Mitsutoshi Umemura

Changes in chemical characteristics of surface soils in hinoki cypress (Chamaecyparis obtusa) forests induced by the invasion of exotic Moso bamboo (Phyllostachys pubescens) in central Japan

Invasion of contiguous forests by a giant bamboo (Moso bamboo, Phyllostachys pubescens) has the potential to induce changes in the chemical characteristics of soils due to the high growth rate of this species. We evaluated the impact of bamboo invasion into hinoki cypress (Chamaecyparis obtusa) forests on soil properties under varying conditions of shoot density at three study sites (Kanpachi, Seto, and Noguchi) in central Japan. We established three successive quadrats along bamboo invasion (allotted to a bamboo stand, a mixed stand of bamboo and hinoki, and a hinoki stand) at every site. Then, we measured the density and basal area of bamboo and hinoki shoots. Surface soil was sampled from each quadrat to analyze pH, water content, and exchangeable cation contents. The values of soil pH were significantly higher in the mixed stands than the hinoki stands at all sites, showing positive correlations with exchangeable Ca contents in the soil. Exchangeable K and Mg contents in the soil of the mixed stand showed significant differences compared with the hinoki stand only in Seto, but these values in the mixed stand were similar to those in the bamboo stand. This characteristic is consistent with the invasion degree determined from the density ratio of living bamboo culms to living hinoki trunks: Seto > Kanpachi > Noguchi. We conclude that increases in the soil pH due to bamboo invasion into hinoki forests resulted in distinct and sensitive changes in the soil chemistry.

Retranslocation and localization of nutrient elements in various organs of moso bamboo (Phyllostachys pubescens)

Moso bamboo (Phyllostachys pubescens) is one of the major giant bamboo species growing in Japan, and the invasion of mismanaged bamboo populations into contiguous forests has been a serious problem. To understand expansion mechanisms of the bamboo, it is important to obtain some first insights into the plants rapid growth from the viewpoints of the nutrient dynamics in bamboo organs. We have investigated seasonal changes in the concentrations of several nutrient elements in leaves of the plants from three P. pubescens forests and the distributions of those elements in both mature (culms, branches, leaves, roots, and rhizomes) and growing organs (shoots and rhizomes). Among all elements analyzed, boron (B) concentrations in leaves showed a specific seasonal variation that was synchronous across all study sites. Boron was detected at high concentrations in the younger parts of growing rhizomes and shoots, and in mature leaves. These results indicate that P. pubescens could actively utilize B for vegetative reproduction by the retranslocation and the local accumulation behaving as mobile B. Silicon (Si) was found in high concentrations in surface parts of culms and in the mature sheaths of growing rhizomes and shoots following those in mature leaves. P. pubescens, a plant known to accumulate Si, accumulated only low levels of Ca and B in the leaves, indicating that it is possible to utilize more Si for cell wall enhancement than Ca or B. In both mature culms and rhizomes, zinc (Zn) was found at much higher concentrations in the nodes with meristematic tissue than those in internodes, indicating that Zn might play a role in promoting culm and rhizome elongation. We suggest that specific and local utilization of B, Si, and Zn in P. pubescens might support the vegetative reproduction and rapid growth.