The parameters of N mineralization potential (N_0), the N mineralization rate constant (k) and apparent activation energy (Ea) are normally estimated by mathematical analysis using a kinetics model based on results of the in vitro incubation in forest soil of the Kanto region, Japan. The relationships between N mineralization parameters and chemical properties and carbon mineralization potential (C_0) in forest soil were investigated. Soil samples were taken from Japanese cedar (Cyptomeria japonica) stands (3 plots), Japanese cypress (Chamaecyparis obtusa) stands (3 plots) and deciduous broad-leaved stands (1 plots) in Gunma Prefecture, Japan, and from evergreen broad-leaved stands, a matebasii (Lithocarpus edulis) stand (1 plot) and a sudajii (Castanopsis cuspidata var sieboldii) stand (1 plot) in Chiba Prefecture, Japan. Soil samples were taken at depths of 0-10cm (or 0-5cm and 5-10cm) and 10-20cm in each plot. The relationship between the C/N ratio and N mineralization parameters was not significant in any of the soil samples. However, in soil samples where the C/N ratio was ≧20, N_0 increased and Ea decreased as the C/N ratio decreased. There was a positive correlation between C_0 and N_0 the regression line was C_0/N_0≒20. k was the greatest and Ea was the smallest when C_0 was between 7 and 8% of total C (C_0/C). This suggests that there is little C_0 available for N mineralization when C_0/C<7-8% and that there is sufficient C_0 for N immobilization when C_0/C>7-8%. Thus, C properties are important as indicators of movements of the amount of available N in forest soil.

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Jpn. J. For. Environment 41, 67-76, 1999. An investigation was performed on the changes in physical and chemical properties of soil in a Pinus massoniana (masson pine) plantation after clear-cutting and burning (CCB) on upper, middle and lower slopes in Fujian Province, China. The monthly mean temperature of the CCB site at 0 cm soil depth was respectively 3.0℃ and 5.9℃ higher in July and August than in the masson pine stand (control). The pF of surface soil (0-10cm) after CCB ranged from 3.7 to 4.2 during low rainfall from November to January, which is clearly higher than that of the control. The volume of capillary water at the CCB site was very low, and was 10-30% of the control. The increments of pH at the surface soil caused by CCB after two weeks about one, and they sharply decreased after one year. After two years it was a little lower than that before CCB. The increments of mineralized nitrogen and cation in the soil caused by CCB decreased sharply during the first year, and were basically equal to those of the control after two years. The loss of total nitrogen caused by CCB (including the loss of nitrogen in soil and the residual organic matter) was estimated to be 417kg ha^<-1> at the upper slope, 619kg ha^<-1> at the middle slope and 694kg ha^<-1> at the lower slope. If CCB preparations are repeated in short rotation, the physical and chemical properties of the soil will deteriorate, especially with a deficiency of nitrogen.

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Growth responses of Pinus thunbergii seedlings to weakly acidified soil by application of acidic solution were studied. P. thunbergii seedlings colonized by ectomycorrhizal fungi naturally were transplanted from the nursery to pots filled with infertile soil. We made four plots with or without application of acidic solution and leaf-thinning. The pHs of surface soils were about 5 at the acidified plots and about 6 at the control plot. The pHs of sub-soils did not decreased by application of acidic solution. Soil solutions from the acidified plots contained more base cations than those from the control plots. Concentrations of manganese and aluminum in soil solutions were very low even from acidified plots. Nutrient status of P. thunbergii seedlings was not affected by the soil acidification. Growth of the seedlings was smaller at the leaf-thinning plot than at the control plot. Growth of the seedlings was a little bigger at the acidified plot than at the control plot. Although leaf-thinning would decrease carbon flow from the host tree to ectomycorrhizal fungi, it did not affect on the responses of the seedlings to soil acidification. The formation ratios of ectomycorrhizal roots did not differ among four plots. Development of Inocybe lacera basidiome was significantly depressed by soil acidification. It was implied that ectomycorrhizal fungi were more sensitive to soil acidification than P. thunbergii seedlings.

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We investigated growth and photosynthetic responses to light and nutrients in seedlings of two tropical tree species. Swietenia macrophylla and Schizolobium parahybum were grown for ca. 150 days under five light regimes and three nutrient applications. Nutrient treatments were less effective on examined parameters than light regimes for both species. In both species, nutrient amendments determined differences in growth but not in photosynthetic characteristics. S. macrophylla grew faster with high nutrient application while S. parahybum showed best growth with medium nutrient application. Both species had best growth performance under moderate light conditions. However, they differed in their minimal light requirements for survival. High tolerance to deep shade (5% in relative light intensity) in S. macrophylla was associated with changes in apparent quantum yield across a wide range of irradiance. S. parahybum, which did not survive in deep shade, lacked such adaptive features. Changes in maximum net photosynthesis in response to light regimes contributed to explaining an important fraction of variation in growth rates in S. macrophylla but not in S. parahybum. Photosynthetic capacity did not change consistently between species, while height growth rates were higher in S. parahybum than in S. macrophylla at all light levels except for deep shade. We suggest that faster growth of S. parahybum compared to that of S. macrophylla might be more strongly influenced by differences in carbon allocation than in carbon assimilation capacity at the single leaf level.

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In the autumn of 1995, high mortality of Cryptomeria trees occurred in southern part of Miyazaki Prefecture. It was estimated that damaged square was about 41 hectares and the number of mortality were 800 hundreds. The drought was considered to be the main cause of the damage, but we often observed symptoms of guignardia dieback on dead trees. In this area, it only rained a little in the summer of 1995. At the same period, the mean annual wind velocity and mean annual temperature were higher than ordinary years. Severe damages occurred in the southern area of Miyazaki group, but damage in the Nichinan group adjacent to the northern and western territories of the Miyazaki group were not severe. In the Nichinan group, hill slopes are characteristically gentle with little soil eroded areas, and accumulation of black soil was observed. In contrast, hill slopes in the Miyazaki group are typically steep, and have a lot of soil eroded areas. In the Miyazaki group, soil is characterized by containing a lot of gravel, and the effective soil depth is shallower than in the Nichinan group. There were no topographical differences between damaged and non-damaged areas in the Miyazaki group. We tried to analyze the relationship between the damage and topographical characteristics by mapping the damaged sites. The map showed us that damage was concentrated on a particular direction on slopes near ridge tops. We speculate that damage occurred due to the wind from the sea under a particular condition. Weight-differences of soil core samples between field moisture condition and saturated condition in damaged areas were less than those in non-damaged areas both A and B horizons. Percolation index of the A horizon was larger in the damaged area than in the non-damaged area. No differences in percolation index in the B horizon were observed between damaged and non-damaged areas. The maximum water holding capacity of damaged area soil was slightly lower, and the minimum air capacity of it was slightly higher than those of non-damaged area soil. Those results show that water holding capacity of damaged areas soil is smaller than it of non-damaged areas. From the above mentioned investigations, it can be concluded that the damage of Cryptomeria stands in 1995 was caused by a water deficiency that derived from the complex factors such as meteorological condition, geological features, soil moisture condition associated with soil physical properties, and susceptibility to guignardia dieback disease.

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To clarify the gas exchange characteristics of temperate broad-leaved tree species, we investigated net photosynthetic rate (Pn), stomatal conductance (Gw), and intrinsic water-use efficiency (WUE,=Pn/Gw) of leaves of 41 species grown in the arboretum within the campus of Forestry and Forest Products Research Institute. Maximum value of Pn (Pn_<max>) varied 9 to 24μmolCO_2m^<-2>s^<-1> among species, and was not different between deciduous and evergreen species. Maximum value of Gw (Gw_<max>) varied 50 to 900mmol m^<-2>s^<-1>, and was relatively high in deciduous species than evergreen species. WUE (Pn_<max>/Gw_<max>) varied 10 to 90×10^<-6>molCO_2molH_2O^<-1>, and was relatively high in deciduous species than evergreen species. Based on these gas exchange traits, we classified the 41 species into three categories; dry type, wet type, and medium type. In 21 species, results of this study coincided with the ecological traits of the species. However, the gas exchange traits were not consistent with the ecological traits in the other species.

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