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.
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.
At a sedimentary site in an old mine site, Miscanthus sinensis formed patches, where Pinus densiflora seedlings could grow better compared with those outside the patches, indicating that M. sinensis ...would improve P. densiflora seedling establishment. The purpose of this study was to understand the mechanisms by which M. sinensis facilitates the survival of P. densiflora seedlings by considering the soil properties, heavy metal tolerance, and root endophytes in P. densiflora seedlings at the sedimentary site. The sedimentary site, which is a bare ground, contained high concentrations of Fe, indicating that plants should be exposed to Fe and high soil temperature stresses. Measurement of soil temperature revealed that M. sinensis suppressed sharp increases and alternation of soil temperature, resulting in reducing high soil temperature stress in P. densiflora seedlings. To adapt to the Fe stress environment, P. densiflora outside and inside the patches produced Fe detoxicants, including catechin, condensed tannin, and malic acid. Ceratobasidium bicorne and Aquapteridospora sp. were commonly isolated from P. densiflora seedlings outside and inside the patches as root endophytes, which might enhance Fe tolerance in the seedlings. Aquapteridospora sp., which is considered as a dark-septate endophyte (DSE), was also isolated from the roots of M. sinensis, suggesting that M. sinensis might play a source of a root endophyte to P. densiflora seedlings. Ceratobasidium bicorne could be classified into root endophytes showing symbiosis and weak pathogenicity to host plants. Therefore, high soil temperature stress would weaken P. densiflora seedlings, causing root endophytic C. bicorne to appear pathogenic. We suggested that P. densiflora could adapt to the Fe stress environment via producing Fe detoxicants, and M. sinensis would facilitate the establishment of P. densiflora seedlings in the sedimentary site by providing a DSE, Aquapteridospora sp., and maintaining symbiosis of C. bicorne from high soil temperature stress.
Metallophores are low-molecular-weight compounds capable of chelating heavy metals, which have recently been reported to alleviate heavy metal stress in plants. We isolated two undescribed compounds ...as Zn-chelating metallophores from the culture broth of the root endophytic Pezicula ericae w12-25, which was collected from a Zn-accumulating plant, Aucuba japonica Thunb. These two compounds were determined to be (3aS,4S,6aR)-3a-hydroxy-3-methylene-4-octyldihydrofuro3,4-bfuran-2,6(3H,4H)-dione and (3S,3aS,4S,6aR)-3a-hydroxy-3-(hydroxymethyl)-4-octyldihydrofuro3,4-bfuran-2,6(3H,4H)-dione using spectroscopic methods (HRMS, 1H and 13C NMR, and 2D NMR) and X-ray crystallography, respectively. The two compounds, classified as furofurandiones, were named isoavenaciol and 7-hydroxy-isoavenaciol. After the hydrolysis of the lactone moiety, isoavenaciol would release the carboxyl group to show Zn-chelating activity. Their antifungal activities were confirmed using Cladosporium herbarum (AHU9262).
Root endophytic Pezicula ericae, isolated from Zn-accumulating plant, Aucuba japonica, produced two undescribed metallophores showing Zn chelating activity. Display omitted
•Pezicula ericae were isolated from Zn-accumulating plant, Aucuba japonoica.•P. ericae produced two undescribed furofurandiones as Zn-chelating metallophores.•Two compounds were named isoavenaciol and 7-hydroxy-avenaciol.•Hydrolysis of lactone moiety would increase the Zn-chelating activity.•Their antifungal activities were evaluated using Cladosporium herbarum.
Miscanthus sinensis Andersson naturally grows at mining sites and accumulates heavy metals, suggesting heavy metal tolerance. This study aimed to elucidate the heavy metal tolerance mechanisms of M. ...sinensis, which naturally grew at a mine site, considering root endophytes. Elemental analysis by inductively coupled plasma-optical emission spectroscopy showed that M. sinensis highly accumulated zinc and lead in adventitious roots and dead root bark, exhibiting tolerance via these elemental removals in dead root bark. Phenolic analysis by high-performance liquid chromatography revealed chlorogenic acid production in adventitious roots. Phialocephala fortinii, which showed the highest appearance, and Talaromyces verruculosus, which produced gluconic acid as a zinc detoxicant, were isolated from adventitious roots of M. sinensis. In inoculation tests, P. fortinii and T. verruculosus significantly enhanced seedling growth by increasing potassium uptake and possibly indole-3-acetic acid production. Our results provide fundamental knowledge for using M. sinensis and root endophytes for revegetation at mining sites.
For growing plants at mine sites, plant species that accumulate metals in tissues and are tolerant to high metal concentrations should be selected from the perspective of phytostabilization. However, ...the eco-chemical or elemental information of the plant species at the mine sites is limited. The purpose of this study was to identify plants that can adapt to natural growth at mine sites, via: (1) vegetation survey, (2) elemental analysis in soil and plants, and (3) detoxicant detection in plant cells. Our vegetation survey indicated that plants growing at our study site are consistent with plant species confirmed at other mine sites in previous reports. A. indica var. maximowiczii and F. sachalinensis, present at the mine site, highly accumulated Fe, Al, and Cu in the roots, indicating their metal tolerance. Furthermore, A. indica var. maximowiczii produced detoxicants such as chlorogenic acid and 3,5-dicaffeoylquinic acid in the roots, which exhibited high antioxidative activity that would play an important role in metal tolerance in A. indica var. maximowiczii. This study will be effective in providing fundamental information on phytostabilization at mine sites.
, a root endophyte in
, enhances Al tolerance in
by changing aluminum (Al) localization and the production of a siderophore, oosporein, which chelates Al for detoxification. Oosporein has various ...functions, including insecticidal activity, phytotoxicity, antifungal activity, and a siderophore. In our study, we focused on the detoxification effect of oosporein as a siderophore and on the growth of
under Al exposure. In addition, the phytotoxicity of oosporein to
was confirmed to compare with those in
and
as control plants. Under Al stress, oosporein promoted plant growth in
seedlings at 10 ppm, which was the same concentration as that detected in
roots infected with
in our previous study. Oosporein also showed low phytotoxicity to
compared with
at even high concentrations of oosporein. These results suggest that the concentration of oosporein in
roots would be maintained at the appropriate concentration to detoxify Al and would promote
growth under Al stress, although oosporein would show low phytotoxicity to the natural host plant,
, compared with the non-host plant,
.
Mine drainage is a vital water problem in the mining industry worldwide because of the heavy metal elements and low pH. Rhizofiltration using wetland plants is an appropriate method to remove heavy ...metals from the water via accumulation in the rhizosphere. Phragmites australis is one of the candidate plants for this method because of metal accumulation, forming iron plaque around the roots. At the study site, which was the mill tailings pond in the Ningyo-toge uranium mine, P. australis has been naturally growing since 1998. The results showed that P. australis accumulated Fe, Mn, and 238U in the nodal roots without/with iron plaque compared with other plant tissues. Among the 837 bacterial colonies isolated from nodal roots, 88.6% showed siderophore production activities. Considering iron plaque formation around P. australis roots, we hypothesized that microbial siderophores might influence iron plaque formation because bacterial siderophores have catechol-like functional groups. The complex of catechol or other phenolics with Fe was precipitated due to the networks between Fe and phenolic derivatives. The experiment using bacterial products of root endophytes, such as Pseudomonas spp. and Rhizobium spp., showed precipitation with Fe ions, and we confirmed that several Pseudomonas spp. and Rhizobium spp. produced unidentified phenolic compounds. In conclusion, root-endophytic bacteria such as Pseudomonas spp. and Rhizobium spp., isolated from metal-accumulating roots of P. australis, might influence iron plaque formation as the metal accumulation site. Iron plaque formation is related to tolerance in P. australis, and Pseudomonas spp. and Rhizobium spp. might indirectly contribute to tolerance. Although there are many issues to be resolved in this research, we hope that the fundamental analysis of plant-microbe interactions would be helpful for phytoremediation at mine sites.
Soil cover is a prevailing method used at mine sites to ensure the safety of hazardous materials and restore ecological functions when the base materials are unfavorable for plant growth. The former ...open-pit Ningyo-toge Mine was backfilled with overburden and neutralized smelting residues and covered with soil in 1987. After 36 years, the vegetation remained dominated by the perennial herb Miscanthus sinensis, and woody plant establishment did not progress successfully. This study investigated the factors that inhibited woody plant establishment at the site. The soil profile survey revealed that the soil cover formed Bg horizons (pseudogley soil) with cloudy mottling, representative of poorly drained soil. In the Bg horizon, woody plant roots of Pinus densiflora and Weigela hortensis exhibited growth inhibition. Elemental analysis revealed that in the Bg horizon the roots of P. densiflora and W. hortensis accumulated high Fe concentrations exceeding 10,000 mg/kg DW at critical levels. Our results suggested that woody plant roots in the Bg horizon may have suffered from chronic oxygen deficiency accompanied by excessive Fe stress in the soil cover. Topsoil water content (<50 mm) and microtopographic features were not critical factors disrupting woody plant establishment because some individuals were growing in areas with high soil water content, exceeding 60%. Considering that woody plant roots were developed primarily in the shallow A horizon, A horizon formation by M. sinensis is a key step in initiating woody plant establishment by improving the soil structure and physiochemical characteristics of the soil cover, such as carbon content, exchangeable nutrients, and air-filled porosity. For successful mine pollution control and vegetation recovery, implementing an appropriate topsoil system, such as native forest soil, loosely graded and minor infiltration layer above the overburden would be necessary.
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•Woody plant establishment was inhibited on soil-covered mine site for 36 years.•Pseudogley soil (Bg horizon) formation inhibited woody plant root growth.•Oxygen deficiency and Fe dissolution may have caused root growth inhibition.•A horizon formation by M. sinensis is key for initiating woody plants establishment.•Proper soil cover system would be necessary for successful forest recovery.
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.
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