Abstract
In recent years, bamboo species have expanded into neighboring artificial forests of western Japan. The bamboo colonization has caused dieback of the planted Japanese cedar (C. japonica) and Hinoki cypress (C. obtusa). We investigated the water relations of the two planted species in bamboo colonized and uncolonized stands to clarify whether water stress contributed to their decline. The midday shoot water potentials (Ψwmid) of the planted species were significantly lower in the bamboo colonized stands than in uncolonized stands. In addition, Ψwmid approached shoot water potentials at turgor loss point (Ψwtlp) for C. japonica in colonized stands. The Ψwmid of Moso bamboo (Phyllostachys heterocycla) and Madake bamboo (Phyllostachys bambusoides) were from 2.0 to 3.0 MPa, and were much lower than the values of the planted species. Predawn leaf water potentials (Ψwpd) of P. heterocycla approached zero, indicating that it actively absorbed water from soil during the night. The root densities of the bamboo species were 5 to 14 times higher than those of the planted species. These results suggest that the planted species in the bamboo colonized stands tend to be under water stress due to the underground competition for water resources, and are sometimes subject to severe water stress, resulting in wilting shoots.
