热带季节性湿润林苦楝(Melia azedarach)径向生长季节动态及其对环境因子的响应

气候变化导致的温度升高和降水格局改变可能会影响到树木的生长速率和季节物候。西双版纳热带季节性湿润林分布在石灰岩山中部，属于热带喀斯特生境。由于土层浅薄，土壤保水能力极差，植物生长更容易遭到受到季节性干旱气候的影响。为探究热带季节性湿润林的树木径向生长季节动态及其对环境因子的响应，利用高精度树木生长仪连续两年监测了云南西双版纳热带季节性湿润林中落叶树种苦楝（Melia azedarach）的树干径向变化，并与同步监测的环境因子进行相关分析。结果表明，苦楝径向生长开始、结束以及持续生长的时间在年际间存在差异。与2018年相比，2019年苦楝生长开始和结束的时间较晚，且年生长量较小，这可能是与2019年雨季开始较晚且在生长季早期经历了严重的高温干旱有关。苦楝的径向日生长量与日降水量和相对湿度呈正相关关系，与光合有效辐射、水汽压亏缺和风速呈负相关关系，表明了在苦楝的径向生长主要受水分条件限制。在干旱年份（2019年），苦楝的日生长量与降水和相对湿度的相关性更强。研究结果有助于进一步了解热带喀斯特生境树木生长对气候变化的敏感性以及树木适应季节性干旱气候的策略。

Intra-annual Radial Growth of Melia azedarach in a Tropical Moist Seasonal Forest and its Response to Environmental Factors in Xishuangbanna, Southwest China

Temperature increases and altered precipitation amounts and distribution may affect tree growth rates and seasonal dynamics. Tropical moist seasonal forests are distributed on limestones (karst) with shallow soil layers and poor soil water-retention capacity, making plant growth more vulnerable to seasonal drought. This study aims to investigate the seasonal dynamics of radial tree growth in a tropical moist seasonal forest and their response to environmental factors. Using a high resolution dendrometer, we monitored the radial stem growth of a deciduous tree species (Melia azedarach) in a tropical moist seasonal forest in Xishuangbanna, Yunnan for two consecutive years. We analyzed the seasonal dynamics of its radial growth and their associations with environmental factors. Our results showed considerable inter-annual differences in growth phenology (start, end, and duration) of Melia azedarach. Compared to a normal year (2018), the radial growth started and ended later in a drier year (2019), resulting in decreased annual growth. The decreased growth rate and shorter duration in 2019 may be due to the late onset of the rainy season and a severe and persistent heat wave during the early growing season. Daily growth of Melia azedarach correlated positively with daily rainfall and relative humidity, but negatively with photosynthetically active radiation, water vapor pressure deficit, and wind speed, indicating that the radial growth was mainly limited by water deficit. Moreover, the radial growth of Melia azedarach in the dry year (2019) showed a high correlation with precipitation and relative humidity. Our results provide clues for understanding climate sensitivity of tree growth in tropical moist seasonal forests and their adaptations to seasonal dry climates.