Abstract: The Hengduan Mountains region is sensitive to climate change. Although many dendrochronological studies have been conducted in this region, few researches examined seasonal variations of stem radial growth and their responses to environmental factors of subalpine coniferous tree species. We monitored stem radial variations of four dominant coniferous species i.e. Abies georgei, Larix potaninii, Picea brachytyla var. complanata, and Pinus densata, in Shangri-La National Park, using high-resolution dendrometers. We analyzed the diurnal patterns of stem growth and their responses to the variations of atmospheric and soil moisture in 2022 and 2023. The results showed that: 1) stem radial growth of the four tree species mainly occurred at night, with the species that reached peak growth earlier at night, such as A. georgei, showing greater radial growth and more growth hours. 2) Stem radial growths of the four tree species were negatively correlated with vapor pressure deficit (VPD) and soil water content (SWC). 3) Stem radial growths of A. georgei and L. potaninii at higher altitudes were more sensitive to changes in VPD. However, stem radial growths of P. brachytyla var. complanate and P. densata at lower elevations were more influenced by soil water content. By revealing differential responses of subalpine conifer species at a diurnal scale and the main environmental limiting factors, our results would provide new insights into understanding how subalpine coniferous trees respond to climate change in the Hengduan Mountains.

Key words: Nowthwest Yunnan, stem radial growth, diel growth dynamic, climate response, vapor pressure deficit, soil water content