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Seasonal variation in non-assimilatory organ and leaf biomass and necromass, leaf area index (LAI), leaf mass per unit area (LMA), and leaf nitrogen content per unit leaf area of managed C3 cool-season turfgrass (Kentucky bluegrass, Poa pratensis L.) fields under four light conditions (irradiance levels: 100, 62, 48, 20 ) were examined in situ over 2 years. Seasonal fluctuations in light and the temperature dependence of the gas exchange of intact leaves grown under three light conditions (irradiance levels: 100, 48, 20 ) were also examined for 1 year. The magnitude of spring growth and summer decline in non-assimilatory organ and leaf biomass depended on the light conditions. Both non-assimilatory organ and leaf biomass were higher in the sunnier plots, as was the ratio of non-assimilatory organs to whole biomass. A step wise acclimatization to low irradiance reduced the allocation to non-assimilatory organs to maintain leaf biomass, limited LMA to maintain the LAI, and limited the latter to retain leaf nitrogen per unit leaf area, depending on the shade level. Kentucky bluegrass growing under lower light conditions had similar single-leaf photosynthetic abilities until early summer, but the normalized maximum carboxylation rate at 25 [Vcmax25] decreased during the decline of turfgrass in summer, depending on the shade level, which corresponded to the decline in leaf nitrogen content per unit leaf area.

Apart from certain studies on Macrocystis pyrifera (Linnaeus) C. Agardh, very few in situ experimental studies on production have been carried out to verify that "bottom-up effects" (relating to nutrient supply) are more important than "top-down" effects (relating to herbivory) in temperate kelp forests. The effects of nutrient supply on recruitment and production of hatchery-raised gametophytes of Saccharina japonica, cultivated on a rope, and wild Saccharina religiosa, cultivated on a rope and on new concrete reefs placed at the sea bottom, were examined at an experimental site with artificial nutrient addition continuously from without nutrient supply, at a natural site in Tomari (Sea of Japan, southwestern Hokkaido, Japan). At both sites, sea urchins were removed for exclusion of top-down effect. At the natural site, no hatchery-raised S. japonica and wild S. religiosa grew on the rope. No wild S. religiosa grew on the porous-concrete reefs and rocks. At the nutrient-enhanced site, S. japonica and S. religiosa grew rapidly on the rope, at rates of 47.7 and 33.3 plants/10 cm length rope, respectively. S. religiosa grew on the concrete reefs at a concentration of 9.7 plants/0.3 m 2 . At the nutrientenhanced site, the concentrations of NH 4 -N, NO 3 -N, NO 2 -N, and PO 4 -P ranged from 35.2-173.2, 2.1-10.9, 0.3-1.5, and 0.8-2.6 μmol L −1 , respectively, being markedly higher than those at the natural site, where these nutrient concentrations were almost equal to the averages off Tomari. These results indicate that the production of Saccharina kelp is restricted by bottom-up effects (at a low nutrient concentration) in the Sea of Japan, southwestern Hokkaido. Nutrient supply would be essential for growth enhancement of Saccharina kelp production in a marine environment around Japan where, in recent times, water temperatures have increased by ca. 0.5°C and nutrient concentrations have decreased.

We have carried out a paleomagnetic study on well-dated Early Miocene volcanic rocks from the Ninohe area in northern NE Japan. Dacitic welded tuffs ranging from 24 to 21 Ma possess westerly paleomagnetic directions with normal polarity (formation-mean: D/I = 294.5°/44.2° with α 95 = 8.3°, 8 sites), while the andesite flows formed at 17 Ma exhibit southerly directions with reversed polarity (D/I = 186.6°/-61.9°, 2 sites). A positive conglomerate test assures the stability of high-temperature components of remanent magnetization. Our results demonstrate that northern NE Japan rotated counter-clockwise through more than 60° between 21 and 17 Ma, most likely in association with the opening of the Japan Sea. The rotation of northern NE Japan thus preceded the about 15 Ma rapid clockwise rotation of SW Japan, and was synchronous with the possible pre-16 Ma southward translation of it. In comparison with published data, we further suggest that intra-arc block rotations occurred in the back-arc region of NE Japan during and after the arc rotation.

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