Language：English   Publishing type：Research paper (scientific journal)  

BACKGROUND: Plants invest photosynthates in construction and maintenance of their structures and functions. Such investments are considered costs. These costs are recovered by CO2 assimilation rate (A) in the leaves and thus A is regarded as the immediate, short-term benefit. In photosynthesising leaves, CO2 diffusion from the air to the carboxylation site is hindered by several structural and biochemical barriers. CO2 diffusion from the intercellular air space to the chloroplast stroma is obstructed by the mesophyll resistance. The inverses is the mesophyll conductance (gm). Whether various plants realize an optimal gm, and how much investments are needed for relevant gm, remain unsolved. SCOPE: This review examines relationships among leaf construction costs (CC), leaf maintenance costs (MC) and gm in various plants under diverse growth conditions. Through a literature survey, we demonstrate a strong linear relationship between leaf mass per area (LMA) and leaf CC. The overall correlation of CC versus gm across plant phylogenetic groups is weak, but significant trends are evident within specific groups and/or environments. Investment in CC is necessary for increase in LMA and mesophyll cell surface area (Smes). This allows the leaf to accommodate more chloroplasts, thus increasing A. However, increases in LMA and/or Smes often accompany other changes, such as cell wall thickening, which diminishes gm. Such factors that make the correlations of CC-gm elusive are identified. CONCLUSIONS: For evaluation of contribution of gm to recover CC, leaf life-span is the key factor. The estimation of MC in relation to gm, especially in terms of costs required to regulate aquaporins, could be essential for efficient control of gm over the short-term. Over the long-term, costs are mainly reflected in CC, while benefits also include ultimate fitness attributes in terms of integrated carbon gain over the life of a leaf, plant survival and reproductive output.

DOI： 10.1093/aob/mcac100

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.bbrc.2022.06.097

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Language：English   Publishing type：Research paper (scientific journal)  

Understanding water use characteristics of C3 and C4 crops is important for food security under climate change. Here, we aimed to clarify how stomatal dynamics and water use efficiency (WUE) differ in fluctuating environments in major C3 and C4 crops. Under high and low nitrogen conditions, we evaluated stomatal morphology and kinetics of stomatal conductance (gs) at leaf and whole-plant levels in controlled fluctuating light environments in four C3 and five C4 Poaceae species. We developed a dynamic photosynthesis model, which incorporates C3 and C4 photosynthesis models that consider stomatal dynamics, to evaluate the contribution of rapid stomatal opening and closing to photosynthesis and WUE. C4 crops showed more rapid stomatal opening and closure than C3 crops, which could be explained by smaller stomatal size and higher stomatal density in plants grown at high nitrogen conditions. Our model analysis indicated that accelerating the speed of stomatal closure in C3 crops to the level of C4 crops could enhance WUE up to 16% by reducing unnecessary water loss during low light periods, whereas accelerating stomatal opening only minimally enhanced photosynthesis. The present results suggest that accelerating the speed of stomatal closure in major C3 crops to the level of major C4 crops is a potential breeding target for the realization of water-saving agriculture.

DOI： 10.1093/plphys/kiac040

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Understanding the yield potential and yield-determining factors of recent high-yielding cultivars is essential for further increasing rice yield. In this study, a cross-locational field experiment was conducted across 3 years using 'Hokuriku 193MODIFIER LETTER PRIME (H193), a high-yielding cultivar, at four sites including one in Nagano Prefecture, which is the highest-yielding region in Japan. The highest mean yields of 3 years, 1214 g m(-2) for brown rice grains and 1586 g m(-2) for rough grains, were recorded at the Nagano site. The yields from the 17 environments were strongly correlated with spikelet number per square meter while percentage of filled grain was relatively stable, suggesting that sink capacity is the primary determining factor for grain yield of H193. The climatic factors for high spikelet number at the Nagano site can be explained by the high cumulative radiation before heading associated with longer duration until heading by low night temperature. In addition, a large increase in shoot dry weight during grain filling (Delta W) and high radiation use efficiency (Delta W/rad) at the Nagano site could satisfy large source demand by the large sink size. The high Delta W/rad at the Nagano site associated with low night temperature. This study demonstrated high yield potential of H193 and revealed an environment that achieves extra-high yields in H193, which provided insight to attain further increase in rice yield.[GRAPHICS].

DOI： 10.1080/1343943X.2021.1981140

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Sago palm (Metroxylon sagu Rottb.) grows in well-drained mineral soil and in peatland with high groundwater levels until complete submersion. However, the published information on nutrient uptake and carbohydrate content in sago palms growing under waterlogging remains unreported. This experiment observed sago palm growth performance under normal soil conditions (non-submerged conditions) as a control plot and extended waterlogged conditions. Several parameters were analyzed: Plant morphological growth traits, nitrogen, phosphorus, potassium, and sugar concentration in the plant organ, including sucrose, glucose, starch, and non-structural carbohydrate. The analysis found that sago palm morphological growth traits were not significantly affected by extended waterlogging. However, waterlogging reduced carbohydrate levels in the upper part of the sago palm, especially the petiole, and increased sugar levels, especially glucose, in roots. Waterlogging also reduced N concentration in roots and leaflets and P in petioles. The K level was independent of waterlogging as the sago palm maintained a sufficient level in all of the plant organs. Long duration waterlogging may reduce the plant's economic value as the starch level in the trunk decreases, although sago palm can grow while waterlogged.

DOI： 10.3390/plants11050710

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Plants use nitrate, ammonium, and organic nitrogen in the soil as nitrogen sources. Since the elevated CO2 environment predicted for the near future will reduce nitrate utilization by C3 species, ammonium is attracting great interest. However, abundant ammonium nutrition impairs growth, i.e., ammonium toxicity, the primary cause of which remains to be determined. Here, we show that ammonium assimilation by GLUTAMINE SYNTHETASE 2 (GLN2) localized in the plastid rather than ammonium accumulation is a primary cause for toxicity, which challenges the textbook knowledge. With exposure to toxic levels of ammonium, the shoot GLN2 reaction produced an abundance of protons within cells, thereby elevating shoot acidity and stimulating expression of acidic stress-responsive genes. Application of an alkaline ammonia solution to the ammonium medium efficiently alleviated the ammonium toxicity with a concomitant reduction in shoot acidity. Consequently, we conclude that a primary cause of ammonium toxicity is acidic stress.

DOI： 10.1038/s41467-021-25238-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FRONTIERS MEDIA SA  

Enhancement of the nitrogen-fixing ability of endophytic bacteria in rice is expected to result in improved nitrogen use under low-nitrogen conditions. Endophytic nitrogen-fixing bacteria require a large amount of energy to fix atmospheric nitrogen. However, it is unknown which carbon source and bacteria would affect nitrogen-fixing activity in rice. Therefore, this study examined genotypic variations in the nitrogen-fixing ability of rice plant stem as affected by non-structural carbohydrates and endophytic bacterial flora in field-grown rice. In the field experiments, six varieties and 10 genotypes of rice were grown in 2017 and 2018 to compare the acetylene reduction activity (nitrogen-fixing activity) and non-structural carbohydrates (glucose, sucrose, and starch) concentration in their stems at the heading stage. For the bacterial flora analysis, two genes were amplified using a primer set of 16S rRNA and nitrogenase (NifH) gene-specific primers. Next, acetylene reduction activity was correlated with sugar concentration among genotypes in both years, suggesting that the levels of soluble sugars influenced stem nitrogen-fixing activity. Bacterial flora analysis also suggested the presence of common and genotype-specific bacterial flora in both 16S rRNA and nifH genes. Similarly, bacteria classified as rhizobia, such as Bradyrhizobium sp. (Alphaproteobacteria) and Paraburkholderia sp. (Betaproteobacteria), were highly abundant in all rice genotypes, suggesting that these bacteria make major contributions to the nitrogen fixation process in rice stems. Gammaproteobacteria were more abundant in CG14 as well, which showed the highest acetylene reduction activity and sugar concentration among genotypes and is also proposed to contribute to the higher amount of nitrogen-fixing activity.

DOI： 10.3389/fpls.2021.719259

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

This account presents information on all aspects of the biology of Nervilia nipponica Makino (mukago-saishin) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the International Biological Flora: distribution, habitat, communities, responses to biotic factors, responses to the environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, conservation and global heterogeneity.Nervilia nipponica is a small, stoloniferous, seasonally dormant herb that grows in the understorey of evergreen forests in the humid subtropical zone of central and western Japan, with a few outlying populations on Jeju Island in South Korea. Its northern extent is defined by the 0 degrees C winter isotherm, and its occurrence is also limited by site aspect and incline. It is a weak competitor that occupies species-poor microsites in which bare ground and leaf litter predominate. Plant numbers tend to decline as percentage ground cover of surrounding understorey vegetation increases.The inflorescence sprouts from a short-lived, subterranean tuber in late spring and leaf-flush occurs after fruit-set. However, most tubers do not flower in any one annual growth cycle. Long-term monitoring of individually marked plants suggests that tubers are resource-limited and that flowering constrains future genet growth. Nervilia nipponica is exclusively autogamous and has a strong capacity for vegetative propagation. The species is genetically depauperate but exhibits significant differentiation between populations, which comprise clonal clusters in phalanx formation.The level of mycorrhizal infection differs between plant parts and through successive phenological stages. Stable isotope signatures indicate that the species is partially mycoheterotrophic, with fungal partners supporting growth particularly at lower light intensities. Despite this, falling light availability associated with forest succession can lead to population decline.Populations tend to be small and prone to extirpation, but the species is probably under-recorded as a result of its ephemeral emergence above-ground and inconspicuous habit. Management interventions likely to benefit the species at the site level include thinning dense forest canopy and removing encroaching ground cover.

DOI： 10.1111/1365-2745.13683

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The key role of cell walls in setting mesophyll conductance to CO2 (gm) and, consequently, photosynthesis, is reviewed. First, the theoretical properties of cell walls that can affect gm are presented. Then, we focus on cell wall thickness (Tcw) reviewing empirical evidence showing that Tcw varies strongly among species and phylogenetic groups in a way that correlates with gm and photosynthesis i.e. the thicker the mesophyll cell walls, the lower gm and photosynthesis. Potential interplays of gm, Tcw, dehydration tolerance and hydraulic properties of leaves are also discussed. Dynamic variations of Tcw in response to the environment and their implications in the regulation of photosynthesis are discussed, and recent evidence suggesting an influence of cell wall composition on gm are presented. We then propose a hypothetical mechanism for the influence of cell walls on photosynthesis, combining the effects of thickness and composition, particularly pectins. Finally, we discuss the prospects for using biotechnology for enhancing photosynthesis by means of altering cell wall-related genes.

DOI： 10.1093/jxb/erab144

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Language：English   Publishing type：Research paper (scientific journal)  

Although leaf area index (LAI) is a useful index of crop growth, evaluating LAI by destructive sampling is laborious and time-consuming. In the present study, we developed a novel technique to determine rice LAI non-destructively and accurately throughout growth period in paddy field. Near-infrared radiation (NIR) and photosynthetically active radiation (PAR) were measured by a pair of optical sensors inside and outside rice canopy at 1-min intervals. Simple ratio (SR) and NIR to PAR ratio (N/P) were measured depending on growth stage, and the criteria to extract valid SR and N/P that represent LAI accurately were determined. SR and N/P obtained under cloudy conditions were found to represent LAI with high accuracy (R = 0.91), and seasonal dynamics of canopy growth curves were successfully drawn for two rice cultivars at two experimental fields. Mathematical analysis revealed that not cumulative PAR but cumulative temperature could trigger exponential canopy growth. The present technique can be used as a powerful tool for evaluating, modelling, and phenotyping crop growth characteristics in various rice cultivars as well as other crops. 2

DOI： 10.1016/j.fcr.2021.108070

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

Key message Distributions of water- and air-filled conduits can be distinguished by observing a xylem cross-section of frozen conifer stem. This method is applicable to field observation in cold winter. Xylem embolism resulting from summer drought and frost drought is one of the critical stresses responsible for the dieback of stems and individuals of subalpine evergreen conifers. The occurrence of xylem embolism in conifers depends not only on the species but also on the plant microhabitats, causing difficulties in understanding possible adaptive strategies against xylem embolism. This study examines a simple method of using a digital camera to photograph the xylem water distribution (CXW method) in cross-sections of frozen stems. Light is transmitted through the water-filled tracheid lumen but reflects and scatters at the surface of embolized tracheids, resulting in contrast in wood color between darker (water-filled tracheids) and lighter (air-filled tracheids) colored regions. The CXW method was effective in detecting water distribution in conifers, although the colored xylem in latewood and reaction wood decreased the color contrast between air- and water-filled regions. By cutting the frozen stem with a cryostat, sequential changes in the water distribution of stem xylem were easily monitored. In the cold winter of the subalpine region, the spatial distribution of embolized conduits can be detected when a branch is collected. If a cryostat is available, this method is applicable to other tracheid-bearing wood collected in any season and does not require additional instruments or time-consuming intensive labor in the field. Information about the hydraulics of conifers growing in extreme environments contributes to the understanding of their adaptive strategy and facilitates accurate prediction of forest dynamics under future climatic conditions.

DOI： 10.1007/s00468-020-02070-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/agg2.20191

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/agg2.20191

Language：English   Publishing type：Research paper (scientific journal)  

Lateral roots (LRs) are indispensable for plant growth, adaptability and productivity. We previously reported a rice mutant, exhibiting a high density of thick and long LRs (L-type LRs) with long parental roots and herein referred to as promoted lateral root1 (plr1). In this study, we describe that the mutant exhibited decreased basal shoot starch accumulation, suggesting that carbohydrates might regulate the mutant root phenotype. Further analysis revealed that plr1 mutation gene regulated reduced starch accumulation resulting in increased root sugars for the regulation of promoted LR development. This was supported by the exogenous glucose application that promoted L-type LRs. Moreover, nitrogen (N) application was found to reduce basal shoot starch accumulation in both plr1 mutant and wild-type seedlings, which was due to the repressed expression of starch biosynthesis genes. However, unlike the wild-type that responded to N treatment only at seedling stage, the plr1 mutant regulated LR development under low to increasing N levels, both at seedling and higher growth stages. These results suggest that plr1 mutation gene is involved in reduced basal shoot starch accumulation and increased root sugar level for the promotion of L-type LR development, and thus would be very useful in improving rice root architecture.

DOI： 10.1016/j.plantsci.2020.110667

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC PLANT BIOLOGISTS  

It has been argued that accumulation of nonstructural carbohydrates triggers a decrease in Rubisco content, which downregulates photosynthesis. However, a decrease in the sink-source ratio in several plant species leads to a decrease in photosynthesis and increases in both structural and nonstructural carbohydrate content. Here, we tested whether increases in cell-wall materials, rather than starch content, impact directly on photosynthesis by decreasing mesophyll conductance. We measured various morphological, anatomical, and physiological traits in primary leaves of soybean (Glycine max) and French bean (Phaseolus vulgaris) grown under high- or low-nitrogen conditions. We removed other leaves 2 weeks after sowing to decrease the sink-source ratio and conducted measurements 0, 1, and 2 weeks after defoliation.Cell-wall thickening, rather than starch accumulation, leads to a decrease in mesophyll conductance after a reduction in the sink-source ratio in soybean and French bean.

DOI： 10.1104/pp.20.00328

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Crop growth promotion utilizing elevated carbon dioxide concentrations (e[CO2]) may be limited by soil nutrient availability. Although numerous studies have suggested the importance of nitrogen (N) for the promotion of growth under e[CO2], N requirement for maximum plant growth is rarely examined. We have found that increase in potato (Solarium tuberosum L.) biomass depends on phosphorus (P) availability under doubled [CO2] conditions. To address whether the N requirement for maximum growth under e[CO2] is dependent on P supply or not in potatoes, we quantified potato growth and water consumption in response to five N supply rates at low P (LP) and high P (HP) conditions. A pot experiment was conducted in controlled-environment chambers with ambient CO2 concentrations (a[CO2]) and an e[CO2] level of double a[CO2]. Foliar critical N concentration per area (critical [N](area)), the minimum N requirement for 90% maximum plant growth, was similar (1.43 g m(-2)) regardless of [CO2] conditions under LP. Under HP, however, the critical [N](area) increased under e[CO2] conditions (1.65 g m(-2)) compared with a[CO2] conditions (1.52 g m(-2)). Water use did not change with e[CO2] under HP conditions, whereas it decreased with e[CO2] under LP conditions despite the increase in biomass owing to higher water-use efficiency (WUE). Although WUE with e[CO2] or HP was independent of N supply, biomass increment with e[CO2] or HP depended on N supply. We concluded that the N and water required by potato plants under e[CO2] would be dependent on P supply. Although under HP, e[CO2] increased N but not water required to obtain maximum growth during the early growth stage, N demand was unchanged and water demand decreased by e[CO2] under LP conditions, probably owing to growth limited by P availability.

DOI： 10.1016/j.envexpbot.2020.104089

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Aims The aim of this study was to provide a comprehensive understanding of the mechanisms underlying response of rice (Oryza sativa L.) to the endophytic N-2-fixing bacterium Burkholderia vietnamiensis strain RS1 in growth and nitrogen (N) accumulation using transcriptome and hormonome analyses. Methods The effects of B. vietnamiensis RS1 on rice growth and root architecture were examined in pot and field conditions. To identify candidate plant genes that affect the growth of plants inoculated with B. vietnamiensis RS1, transcriptome analysis was conducted. We also examined the hormonal changes by hormonome analysis in relation to the morphological changes in roots. The contribution of N-2 fixation by B. vietnamiensis RS1 was estimated by the acetylene reduction activity (ARA). Results The inoculation of B. vietnamiensis RS1 resulted in increased shoot and root growth of rice plants accompanied by an increased root N absorption rate, especially under high N conditions. The contribution from N-2 fixation was minor because no effect of B. vietnamiensis RS1 on ARA was detected. Transcriptome analysis revealed an increase in the expression of genes related to the transportation and assimilation of N compounds, supporting the enhanced N absorption by roots. The expression of indole-3-acetic acid (IAA) signaling genes and concentrations of IAA increased, which may be related to the increased root development. Conclusions B. vietnamiensis RS1 enhanced rice growth by promoting N accumulation through enhanced root morphological development and N absorption ability; this outcome was probably related to the increased activities of N transportation and assimilation in the presence of a rich N supply.

DOI： 10.1007/s11104-020-04506-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FRONTIERS MEDIA SA  

Growth promotion by ambient CO2 enrichment may be advantageous for crop growth but this may be influenced by soil nutrient availability. Therefore, we quantified potato (Solanum tuberosum L.) growth responses to phosphorus (P) supply under ambient (a[CO2]) and elevated (doubled) CO2 concentration (e[CO2]). A pot experiment was conducted in controlled-environment chambers with a[CO2] and e[CO2] combined with six P supply rates. We obtained response curves of biomass against P supply rates under a[CO2] and e[CO2] (R-2 = 0.996 and R-2 = 0.992, respectively). A strong interaction between [CO2] and P was found. Overall, e[CO2] enhanced maximum biomass accumulation (1.5-fold) and water-use efficiency (WUE) (1.5-fold), but not total water use. To reach these maxima, minimum P supply rate at both [CO2] conditions was similar. Foliar critical P concentration (i.e., minimum [P] to reach 90% of maximum growth) was also similar at nearly 110 mg P m(-2). Doubling [CO2] did not increase P and water demand of potato plants, thus enabling the promotion of maximum growth without additional P or water supply, but via a significant increase in WUE (9.6 g biomass kg(-1) water transpired), presumably owing to the interaction between CO2 and P.

DOI： 10.3389/fpls.2019.01417

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DOI： 10.1093/jxb/erz208

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DOI： 10.1111/ens.12362

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DOI： 10.1270/jsbbs.18203

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DOI： 10.1093/aob/mcy204

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DOI： 10.1080/00380768.2018.1537643

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DOI： 10.1093/pcp/pcy017

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DOI： 10.1093/pcp/pcx132

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DOI： 10.3389/fpls.2017.01847

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DOI： 10.1111/pce.12594

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DOI： 10.3389/fpls.2016.01189

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

To reveal whether hypocotyl sink activities are regulated by the aboveground parts, and whether physiology and morphology of source leaves are affected by the hypocotyl sink activities, we conducted grafting experiments using two Raphanus sativus varieties with different hypocotyl sink activities. Comet (C) and Leafy (L) varieties with high and low hypocotyl sink activities were reciprocally grafted and resultant plants were called by their scion and stock such as CC, LC, CL and LL. Growth, leaf mass per area (LMA), total non-structural carbohydrates (TNCs) and photosynthetic characteristics were compared among them. Comet hypocotyls in CC and LC grew well regardless of the scions, whereas Leafy hypocotyls in CL and LL did not. Relative growth rate was highest in LL and lowest in CC. Photosynthetic capacity was correlated with Rubisco (ribulose 15-bisphosphate carboxylase/oxygenase) content but unaffected by TNC. High C/N ratio and accumulation of TNC led to high LMA and structural LMA. These results showed that the hypocotyl sink activity was autonomously regulated by hypocotyl and that the down-regulation of photosynthesis was not induced by TNC. We conclude that the change in the sink activity alters whole-plant growth through the changes in both biomass allocation and leaf morphological characteristics in R. sativus.

DOI： 10.1111/pce.12573

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CSIRO PUBLISHING  

We evaluated the roles of gibberellins (GAs) and cytokinins (CKs) in regulation of morphological traits such as biomass allocation and leaf mass per area (LMA). Seedlings of Polygonum cuspidatum Siebold & Zucc. were grown under various light and N availabilities. We exogenously sprayed solutions of gibberellin (GA(3)), benzyl adenine (BA), uniconazole (an inhibitor of GA biosynthesis) or their mixtures on the aboveground parts, and changes in morphological and physiological traits and relative growth rate (RGR) were analysed. Endogenous levels of GAs and CKs in the control plants were also quantified. The morphological traits were changed markedly by the spraying. Biomass allocation to leaves was increased by GA(3) and BA, whereas it decreased by uniconazole. GA(3) decreased LMA, whereas uniconazole increased it. We found close relationships among morphological and physiological traits such as photosynthetic rate and net assimilation rate, and RGR under all growth conditions. Seedlings with high levels of endogenous GAs or CKs and low levels of endogenous GAs or CKs showed morphologies similar to those sprayed with GA(3) or BA, and those sprayed with uniconazole, respectively. Thus we concluded these phytohormones are involved in the regulation of biomass allocation responding to either light or N availability.

DOI： 10.1071/FP14212

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Water is absorbed by fine roots and transported with essential substances to conduct photosynthesis in leaves. To determine how many fine roots are required to absorb adequate water and maximise photosynthesis, the effects of decreasing fine root biomass on stomatal conductance (G(s)) and photosynthetic rate (A) were evaluated using theoretical simulations and laboratory experiments. We used saplings of devil maple (Acer diabolicum), a typical woody species in the cool temperate regions of Japan, grown in high- and low-light environments. A-G(s) relationships and whole-plant hydraulic conductance (K-w) were determined and used for the simulations. Gradual changes in K-w, A, and G(s) were also evaluated with a stepwise decrease in fine roots in the laboratory experiments. The model predicted that K-w, G(s), and A decreased moderately with a decrease in fine roots. For example, A decreased by only 12% when fine roots were decreased by 50%. The model predictions were nearly consistent with the results from laboratory experiments. In conclusion, saplings of devil maple produced fine roots that were more than sufficient in meeting the water demands of photosynthesis. These characteristics may be beneficial in surviving severe drought and in maintaining adequate hydraulic conductance under conditions of moderate water stress. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.envexpbot.2013.12.020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Biomass allocation between shoots and roots is an important strategy used by plants to optimize growth in various environments. Root to shoot mass ratios typically increase in response to high CO2, a trend particularly evident under abiotic stress. We investigated this preferential root growth (PRG) in Arabidopsis thaliana plants cultivated under low pH/high CO2 or low nitrogen (N)/high CO2 conditions. Previous studies have suggested that changes in plant hormone, carbon (C) and N status may be related to PRG. We therefore examined the mechanisms underlying PRG by genetically modifying cytokinin (CK) levels, C and N status, and sugar signaling, performing sugar application experiments and determining primary metabolites, plant hormones and expression of related genes. Both low pH/high CO2 and low N/high CO2 stresses induced increases in lateral root (LR) number and led to high C/N ratios; however, under low pH/high CO2 conditions, large quantities of C were accumulated, whereas under low N/high CO2 conditions, N was severely depleted. Analyses of a CK-deficient mutant and a starchless mutant, in conjunction with sugar application experiments, revealed that these stresses induce PRG via different mechanisms. Metabolite and hormone profile analysis indicated that under low pH/high CO2 conditions, excess C accumulation may enhance LR number through the dual actions of increased auxin and decreased CKs.

DOI： 10.1093/pcp/pcu001

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DOI： 10.1007/s00442-012-2558-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Long-term, short-interval measurements of incident photosynthetically active photon flux density (PPFD; mu mol m(-2) s(-1)) on the forest floor are essential for estimating the leaf carbon gain of understory plants. Such PPFD data, however, are scarce. We measured PPFD at 1-min intervals for more than 12 months in cool-temperate forest sites and reported the data as a PPFD frequency distribution. We chose five sites: an open site (OPN), the understory of a deciduous broad-leaved tree stand with no visible gaps (DCD), that of an evergreen conifer stand (EVG), that of a deciduous broad-leaved tree stand with a gap of approximately 80 m(2) (GAPDCD), and that of an evergreen conifer stand with a gap of approximately 100 m(2) (GAPEVG). DCD were divided into three sub sites (DCD1-3) to investigate variation within a small area. GAP-sites were consisted of two sub sites (GAPDCD1-2 and GAPEVG1-2) differing in the distance from the gap center. Using the PPFD data, we estimated the summer seasonal (May-October) net assimilation rate of leaves (NAR(L)) at each site for various photosynthetic capacities (A(max): mu mol m(-2) s(-1)) and other parameters of a light response curve of CO2 assimilation rates. At OPN, the average daily accumulated PPFD (mol m(-2) day(-1)) was highest in May (28.2) and lowest in December (8.2). Even at OPN, the class of instantaneous PPFD that contributed most to NAR(L) was 250-300 mu mol m(-2) s(-1). Such a large contribution of lower PPFD is suggested to be an important feature of a field light-availability. At DCD, the relative PPFD (RPPFD, %) to OPN was 7.2 during canopy closure and 49.4 after leaf shedding (averaged for 3 sites). EVG had the lowest light environment throughout the year. Its average RPPFD was 3%. For GAP sites, summer seasonal RPPFD (%) was 15.6, 18.8, 6.4 and 15.6 for GAPDCD1, GAPDCD2, GAPEVG1 and GAPEVG2, respectively. At OPN, the NAR(L) increased with A(max) (which ranged from 1 to 40), suggesting that plants at OPN do not maximize NAR(L). In contrast, at DCD and EVG, A(max) values were attained that did maximize NAR(L), suggesting that plants at these sites could maximize the NAR(L). A(max)-NAR(L) relationships for GAPDCD and GAPEVG showed similar trend to closed canopy sites, DCD and EVG, while NAR(L) and A(max)* of GAP sites were larger than at these sites. Among DCD1-3, the daily accumulated PPFD (mol m-2 day-1) averaged in summer ranged 1.3-1.8 and the maximum NAR(L) value differed up to 1.5 times. It indicates that A(max) and NAR(L) can be various among plants under a similar canopy conditions. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.agrformet.2011.08.001

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PUBLIC LIBRARY SCIENCE  

Plants exhibit higher leaf-to-root ratios (L/R) and lower leaf nitrogen content (N(area)) in low-light than in high-light environments, but an ecological significance of this trait has not been explained from a whole-plant perspective. This study aimed to theoretically and experimentally demonstrate whether these observed L/R and N(area) are explained as optimal biomass allocation that maximize whole-plant relative growth rate (RGR). We developed a model which predicts optimal L/R and N(area) in response to nitrogen and light availability. In the model, net assimilation rate (NAR) was determined by light-photosynthesis curve, light availability measured during experiments, and leaf temperature affecting the photosynthesis and leaf dark respiration rate in high and low-light environments. Two pioneer trees, Morus bombycis and Acer buergerianum, were grown in various light and nitrogen availabilities in an experimental garden and used for parameterizing and testing the model predictions. They were grouped into four treatment groups (relative photosynthetic photon flux density, RPPFD 100% or 10% x nitrogen-rich or nitrogen-poor conditions) and grown in an experimental garden for 60 to 100 days. The model predicted that optimal L/R is higher and N(area) is lower in low-light than high-light environments when compared in the same soil nitrogen availability. Observed L/R and N(area) of the two pioneer trees were close to the predicted optimums. From the model predictions and pot experiments, we conclude that the pioneer trees, M. bombycis and A. buergerianum, regulated L/R and N(area) to maximize RGR in response to nitrogen and light availability.

DOI： 10.1371/journal.pone.0022236

Web of Science

PubMed

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