Yoshitaka Kakubari

Antisense suppression of proline degradation improves tolerance to freezing and salinity in Arabidopsis thaliana

Synthesis, degradation, and transport of proline (Pro) are thought to cooperatively control its endogenous levels in higher plants in response to environmental conditions. To evaluate the function of Pro degradation in the regulation of the levels of Pro and to elucidate roles of Pro in stress tolerance, we generated antisense transgenic Arabidopsis plants with an AtProDH cDNA encoding proline dehydrogenase (ProDH), which catalyzes Pro degradation. Several transgenic lines accumulated Pro at higher levels than wild‐type plants, providing evidence for a key role of ProDH in Pro degradation in Arabidopsis. These antisense transgenics were more tolerant to freezing and high salinity than wild‐type plants, showing a positive correlation between Pro accumulation and stress tolerance in plants.

Stomatal closure induced by high vapor pressure deficit limited midday photosynthesis at the canopy top of Fagus crenata Blume on Naeba mountain in Japan

Diurnal changes in gas exchange, chlorophyll fluorescence and leaf water potential (ψleaf) were measured to determine the environmental and physiological factors that limit carbon gain in the horizontal leaves of Fagus crenata Blume at the canopy top. Although midday depression of the net CO2 assimilation rate (An) and stomatal conductance (gH2O) were clearly evident on a fine day, the potential quantum yield of PS II (Fv/Fm) was fairly constant around 0.83 throughout the day. This result indicates that the leaves at the canopy top do not suffer from chronic photoinhibition, and the excess energy is dissipated safely. Large reversible increases in non-photochemical quenching (NPQ) were evident on fine days. Therefore, the non-radiative energy dissipation of excess light energy contributed to avoid chronic photoinhibition. The electron transfer rate (ETR) reached maximum during the midday depression, and thus there was no positive relation between ETR and An under high light conditions, indicating a high rate of photorespiration and the absence of non-stomatal effect during midday. The protective mechanisms such as non-radiative energy dissipation and photorespiration play an important role in preventing photoinhibitory damage, and stomatal limitation is the main factor of midday depression of An. To separate the effect of air to leaf vapor pressure deficit (ALVPD) and leaf temperature (Tleaf) on gas exchange, the dependencies of An and gH2O on ALVPD and Tleaf were measured using detached branches under controlled conditions. An and gH2O were insensitive to an increase in Tleaf. With the increase in ALVPD, An and gH2O exhibited more than a 50% decrease even though water supply was optimum, suggesting the dominant role of high ALVPD in the midday depression of gH2O. We conclude that midday depression of An results from the midday stomatal closure caused by high ALVPD.

Seasonal changes in photosynthesis and nitrogen allocation in leaves of different ages in evergreen understory shrub Daphniphyllum humile

Seasonal changes in photosynthetic capacity, leaf nitrogen (N) content, leaf chlorophyll (Chl) content and leaf N allocation patterns in leaves of different ages in the evergreen understory shrub, Daphniphyllumhumile Maxim, growing at a forest border and an understory site were studied. In current-year leaves at the understory site, the N and Rubisco contents increased from spring to autumn although their light-saturated photosynthetic rate at 22°C (Pmax22) remained stable, indicating that their mesophyll conductance rates declined as they completed their development and/or that they invested increasing amounts of their resources in photosynthetic enzymes during this period. In contrast, seasonal changes in Pmax22 in current-year leaves at the forest border site were correlated with changes in Rubisco content. In 1-year old leaves at the understory site, Pmax22 and contents of Chl, leaf N, and Rubisco remained stable from spring to autumn, while these parameters decreased in 1-year-old forest border leaves, indicating that N may have been remobilized from shaded 1-year-old leaves to sunlit current-year leaves. When leaves senesced at the forest border site the Rubisco content decreased more rapidly than that of light-harvesting proteins such as LHCII, suggesting that N remobilization from Rubisco may be more efficient, possibly because Rubisco has greater N costs and is soluble, whereas the light-harvesting proteins are membrane components.

Seasonal variation of branch respiration of a treeline forming (Betula ermanii Cham.) and a montane (Fagus crenata Blume) deciduous broad-leaved tree species on Mt. Fuji, Japan

Summary In this study we focus on four particular aspects in the field of ecological studies of woody tissue respiration: 1) the application of the non-destructive soda lime technique to the in situ measurement of CO 2 efflux rates from branches or stems of standing trees all year round; 2) the investigation of respiration rates of branches of similar diameter but different positions in the canopy; 3) the comparative study of seasonal variation and long-term thermal acclimation of branch respiration along an altitudinal transect up to the treeline; 4) the comparison of branch respiration between a treeline forming ( Betula ermanii ) and a montane ( Fagus crenata ) deciduous broad-leaved tree species in order to evaluate the relevance of woody tissue respiration to tree survival in low temperature climates. No qualitative differences in respiratory behaviour between the treeline forming B. ermanii and the montane F. crenata were found in this study. Significantly higher respiration rates of upper crown branches of both tree species were due to biogenic factors which were spatio-temporally unevenly effective within the crown. In early spring, branch respiration rose independently of xylem temperature. This was caused by an increase in metabolic activity of branch parenchymatous tissues associated with the phenological development of the buds. During summer, the CO 2 efflux of upper crown branches reached up to sixfold higher rates than that of lower crown branches. This was associated with secondary thickening being more pronounced in the upper crown. During winter, higher rates of maintenance respiration in the upper crown reflected different physiological states of branches, probably with respect to protein metabolism involved in processes of cold resistance of live branch tissues. As shown in this study, thermal acclimation of branch respiration is occuring at a similar level as was reported for leaves of herbaceous alpine plants. The tendency for a lower activation energy for respiration towards low temperature climatic conditions points to a physiologically driven increase in respiratory capacity in branches of B. ermanii and F. crenata . In treeline forming tree species a decrease in activation energy may contribute to keep respiratory activity relatively unaffected by large daily temperature fluctuations of more than 25°C during the cold season. In this study, no evidence was found that branch respiration may act as an ecophysiologically limiting parameter for the survival of Betula ermanii at its present upper distribution limit in the Japanese Alps.

Spatial and seasonal variations in photosynthetic properties within a beech (Fagus crenata Blume) crown

The light response curve and the intercellular CO2 concentration response curve of CO2 assimilation rate were investigated together with the light conditions at the four different heights within the beech crown from 1995 to 1997 on Mt. Fuji in Japan. On the seasonal fluctuation, the CO2 assimilation rate at light saturated condition increased rapidly in May, and attained to the maximum between the end of June and July, thereafter, slightly decreased until the middle of August and rapidly decreased in September and October. The daily sum of photosynthetic photon flux density attenuated with deeping within the crown, and particularly, the relative value on 2nd position dropped to only 30%. TheAmax decreased from 10 to 5μmol m−2 s−1, approximately, with deeping within the crown. The light saturation point, quantum yield, light compensation point and dark respiration rate also varied with deeping. These results suggest that the photosynthetic properties vary gradually from sun to shade leaves along the light attenuation within a beech crown. At light saturated condition, the stomatal conductance and mesophyll conductance were strongly correlated withAmax among the four different heights (r > 0.96, respectively). TheCi/Ca ratio was around 0.8, and there were no remarkable differences among the four different heights. These results suggest that the vertical gradient ofAmax depends on the variation of mesophyll conductance. The stomatal conductance may be also one of the major factor in the vertical gradient ofAmax. However the intercellular CO2 concentration doesn’t influence the vertical gradient ofAmax within the crown.

Improved Forest Cover Classification in an Industrialized Mountain Area in Japan

Abstract Space-borne satellite imagery is increasingly used for classifying and characterizing forest cover in mountain environments. Using medium resolution satellite imagery, acquired over an industrial mountain area near the city of Naeba, in the central part of Honshu, Japan, this study attempts to characterize forest cover types situated in an area affected by prolonged anthropogenic land use and land cover change (LUCC) processes. The image was topographically corrected, and training sites selected and assessed for their spectral separability between forest classes. Using the ground truthed training sites and a supervised spectral angle mapper (SAM) classifier, dominant forest cover types were classified. Post-classification forest cover classification accuracies range between 77–89%. Results highlight how an assessment of the spectral separability of forest cover types prior to image classification, combined with ground validation that focuses on documenting and noting areas affected by human modifications to the forest, can aid in refining the forest classification training areas, which in turn can lead to improved image classification accuracies. Through refinement of the training areas used in the classification via ground truthing, it is possible to account for localized land use and land cover disturbances (ie forest harvesting, thinning) that create non-representative training areas. It is then possible to select additional training areas that are more representative of a forest spectral class and not a localized anomaly created via human disturbance.

Drought-dependent Responses of Photosynthesis,Transpiration and Water Use Efficiency of Japanese Cypress and Japanese Red Pine Seedlings

This study was conducted to investigate the potential for modifying drought tolerance of Japanese cypress (Chamaecyparis obtusa Endl.) and Japanese red pine (Pinus densiflora Sieb. et Zucc.). Three-year-old seedlings were controlled for five-months at three different soil water potentials ({ie73-1}). Japanese cypress exposed to high {ie73-2} was able to maintain higher photosynthesis (Phn), transpiration (Tr) and stomatal conductance to H2O (gH2O) in comparison to low {ie73-3} pretreatments, however, there was no significant difference in Phn for Japanese red pine. Soil water potential at the threshold from the maximum to limited Phn was higher in high {ie73-4} pretreatments than in low {ie73-5} pretreatments. Net photosynthesis, Tr and gH2O decreased more rapidly in high {ie73-6} pretreatments than in low {ie73-7} pretreatments. Transpiration decreased more significantly than Phn, thus, resulted in increased water use efficiency. All these factors are likely to result in significant improvements in the drought tolerance. Japanese red pine seems more drought-tolerant than Japanese cypress. Japanese cypress is suitable to soil of −0.05 MPa water potential, and Japanese red pine is suitable to −0.16 MPa and even dryer soils.

Photosynthesis and Chlorophyll a Fluorescence of Two Poplars under Water Stress

In order to estimate drought tolerance in two species ofPopulus, Populus alba var. pyramidalis Bunge andPopulus nigra L. var. thevestina (Dode), widely planted at the southern margin of the Taklimakan Desert, responses of net photosynthesis and chlorophylla fluorescence to irradiance and water stress were examined under laboratory conditions. Results showed thatP. alba exhibited stronger drought tolerance thanP. nigra. A linear relationship between net photosynthetic rates (An) and electron transport rates (ETR) was found in both poplars under different irradiance and leaf water potentials. Net photosynthetic rates (An) in the two poplars significantly correlated linearly with the photochemical efficiency of the saturation light-adapted leaves throughout the range of leaf water potentials, suggesting that the leaf photochemical efficiency in saturation light-adapted leaves can be used to estimate leaf photosynthetic capacity and leaf water conditions in the two poplars within a magnitude of air temperature between 20 and 30°C.

Seasonal dynamics of soil microbial biomass C shows close correlation with environmental factors in natural Fagus crenata forests

Abstract Soil microbial biomass (Cmic) is an important factor regulating a number of ecosystem processes. In this study, we investigated seasonal variations in soil microbial biomass in natural climax beech (Fagus crenata) forests in a typical cold-temperate mountain region of Japan. Four permanent tower sites along an altitudinal gradient were selected and soil samples were collected once every month during the growing season of 2007. Soil microbial biomass (by fumigation-extraction method) and soil properties were later measured in the laboratory, while environmental factors (soil temperature, soil moisture) were continuously recorded in the field. Our results indicated large seasonal variations (130.4 ~ 5558.0 µg g−1) in soil microbial biomass in beech forests – a range that is much larger than previously reported. Statistically significant correlations are noted between soil properties with Cmic, but largely due to spatial linkages. On the other hand, the environmental factors of soil temperature and especially soil moisture largely control seasonal variations in Cmic. Furthermore, pH could be an important factor influencing seasonal change in Cmic at the 20–30 cm deep soil layer. The study suggests no direct correlation between plant eco-physiology and soil microbial biomass in seasonal courses of the forests.

Photosynthetic Responses to Lightflecks of Fagus crenata Seedlings Grown in a Gap and Understory of a Deciduous Forest

Photosynthetic responses to a series of 1-min lightflecks (1,000µmol m−2 s−1) superimposed on a background with different duration (1, 5, and 10 min) and intensity (25 and 50µmol m−2 s−1) of low background photosynthetic photon flux density (PPFD) were measured in the leaves ofFagus crenata grown in a gap and understory of aFagus crenata forest in the Naeba Mountains. The two background PPFD intensities most frequently occurred in understory and gap sites respectively. The maximum net photosynthetic rate (PNmax) and maximum stomatal conductance (gsmax) were higher in the gap seedlings than in the understory seedlings. However, when the background PPFD was 25µmol m−2s−1, the net photosynthetic rate (P25) and stomatal conductance (gs25) were almost the same between the gap and understory. When the background PPFD duration was 1-min, the net photosynthetic rate (PN) at the end of each lightfleck increased progressively. When the background PPFD duration was 5- and 10-min, the increase inPN at the end of each lightfleck was less. This indicates that background PPFD duration is important to photosynthetic responses to lightflecks. The higher ratios ofP25/PNmax andgs25/gsmax in the understory seedlings indicate that the understory seedlings can maintain relatively lower levels of biochemical and stomatal limitations than the gap seedlings under low light conditions. The ratios ofPN/PNmax at the end of each lightfleck (IS) and light utilization efficiency of single lightflecks (LUEs) that showed the influence of lightflecks on carbon gain were higher in the understory seedlings than in the gap seedlings when the background PPFD was 25µmol m−2 s−1. This means that understory seedling are capable of utilizing fluctuating light more efficiently under low light conditions than the gap seedlings although the net carbon gain of single lightflecks (CGs) in the understory seedlings was not higher than that in the gap seedlings. There were no significant differences inIS andLUEs between understory seedlings at a background PPFD of 25µmol m−2 s−1 and gap seedlings at a background PPFD of 50µmol m−2 s−1. However,CGs in gap seedlings was higher than in understory seedlings. These results provide more evidence thatF. crenata acclimate to a natural light environment in respect to relative induction state at low background PPFD and can capture the fluctuating light at the same efficiency in both the gap and understory seedlings under natural light environments.