Correlation Analysis Of Leaf Nutrients,photosynthetic Characteristics And Soil Factors Of Betula Albo-sinensis Burk At Different Altitudes In The Matoutan Forest Region Of Qinling Mountains

Betula albo-sinensis Burk is an important pioneer afforestation tree species in high-altitude areas of northern China.As the main tree species in the Matoutan forest area of the Qinling Mountains,Betula albo-sinensis Burk forest has important research value.Currently,research on the Betula albo-sinensis Burk focuses on macro perspectives such as population structure and community distribution,and there is little research on its growth,physiology,biochemistry,and environmental adaptation mechanisms.In response to the current situation of differences in the growth of Betula albo-sinensis Burk at different altitudes,this study designed six altitude gradients within the range of 1900-2400 m above sea level,measured the changes in nutrient content,photosynthetic physiological characteristics,and soil nutrient content in different soil layers of Betula albo-sinensis Burk at different altitudes,and analyzed the correlation between soil nutrients,leaf nutrients,and photosynthesis.The aim is to explore the adaptive changes of Betula albo-sinensis Burk with increasing altitude,and to identify the optimal growth environment for Betula albo-sinensis Burk in the forest area,providing a basis for the breeding of improved Betula albo-sinensis Burk varieties and the cultivation of ecological forests.The results indicate that:（1）The trend of soil nutrient content in different soil depths is basically consistent with the increase of altitude,mostly with surface soil having more content than deep soil,but the trend of changes in various nutrient contents is different.The content of soil carbon and nitrogen gradually decreases with increasing altitude,and begins to rise at an altitude of 2300m;The phosphorus content in soil gradually increases with increasing altitude;The potassium content starts to decrease after reaching an altitude of 2300 m.（2）The photosynthetic pigment content in the leaves of Betula albo-sinensis Burk has a highly significant correlation with altitude（R²>0.9）,and shows a decreasing trend with altitude.The content of chlorophyll a is 0.13-0.31 mg·g^-1;Chlorophyll b content 0.07-0.14mg·g^-1;The content of carotenoids is 0.02-0.07 mg·g^-1.The net photosynthetic rate of Betula albo-sinensis Burk leaves shows a unimodal change with increasing altitude,with the peak appearing at an altitude of 2000-2100 m;The stomatal conductance,intercellular CO₂concentration,and transpiration rate showed two highest values,ranging from 2000 to 2100m and 2400 m respectively,with the lowest values occurring at an altitude of 1900 m.（3）The length of new branches of Betula albo-sinensis Burk is relatively short,and there is an increasing trend with altitude.At an altitude of 2300 m,the length of branches increases from 7.67 to 21.38 cm,indicating that at an altitude of 2300 m,Betula albo-sinensis Burk branches have the best growth potential and the fastest growth rate.There was no significant difference in the organic carbon content of leaves and branches at different altitude gradients;The nitrogen content in leaves significantly increased from an altitude above 2300 m,reaching26.99 g·kg^-1 at 2400 m,and the highest nitrogen content in branches was 16.44 g·kg^-1;The variation trend of phosphorus content in branches and leaves with altitude is similar,with peaks appearing at 2000 m and 2400 m respectively;The potassium content is also bimodal distribution,reaching the peak at the altitude of 1900-2000 m and 2300 m.（4）In the study of the correlation between soil nutrients,leaf nutrients,and photosynthesis,it was found that the stomatal conductance,intercellular CO₂ concentration,transpiration rate of Betula albo-sinensis Burk were significantly correlated with the carbon and nitrogen content of the leaves;The phosphorus and potassium elements in soil are also closely related to plant photosynthesis,especially in the topsoil,but there is little significant correlation between potassium and photosynthesis at a depth of 20-30 cm.（5）The length of new branches and nutrient content in leaves of Betula albo-sinensis Burk at an altitude of 2300 m are at a high level,making it the area with the best growth potential of Betula albo-sinensis Burk in the Matoutan forest area.At this altitude,the average soil total nitrogen content is 1.23 g·kg^-1,the average total phosphorus content is 0.94 g·kg^-1,the average effective phosphorus content is 0.89 mg·kg^-1,and the average total potassium content is 25.31 g·kg^-1.A fertile soil environment is an important factor for the optimal growth of Betula albo-sinensis Burk plants at this altitude.In summary,This study starts with the necessary environmental factors for plant growth,revealing the adaptive changes of Betula albo-sinensis Burk to high altitude,and finds that the growth of Betula albo-sinensis Burk is the best within the range of 2100 to 2300 meters above sea level,providing a basis for further research on the growth and breeding of Betula albo-sinensis Burk.