Mutsumi Nomura

Diurnal fluctuation in stream flow and in specific electric conductance during drought periods.

Abstract In a headwater basin covered with boreal forest in northern Japan, drought flow was observed in winter and in summer. In summer drought it was found that remarkable diurnal fluctuation of stream flow and of electric conductance is caused by daytime evapotranspiration. It was found that the daily reduction in stream flow was accompanied by a reduction in the total ion concentration. The drought hydrograph was separated into two components, assuming the drought flow to be a mixture of ionically dense throughflow and of ionically dilute groundwater flow entering the stream in its lower reaches.

Ecophysiological responses of the larch species in northern Japan to environmental changes as a basis for afforestation

For sustainable use and suitable management of larch plantations, we must clarify the ecophysiological responses of larch species to environmental changes. The physical environment has been changing dramatically, e.g., increase in atmospheric CO2 concentration ([CO2]), nitrogen (N) deposition, and atmospheric ozone concentration ([O3]), and these changes may negatively affect growth of larch species. This review summarizes the previous experimental studies on the ecophysiological responses of larch species to elevated [CO2], soil acidification, elevated [O3], and N load. Based on the advanced studies, although elevated [CO2] will stimulate the productivity of larch, increase of [O3] and severe soil acidification will reduce it. Increase of N deposition, at least, will not negatively affect larch productivity. Finally, we propose the future direction for investigation to understand the mechanism of the responses of larch species and to predict the associated risk.

Comparison of growth characteristics and tolerance to serpentine soil of three ectomycorrhizal spruce seedlings in northern Japan

Picea glehnii is distributed widely on serpentine soils in northern Japan. Serpentine soil is characterised by the presence of heavy metals (Ni, Cr) and excessive Mg; these elements often suppress plant growth. We have examined the tolerance to serpentine soil and its effects on growth of P. glehnii, P. jezoensis (distributed in the same region) and P. abies (planted for timber production).The dry mass of each organ was not reduced in P. glehnii planted in serpentine soil contained nursery (serpentine nursery). In contrast, growth of P. jezoensis and P. abies was suppressed. Concentrations of Ni and Mg in needles and roots of P. glehnii planted in serpentine nursery were the lowest of the three species. Moreover, the photosynthetic rate of P. glehnii planted in the serpentine nursery was not reduced. P. glehnii has high capability to maintain low concentration of Ni, and ectomycorrhizal symbiosis may have a positive effect to excluding Ni. As a result, P. glehnii has a high tolerance against Ni toxicity, and its photosynthetic capacity is not suppressed by accumulation of Ni.

Nutrient dynamics and carbon partitioning in larch seedlings (Larix kaempferi) regenerated on serpentine soil in northern Japan

Japanese larch (Larix kaempferi) grows at a relatively high rate in northern Japan, even in serpentine soil. Serpentine soil has high concentrations of heavy metals (Ni, Cr), excessive Mg, and is nutrient deficient. These factors often suppress plant growth. We examined the mechanisms of Japanese larch’s tolerance to serpentine soil. We compared growth, photosynthetic capacity, and concentrations of elements in needles and roots between larch seedlings growing in serpentine soil and in nonserpentine (i.e., brown forest) soil. Dry mass of needles, stems, and branches were lower in seedlings grown on serpentine soil than in those grown on brown forest soil. There were lower concentrations of phosphorus and potassium in seedlings grown on serpentine soil than in those grown on brown forest soil. Seedlings growing on serpentine soil had lower Ni in plant organs. Our results suggest that larch seedlings grown on serpentine soil were able to exclude toxic elements. Moreover, the photosynthetic capacity and nitrogen concentration in needles was almost the same for seedlings grown in the two soil types. A wide range in growth was observed among individuals grown on both soil types. This may be regulated by nitrogen storage in the roots.

Growth of regenerated tree seedlings associated with microclimatic change in a mature larch plantation after harvesting

In order to further develop methods of sustainable forest management, we evaluated the effects of logging practices during the winter on microclimatic factors and growth of four seral deciduous broad-leaved tree seedlings regenerated in a larch plantation in northern Japan. We found that winter logging practices drastically changed microclimatic factors, especially in terms of light intensity and the vertical distribution pattern of CO2 concentration. Harvesting overstory larch trees increased photosynthetic photon flux (PPF), which may enhance the photosynthesis of understory plants. We examined the undergrowth for tree seedlings of the following species: two late successional species, Prunus ssiori and Carpinus cordata; one gap phase species, Magnolia hyporeuca; and one mid-late successional species, Quercus mongolica var. crispula. All of the four studied tree species responded well to the practices of winter logging after the second year of harvesting overstoried larch trees. The current shoot diameter and current shoot length increased significantly. Therefore, we conclude that winter logging practices should improve shoot growth of deciduous broad-leaved tree seedlings regenerated in a larch plantation through the change in environmental factors that accompanies larch harvest.

Growth characteristics of Sakhalin spruce (Picea glehnii) planted on the northern Japanese hillsides exposed to strong winds

Sakhalin spruce (Picea glehnii), a native species typically found in northern Japan, has been used in reforestation on hillsides exposed to strong winds. In the reforestation areas, there are south-facing (S-slope) and northwest-facing slopes (NW-slope). Climatic conditions are contrasting between the two slopes, with shallower snow cover on the S-slopes. We compared growth responses of the spruce to micro-environment between the S- and NW-slopes through soil nutrients, needle longevity, water status, photosynthesis, and nutrients in the needles. These parameters were measured in needles exposed above the snow in winter and in lower needles protected by snow cover. High-position needles suffered from drought stress, especially in winter, and needles were shed early in the year on both slopes. Low-position needles did not suffer from drought stress, and maintained a high photosynthetic rate on both slopes. However, needle longevity was reduced on the S-slope, and concentrations of nitrogen, phosphorus, and potassium in the needles decreased with needle age. Soil nutrient concentrations were low on the S-slope, which suggests that the needles on the S-slope may remobilize nutrients from aged needles to younger needles prior to shedding. This characteristic is probably an adaptation in Sakhalin spruce to poor soil conditions.