热带喀斯特森林多花白头树木质部年内生长动态及其对环境因子的响应

多花白头树(Garuga floribunda var.gamblei)是西双版纳热带喀斯特森林中常见的落叶树种，容易受水分亏缺的影响。为探究热带喀斯特森林树木年内生长动态及其对环境因子的响应，该研究利用生长环和微树芯两种方法监测了多花白头树在2020—2021年的树干径向变化和木质部生长动态，并分析了树干径向变化和木质部生长与环境因子的相关性。微树芯法的监测表明，在2020年，多花白头树在3月底开始出现扩大细胞，9月底细胞壁加厚结束；在2021年，多花白头树在4月中旬开始出现扩大细胞，10月中旬细胞壁加厚结束。生长环的监测表明，2020年和2021年的径向生长开始时间均晚于扩大细胞出现时间，径向生长结束时间均早于细胞壁加厚结束时间。多花白头树在2020年和2021年的木质部生长持续时间大致相同，2020年的木质部生长量((2.87±1.46)mm)也与2021年((2.98±1.02)mm)几乎一致。多花白头树的月径向生长量、扩大细胞区域宽度和细胞壁加厚区域宽度均与降水呈显著正相关，这表明水分状况在多花白头树的木质部生长过程中发挥了重要作用；扩大细胞区域宽度还与日平均气温和日最低温显...

Intra-annual xylem growth of Garuga floribunda var. gamblei and its response to environmental factors in a tropical karst forest

Garuga floribunda var. gamblei, a common deciduous species in Xishuangbanna tropical karst forest, is susceptible to water stress. In order to determine the intra-annual xylem growth phenology of trees in tropical karst forest and how environmental factors would affect xylem formation, we monitored the dynamics of stem radius variation and xylem growth for G. floribunda var. gamblei by combining band dendrometer and microcoring during two consecutive years (2020-2021). Meanwhile, we analyzed the correlation of environmental factors with monthly radial growth and bi-weekly xylem growth, respectively. The results of microcoring method showed that enlarging zone began to appear in the end of March and wall thickening zone ceased in late September in 2020, whereas enlarging zone occurred in the middle of April and wall thickening zone stopped in the middle of October in 2021. However, the stem radius variation monitored by band dendrometer method showed that the radial growth of G. floribunda var. gamblei started later and stopped earlier than those of microcoring method in both 2020 and 2021. Annual radial growth of G. floribunda var. gamblei was higher in 2020 ((3.30±2.91) mm) than 2021 ((2.36±0.81) mm) in spite of longer growth duration in 2021. The durations of xylem growth were similar in two years, and the annual xylem growth were also similar in 2020 ((2.87±1.46) mm) and 2021 ((2.98±1.02) mm). Monthly radial growth, the thickness of enlarging zone and the thickness of wall thickening zone were positively correlated to precipitation in 2020 and 2021, indicating that water condition plays an important role in xylem growth of G. floribunda var. gamblei; the thickness of enlarging zone was also positively correlated with daily mean air temperature and daily minimum air temperature during two years, whereas the correlation coefficient between the thickness of enlarging zone and daily minimum air temperature was higher in 2021 than 2020; the thickness of wall thickening zone was positively correlated to relatively humidity, soil water content at a depth of 20 cm, daily mean air temperature and daily minimum air temperature in both years, but all these correlation coefficients were higher in 2021 than 2020. Our results will be helpful to understand how the intra-annual xylem growth of tropical karst forest trees response to environmental factors and provide theoretical knowledge to predict the xylem growth trend in tropical karst forest under global climate change in the future by revealing the patterns of intra-annual xylem growth of G. floribunda var. gamblei in two years.