Analytical Methods for Water Distribution and Water Movement in Secondary Xylem of Trees

Trees essentially require water for their survival. Most of water is in the secondary xylem, and the water is consumed for transpiration and metabolism. Water distribution and movement in the secondary xylem have been analyzed from the microscopic level such as vessel and tracheid to the individual level using various methods depending on the study purpose. Moisture content measurement can evaluate the quantitative water volume at the macro level, and X-ray microscopy, cryo-scanning electron microscopy, magnetic resonance imaging and X-ray computer tomography enable detail analysis of water distribution at the microscopic level. Sap flow measurement is a standard method to quantify the individual tree water movement, and isotope and dye injection methods are useful to assess the water transport pathway. Measurement principle, advantage and disadvantage of each method are discussed, and their application to trees is summarized.