Aucuba japonica Thunb. is an evergreen understory shrub that grows naturally at a mine site. The mine soil contains high concentrations of heavy metals, and A. japonica appears to maintain ...detoxification mechanisms against heavy metals in the study site's understory. This study aimed to investigate the heavy metal tolerance mechanisms in A. japonica, considering the possible roles of arbuscular mycorrhizal and root-endophytic fungi. We conducted fieldwork in summer (canopy-foliation season) and winter (canopy-defoliation season) to measure the heavy metal concentrations in leaves, branches, and roots and analyze possible detoxicants in the roots. The infection rates of arbuscular mycorrhizal and root-endophytic fungi were evaluated via microscopic observation, and heavy metal (Zn) localization in A. japonica roots was observed using confocal laser scanning microscopy. Field analysis showed that A. japonica accumulated excessive Zn and produced aucubin and citric acid in the roots in both summer and winter. Zn localization observations clarified that Zn was distributed in thickened epidermal and cortical cell walls, suggesting that the cell walls functioned as Zn deposition sites, reducing Zn toxicity. It was further clarified that Zn was contained within cortical cells, indicating that Zn might be detoxified by aucubin and citric acid. Arbuscular mycorrhizal and root-endophytic fungi within cortical cells adsorbed Zn on fungal cell walls, indicating that these fungi would reduce Zn content within root cells and might alleviate Zn toxicity. Our results indicated that A. japonica would maintain Zn tolerance in both summer and winter via Zn immobilization in the cell walls and production of aucubin and citric acid, and that arbuscular mycorrhizal and root-endophytic fungi might play important roles in the Zn tolerance of A. japonica.
To date, studies on terrestrial plant ecology and evolution have focused primarily on the trade-off patterns in the allocation of metabolic production to roots and shoots in individual plants and the ...scaling of whole-plant respiration. However, few empirical studies have investigated the root : shoot ratio by considering scaling whole-plant respiration at various sizes throughout ontogeny.
Here, using a whole-plant chamber system, we measured the respiration rates, fresh mass and surface area of entire roots and shoots from 377 Fagus crenata individuals, from germinating seeds to mature trees, collected from five different Japanese provenances. Non-linear regression analysis was performed for scaling of root and shoot respiration, fresh mass and surface area with body size.
Whole-plant respiration increased rapidly in germinating seeds. In the seedling to mature tree size range, the scaling of whole-plant respiration to whole-plant fresh mass was expressed as a linear trend on the log-log coordinates (exponent slightly greater than 0.75). In the same body size range, root and shoot respiration vs. whole-plant fresh mass were modelled by upward-convex (exponent decreased from 2.35 to 0.638) and downward-convex trends (exponent increased from -0.918 to 0.864), respectively. The root fraction in whole-plant respiration, fresh mass and surface area shifted continuously throughout ontogeny, increasing in smaller seedlings during early growth stages and decreasing in larger trees.
Our results suggest a gradual shift in allocation priorities of metabolic energy from roots in seedlings to shoots in mature trees, providing insights into how roots contribute to shoot and whole-plant growth during ontogeny. The models of root : shoot ratio in relation to whole-plant physiology could be applied in tree growth modelling, and in linking the different levels of ecological phenomena, from individuals to ecosystems.
Both Moso bamboo (
Phyllostachys pubescens
) and tree forests have a large biomass; they are considered to play an important role in ecosystem carbon budgets. The scaling relationship between ...individual whole-shoot (i.e., aboveground parts) respiration and whole-shoot mass provides a clue for comparing the carbon budgets of Moso bamboo and tree forests. However, nobody has empirically demonstrated whether there is a difference between these forest types in the whole-shoot scaling relationship. We developed whole-shoot chambers and measured the shoot respiration of 58 individual mature bamboo shoots from the smallest to the largest in a Moso bamboo forest, and then compared them with that of 254 tree shoots previously measured. For 30 bamboo shoots, we measured the respiration rate of leaves, branches, and culms. We found that the scaling exponent of whole-shoot respiration of bamboo fitted by a simple power function on a log–log scale was 0.843 (95 % CI 0.797–0.885), which was consistent with that of trees, 0.826 (95 % CI 0.799–0.851), but higher than 3/4, the value typifying the Kleiber’s rule. The respiration rates of leaves, branches, and culms at the whole-shoot level were proportional to their mass, revealing a constant mean mass-specific respiration of 1.19, 0.224, and 0.0978 µmol CO
2
kg
− 1
s
− 1
, respectively. These constant values suggest common traits of organs among physiologically integrated ramets within a genet. Additionally, the larger the shoots, the smaller the allocation of organ mass to the metabolically active leaves, and the larger the allocation to the metabolically inactive culms. Therefore, these shifts in shoot-mass partitioning to leaves and culms caused a negative metabolic scaling of Moso bamboo shoots. The observed convergent metabolic scaling of Moso bamboo and trees may facilitate comparisons of the ecosystem carbon budgets of Moso bamboo and tree forests.
Although extensive studies have focused on carbon and water balance from aboveground measurements, the link between the belowground and aboveground processes deserves greater attention. In this ...context, the aim of this work was to assess the bi-directional feedback between whole-plant respiration and transpiration. The study was performed on 25 saplings of Sugi (Japanese cedar, Cryptomeria japonica D. Don), including dominant and suppressed individuals (total fresh weight ranging between 0.2 and 8.0 kg). During one week, the integrated water use (WU) was determined using the Deuterium dilution method. After this, the trees were uprooted and the root, stem, and leaf respiration were measured using incubation chambers and CO2 infrared sensors. The stem and root respiration followed a power response to mass (power exponent b < 1), implying a decline in mass-specific respiration with size. Conversely, the leaf respiration followed a near-linear increase with size (power exponent b ≈ 1), but was negatively affected by the stem density, indicating the hydraulic limitations of the leaf metabolism. The water use followed a power response with the tree size (b < 1), showing a decline in the transpiration per leaf mass with the tree size, but was also negatively correlated with the stem density. Our results indicate that dominant trees are more efficient in the use of water, and highlight the role of hydraulic limitations to leaf metabolism in suppressed trees.
Abstract Acer mono is thought to comprise seven varieties, but its classification and nomenclature are controversial. A recent molecular phylogenetic study suggested that A. mono varieties glabrum ...(G) and mayrii (M) do not interbreed, despite occurring syntopically (same location) and having a common genetic origin. However, if these are separate, reproductively isolated species, the basis for that isolation remains unclear. Here, we tested whether G and M can be considered separate species that differ in multiple ecological characteristics. We compared G and M in terms of distribution, habitats, drought tolerance of leaves, and flowering phenology of trees, and we verified their reproductive isolation (RI) in Japan. G showed higher drought and salt tolerance than M, which is consistent with the distribution of G in salt‐stressed coastal areas with relatively low precipitation. In contrast, M occurs in snowy, mesic, and mountain habitats. Even in neighboring M and G trees, the onset of flowering in M is earlier than that of G. Similarly, flower drop in M is completed sooner than in G. Although the presence of post‐zygotic reproductive barriers was not tested, the high calculated RI index probably contributes to RI. Two varieties of A. mono with a common genetic origin but different drought tolerance should be considered separate species. They likely shifted their climatic niches, involving local adaptation to different climatic conditions. This is roughly supported by an ENM‐based niche analysis and significant differences in flowering time. These findings help to understand the physiological diversification of A. mono .
As terrestrial plants are rooted in one place, their metabolism must be acclimatized to continuously changing environmental conditions. This process is influenced by different metabolic traits of ...plant organs during ontogeny. However, direct measurement of organ‐specific metabolic rates is particularly scarce, and little is known about their roles in whole‐plant metabolism. In this study, we investigated size scaling of respiration rate, fresh mass and surface area of leaves, stems and roots in 65 seedlings of Fagus crenata Blume (2 weeks to 16 months old). With the increase in plant mass, the proportion of roots in whole plants increased from 20.8 to 87.3% in fresh mass and from 12.8 to 95.0% in surface area, whereas there was only a 15.6 to 60.2% increase in respiration rate. As a result, the fresh‐mass‐specific and surface‐area‐specific respiration rates in the roots decreased by 85% and 90%, respectively, and these decreases were significantly size dependent. However, such a size‐dependent decrease was not observed for the surface‐area‐specific respiration rate in the leaves and stems. It is likely that this rapid root development is specific to the early growth stage after germination and would help plants acquire water and nutrients efficiently (i.e., at relatively low respiratory carbon costs). Overall, it is probable that the establishment of F. crenata forests and survival of F. crenata seedlings could be promoted by substantial root growth, with a reduction in respiratory carbon cost.
In this study, we investigated size scaling of respiration rate, fresh mass and surface area of leaves, stems and roots in 65 seedlings of Fagus crenata Blume (2 weeks to 16 months old). As a result, we found that a proportion of roots in whole plants increased from 20.8 to 87.3% in fresh mass and from 12.8 to 95.0% in surface area with increasing whole‐plant fresh mass, whereas the fresh‐mass‐specific and surface‐area‐specific respiration rates in the roots decreased by 85 and 90%, respectively. It is probable that the survival of F. crenata seedlings could be promoted by substantial root growth, with a reduction in respiratory carbon cost.
Six-year vegetation survey has been done at four sites of slope covering constructions in the former mine, considering the effects of environmental factors. Spraying of green plants seeds in spring ...enhanced the establishment of Artemisia indica var. maximowiczii from the beginning, compared with Festuca rubra, which shows the wintery grow pattern. On the contrary, spraying of the seeds before snowing enhanced the establishment of F. rubra, which would be tolerant in the winter time. Additionally, high soil volumetric water content influenced the establishment of high wet-tolerant native plants such as Typha latifolia, Salix species and Pinus densiflora. Low relative effective photon flux density would increase the growth of shade-tolerant plant, Festuca rubra. Our results clarified that differences of seed spraying timing, the soil water content, and the light environment influenced the vegetation of green plants and native plants.
For revegetation of mine dumping sites, introduction of tolerant plant species to tailings is needed. We compared initial shoot growth of the plants grown in tailings with that of control plants ...grown in Kanuma pumice to evaluate the tolerance to tailings among various species; one crop species, ine (Oryza sativa L. cv. Nipponbare); three revegetation species, yomogi (Artemisia princeps), medohagi (Lespedeza cuneate G. Don), and creeping red fescue (Festuca rubra L.); and two native species, mizudokusa (Equisetum fluviatile L.) and susuki (Miscanthus sinensis). The growth of the plants grown in tailings was significantly lower than that of control plants for ine, yomogi, and medohagi, but not for mizudokusa and susuki. We evaluated whole-plant respiration of ine, yomogi, and mizudokusa, and did not observed significant difference between the plants grown in tailings and control plants; however, Fe concentration in roots was significantly higher in the plants grown in tailings in all of the evaluated species. It is probable that the high Fe accumulation caused by tailings induces reduction of growth for crop and revegetation species, while does not affects native species because of their tolerance to high Fe concentration. Effective use of native plants may help revegetation of the dumping site.
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