Takehiro Masuzawa

Is photosynthesis suppressed at higher elevations due to low CO2 pressure

plant cell cultures. Proceedings of the National Academy of Sciences (USA) 89:2389-2393. Haukioja, E., J. Suomela, and S. Neuvonen. 1985. Longterm inducible resistance in birch foliage: triggering cues and efficacy on a defoliator. Oecologia 65:363-369. Karban, R., and J. Meyers. 1989. Induced plant responses to herbivory. Annual Review of Ecology and Systematics 20:331-348. Parsons, T., H. Bradshaw, and M. Gordon. 1989. Systemic accumulation of specific mRNAs in response to wounding in poplar trees. Proceedings of the National Academy of Sciences (USA) 86:7895-7899. Penia-Cortes, H., T. Albrecht, S. Prat, E. Weiler, and L. Willmitzer. 1993. Aspirin prevents wound-induced gene-expression in tomato leaves by blocking jasmonic acid biosynthesis. Planta 191:123-128. Rhoades, D. 1983. Responses of alder and willow to attack by tent caterpillars and webworms: Evidence for pheromonal sensitivity of willows. American Chemical Society Symposium Series 208:55-68. Schr6der, J., F Kreuzaler, E. Schafer, and K. Hahlbrock. 1979. Concomitant induction of phenylalanine ammonialyase and flavanone synthase mRNAs in irradiated plant cells. Journal of Biological Chemistry 254:57-65. Staswick, P. 1992. Jasmonate, genes, and fragrant signals. Plant Physiology 99:804-807. Zeringue, H. 1987. Changes in cotton leaf chemistry induced by volatile elicitors. Phytochemistry 26:1357-1360.

Ecological studies on the timberline of Mt. Fuji. I: Structure of plant community and soil development on the timberline

The distribution of the meadow above the timberline and the structure of the forest at and below the timberline were investigated on the southeast slope of Mt. Fuji. At the same time, soil profiles, water content and nutrients in the soil as related to change in the structure of the plant community were examined to obtain the data regarding soil development with the course of succession.In the course of change in structure of forest, the plant community was classified into three types:Salix/Alnus dwarf forest,Larix forest andAbies/Picea forest. The change in the soil profile, from immature to mature soil, was observed. At the timberline the water content increased rapidly from about 10% of bare land to about 25% of timberline. The nitrogen and carbon contents also increased at timberline as compared with bare land.Relationships between successional stage and soil development were clarified on the area from bare land to climax forest. The present state of the timberline at the investigated area is discussed with reference to the course of change in forest structure and soil development. It was concluded that the timberline of the investigated area is in the process of moving to a higher altitude. This conclusion was reasonable in view of the factor of air temperature.

Photosynthetic characteristics of a giant alpine plant, Rheum nobile Hook. f. et Thoms. and of some other alpine species measured at 4300 m, in the Eastern Himalaya, Nepal

The photosynthetic characteristics of a giant alpine plant, Rheum nobile Hook. f. et Thoms. and of some other alpine species were studied in situ at 4300 m, in the Eastern Himalaya, Nepal, during the summer monsoon season. Although rainy and overcast weather was predominant, the daytime photon flux density (400–700 nm) ranged from 300 to 500 μmol quanta m-2 s-1. Under such conditions, the temperature of leaves of R. nobile ranged from 10 to 14°C, and the rate of photosynthetic CO2 exchange ranged from 10 to 16 μmol CO2 m-2 s-1. The ratios of the maximum rate of photosynthetic CO2 fixation to leaf nitrogen content (defined as instantaneous nitrogen-use efficiency, NUE) for the Himalayan forbs that were examined in situ were similar to the NUE values reported for lowland herbaceous species examined under lowland conditions. In contrast to the common belief, theoretical calculations indicate that the decrease in the rate of photosynthesis due to low atmospheric pressure is small. These Himalayan forbs appeared to overcome this small disadvantage by increasing stomatal conductance. Suppression of photosynthesis caused by blockage of stomata by raindrops appeared to be avoided by either of two mechanisms: plants had large hypostomatous leaves that expanded horizontally or they had obliquely oriented amphistomatous leaves without bundle sheath extensions. All these observations indicate that the gas-exchange characteristics of alpine forbs in the Eastern Himalaya are adapted to the local wet and humid monsoon conditions and thus photosynthetic rates attained during the monsoon period are similar to those of lowland plants.

Ecosystem development and carbon cycle on a glacier foreland in the high Arctic, Ny-Alesund, Svalbard

The Arctic terrestrial ecosystem is thought to be extremely susceptible to climate change. However, because of the diverse responses of ecosystem components to change, an overall response of the ecosystem carbon cycle to climate change is still hard to predict. In this review, we focus on several recent studies conducted to clarify the pattern of the carbon cycle on the deglaciated area of Ny-Ålesund, Svalbard in the high Arctic. Vegetation cover and soil carbon pools tended to increase with the progress of succession. However, even in the latter stages of succession, the size of the soil carbon pool was much smaller than those reported for the low Arctic tundra. Cryptogams contributed the major proportion of phytomass in the later stages. However, because of water limitation, their net primary production was smaller than that of the vascular plants. The compartment model that incorporated major carbon pools and flows suggested that the ecosystem of the later stages is likely to be a net sink of carbon at least for the summer season. Based on the eco-physiological characteristics of the major ecosystem components, we suggest several possible scenarios of future changes in the ecosystem carbon cycle.

Ecological studies on the timberline of Mt. Fuji

An ecological study of dry matter production was made in a dwarf forest dominated byAlnus maximowiczii at the timberline of Mt. Fuji.Annual gross production was estimated by two methods, namely the summation method using stem analysis and total photosynthesis calculated from leaf area and photosynthetic rate per leaf area. Seasonal changes in relative light intensity and in leaf area were measured in a quadrat. Photosynthesis and respiration rates of samples were measured in temperature-regulated assimilation chambers.The phytomass was 2,989 g d.w.m−2, and those of stems and branches, leaves, and roots were 1,672 g, 293 g, and 1,024 g respectively. The growing period of this plant was about four months and this plant expanded leaves quickly. The maximum gross photosynthetic rate was 21 mg CO2dm−2 h−1 on September 1.Annual net production estimated by examining the annual rings was 922 g d.w.m−2 year−1 and annual respiration was 735 g. Annual gross production estimated from photosynthetic rates was 1,747 g d.w.m−2 year−1. The sum of annual net production by stem analysis and respiration agree closely with gross production estimated from photosynthetic rate.Gross production of this dwarf forest is comparable to the beech forest of the upper cool temperate zone owing to the high photosynthetic rate ofAlnus maximowiczii.

Intraspecific Sequence Variation of Chloroplast DNA Reflecting Variety and Geographical Distribution of Polygonum cuspidatum (Polygonaceae) in Japan

Polygonum cuspidatum in Japan, we analyzed the chloroplast DNA sequences of a region from the rbcL to the accD gene (ca. 1,420 bp), and found nucleotide variations at 22 sites in 68 samples. The phylogenetic relationship deduced from the sequence variations revealed the existence of at least five groups. The first group consisted of P. cuspidatum var. cuspidatum in the central part of Honshu; in Nagano, Yamanashi, and Shizuoka. The second, a sister of the first, consisted of those plants in Shizuoka-Itoigawa Line. The third group consisted of plants in the northern part of Japan including P. sachalinense in Hokkaido, P. cuspidatum var. cuspidatum in Aomori and var. uzensis in Akita. The fourth consisted of var. uzensis in the Tohoku District. The fifth consisted of var. terminalis in the Izu Islands. P. cuspidatum are differentiated according to their distribution, and two varieties, var. terminalis and var. uzensis, are differentiated genetically. Polygonum sachalinensis, a distinct species morphologically, fell into the accessions of P. cuspidatum on the phylogenetic tree obtained in the present study.

Successional changes in the soil microbial community along a vegetation development sequence in a subalpine volcanic desert on Mount Fuji, Japan

AimsTo study the relationship between vegetation development and changes in the soil microbial community during primary succession in a volcanic desert, we examined successional changes in microbial respiration, biomass, and community structure in a volcanic desert on Mount Fuji, Japan.MethodsSoil samples were collected from six successional stages, including isolated island-like plant communities. We measured microbial respiration and performed phospholipid fatty acid (PLFA) analysis, denaturing gradient gel electrophoresis (DGGE) analysis, and community-level physiological profile (CLPP) analysis using Biolog microplates.ResultsMicrobial biomass (total PLFA content) increased during plant succession and was positively correlated with soil properties including soil water and soil organic matter (SOM) contents. The microbial respiration rate per unit biomass decreased during succession. Nonmetric multidimensional scaling based on the PLFA, DGGE, and CLPP analyses showed a substantial shift in microbial community structure as a result of initial colonization by the pioneer herb Polygonum cuspidatum and subsequent colonization by Larix kaempferi into central areas of island-like communities. These shifts in microbial community structure probably reflect differences in SOM quality.ConclusionsMicrobial succession in the volcanic desert of Mt. Fuji was initially strongly affected by colonization of the pioneer herbaceous plant (P. cuspidatum) associated with substantial changes in the soil environment. Subsequent changes in vegetation, including the invasion of shrubs such as L. kaempferi, also affected the microbial community structure.

Ecological Significance of Different Growth Forms of Purple Saxifrage, Saxifraga oppositifolia L., in the High Arctic, Ny-Ålesund, Svalbard

Saxifraga oppositifolia is morphologically variable, and many scientists recognize two morphs; the Prostrate form (P-form) and Cushion form (C-form). In order to investigate the adaptation of the different growth forms, we analyzed the relationships between growth forms, growth patterns, manner of reproduction, tolerance to disturbance and succession. The distribution of the third internode length of shoots showed bimodality, long-internode shoot, and short-internode shoot, and it was closely related with the growth form-P-form and C-form, respectively. When both C-form and P-form plants were growing in the same moist riverbank, they had similar net photosynthesis per dry weight. The colony expansion rate of P-form was faster than C-form and the shoot fragments of P-form were easy to root and establish. On the other hand, C-form had a larger number of flowers per plant dry weight than P-form, and this caused an increase in seed production. These results showed that growth forms and reproductive characteristics were closely related, and P-form was advantageous in vegetative propagation by shoot fragments while C-form was advantageous in sexual reproduction. Morphological variability within population of S. oppositifolia appeared to be adaptive for this species as a pioneer in the primary succession in High Arctic where the selective forces vary spatially and temporally.

Effects of arbuscular mycorrhizal fungi and soil developmental stages on herbaceous plants growing in the early stage of primary succession on Mount Fuji

A pot culture experiment was conducted to examine the effects of arbuscular mycorrhizal (AM) fungi and soil developmental stages on the growth and nutrient absorption of pioneer plants growing in the early stage of primary succession on Mt. Fuji. Four herbaceous plants, Polygonum cuspidatum (Polygonaceae), Miscanthus oligostachyus (Gramineae), Aster ageratoides var. ovatus (Compositae), and Hedysarum vicioides (Leguminosae), were grown from seed in soils collected from two different successional stages, bare ground and an herbaceous plant community. Spores of indigenous AM fungi collected from the herbaceous plant community were used as inoculum. The initial colonizer P. cuspidatum showed very low levels of AM colonization (<0.4%), whereas the average AM colonization levels of M. oligostachyus, A. ageratoides var. ovatus, and H. vicioides were within the range of 13–49%. AM fungi had positive effects on the growth and N acquisition of the leguminous species (H. vicioides) irrespective of soil developmental stages. In contrast, AM colonization did not increase the plant dry weight and N content of the non-leguminous species (P. cuspidatum, M. oligostachyus, and A. ageratoides var. ovatus) in both soil developmental stages. A positive effect of AM colonization on P content was observed in M. oligostachyus, A. ageratoides var. ovatus, and H. vicioides only in soil collected from the herbaceous plant community. P. cuspidatum showed no or a negative response to AM colonization in all cases. These results suggest that the effect of AM fungi on plant growth depends more on the plant species than soil developmental stages in the early stage of primary succession in this volcanic area.

Diurnal changes in needle gas exchange in alpine Pinus pumila during snow‐melting and summer seasons

Pinus pumila (Pallas) Regel. is a dominant dwarf tree in alpine regions of Japan. The possible factors limiting the net photosynthetic rate (Pn) of the needles of P. pumila were examined in the snow-melting (May) and the summer (August) seasons. In August, in situ maximum Pn was 20 μmol kg−1 needle s−1 in the current-year needles and 25 μmol kg−1 needle s−1 in the 1-year-old needles. Diurnal trends of Pn in August were positively related to fluctuations in photosynthetic photon flux density (PPFD) and no midday depression of Pn was found, indicating that a decrease in PPFD rather than an increase in needle-to-air vapor pressure deficit (ΔW) might cause the reduction of Pn. Both stomatal conductance (gs) and Pn were lower in May than in August. In May, Pn and gs were almost zero in the morning, but gradually increased with decreasing ΔW, reaching maximum Pn values (4 μmol kg−1 needle s−1) and gs (60 mmol kg−1 needle s−1) at 16.00 hours. The daytime Pn in May was positively related to gs. Relative water content in the exposed needles above the snow in May was 83%, which was far above the lethal level. This indicates that the water flow from stems or soils to needles was enough to compensate for a small amount of water loss due to the low gs in May, although the water supplied to needles would be impeded by the low temperatures. Thus, the reduced gs in May would be important for avoiding needle desiccation, and would result in a reduced Pn.