Topsoil samples derived from a granite parent material were taken from a 9 years old burned forest and incubated at different moisture contents. The soil is bare and its ash bed was already depleted by runoff. A close relationship was found between the factors of soil water content, nitrogen (N) mineralization rate and CO₂ release resulting from the activities of soil microorganisms. The samples incubated at relatively high initial moisture content had a high mineralization rate. After the increase of soil moisture content to 70% of its MWHC (Maximum Water Holding Capacity), the rate of increase was higher in samples with low initial moisture content. In other terms, the dryer the soil samples were, the higher was their N mineralization rate after being moistened at the same final level. The peak recorded in the rate of nitrogen mineralization during the first 3 days after the increase of soil moisture content was followed by a gradual decrease. The increase of soil moisture content had more effect on N mineralization in the case it happened 7 days after the beginning of the incubation than 14 days later. As far as carbon dioxide was concerned, the drier the soil samples were, the higher were their CO₂ release after a sudden accretion of their initial water content adjusted to a final 70% MWHC. Instead of decreasing in the same way N mineralization did, the amount of CO₂ released from soil augmented, suggesting a regain in soil microbial activity which may have led to N immobilization.

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In this study, changes in soil microbial biomass carbon and soil development were measured for the first three years in an experimental site of five plots on decomposed granite soil: three plots were of pioneer species, one was of grass, and one was a control (no plants). The total carbon content and total nitrogen content increased in all plots over the three years; however, the increase was clearer for nitrogen than for carbon. For the first six months, soil microbial biomass carbon increased rapidly in all plots; it then varied between 32 and 179 mg/kg soil. The ratio of biomass carbon to total carbon (bioC/totC) in each plot washigher than that in an experimental forest. Therefore, bioC/totC may be a possible indicator of soil development after revegetation. Differences in soil temperatures and in soil moisture contents were significant among the plots, because the pioneer tree species began to grow rapidly from the second year.Soil microbial biomass carbon correlated positively with soil moisture content and total carbon content, but negatively with soil temperature. These three factors were able to explain the temporal fluctuations in soil microbial biomass carbon at the site. Although soil microbial biomass carbon and soil chemical properties showed no significant differences among the plots in the first three years, differences areexpected in the future when soil moisture content and soil temperature are likely to change moreremarkably as vegetation develops.

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In order to clarify the effects of water stress on the photosynthetic and transpiratory activities of 3 species of evergreen broad-leaved trees (Cinnarnornum camphora, Pasania edulis and Quercus glauca), a series of nonirrigating experiments were carried out in summer and autumn in 1996. These trees are widely used as landscaping trees in Southwest Japan.
It was showed that the leaf water potential decreased as the soil conditions became drier and the degree of decrease varied according to the tree species. P. edulis showed the steepest decrease of the leaf water potential and Q. glauca showed the least decrease. The daily net photosynthesis and transpiration also decreased as the soil conditions became drier. Almost no differences between the leaf water potential and the daily net photosynthesis were evident. Similarly little differences were detected between the leaf water potential and the daily transpiration. Therefore, it is supposed that the drought resistance of the trees depends on the ability of water absorption through roots and the ability of water retention in leaves. It can be said then, that among these 3 tree species, P. edulis is the weakest in dry soil conditions and Q. glauca is the strongest.

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The plant root system development model is constructed assuming the gravitropism and the hydrotropism of roots. Then numerical simulations in which the model is applied for the main root system represented by Japanese red pine (Pinus densiflora) are carried out. The results of calculated root system have good correspondences to the observed forms of root system in actual Japanese red pine growing both on the plane and the slope. Moreover, in the calculated form of root system under drought condition, the lateral roots show the deflection for the direction of the gravity, which corresponds to the behavior of actual plant root system go deeper in the droughty soil. These results indicate that the root system development model constructed in this study reflects the actual behavior of gravitropism and hydrotropism of roots. As a result, the appropriateness of proposed hypothesis that both the gravitropism and the hydrotropism dominantly control the root system development is confirmed.

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In this paper we deal with the germination requirements of Calystegia soldanella seeds released from hard seed coat dormancy for the purpose of landscape creation in the coastal dune areas and for the preservation of the species.
Effects of temperature, light, burial in sand and storage on the germination of the seeds released from dormancy were tested in an incubator.
Seeds that are released from dormancy with 36 N sulfuric acid show a 81-95 germination rate from 10 to 30°C within 30 days of sowing. Mean germination time is, however, reduced at 25-30°C and increased markedly at 10°C. Light or dark conditions did not affect these germination temperature characteristics.
Seeds released from dormancy were placed on a sand surface resulted in germination of 38% since they could not absorb sufficient water due to evaporation from the seed surface. However, final germination percentages of seeds buried to depth of 0.5-6 cm in sand reached 73-86%. The deeper the burial depth, the longer the mean germination time. Seeds released from dormancy kept 80-95% germination from 0 to 360 days after storage. Germination of untreated seeds, which have dormancy, however, showed only 9% after 360 days of storage.

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The relationship between spectral properties of tree leaves and components of carotenoids is discussedby the results of absorption spectrum and thin-layer chromatography (TLC). The technical applicationsare also referred. The results of thin-layer chromatography from five different species showed thatphotosynthetically active green leaves include carotenes, lutein, violaxanthin and neoxanthin as majorcomponents. The components of carotenoids altered in yellow leaves and red leaves of deciduous treesduring autumn coloration. Carotenes and lutein were observed with traces of violaxanthin and neoxanthin.Reflectance in the visible blue region with various physiological states of leaves, photosynthetically activegreen, autumn senescence and falling dead, was low by absorption of carotenoids. Only in photosyntheticallyactive leaves, excessive absorbed light causes deepoxidation of the xanthophyll violaxanthin. Thedifference spectrum associated with conversions of the xanthophyll cycle pigments results in a detectableshift in the leaf reflectance. Using functions of leaf spectral properties in the visible blue region, spatialplanning involving trees and plants would abate the overabundant blue light environment harmful to oureyes. From the viewpoint of monitoring terrestrial vegetation in remote sensing, the blue band would beuseful for discriminating vegetative cover.

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We developed an easy method of measuring microbial activities in forest soils containing relativelyabundant organic matter by FDA hydrolysis. The values (A₄₉₀) were assessed as indices of microbialactivities from comparison with cellulose decomposition activities measured in the same soil. The resultsindicated that the A₄₉₀ values almost reflected cellulose decomposition activities and were approximatelyconstant regardless of season. Hence, it is expected that the relative microbial activities in soils wereeasily detected from only a measurement by this method at any season.

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Diurnal courses of gas exchange and chlorophyll fluorescence traits of Japanese red pine (Pinus densiflora Sieb. et Zucc.) were measured for current-year needles at the top foliage of potted seedlingsunder field conditions, and mechanisms of midday depression of photosynthesis were evaluated. Even P.densiflora, which has been known as a sun-preferring and drought-tolerant coniferous species, showed amidday depression of photosynthesis under high irradiance and high temperature in summer. Depressionof photosynthesis was accompanied by low stomatal conductance, a low light-adapted quantum yield (Delta;F/Fm') and a low electron transport rate (ETR) through photosystem II (PS II). Since the pottedseedlings were grown under well-watered conditions, the midday depression of photosynthesis could beascribed to mainly two factors and the interaction between these two factors: 1) stomatal closure inresponse to rising temperature and needle-to-air vapor pressure deficit, i.e., the diffusional limiting of CO₂from the air to the needle internal spaces, and 2) the depletion of PSII activity caused by the excess lightenergy under high irradiance. Increased non-photochemical quenching (NPQ) during the midday mightplay a role in dissipating excess light energy, and thus prevent damage to the photosynthetic membrane.

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