–stoichiometric characteristics had obvious spatio-temporal variation.There were significant differences in the eco-stoichiometric characteristics of various organs of Larix gmelinii at different locations,which were believed to be related to the different adaptation strategies and nutrient utilization strategies of various organs of Larix gmelinii.Among the elements,the geographical variation law of element content is that the trees at high latitude have smaller C and N contents and larger P contents,which should be relatively larger C/N and smaller C/P and N/P.Larix gmelinii in high latitudes has larger specific leaf weight and smaller non–structural carbohydrates.Although the weight per unit leaf area is greater,the content of C may be lower.Regulated by TBH hypothesis and TPPH hypothesis,N and P content showed the opposite response trend to latitude.In addition,it may also be related to the distinctive element requirements of Larix gmelinii.The growth of trees growing in high latitude and low temperature areas is deemed to be limited by soil N content,and more P content is obtained to make up for the deficiency of N content.The seasonal dynamics of ecological stoichiometric characteristics of leaves,branches and roots of Larix gmelinii were studied at three sites in 2013,and the cyclical dynamics of organs were different at different sites.Compared with June and September,the content of C and N in leaves in August was the highest,the content of C and N in branches was the lowest,and the content of P in roots was the highest,which was related to the physiological selection of organs in the growth process,and the change of photosynthetic products and nutrient resource allocation strategy.The comparison of ecological stoichiometric characteristics of Larix gmelinii at four sites in 2013 and 2021 showed that after 8 years of natural growth,the contents of C,N and P in various organs of Larix gmelinii in 2021 were significantly lower than those in 2013,with obvious time variation,but the geographical variation was consistent.The reason for this result is believed to be the inherent temperature rise in the past eight years,which led to the change of the growth rate of Larix gmelinii,resulting in the reduction of elements.The differences in the eco–stoichiometric characteristics of leaves,branches and roots of Larix gmelinii in four sites and Maoershan in 2021 were analyzed.The results showed that the eco–stoichiometric characteristics would be affected by climate warming,and there would be differences in the degree of warming,warming time,organs and elements.To study the effects of different warming degrees on ecological stoichiometric characteristics of Larix gmelinii.The results showed that with the increase of warming degree,the relative growth rates of C content and N content in all organs of Larix gmelinii showed an increasing trend,while the relative growth rates of P content showed a decreasing trend,and the overall growth rates were linearly correlated with the warming range.In terms of individual organs,the relative growth rates of C,N and P contents in only leaves were linearly correlated with the warming range.Climate warming will enhance the production capacity,biological activity and nutrient absorption of trees,and improve the content of elements in their organs to maintain the stability of their production functions.The warming of the climate increased the demand of nutrient elements for all organs,but reduced the element utilization efficiency of the organs with resource acquisition,and the warming effect of limiting element N content was stronger with the warming degree.By comparing the contents of C,N and P in the warming period of 9 years and 17 years,and analyzing the influence of warming time on the organs of Larix gmelinii,it is found that the warming time has a significant effect on the contents of Larix gmelinii,and the warming effect changes.C content of each organ will increase with the warming degree in the warming cycle.The increment of unit warming temperature(1℃)firstly increased and then decreased,while the increment of N and P content gradually increased.This suggests that the response of ecological stoichiometric characteristics to climate warming is lagging.In addition,this study transplanted Larix gmelinii from 4 sites into homogeneous gardens.The results showed that,compared with the original sites,the C content of new and old branches and the N content of old branches became significant,The C content of 1 mm and 2–5 mm roots and the C/N and C/P locations of new branches and leaves were no longer significantly different,but the other differences were little changed.The results indicated that the geographical population variation of ecological stoichiometric characteristics of Larix gmelinii was the result of the combination of genetic effects and environmental effects,and on the other hand,there were differences among organs.The results of this study have certain theoretical significance for examining the response of trees to global warming,and also have potential application value for the change of carbon sequestration ability of Larix gmelinii under the condition of global warming.