Yoshio Ino

Comparison of ecophysiological responses to heavy snow in two varieties of Aucuba japonica with different areas of distribution

Aucuba japonica varieties are common evergreen understory shrubs in Japan. Aucuba japonica var. borealis is distributed on the Sea of Japan side of Honshu and Hokkaido where heavy snow cover lasts for more than 3 months in winter. Aucuba japonica var. japonica is distributed in areas with shallow or no snow on the Pacific Ocean side of Honshu and Shikoku. The ecophysiological characteristics of var. borealis were compared with those of var. japonica to examine the effects of heavy and long-term snow cover on the life cycle of var. borealis. Shoots of both varieties were shaded in crushed ice for 110 days, but their photosynthetic activities, chlorophyll contents and the chlorophyll a/b ratio was not affected. The leaves of var. borealis were no less frost tolerant than those of var. japonica. In spite of the difference in environmental factors, both varieties had similar characteristics in seasonal changes of photosynthesis, respiration and chlorophyll a/b ratio. These results suggest that var. japonica could survive in areas with heavy snow where it does not normally occur. Leaf net production (LNP) was estimated based on the microclimatic data and seasonal photosynthetic and respiration rates. The difference in the annual LNP between the two varieties was equivalent to the difference in the LNP during the snow season. One of the major effects of snow cover is to interrupt and reduce the production period of var. borealis.

Effects of slope and canopy trees on light conditions and biomass of dwarf bamboo under a coppice canopy

Dwarf bamboo, Pleioblastus chino, grows extensively in abandoned coppice woodlands on the Kanto Plain in central Japan and suppresses other understory plants. In order to clarify the factors determining the growth of P. chino, we considered the effect of light conditions under a coppice canopy and examined its relationship with slope aspect, slope angle, and basal area of the trees. The relative photon flux density under the canopy was highly correlated with canopy coverage (R2 = 0.97). The light conditions under the canopy were almost the same at all sites in the summer leafy season regardless of the stand type, while they were remarkably different among the sites and depended on the basal area of evergreen trees in the winter leafless season. The biomass of P. chino on the forest floor was described by the equation: y = 3.18 x1 − 0.05 x2 + 3.11 (R2 = 0.77, P < 0.01), where y is the log-transformed value of P. chino biomass (g dry mass m−2), x1 is cos ξ at solar noon at the winter solstice, and x2 is the canopy coverage during the winter leafless season. ξ is the angle between the sun’s rays and the normal to the surface and changes with slope aspect and angle. We concluded that light conditions under the canopy in the leafless season had a great effect on P. chino biomass, and that the basal area of evergreen trees and slope characteristics can provide useful guidelines in the control and management of P. chino.

Tubers and rhizome fragments as propagules: competence for vegetative reproduction in Equisetum arvense

Rhizome fragments (referred to as “fragments”) and tubers of Equisetum arvense L. were cultured in order to investigate their competence with respect to vegetative reproduction. The starch concentration of the fragments was lower than that of the tubers, but the initial growth of new individuals from these fragments was superior to that from tubers obtained from the same dry mass. This superior growth was due to the large number of buds (grown from nodes) and aerial shoots on the fragments. The competence for vegetative reproduction depended on the relationship between the stored starch and the number of buds.

Evaluation of direct and diffuse radiation densities under forest canopies and validation of the light diffusion effect

In order to consider the effects of light quality on the growth of understory plants, both the direct and diffuse components of solar radiation must be evaluated. However, the basis for choosing the threshold between the two components of radiation has not been systematically determined. We evaluated the basis and methods for separating direct and diffuse radiation under field conditions. Daily courses of direct and diffuse photosynthetic photon flux densities (PPFDs) over and under canopies were measured with quantum sensors and were predicted from hemispherical photographs. We proposed a new variable, called the diffuse coefficient of canopy (dc), to compensate for the increase in the diffuse radiation component as the sunlight passes through the overstory canopy. dc was highly correlated with canopy coverage (cc) (dc = 0.01cc − 0.3, r2 = 0.95). For woodland sites, PPFD can be predicted from hemispherical photographs according to the following equations: Wdir = Sout(τ − dc)M sinα and Wdif = Sout (0.271 − 0.294(τ − dc)M) sinα, where Wdir and Wdif are the direct and diffuse radiation components in woodland sites, Sout is the extraterrestrial PPFD normal to the solar beam, τ is the atmospheric transmittance, M is the optical airmass number and α is the solar elevation. The daily courses of PPFD and sunflecks under canopies can be estimated from hemispherical photographs when the effects of dc are considered.

Differences in Shoot Size and Allometry between Two Evergreen Broad-Leaved Shrubs, Aucuba japonica Varieties in Two Contrasting Snowfall Habitats

Aucuba japonica, an evergreen broad-leaved shrub. Aucuba Japonica var. borealis is widely distributed in heavy snowfall areas in Japan and is covered, shaded and physically pressured by snow for more than four months of the year. On the other hand, var. japonica is widely distributed in light snowfall areas. The sizes of new shoots and leaves were significantly different between the two varieties with different critical shoot sizes for flowering. The average new shoot dry mass of var. borealis was about one third of that of var. japonica. Despite the differences in growing conditions and shoot size, no significant differences were observed in the allometry of their shoot organs between the two varieties. Large new shoots had thicker and longer stems per biomass than small shoots because of their larger pith volume. The large shoots showed higher efficiency of stem growth per invested biomass and had a higher rate of annual height increase than small shoots. When the size of new shoot rapidly increased from year to year, i.e. the plants are growing well, initiation of flowering was postponed and vegetative growth continued. Small new shoots were tolerant of low productivity conditions but traded vertical growth for an increase in matter allocation to leaves.

Response patterns of net photosynthesis to moisture of mosses in xeric habitats

The response patterns of net photosynthesis to moisture level of mosses in xeric habitats were compared with those in mesic habitats, in order to determine whether the former species are better adapted to the xeric condition with regard to carbon gain.Moss species examined wereRhacomitrium lanuginosum andR. barbuloides in xeric open habitats andDicranum japonicum, Hypnum plicatulum, Ptilium crista-castrensis, Pleurozium schreberi andHylocomium splendens in mesic habitats on the coniferous forest floor in the upper subalpine zone of Mt. Fuji. Three additional xerophytic species collected at other localities,Ptychomitrium polyphylloides, Grimmia pilifera andHedwigia ciliata, were also examined.Five species in the xeric habitats showed an optimum range of moisture level for net photosynthesis, 2 to 3g·g−1. On the other hand, species in the forest showed a wider optimum range, 3 to 8g·g−1. Net photosynthetic rate at the moisture level of 0.5g·g−1 was positive in xerophytic mosses, but negative in most forest mosses.Moisture levels where external capillary water disappeared and drop of water potential began was determined by blotting water-saturated shoots with membrane filters. These moisture levels were low in the xerophytic mosses and high in the forest mosses, although there were some exceptions.It was concluded that mosses in xeric habitats are better adapted for the efficient use of water for photosynthesis than those in mesic habitats.

Contribution of fern gametophytes to the growth of produced sporophytes on the basis of carbon gain

Sporophytes appeared on most gametophytes of Thelypteris palustris (Salisb.) Schott that reached a certain size, which is interpreted to be a critical size of gametophytes for the production of sporophytes. After sporophytes were produced, attached gametophytes ceased dry weight growth, but the gametophytes which did not produce sporophytes grew successively. It was hypothesized that matter produced by gametophytes was being supplied to young sporophytes. Photosynthesis and respiration of gametophytes with attached sporophytes were not significantly different from that of gametophytes without sporophytes. Photosynthetic activity of gametophytes dropped from 0.18 to 0.03 μmol CO2 g−1 s−1 during the growth period. The higher photosynthetic rates of gametophytes in the early growth stage were important for reaching the critical size for sporophyte production in a short time. Sporophytes in the ‘one leaf stage’ averaged 0.14 μmol CO2 g−1 s−1 of photosynthetic activity. The results show that sporophytes that had expanded the first leaf grow by their own photosynthetic production. Gametophytes allocated the photosynthate for sporophytes and it was an important aid before the one-leaf stage. The supportive role of gametophytes ended at that stage.

Physiological tolerance of Camellia rusticana leaves to heavy snowfall environments: The effects of prolonged snow cover on evergreen leaves

Camelliarusticana is an evergreen broad-leaved shrub found only in areas of heavy snowfall in Japan. The ecophysiological tolerance of this species to prolonged snow cover was studied in comparison with those of Camellia japonica found in areas of light snowfall. The shoots of C. rusticana and C. japonica were stored under a simulated snow cover for 1 year. During the experimental period, about 20% of the leaves of C. japonica defoliated after 90–140 days of storage and more than 80% of the leaves browned within 360 days. The proliferation of fungi was observed on all shoots of C. japonica after 200 days. In contrast, the leaves of C. rusticana showed no visible changes throughout the experimental period. The decline in the rate of soluble carbohydrate content in C. rusticana was about one-sixth of that in C.␣japonica. The photosynthetic capacity (O2 exchange rates at saturated light and CO2 at 20°C) of C.␣japonica dropped to about half its initial value after 140 days, while that of the C. rusticana did not change even after 360 days. Under dark conditions, the stomata of C. rusticana were always closed through the experiment, but those of C. japonica were not completely closed after 90 days. The differences in stomata characteristics and the consumption rate of soluble carbohydrates under snow-covered conditions between the two Camellia species are important factors for determining their habitat segregation by snow depth.

Comparative study of the effects of temperature on net photosynthesis and respiration in lichens from the Antarctic and subalpine zones in Japan

Photosynthetic activity and dark respiration were measured in some species of lichens,Umbilicaria, Cladonia, Stereocaulon, Usnea, etc. sampled in the Antarctic and subalpine zones of central and northern Japan. On the basis of the responses of their activities to thallus temperature, the response patterns were divived into three groups, and further, each group was subdvided into some adaptation types for net photosynthesis and repiration. Lichens collected in the Antarctic were adapted to cool condition and some species collected in subalpine zones were adapted to warm condition. For exmaple, the optimal temperatures for net photosynthetic rates in Antarctic lichens were lower than 5 C and those in lichens which lived on rock surface at a southern slope in mountains of Japan were higher than 20 C.

Field measurement of net photosynthesis of mosses at Langhovde, East Antarctica

Net photosynthesis and dark respiration (CO2 flux) of Antarctic mosses were measured at Langhovde, East Antarctica, from 9 to 17 January 1988. Moss blocks were taken from communities in the Yukidori Valley (69°14′30″S, 39°46′00″E) at Langhovde. Each block was composed ofCeratodon purpureus andBryum pseudotriquetrum, orB. pseudotriquetrum. The upper part of the block was used to measure net photosynthesis and dark respiration. The net photosynthesis of each sample was measured in the field for one or three days with two infrared CO2 gas analyzers and an assimilation chamber. The relationships of net photosynthetic rate and dark respiration rate, to the water content of the sample, the intensity of solar radiation and the moss temperature were estimated from the field data. The maximum rate of net photosynthesis was about 4 μmol CO2 m−2s−1 at saturating radiation intensity and at optimum temperature, about 10°C. Environmental features of moss habitats in the Yukidori Valley are discussed in relation to these results.