A Newly Identified Passive Hyperaccumulator Eucalyptus grandis × E. urophylla under Manganese Stress

Functional trait divergence associated with heteromorphic leaves in a climbing fig

Introduction

Plants that display heteroblasty possess conspicuous variations in leaf morphology between their juvenile and adult phases, with certain species retaining juvenile-like leaves even in adulthood. Nevertheless, the ecological advantages of maintaining two or more distinct leaf types in heteroblastic plants at the adult stage remain unclear.

Method

The aim of this study is to examine the adaptive significance of heteroblastic leaves sampled from branches with divergent functions (sterile and fertile branches) of mature Ficus pumila individuals by comparing their morphological, anatomical, and physiological characteristics.

Result

Leaves on sterile branches (LSs) exhibited a significantly larger specific leaf area, thinner palisade and spongy tissues, lower chlorophyll contents, and lower light saturation points than leaves on fertile branches (LFs). These results demonstrate that LSs are better adapted to low light environments, while LFs are well equipped to take advantages of high light conditions. However, both LFs and LSs have a low light compensation point with no significant difference between them, indicating that they start to accumulate photosynthetic products under similar light conditions. Interestingly, significant higher net photosynthetic rate was detected in LFs, showing they have higher photosynthetic capacity. Furthermore, LFs produced significant more nutrients compared to LSs, which may associate to their ability of accumulating more photosynthetic products under full light conditions and higher photosynthetic capacity.

Discussion

Overall, we observed a pattern of divergence in morphological features of leaves on two functional branches. Anatomical and physiological features indicate that LFs have an advantage in varied light conditions, providing amounts of photosynthetic products to support the sexual reproduction, while LSs adapt to low light environments. Our findings provide evidence that heteroblasty facilitates F. pumila to utilize varying light environments, likely associated with its growth form as a climbing plant. This strategy allows the plant to allocate resources more effectively and optimize its overall fitness.

Sex-specific competition differently regulates the response of the rhizosphere fungal community of Hippophae rhamnoides-A dioecious plant, under Mn stress

In this study, we investigated the soil physicochemical parameters and responses of rhizospheric fungal communities of Hippophae rhamnoides to Mn stress under different sexual competition patterns. The results showed that competition significantly affects soil physicochemical properties, enzyme activity, and rhizosphere-associated fungal community structures. Under Mn stress, soils with intersexual competition had higher levels of N supply than those with the intrasexual competition. Moreover, fungal communities under intersexual interaction were more positive to Mn stress than intrasexual interaction. Under intrasexual competition, female plants had higher total phosphorus content, neutral phosphatase activity, and relative abundance of symbiotic fungi in soils to obtain phosphorus nutrients to alleviate Mn stress. In contrast, male plants had relatively stable fungal communities in soils. In the intersexual competition, rhizosphere fungal diversity and relative abundance of saprophytic fungi in male plants were significantly higher than in female plants under Mn stress. In addition, female plants showed greater plasticity in the response of rhizosphere microorganisms to their neighbors of different sexes. The microbial composition in soils of female plants varied more than male plants between intrasexual and intersexual competition. These results indicated that sex-specific competition and neighbor effects regulate the microbial community structure and function of dioecious plants under heavy metal stress, which might affect nutrient cycling and phytoremediation potential in heavy metal-contaminated soils.

Trace Elements in Leaf Extracts of Eucalyptus grandis Traditionally Used to Treat Common Cold and Flu

BACKGROUND

Eucalyptus species have been used for the remediation of mine tailings dams in Zimbabwe. However, a traditional medicinal remedy (TMR) for the treatment of mild acute respiratory infections, such as common cold and flu includes the use of Eucalyptus leaves.

OBJECTIVES

The aim of the present study was to determine total concentrations of selected potentially toxic trace elements (PTEs) in gold mine tailings and leaves of Eucalyptus grandis and to identify extractable fractions of PTEs in leaves via boiling for 10 minutes in water, which is the process used to create TMRs to treat common cold and flu.

METHODS

Mine tailings and leaves of E. grandis were randomly collected at a gold mine tailings dam between April and June 2019. They were digested for laboratory analysis using standard analytical methods. Leaves were boiled in water for 10 minutes to prepare the TMR as practiced by the local community. The concentrations of PTEs were determined spectrometrically. Significant differences between PTEs in young and mature leaves were determined by analysis of variance.

RESULTS

Mine tailings were acidic (pH 4.52±0.62) with very low content of organic matter (0.02%) and contained PTEs in increasing concentrations of cadmium (Cd) < nickel (Ni) < lead (Pb) < chromium (Cr) < copper (Cu) < zinc (Zn) (n = 27). Mature leaves of E. grandis had higher concentrations than young leaves for Cr, Pb and Zn (p <0.05) which were lower than permissible limits in medicinal plants. Overall, boiling leaves in water for 10 minutes resulted in low extraction of PTEs (< 20%).

PARTICIPANT CONSENT

Obtained.

CONCLUSIONS

Concentrations of PTEs in leaves and leaf extracts of E. grandis were very low. However, TMRs should not be prepared from medicinal plants growing on metalliferous environments, such as mine tailings dams, due to the presence of cumulative toxins such as Cd and Pb. Further studies are needed to investigate the effect of various boiling times and should include arsenic in the studied PTEs.

COMPETING INTERESTS

The authors declare no competing interests for this study.

Phytoremediation of Mn-contaminated paddy soil by two hyperaccumulators (Phytolacca americana and Polygonum hydropiper) aided with citric acid

The purpose of this study was to investigate the phytoremediation potential of two hyperaccumulator plants, Phytolacca americana L. and Polygonum hydropiper L., on manganese-contaminated paddy soils. The biomass growth, Mn concentrations in plant tissues, and potential Mn removal efficiency from soils of these two plants were studied with citric acid, and the mechanisms of citric acid on these two plants were analyzed by examining the root activity, the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in leaves, as well as the concentrations of O₂·^- and H₂O₂ in leaves. The results showed that the biomass of these two plants were both promoted under low level of citric acid (3 mmol kg^-1). The concentration of Mn in the plants and the amount of Mn removed from the soil by the plants through harvesting were enhanced at low and intermediate (10 mmol kg^-1) citric acid application levels. The results also showed that root activity was enhanced at the low citric acid level and significantly inhibited under the intermediate and high levels (15 mmol kg^-1), which indicates the facilitative function of the low level of citric acid and the inhibitive function of the high level of citric acid application on plant biomass growth. Under the low and intermediate levels of citric acid application, O₂·^- in the plant leaves increased sharply, and the SOD, POD, and CAT activities also increased sharply, which made the level of H₂O₂ very similar to that of the control, ensuring the health of the plants. At the high level of citric acid application, however, the O₂·^- continued to rise sharply, while the activity of the three antioxidant enzymes declined sharply, causing the concentration of hydrogen peroxide to be much higher than that in the control, thus endangering the plants. The present study shows the potential of P. hydropiper for use in the phytoremediation of soil contaminated with a relatively low level of manganese.

Potential of Eucalyptus camaldulensis for phytostabilization and biomonitoring of trace-element contaminated soils

Soil pollution by trace elements (TEs) from mining and industrial activity is widespread and presents a risk to humans and ecosystems. The use of trees to immobilize TEs (phytostabilization) is a low-cost and effective method of soil remediation. We aimed to determine the chemical composition of leaves and flower buds of Eucalyptus camaldulensis in seven sites along the Guadiamar River valley (SW Spain), an area contaminated by a mine-spill in 1998. E. camaldulensis trees in the spill-affected area and adjacent non affected areas were growing on a variety of soils with pH from 5.6 to 8.1 with low concentration of plant nutrients. The spill affected soils contained up to 1069 mg kg^-1 of As and 4086 mg kg^-1 of Pb. E. camaldulensis tolerated elevated TE concentrations in soil and, compared to other species growing in the same environment, had low TE concentrations in the aerial portions. Besides tolerance to soil contamination, E. camaldulensis had low bioaccumulation coefficients for soil contaminants. TE concentrations in the aboveground portions were below levels reported to be toxic to plants or ecosystems. Flower buds had even lower TE concentrations than leaves. Despite the relatively low concentration of TEs in leaves they were significantly correlated with the soil extractable (0.01 M CaCl₂) Cd, Mn and Zn (but not Cu and Pb). The general features of this tree species: tolerance to impoverished and contaminated soils, fast growth and deep root system, and low transfer of TEs from soil to aboveground organs makes it suitable for phytostabilization of soils contaminated by TEs. In addition, eucalyptus leaves could be used for biomonitoring the soil extractability of Cd, Mn and Zn but not Cu or Pb.

The Key to Mn Homeostasis in Plants: Regulation of Mn Transporters

Plants only require small amounts of manganese (Mn) for healthy growth, but Mn concentrations in soil solution vary from sub-micromolar to hundreds of micromolar across the growth period. Therefore, plants must deal with large Mn concentration fluctuations, but the molecular mechanisms underlying how plants cope with low and high Mn concentrations are poorly understood. In this Opinion we discuss the role of Mn transporters in the uptake, distribution, and detoxification of Mn in response to changes in Mn concentrations through their regulation at the transcriptional and protein levels, mainly focusing on rice, an Mn-tolerant and -accumulating species. We also propose mechanisms involved in the hyperaccumulation of Mn and future prospects for studying this specific trait.