为探明树干解剖特征对液流速度和树干表面CO2 释放通量的影响,采用红外气体分析法(IRGA)原位连续测定白桦、兴安落叶松和水曲柳树干表面CO2 释放通量,同时测定树干液流速度及树干温度,并采用铸型法观察其树干木质部导管和管胞解剖结构。结果表明:液流速度呈动态变化,而且3 个树种液流速度的总体变化趋势相同,但不同树种液流速度差异显著,即白桦和兴安落叶松大于水曲柳;6、9 月日平均液流速度白桦比水曲柳分别高38.01%和65.80%,兴安落叶松比水曲柳高82郾91%和71郾89%。兴安落叶松、白桦和水曲柳的树干表面CO2 释放通量有显著差别,水曲柳树干的CO2 释放通量远远大于白桦和兴安落叶松树干的CO2 释放通量,6、9 月分别是白桦CO2 释放通量的1.92 和2.17 倍,兴安落叶松的1.49 和2.17 倍。3 树种输导组织的管腔长度、宽度、端壁斜度角、导管壁上的次生增厚方式及纹孔类型存在差异,通过逐步回归分析表明,管腔直径是影响液流速度和树干表面 CO2 释放通量的主要因子,随着管腔内径的增加,液流速度呈减小趋势,树干表面CO2 释放通量呈增加趋势。由于 液流速度在一定程度上影响树干表面的CO2 通量,所以输导组织结构对液流速度的影响也间接影响了树干的CO2 释放通量。
To examine the relationships between xylem anatomical characters of tree stem and sap flow stem CO2 efflux, we instrumented Betula platyphylla, Larix gmelinii and Flaxinus mandshurica to measure the stem CO2 efflux using infrared gas analysis (IRGA) method in situ, and simultaneously measured sap flow density and stem temperature, as well as the anatomical characters of the xylem vessels and tracheid of the three tree species using casting method. The results showed that sap flow density changes dynamically in the three species with the same trend. Significant differences of sap flow density among the three species were found. Mean sap flow density of birch was 38.01% and 65.80% higher than of ash in June and September, respectively, and for larch that was about 82.91% and 71.89% higher than ash. The difference in stem CO2 efflux among the trees was also significant. The figures of ash were 1.92 and 2.17 times of birch and 1.49 and 2.17 times of larch in June and September, respectively. There were differences in catheter molecular lumen length, width, side wall slope angle, type of the secondary duct wall thickening and pits between trees, and stepwise regression analysis showed that vessels (tracheids) lumen diameter was the main factor affecting sap flow density and stem CO2 efflux. With the increase of lumen diameter, sap flow density showed decreasing trend while stem CO2 efflux showed a contrary trend. Our results imply that sap flow density can influence the stem CO2 efflux to some extent; therefore, the indirect impact of conducting tissue structure on stem CO2 efflux could show up.