SEM-EDXA法によるミズナラ苗木樹幹横断面における無機質成分の分布とその移動

This study investigated the radial transport of water containing mineral elements in the stem of a 2-year-old Japanese oak (Quercus crispula Blume) sapling using the scanning electron microscope energy dispersive X-ray microanalyzer (SEM-EDXA) method. The results obtained were summarized as follows.
1) Seven kinds of mineral element, which are calcium (Ca), phosphorus (P), potassium (K), silicon (Si), chlorine (Cl), sulfur (S) and magnesium (Mg), were detected from the element qualitative analysis of wood sample with the EDXA apparatus.
2) In the xylem right before lights-off / lights-on, the contents of either mineral element showed the almost constant low value, and gradually increased toward the outer part of the xylem.
3) The highest contents of mineral elements except for the Ca right before lights-on were found in the cambium and, in the case of Ca, in the phloem.
4) The water containing mineral elements as mentioned above was transported, via transpiration, in both directions between the mature xylem zone and the phloem zone through differentiating xylem cells.
5) The model as shown in Figure 5 suggests that xylem is divided into four parts: the cambial and phloem zone (zone A), expanding zone (zone B), developing zone (zone C), and mature xylem zone (zone D).
6) The water was transported through the apoplastic passageways and diffused into the tissue from zone D to zone A when transpiration was restricted in the dark period. As a result, mineral element ions in the water were distributed in high concentration in zone A and gradually decreased toward the inner part of the xylem through zones B and C.
7) In contrast, when transpiration was accelerated during the light period, water mainly flowed through vessels in zone D and was transported to the upper part of the sapling. Then, water containing mineral elements in zones A, B, and C was drawn toward zone D.