Simultaneous measurements of quantum yield and CO2 uptake for the assessment of non-assimilative electron flow in tree leaves

Using attached and detached leaves ofAcer palmatum Thunb. andRhaphiolepsis umbellata Makino, pulse-modulated chlorophyll fluorescence and CO₂ exchange were measured. Quantum yield of photosynthesis was determined from the fluorescence parameter(Fm′−Fs)/Fm′, where (Fm′−Fs) was defined as the difference between steady state chlorophyll fluorescence (Fs) and maximum fluorescence (Fm′) elicited by a saturating light pulse. The rate of electron transport through photosystem II (total electron flow) was calculated from the product of quantum yield andA (PFD), whereA is the rate of absorbed photons as given by leaf absorptance, and PFD is the photon flux density at the leaf surface. The rate of electron transport dependant on CO₂ uptake (assimilative electron flow) was calculated from the gross photosynthetic rate in a leaf. The difference between the rates of total and assimilative electron transport was denoted as the rate of non-assimilative electron transport which depends on photorespiration and oxygen reduction. Available data provided quantitative information on the rate of non-assimilative electron flow in intact leaves. When leaf photosynthesis ofA. palmatum was measured under sunlight, the rates of total and assimilative electron transport were determined to be approximately 900 and 150 μmol equiv. e/mg Chl·h, respectively. The difference (750 μmol equiv. e/mg Chl·h) was attributed to the activity of non-assimilative electron flow. The ratio of total to assimilative electron flow was found to increase gradually with rising in irradiance. The results suggest that non-assimilative electron flow occurred at much higher rate than assimilative electron flow at high irradiance. Implications of the results are briefly discussed in relation to photosynthesis limitation in tree leaves.     

Relationship between zooplankton abundance and the early marine life history of juvenile chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> in eastern Hokkaido,Japan

Interannual variations in abundance, timing of outmigration from rivers, growth rate and condition of juvenile chum salmon (Oncorhynchus keta) were studied in the Nemuro Strait (eastern Hokkaido, Japan) during 1999–2002 to establish a possible relationship to zooplankton abundance. The otolith microstructure of juveniles was examined each year in late June to determine their time and size at sea entry (i.e., outmigration), and to estimate the early marine growth rates. Salmon outmigration peaked in mid- or late May, which coincided, in three of the four study years, with the peak release of juveniles into rivers within the study area. Abundance, growth rate and condition of fish were higher in 2001, when—compared to other years—smaller fish experienced higher growth rates, coinciding with greater zooplankton abundance for that year. Our results suggest that high zooplankton abundance positively influenced juvenile chum salmon growth and the condition of the fish during their early marine life despite their small size at sea entry.     

Does future climate change facilitate expansion of evergreen broad-leaved tree species in the human-disturbed landscape of the Korean Peninsula? Implication for monitoring design of the impact assessment

To quantitatively assess future change of evergreen broad-leaved tree species’ distributions in human-disturbed landscapes of the Korean Peninsula under climate change, potential habitats (PHs) were projected for four important evergreen broad-leaved tree species (Quercus acuta, Castanopsis sieboldii, Machilus thunbergii, and Neolitsea sericea) by species distribution models (SDMs). The distribution data (presence/absence) of the target species in Korea and Japan were used as response variables for SDMs, and climatic data were used as explanatory variables. Three general circulation models under A2 emission scenarios were used as future climate scenarios for the years 2070–2099. Potential habitats masked by land-use data (PHLUs) were projected to assess the impact of anthropogenic activities. Highly accurate SDMs were obtained for all the target species. The current PHs were decreased to 21–35 % by the anthropogenic activities. Future PHLUs for all the target species were projected to increase by 2.0–18.5 times of current PHLUs. These results suggest that all the target species are applicable as indicator species for monitoring in the Korean Peninsula, even if anthropogenic effects are incorporated. Variation of the increasing rate was caused by the differences in the response to temperature changes. M. thunbergii responded sensitively to the increase of minimum temperature of coldest month and had a largest increase in PHLUs under future climate. Therefore, M. thunbergii is considered to be most appropriate species for monitoring the changes of horizontal distributions above all focal evergreen broad-leaved tree species.     

Climatic controls of a keystone understory species, <Emphasis Type="Italic">Sasamorpha borealis</Emphasis>, and an impact assessment of climate change in Japan

Introduction   

The aims of this study were to identify the climatic conditions controlling the distribution of Sasamorpha borealis and to assess the impact of climate change on the species in Japan.     

What controls the distribution of the Japanese endemic hemlock, Tsuga diversifolia? Footprint of climate in the glacial period on current habitat occupancy

Plant distributions are thought to be controlled by climate at large scales, and by non-climatic factors including soil conditions, topography and biotic interactions at smaller scales. However, not all plant distributions are explained by the current environment. Lags between current plant distributions and suitable environment for them are suggested to exist, which is often called empty habitat. To identify the existence and cause of lags between current climate and the distribution of Tsuga diversifolia, climatic conditions for the species distribution were clarified and potential habitats under current and the last glacial maximum (LGM; 21 ka) climates have been projected. The relationships between T. diversifolia distribution and climatic variables were explored using a classification tree model and a generalized additive model based on high-resolution (ca. 1 km) climatic data and a nationwide distribution database. The models were highly accurate. We revealed that T. diversifolia requires high summer precipitation even in humid Japanese environments. Areas with cool and wet summers were classified as potential habitat. Empty habitat for the focal species was identified in Hokkaido. Meanwhile, no potential habitat was projected in Hokkaido under the LGM. Additional experiments that varied temperature and summer precipitation during the LGM showed that the potential habitat was projected in Hokkaido irrespective of temperature decrease if summer precipitation increased nearly equal to the current climate. These results suggest that T. diversifolia vanished from Hokkaido, where fossil evidence indicated its occurrence until the late Neogene, during the glacial periods of the Pleistocene because of increased summer dryness.     

Factors determining the distribution of a keystone understory taxon, dwarf bamboo of the section Crassinodi, on a national scale: application to impact assessment of climate change in Japan

The objective of this study was to identify climatic factors determining the distribution of a keystone understory taxon, section Crassinodi of the genus Sasa, and assess the impacts of climate change on the taxon. Relationships between the distribution of sect. Crassinodi and five climatic variables were explored using classification tree analysis. Potential habitats under current climate and future climate in 2081–2100 were predicted. Potential habitats were further divided into suitable and marginal habitats. The predictive accuracy of the model was assessed using receiver operating characteristic analysis and by comparing model predictions with an independent dataset. The model was reasonably accurate. It showed that the warmth index (WI) and snow cover were the most important climatic variables for Crassinodi distribution. Potential habitats were limited to cooler regions with WI <102.7°C month. Suitable habitats were limited to even cooler regions with WI <84.8°C month. The model also showed that areas with deeper snow than previously reported would provide suitable habitats for Crassinodi under some climatic conditions. In 2081–2100, 37.4% of current potential habitats are predicted to become non-habitats because of increases in WI. Most currently suitable habitats are predicted to vanish from western Japan by 2081–2100. Meanwhile, Hokkaido and high-elevation areas of eastern Honshu will sustain suitable habitats. Sect. Crassinodi, which is adapted to less snowy climates, is predicted to be more affected by climate change than sect. Sasa and Macrochlamys, which are adapted to snowy climates.     

Distribution of lignin and lignin precursors in differentiating xylem of Japanese cypress and poplar

Lignin is an integral component of the cell wall of vascular plants. The mechanism of supply of lignin precursors from the cytosol into the cell wall of differentiating xylem has not yet been elucidated. The present study showed that a certain amount of coniferyl alcohol glucoside (coniferin) occurred in the differentiating xylem of Japanese cypress (Chamaecyparis obtusa), as previously reported in gymnosperms. Coniferin content peaked in the early stages of secondary wall formation and decreased during lignification. In contrast to gymnosperms, coniferin content was limited in the differentiating xylem of poplar (Populus sieboldii × Populus grandidentata). Moreover, coniferyl alcohol was not detected in all specimens. In the differentiating xylem of poplar, a higher amount of sinapyl alcohol occurred than glucoside (syringin). However, the phloem contained syringin and not sinapyl alcohol. The sinapyl alcohol content in the xylem peaked in the cells with ceasing cell wall formation, and decreased gradually towards the boundary of the annual ring, where the lignin content kept increasing. Sinapyl alcohol in the differentiating xylem of poplar may be used for the lignification of the xylem.     

Seasonal variations of tracheid formation and amount of auxin (IAA) and gibberellin A4 (GA4) in cambial-region tissues of mature sugi (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) cultivar grown in a Nelder plot with different tree densities

The role of phytohormones in tracheid formation remains unclear in conifers. In this study, to obtain information on the role of auxin (IAA) and gibberellin A4 (GA4), we examined seasonal variation in the amount of phytohormones in cambial-region tissues and tracheid formation of sugi cultivar planted in a Nelder plot with different tree densities. We demonstrated that the amount of IAA was positively correlated with the number of tracheids formed in early and mid-season, but not in late season, and had no relation to tracheid differentiation. Crown length and height at the crown base had a positive and negative effect, respectively, on IAA amounts in early and mid-season, but not in late season. Height-to-diameter ratio was negatively correlated with IAA amounts in early and mid-season, but not in late season. Sugi trees with wider spacing continued tracheid formation in late season with smaller amounts of IAA, although the trees with narrower spacing ceased tracheid formation with larger amounts of IAA. Cambial growth cessation in late season might be controlled not by IAA amount, but by short-day-induced insensitivity to IAA. GA4 had no relation with the indexes of growth traits or tracheid formation.