Seed production and seed bank of Sabina vulgaris were studied to clarify the regeneration mechanism by seeds in the Mu Us desert of Inner Mongolia, China. Seed production of S. vulgaris was greater at the bottom part of stabilized dune than at the ridge. A number of buried seeds were obserbed under the canopy of S. vulgaris, but, on the other hand there were very few seeds at the out of canopy. Mean size of seed bank under canopy was 2600-4800/m² at the bottom, and 567-1575/m² at the ridge. The ratio of buried viable seeds was 2.9-3.8% at the bottom, and 4.0-8.8% at the ridge. Seedlings of S. vulgaris were only found under canopy at the bottom part of stabilized dune, where distance to ground water was short, and such habitat was considered to be suitable for germination.

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Effects of the light and soil moisture conditions on the emergence and growth of current year seedlings were experimentally examined for Quercus serrata and Q. variabilis. We established 3%, 10% and 30% in the relative light intensity for the light conditions, and 5%, 10% and 20% in the soil moisture content for the soil moisture conditions. The emergence rate of seedlings for Q. serrata was significantly lower in 5% soil moisture content than that for Q. serrata in the other soil moisture contents and that for Q. variabilis in all the soil moisture contents. The emergence duration of seedlings was the shortest in the 20% soil moisture content for both the two species. The difference of the survival rate was not significant between Q. serrata and Q. variabilis and also among the light conditions or the soil moisture conditions. The dry weight of roots, stems, branches and leaves of seedlings increased significantly with the increase of the relative light intensity and the soil moisture content. T/R ratio and the ratio of dry weight of leaves for Q. serrata did not vary among the different light conditions. On the other hand, T/R ratio and the ratio of dry weight of leaves for Q. variabilis increased as the relative light intensity decreased. T/R ratio and the ratio of dry weight of leaves for both the two species decreased as the soil moisture contents decreased.

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Two year-old seedlings of Quercus glauca, Quercus serrata and Zelkova serrata were grown in gravel cultures using water solutions. In order to examine the effects of long-term water stress, the osmotic potential of the water solutions were maintained at -0.02 MPa, -0.04 MPa, and -0.30 MPa for about a year by polyethylene glycol (PEG) treatments.
Different effect patterns were detected in each species. In Quercus glauca, quantitative and physiological effects were detected, but morphological effects did not appear. However in Quercus serrata and Zelkova serrata, not only quantitative and physiological effects, but morphological effects were observed. These effects appeared in different degree depending on the amount of water stress.
In Quercus glauca, new leaves of lower chlorophyll content were produced in the -0.04 MPa treatment, keeping chlorphyll content high in old leaves. In the -0.30 MPa treatment, old leaves fell rapidly and new leaves of high chlorophyll content were produced. Growth rates of new leaves and lengths of leaves showed no difference among treatments. On the other hand, in Quercus serrata and Zelkova serrata, old leaves survived longer and the number of bud breaks were suppressed by water stress. Growth rates of new leaves were lowered, which made lengths of new leaves short. Chlorophyll content of new leaves were decreased by water stress. The threshold of effects in leaf size and chlorophyll content were at lower water stress levels in Quercus serrata than in Zelkova serrata, indicating greater sensitivity in Quercus serrata to water stress.

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The effect of ammonium and nitrate as nitrogen source on growth, water relation and ions concentration were studied in Nerium oleander L. under NaCl salinity. Plants were grown in semi automatic sand culture system in the greenhouse. It was revealed that salt tolerance of Nerium plants was significantly increased when supplemented with nitrate as sole nitrogen source than that of ammonium. Total dry weight, leaf area and number were reduced more drastically in ammonium than nitrate treated plants. A higher level of Na⁺ and Cl^- was observed in leaves and branches in ammonium treated plants under salinity whereas these ions were accumulated in roots in nitrate. Additionally, salinity induced more decrease in K⁺/Na⁺ selectivity and K⁺ concentration in leaves and branches of ammonium fed plants. Osmotic adjustment was done faster in nitrate treatment and leaves succulence ratio as weight per leaf area did not decrease due to salinity. Decrease in photosynthetic rate was almost similar in both nitrogen treatments under salinity. Our result indicates that nitrate fed plant reduced the level of stress by reducing concentration of Na⁺ and Cl^- in leaves. In contrast, sequestration and counterbalance of high concentration of Na+ and Cl^- in leaves of ammonium fed plants is highly energy required process and diverted the energy from plant production.

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Aerial revegetation project has been taken place on the slope devastated by pyroclastic flows in Mt. Unzen Volcano. In order to clarify its effect to stabilization of the mountain slope, we made observation of surface runoff and sediment discharge on a revegetated slope and a bare slope. The surface runoff and sediment concentration of the revegetated slope were about 1/2 and 1/3 of those of the bare slope, hence the sediment production may have decreased to 1/6 by the revegetation.

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[in Japanese]

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