Quercus hondae, an endangered evergreen oak, mostly inhabits on a lower position of slopes in southeastern Kyushu, Japan, while Q. gilva, a common species of the same region, has a wider range of topographic distribution. We compared the ecophysiological plasticity of leaves and shoots of Q. hondae with that of Q. gilva in order to examine the reason of its limited distribution. We determined parameters of leaf gas exchange, water relations, and leaf and shoot morphology for those corrected from three growing habitats (sunny and shaded crown under a moist soil, and sunny crown under a xeric soil). Based on the results, we examine the two hypotheses for the habitat characteristics of lower slopes in comparison with upper slopes; 1) better light regime maintained by frequent natural disturbances, and 2) better soil moisture condition. The two species showed almost same trends in maximum net photosynthesis, dark respiration and the light compensation point in response to three habitats, indicating the similar shade tolerance. On the other hand, the water relation parameters demonstrated clear differences between the two species. Q. hondae showed quite low plasticity of its leaf water relations in terms of small variations through the three habitats for each of osmotic potential at full turgor (Ψs,sat), leaf water potential at the turgor loss point (Ψl,tlp), relative water content at the turgor loss point (RWCtlp), and amount of losable water per unit leaf area until the turgor loss point (Wtlp/LA). In contrast, Q. gilva had lower Ψs,sat, Ψl,tlp and higher Wtlp/LA under the environment where leaves are easier to loss water. Q. gilva also had a wider range of the ratio of branch basal area to total leaf area per shoot. These suggested a high plasticity of leaf water relations and shoot morphology of Q. gilva against water stress. We concluded that the low plasticity of leaf and shoot water relations of Q. hondae must be one of the reasons for its natural distribution limited to lower slopes.

We observed diurnal changes in the sap flow rates of culms and rhizomes of Sasa kurilensis in different light environments to clarify: 1) the contribution of physiological integration to the water budget in ramets and 2) the time at which water transportation through rhizomes fulfills the function of physiological integration. We defined two culms through the rhizome as a clonal-fragment and measured the water flow in the culms and rhizome of a clonal-fragment using the stem heat balance method under different light conditions: the understory and in one small gap. We observed that the direction of water flow of intermediate rhizomes that were sandwiched in culms changed clearly during the daytime. This was not due to instantaneous phenomena such as noise. The flow direction was synchronized with the balance of the tug-of-war relationship of sap flow from both fragment ends in a small gap. Interestingly enough, the significant downward water flow from the culms to the rhizome was observed even in the daytime and in good weather, and the downward water flow was approximately 60% of the total daily flow of a culm in the understory. The water of clonal-fragments in the understory flowed from the fragment to the outside through rhizomes, and the water supply from the rhizomes to the clonal-fragment was 57.4-82.3% of the total transpiration (water flow from the clonal-fragment to the atmosphere) in a small gap. We suggest that ramets in small gaps and the understory play the roles of consumers and suppliers, respectively, and water supply through the rhizomes enables rapid and flexible water sharing among ramets to cover any daytime water shortage in the ramets.

Spatial distributions of conifer seedlings and ground-surface environmental factors were investigated in an even-aged sub-boreal coniferous forest in Akan region, eastern Hokkaido, Japan. The studied stand was approximately 120 years old and mainly composed of Abies sachalinensis with a small percentage of Picea glehnii and Picea jezoensis. The forest floor of the experimental plot was characterized by the following three features: 1) high dominance of moss vegetation, 2) little in the way of coarse woody debris (CWD) except for pole-size fallen stems, and 3) no dwarf bamboo (Sasa spp.), which has been reported to be common undergrowth in most old-growth sub-boreal forests in Hokkaido. The densities and maximum heights of the seedlings in the plot, with the exception of the current-year seedlings, were 35,859 and 4,902 seedlings/ha, and 23 and 26 cm for A. sachalinensis and Picea spp, respectively. All these seedlings grew on the ground surface. Spatial patterns of seedling distribution were “aggregated distribution" at the smallest grid size of 0.5-2 m for A. sachalinensis and Picea spp, and the seedlings of these two genera showed a sympatric distribution at this spatial scale. Ground-surface environments, such as moss coverage, moss height, soil pH, C, N or C/N ratio varied substantially within the plot (32 m × 32 m) or subplot (4 m × 4 m). Statistical analysis using the conditional autoregressive (CAR) model suggested the potential negative and positive effects of total C content and C/N ratio of the surface soil, respectively, on the local seedling densities of both A. sachalinensis and Picea spp seedlings, and also the negative effect of moss height on the local density of Picea seedlings. These results may suggest that the small-scale spatial heterogeneity of ground-surface environmental conditions in this site may have an influence on the seedling distribution through various abiotic and/or biotic processes, including microbiological interactions.