Ryuji Ichihashi

Ras recruits mitotic exit regulator Lte1 to the bud cortex in budding yeast

ACdc25 family protein Lte1 (low temperature essential) is essential for mitotic exit at a lowered temperature and has been presumed to be a guanine nucleotide exchange factor (GEF) for a small GTPase Tem1, which is a key regulator of mitotic exit. We found that Lte1 physically associates with Ras2-GTP both in vivo and in vitro and that the Cdc25 homology domain (CHD) of Lte1 is essential for the interaction with Ras2. Furthermore, we found that the proper localization of Lte1 to the bud cortex is dependent on active Ras and that the overexpression of a derivative of Lte1 without the CHD suppresses defects in mitotic exit of a Δlte1 mutant and a Δras1 Δras2 mutant. These results suggest that Lte1 is a downstream effector protein of Ras in mitotic exit and that the Ras GEF domain of Lte1 is not essential for mitotic exit but required for its localization.

effects of logging and recruitment on community phylogenetic structure in 32 permanent forest plots of kampong thom, cambodia

Ecological communities including tropical rainforest are rapidly changing under various disturbances caused by increasing human activities. Recently in Cambodia, illegal logging and clear-felling for agriculture have been increasing. Here, we study the effects of logging, mortality and recruitment of plot trees on phylogenetic community structure in 32 plots in Kampong Thom, Cambodia. Each plot was 0.25 ha; 28 plots were established in primary evergreen forests and four were established in secondary dry deciduous forests. Measurements were made in 1998, 2000, 2004 and 2010, and logging, recruitment and mortality of each tree were recorded. We estimated phylogeny using rbcL and matK gene sequences and quantified phylogenetic α and β diversity. Within communities, logging decreased phylogenetic diversity, and increased overall phylogenetic clustering and terminal phylogenetic evenness. Between communities, logging increased phylogenetic similarity between evergreen and deciduous plots. On the other hand, recruitment had opposite effects both within and between communities. The observed patterns can be explained by environmental homogenization under logging. Logging is biased to particular species and larger diameter at breast height, and forest patrol has been effective in decreasing logging.

Biomass allocation and long‐term growth patterns of temperate lianas in comparison with trees

The host-dependent support habit of lianas is generally interpreted as a strategy designed to reduce resource investment in mechanical tissues; this allows preferential allocation to leaf and stem extension, thereby enhancing productivity and competitive abilities. However, this hypothesis has not been rigorously tested. We examined the aboveground allometries regarding biomass allocation (leaf mass and current-year stem mass (approximated as biomass allocated to extension growth) vs total aboveground mass) and long-term apparent growth patterns (height and aboveground mass vs age, i.e. numbers of growth rings) for nine deciduous liana species in Japan. Lianas had, on average, three- and five-fold greater leaf and current-year stem mass, respectively, than trees for a given aboveground mass, whereas the time course to reach the forest canopy was comparable and biomass accumulation during that period was only one-tenth that of co-occurring canopy trees. The balance between the lengths of yearly stem extension and existing older stems indicated that lianas lost c. 75% of stem length during growth to the canopy, which is probably a consequence of the host-dependent growth. Our observations suggest that, although lianas rely on hosts mechanically, allowing for short-term vigorous growth, this habit requires a large cost and could limit plant growth over protracted periods.

Vertical variations in wood CO2 efflux for live emergent trees in a Bornean tropical rainforest

Difficult access to 40-m-tall emergent trees in tropical rainforests has resulted in a lack of data related to vertical variations in wood CO2 efflux, even though significant variations in wood CO2 efflux are an important source of errors when estimating whole-tree total wood CO2 efflux. This study aimed to clarify vertical variations in wood CO2 efflux for emergent trees and to document the impact of the variations on the whole-tree estimates of stem and branch CO2 efflux. First, we measured wood CO2 efflux and factors related to tree morphology and environment for seven live emergent trees of two dipterocarp species at four to seven heights of up to ∼ 40 m for each tree using ladders and a crane. No systematic tendencies in vertical variations were observed for all the trees. Wood CO2 efflux was not affected by stem and air temperature, stem diameter, stem height or stem growth. The ratios of wood CO2 efflux at the treetop to that at breast height were larger in emergent trees with relatively smaller diameters at breast height. Second, we compared whole-tree stem CO2 efflux estimates using vertical measurements with those based on solely breast height measurements. We found similar whole-tree stem CO2 efflux estimates regardless of the patterns of vertical variations in CO2 efflux because the surface area in the canopy, where wood CO2 efflux often differed from that at breast height, was very small compared with that at low stem heights, resulting in little effect of the vertical variations on the estimate. Additionally, whole-tree branch CO2 efflux estimates using measured wood CO2 efflux in the canopy were considerably different from those measured using only breast height measurements. Uncertainties in wood CO2 efflux in the canopy did not cause any bias in stem CO2 efflux scaling, but affected branch CO2 efflux.

Morphological differentiation of current-year shoots of deciduous and evergreen lianas in temperate forests in Japan

Morphological variation in current-year shoots within plants was examined in five deciduous and four evergreen liana species from temperate forests in Japan to elucidate the role differentiation in shoots. All lianas had both shoots that twined or developed adventitious roots to gain support on host materials (searcher shoots) and self-supporting shoots with no climbing structures (ordinary shoots). Searcher shoots were 20–295 times longer than ordinary shoots. The allometric relationships between stem length and leaf area differed between searcher and ordinary shoots, and the stem length for a given leaf area was greater in searcher shoots. Leaf area per shoot mass was 1.4–4.3 times higher in ordinary shoots because of the greater allocation to leaf biomass. Searcher shoots comprised only 1–6% of total shoots but 30–85% of total shoot length in deciduous lianas. Ordinary shoots accounted for 70–95% of the total leaf area in these liana species. These results suggest that the exploration of new space was primarily achieved by searcher shoots, whereas a large proportion of current photosynthetic production was achieved by ordinary shoots. The range of stem length and leaf mass ratio of ordinary shoots was similar to that in shoots of tree species. Specialization of shoots in lianas is discussed.

Strategies to Observe and Assess Changes of Terrestrial Biodiversity in the Asia-Pacific Regions

Biodiversity loss is one of the most critical threats to global environments that has already transgressed planetary boundaries (Rockstrom et al. 2009). Indeed, nonlinear, often abrupt changes can drive unacceptable and irreversible deterioration. Rockstrom et al. (2009) claimed that earth’s system cannot sustain the current rate of biodiversity loss without significant erosion of resilience. To halt this biodiversity loss, global efforts to achieve “by 2010 a significant reduction of the current rate of biodiversity loss at the global, regional, and national level,” called the 2010 biodiversity targets, have been made since the agreement by the world’s governments in 2002. However, the latest data on the status and trends of biodiversity summarized in the third edition of Global Biodiversity Outlook (GBO-3) show that the target had not been met (Secretariat of the Convention on Biological Diversity 2010).

Contribution of lianas to community‐level canopy transpiration in a warm‐temperate forest

Summary 1.Lianas (woody climbers) have a greater amount of leaves relative to basal area or standing biomass than trees, and very wide vessels that permit efficient water transport. These features suggest that lianas possibly consume proportionally more water through transpiration than trees. Despite their potential importance, researchers have made only limited attempts to evaluate effects of lianas on forest water dynamics. 2.We conducted sap flow measurements for 1 year using a thermal-dissipation method for four species each of lianas and trees in a liana-rich, warm-temperate forest in Japan and estimated the contribution of lianas to stand canopy transpiration. 3.Based on a calibration measuring water uptake rates from cut-stem ends, the actual sap flux (Fd) in liana stems was several times greater than those estimated from the original calibration provided for the method. In the field, lianas showed an average of 2–4 times greater Fd than trees throughout the year. Except for this difference, diurnal and seasonal patterns of relative changes of Fd were similar in both groups. The whole-plant transpiration (Qt) of sample plants were exponentially related to basal diameter for both lianas and trees; Qt of lianas increased more steeply with basal diameter than that of trees. By extrapolating the relationships between Qt and basal diameter to the inventory data of the study plot, we estimated that lianas contributed 12.8% to the annual stand canopy transpiration while comprising 2.3% of stand basal area, which probably reflected the top-heavy architecture of lianas. 4.Our results indicate that the contribution of lianas to forest water dynamics may be several times greater than their contribution to forest basal area. This implies that a slight increase of liana abundance might have greater effects on water dynamics and, through competitions with trees for limited water, the carbon sequestration capacity of forests than expected from the increase in basal area. This study underlines the necessity of evaluating the relative importance of lianas to forest water dynamics in forests worldwide. This article is protected by copyright. All rights reserved.

Microscale phloem sap extraction sensor device for measuring biological information in plant branches

In this study, a microscale phloem sap extraction sensor device based on MEMS technology is proposed to artificially extract phloem sap and monitor biological information in plant branches. The device consists of electrical resistance sensors to distinguish the positions of vascular bundles (xylem/phloem) and hollow-structured cantilevers with reservoirs for fluid extraction. A prototype of the proposed sensor device was fabricated. Furthermore, the performance of the position-distinction sensor was evaluated, and the feasibility of the fluid-extraction structure was validated.

Highly pure phloem-sap-extraction sensor device for direct component analysis of nutrition in plant shoots

This paper describes a highly pure phloem-sap-extraction sensor device that mounts a phloem position-identification sensor. Convenient methods of artificially extracting highly pure phloem sap for quantitative analysis of plant nutrition have yet to be established. To realize direct analysis of nutrition as well as long-term monitoring of its component fluctuation, we propose a novel sensor device that can distinguish phloem and xylem positions stably for a long time and extract only pure phloem sap.

Growth and photosynthesis characteristics of invading larch saplings in an occasionally flooded dry stream bed in cool-temperate Japan

ABSTRACT Semi-naturally occurring Japanese larch (Larix kaempferi) saplings originating from planted trees are often observed in riparian habitats around Nikko National Park, Japan, and they may be affecting the structure and functioning of endemic riparian vegetation. To evaluate possible larch establishment in riparian habitats, we examined the aboveground structure and leaf (needle)-level ecophysiological characteristics of larch saplings (~3 m in height and ~8 years old) grown in a dry-wet stream bed (site DW, well-drained but floods after heavy rains) and in neighboring non-riparian vegetation (site M, stably mesic) for comparison. DW saplings were generally shorter than M saplings for their ages, and the total length of current-year stems in DW saplings was about a half that of M saplings. DW saplings produced a larger number of short shoots (shoots without apparent stem elongation), resulting in a similar amount of leaves to those of the M saplings. Leaves of DW saplings had lower nitrogen contents (N) and photosynthetic capacity (light-saturated net CO2 assimilation rate and electron transport rate measured on excised branches) than those of M saplings. These results suggest that larch saplings were subject to some environmental stressor, but were able to grow slowly yet steadily in riparian environments for a relatively long period, implying considerable potential for colonization of riparian ecosystems. Further studies on the structure, functioning and management of cool-temperate Japanese ecosystems should consider the unintended expansion of introduced larch into surrounding habitats.