Study on the Characteristics and Influencing Factors of Sensible Heat Flux and Latent Heat Flux in the Coniferous and Broad-leaved Mixed Forest of Lesser Khingan Mountains

Located in the temperate monsoon climate zone of northeast China， dominated by coniferous and broad-leaved mixed forest the Lesser Khingan Mountains has the largest and most complete primary forest of Korean pine in Asia， which plays an important role in regulating the regional climate.In order to explore the sensible heat flux （H） and latent heat flux （LE） characteristics of the coniferous and broad-leaved mixed forest in the Lesser Khingan Mountains and the regulation effect of environmental， biological factors on H and LE， H and LE at 40 m and 50 m altitude of Wuying National Climate Observatory from 2007 to 2023 were studied by using the eddy correlation method， and a structural equation model was constructed to analyze the influencing factors in detail.The results show that： The interannual variation of H and LE in the coniferous and broad-leaved mixed forest in the Lesser Khingan Mountains showed a decreasing trend， but the variation trend was not completely consistent.The annual average of H and LE at 40 m height was 19.84±1.83 W·m-2 and 29.39±2.93 W·m-2， respectively.The annual average of H and LE at 50 m altitude was 22.71±1.29 W·m-2 and 31.76±1.07 W·m-2， respectively.The peak of H appeared in April， the secondary peak in October， and the peak of LE appeared in July， in which LE was greater than H from May to September， indicating that the energy conversion was dominated by latent heat exchange in May to September， and by sensible heat exchange in other months.The 30-min scale energy closure rate was 49%， the monthly energy closure rate ranged from 32 to 61%， in which the growing season and non-growing season were 53% and 38%， respectively， and the daily scale energy closure rate was 52%.The structural equation model showed that the heat transfer process of the coniferous and broad-leaved mixed forest in the Lesser Khingan Mountains was mainly limited by energy.Net radiation had a positive effect on H and LE， while air temperature， vapor pressure deficit， soil volumetric water content and leaf area index had opposite effects on H and LE.Climate change has a complex regulatory mechanism on H and LE.The complex interannual variation of H and LE can be partially explained by constructing structural equation models for different years.