Summary 1.To increase understanding of the water table's influence on both fine-root growth and wholeplant growth of tree species in arid and semi-arid regions, we exposed Populus alba L. cuttings to contrasting soil water conditions via various water table gradients. 2. One-year-old rooted cuttings were grown individually in pots containing sandy soil in a greenhouse for 90 days in four water-table depth treatments: constant depth at 45 cm from the soil surface, constant depth at 30 cm, constant depth at 15 cm, and fluctuating depths between 45 and 30 cm. Growth responses, biomass partitioning, and structure and morphology of leaves and roots were determined for harvested trees every 30 days. 3. Fine (< 1-mm diameter) root growth was affected by water-table levels and water profiles, even in the fluctuating water-table depth treatment. Fine root proliferation was inhibited below the water table and was stimulated in the layers just above the water table and near the soil surface. 4. At the whole-plant level, with deeper water tables, P. alba allocated more biomass to roots and root morphology changed, but total root length did not increase, suggesting that trees faced with soil water deficits are not likely to increase root surface area to obtain more water. 5. Total biomass and root length in each treatment were positively correlated and the relationships were similar among the treatments, although the growth responses varied under the various watertable conditions. These results suggest that variation in root length may have an important effect on the biomass of the rooted cuttings across a gradient of water-table depths.

Summary• In this study we examined the role of the nitrogen-fixing tree, Robinia pseudoacacia (black locust), in ectomycorrhizal (ECM) formation and ECM community of Pinus thunbergii (Japanese black pine) seedlings.• Two 200 m 2 experimental plots were established at the border between a Japanese black pine-and a black locust-dominated area in a coastal forest. The ECM fungal community of pine seedlings was examined by PCR-RFLP and sequence analysis. We analyzed the relationship between ECM formation, ECM community, growth, and nutrient status of pine seedlings and environmental conditions using the Mantel test and structural equation model.• Percentages of ECM root tips, the number of ECM fungal species and ECM diversity on pine seedlings decreased in the black locust-dominated area. Cenococcum geophilum and Russula spp. were dominant in the Japanese black pine-dominated area, whereas Tomentella spp. were dominant in the black locust-dominated area. Nitrogen (N) concentration in soils or pine seedlings strongly influenced the percentage of ECM root tips, the number of ECM fungal species and ECM fungal similarity.• These results imply the long-term eutrophication caused by N-fixing trees can change ECM formation and ECM community structure.

Pine forests are declining because of pine wilt disease and Robinia pseudoacacia, a nitrogen-fixing species, is dominating coastal forests along the Sea of Japan. We examined the effects of R. pseudoacacia on the regeneration of a native pine species, Pinus thunbergii. Two 200 m 2 plots were set up at the border of a P. thunbergii and R. pseudoacacia-dominated area in a coastal forest. We conducted monthly censuses of emergence, distribution and survival of pine seedlings in the plots from May 2003 to December 2004. Light intensity and soil properties were also measured to analyze the relationships between the survival of pine seedlings and environmental conditions using the Mantel test and the structural equation model. Pinus thunbergii seedlings emerged in spring-early summer and in late autumn. Survival of pine seedlings in the R. pseudoacacia-dominated subplots was less than half that in the pine-dominated subplots. Survival of pine seedlings emerging in May 2003 was significantly reduced by the lower light intensity and higher soil nitrogen in R. pseudoacacia-dominated subplots. The tendency was the same for seedlings emerging from April to May 2004. We concluded that R. pseudoacacia reduced the intensity of light during the growing season and increased the nitrogen content of soil, which resulted in inhibition of the natural regeneration of P. thunbergii.

The demography and growth of mangrove seedlings in southern Thailand were studied for an 18-month period. Plots for measurement of seedlings were established using gradients of light and surface soil texture.The number of established propagutes peaked from April to August, the peak for It has noted that light conditions affected the growth of young trees (> 1 year old) to a greater degree than that of current-year seedlings.

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