基于液流格型特征值和标准化方法分析胸径和土壤水分对荷木液流的影响

基于液流格型特征值-偏度和峰度分析了不同胸径荷木在水分利用方面的差异，并利用标准化的方法消除强影响因子(光合有效辐射，PAR)对液流的影响，研究了弱影响因子(土壤湿度)与液流的关系.结果表明：荷木胸径越大，偏度越小，液流密度峰值越靠后，相应的液流峰值越大，蒸腾量也越大.与旱季相比，荷木大树在湿季偏度较小，液流密度到达峰值时间靠后，峰值大，蒸腾量也大；而小树偏度在旱、湿季的差异不明显，蒸腾量差异也不大.用PAR峰值对荷木个体蒸腾和土壤湿度进行标准化后，荷木个体蒸腾与土壤湿度呈更明显的正相关关系.在土壤湿度较大的季节，荷木大树的蒸腾量随土壤湿度增加而上升的速率基本稳定；而中等木和小树的某些个体则明显下降，说明这些树木的蒸腾和吸收土壤水分的能力可能接近极限.

Effects of tree diameter at breast height and soil moisture on transpiration of Schima superba based on sap flow pattern and normalization

The eigenvalues of continuous sap flow pattern, i.e., skewness and kurtosis, were used to investigate the water usage of Schima superba with different diameter at breast height (DBH), and the method of normalization was firstly applied to eliminate the effects of strong affecting factor （photosynthetic active radiation，PAR) to explore the possible relationship between weak affecting factor (soil moisture) and sap flow. Generally, the trees with larger DBH had smaller skewness of sap flux density and later-appeared but larger peak values, suggesting that much more water was transpired, and the larger trees showed smaller skewness and later-appeared larger peak values in wet season than in dry season, suggesting that more water was transpired in wet season. On the other hand, smaller trees had lesser differences in the skewness between dry and wet seasons,suggesting that there was no significant difference in the transpiration between the two seasons. The relationship between individual tree’s transpiration and soil moisture was significant and positive after the two parameters being normalized with PAR peak values. When the soil moisture content was higher, the transpiration of the trees with larger DBH was steadily increasing with soil moisture, while that of the trees with moderate or smaller DBH had opposite trend, presumably due to their transpiration and water absorption were approached to the limit.