Abstract:The subtropical zonal vegetation is monsoon evergreen broad-leaved forest (altitude 300-600 m, monsoon forest), and the mountain evergreen broad-leaved forest (mountain forest) is distributed in the middle mountains (1 000-1 500 m). The ecological value of mountain forest has been paid more and more attention, but the environmental adaptability of its tree species is still not well understood. Based on fixed plots of typical mountain forest (Daming Mountain, Guangxi) and monsoon forest (Dinghu Mountain, Guangdong) in south subtropical region, leaf morphological and anatomical characteristics, mechanical strength and hydraulic properties of 57 representative tree species were measured, and leaf traits and correlation of various traits of evergreen broad-leaved forest species at different elevations were compared. The results showed that compared with monsoon forest species, the leaves of mountain forest species were thicker, the specific leaf area was smaller, and the mechanical strength was higher, which was conducive to improving the adaptability to winter freezing in the mountains at higher altitude. Under extreme hot-dry weather in 2022 summer, leaf water potential and hydraulic safety margin were significantly lower in the low-elevation forest than those in the high-elevation forest. However, leaf hydraulic safety margins were positive for most studied tree species and showed large inter-specific variations, indicating a low hydraulic risk in subtropical evergreen broadleaved forests. Leaf traits networks differed between the two forests. There was no tradeoff relationship between leaf hydraulic security and efficiency in mountain forest, while the correlation between leaf economic traits (such as specific leaf area) and other indexes was weak in monsoon forest. Based on leaf traits, the differences and diversity of adaptive strategies of evergreen broad-leaved forest species at different elevations in south subtropical region were revealed.
