Mixed nitrogen form addition facilitates the growth adaptation of legume plant to heavy metal contamination in degraded mining areas

High correlations between plant clonality and ecosystem service functions after management in a chronosequence of evergreen conifer plantations

Introduction

Climate change and mono-afforestation or mono-reforestation have continuously caused a decline in biodiversity and ecosystem services on forest plantations. Key plant functional traits in forests or plantations may affect ecosystem functions after forest management practices. Plant clonality, a key functional trait, frequently links to biodiversity and ecosystem functions and affects the biodiversity-ecosystem functioning relationship. However, little is known about how plant clonality affects ecosystem functions and services of plantations after forest management.

Methods

We conducted a field experiment to discuss the diversity and proportion of clonal plants, plant diversity of the communities, and ecosystem service functions and their relationships under 10 years of close-to-nature (CTN) management, artificial gap management, and control (i.e., without management) in the three stages of C. Lanceolata plantations.

Results

Our results showed that CTN and gap management modes significantly facilitated diversity of clonal plants, plant diversity of the communities, and parameters of ecosystem service functions in C. lanceolata plantations. Moreover, CTN management promoted plant community diversity, soil water conservation, and carbon storage the most in the earlier stand stages. Diversity of clonal plants was significantly positively correlated with ecosystem service functions after forest management. Structural equation modeling analysis indicated that forest gap or CTN management indirectly positively affected ecosystem service functions through increasing diversity of clonal woody plants and plant diversity of the communities.

Conclusion

Our results indicate a highly positive effect of gap or CTN management on diversity and proportion of clonal plants and on plant diversity of the communities, which link to improvements in ecosystem service functions (i.e., water and soil conservation and carbon storage). The link between forest management, diversity, and ecosystem functions suggests that key functional traits or plant functional groups should be considered to underline the mechanism of traits-ecosystem functioning relationships and the restoration of degraded plantations.

Graphitic carbon nitride alleviates cadmium toxicity to microbial communities in soybean rhizosphere

Cadmium (Cd) contamination has led to various harmful impacts on soil microbial ecosystem, agricultural crops, and thus human health. Nanomaterials are promising candidates for reducing the accumulation of heavy metals in plants. In this study, graphitic carbon nitride (g-C3N4), a two-dimensional polymeric nanomaterial, was applied for ameliorating Cd phytotoxicity to soybean (Glycine max (L.) Merr.). Its impacts on rhizosphere variables, microorganisms, and metabolism were examined. It was found that g-C3N4 increased carbon/nitrogen/phosphorus (C/N/P) content, especially when N contents were averagely 4.2 times higher in the g-C3N4-treated groups. g-C3N4 significantly induced alterations in microbial community structures (P < 0.05). The abundance of the probiotics class Nitrososphaeria was enriched (on average 70% higher in the g-C3N4-treated groups) as was Actinobacteria (226% higher in the g-C3N4 group than in the CK group). At the genus level, g-C3N4 recruited more Bradyrhizobium (122% higher) in the Cd + g-C3N4 group than in the Cd group and more Sphingomonas (on average 24% higher) in the g-C3N4-treated groups. The changes of microbial clusters demonstrated the potential of g-C3N4 to shape microbial functions, promote plant growth, and enhance Cd resistance, despite observing less pronounced modifications in microbial communities in Cd-contaminated soil compared to Cd-free soil. Moreover, abundance of functional genes related to C/N/P transformation was more significantly promoted by g-C3N4 in Cd-contaminated soil (increased by 146%) than in Cd-free one (increased by 32.8%). Therefore, g-C3N4 facilitated enhanced microbial survival and adaptation through the amplification of functional genes. These results validated the alleviation of g-C3N4 on the microbial communities in the soybean rhizosphere and shed a new light on the application of environmental-friendly nanomaterials for secure production of the crop under soil Cd exposure.

Physiological and biochemical alterations in Vigna rdiate L. triggered by sesame derived elicitors as defense mechanism against Rhizoctonia and Macrophomina infestation

Improving agricultural products by the stimulation of plant growth and defense mechanisms by priming with plant extracts is needed to attain sustainability in agriculture. This study focused to consider the possible improvement in Vigna radiata L. seed germination rate, plant growth, and protection against the natural stress by increasing the defense mechanisms through the incorporation of Sesamum indicum phytochemical compounds with pre-sowing seed treatment technologies. The gas chromatography coupled with mass spectroscopy (GC-MS) analysis revealed that the methanol extract of S. indicum leaf extract contained eight major bioactive compounds, namely, 2-ethylacridine (8.24%), tert-butyl (5-isopropyl-2-methylphenoxy) dimethylsilane (13.25%), tris(tert-butyldimethylsilyloxy) arsane (10.66%), 1,1,1,3,5,5,5-heptamethyltrisiloxane (18.50%), acetamide, N-[4-(trimethylsilyl) phenyl (19.97%), 3,3-diisopropoxy-1,1,1,5,5,5-hexamethyltrisiloxane (6.78%), silicic acid, diethyl bis(trimethylsilyl) ester (17.71%) and cylotrisiloxane, hexamethyl-(4.89%). The V. radiata seeds were treated with sesame leaf extract seeds at concentrations 0, 10, 25, 50, and 100 mg/L. Sesame leaf extract at 50 and 100 mg/L concentrations was effective in increasing the germination percentage and the fresh and dry weights of roots and shoots. The increased peroxidase activity was noticed after treatment with S. indicum extract. In addition, disease percentage (< 60%) of both fungal pathogens (Rhizoctonia and Macrophomina) was significantly reduced in V. radiata plants treated with 100 mg/L of sesame leaf extract. These results revealed that physiochemical components present in S. indicum mature leaf extract significantly enhanced growth and defense mechanism in green gram plants.

Leaf Functional Traits of Invasive Grasses Conferring High-Cadmium Adaptation Over Natives

Heavy metal (HM) contamination resulting from industrialization and urbanization during the Anthropocene along with plant invasion can severely threaten the growth and adaptation of local flora. Invasive alien plant species generally exhibit a growth pattern consistent with their functional traits in non-contaminated environments in the introduced range. However, it remains unclear whether invasive alien plants have an advantage over native plants in contaminated environments and whether this growth pattern is dependent on the adaptation of their leaf functional traits. Here, we selected two congeneric pairs of invasive alien and native grasses that naturally co-exist in China and are commonly found growing in contaminated soil. To evaluate the effect of cadmium (Cd) on the structural and physiological leaf traits, we grew all four species in soil contaminated without or with 80 mg/kg Cd. Invasive plants contained significantly higher concentrations of Cd in all three organs (leaf, stem, and root). They displayed a higher transfer factor and bioconcentration factor (BCF) of shoot and root than natives, indicating that invasive species are potential Cd hyperaccumulators. Invasive plants accumulated polyphenol oxidase (PPO) to higher levels than natives and showed similar patterns of leaf structural and physiological traits in response to changes in Cd bioconcentration. The quantifiable leaf structural traits of invasive plants were significantly greater (except for stomatal density and number of dead leaves) than native plants. Leaf physiological traits, chlorophyll content, and flavonoid content were also significantly higher in invasive plants than in natives under Cd stress conditions after 4 weeks, although nitrogen balance index (NBI) showed no significant difference between the two species. Chlorophyll fluorescence parameters decreased, except for the quantum yield of photosystem II (ΦPSII) and the proportion of open photosystem II (qP), which increased under Cd stress conditions in both species. However, invasive plants exhibited higher fluorescence parameters than natives under Cd stress, and the decrement observed in invasive plants under Cd stress was greater than that in natives. High Cd adaptation of invasive grasses over natives suggests that invasive plants possess optimal leaf structural and physiological traits, which enable them to adapt to stressful conditions and capture resources more quickly than natives. This study further emphasizes the potential invasion of alien plants in contaminated soil environments within the introduced range. To a certain extent, some non-invasive alien plants might adapt to metalliferous environments and serve as hyperaccumulator candidates in phytoremediation projects in contaminated environments.

Utilization of Legume-Nodule Bacterial Symbiosis in Phytoremediation of Heavy Metal-Contaminated Soils

Simple Summary

The legume–rhizobium symbiosis is one of the most beneficial interactions with high importance in agriculture, as it delivers nitrogen to plants and soil, thereby enhancing plant growth. Currently, this symbiosis is increasingly being exploited in phytoremediation of metal contaminated soil to improve soil fertility and simultaneously metal extraction or stabilization. Rhizobia increase phytoremediation directly by nitrogen fixation, protection of plants from pathogens, and production of plant growth-promoting factors and phytohormones.

Abstract

With the increasing industrial activity of the growing human population, the accumulation of various contaminants in soil, including heavy metals, has increased rapidly. Heavy metals as non-biodegradable elements persist in the soil environment and may pollute crop plants, further accumulating in the human body causing serious conditions. Hence, phytoremediation of land contamination as an environmental restoration technology is desirable for both human health and broad-sense ecology. Legumes (Fabaceae), which play a special role in nitrogen cycling, are dominant plants in contaminated areas. Therefore, the use of legumes and associated nitrogen-fixing rhizobia to reduce the concentrations or toxic effects of contaminants in the soil is environmentally friendly and becomes a promising strategy for phytoremediation and phytostabilization. Rhizobia, which have such plant growth-promoting (PGP) features as phosphorus solubilization, phytohormone synthesis, siderophore release, production of beneficial compounds for plants, and most of all nitrogen fixation, may promote legume growth while diminishing metal toxicity. The aim of the present review is to provide a comprehensive description of the main effects of metal contaminants in nitrogen-fixing leguminous plants and the benefits of using the legume–rhizobium symbiosis with both wild-type and genetically modified plants and bacteria to enhance an efficient recovery of contaminated lands.

Effects of Different Nitrogen Forms and Competitive Treatments on the Growth and Antioxidant System of Wedelia trilobata and Wedelia chinensis Under High Nitrogen Concentrations

Nitrogen (N) is one of the essential nutrients for plant growth. Appropriate application of N can improve the N use efficiency (NUE) and significantly promote plants' growth. However, under N toxic conditions, the relationship between the growth and antioxidant system of invasive plants under different N forms and competitive treatments is not fully understood. Therefore, in this study, the performance of invasive species Wedelia trilobata and its native species Wedelia chinensis was evaluated under two sets of N forms and ratios, namely, NH₄ ⁺-N(AN)/NO₃ ^--N(NN) = 2:1 and NH₄ ⁺-N(AN)/NO₃ ^--N(NN) = 1:2 along with two intraspecific and interspecific competitions under without N and high N level of 15 g N⋅m^-2 year^-1, respectively. Data regarding the growth indices, antioxidant enzyme activities, including peroxidase (POD) and catalase (CAT), malondialdehyde (MDA), and proline contents were determined. Results showed that for competitive treatments, growth status was better for interspecific competition than intraspecific competition. The plant biomass of W. trilobata was significantly higher than that of W. chinensis. N significantly promoted the plants' growth in terms of leaf area and biomass yield, and the antioxidant enzyme activities were significantly increased under a high N treatment than that of the control. Among N forms/ratios, ammonium N (AN)/nitrate N (NN) = 2:1 significantly enhanced the enzyme activity, particularly in W. trilobata. Furthermore, for intraspecific competition, MDA contents of W. trilobata were significantly decreased compared to that of W. chinensis. In conclusion, our results showed that W. trilobata adapted well under competitive conditions through better growth and antioxidant defense system.

Heavy metal accumulation by roadside vegetation and implications for pollution control

Vehicular emissions cause heavy metal pollution and exert negative impacts on environment and roadside vegetation. Wild plants growing along roadsides are capable of absorbing considerable amounts of heavy metals; thus, could be helpful in reducing heavy metal pollution. Therefore, current study inferred heavy metal absorbance capacity of some wild plant species growing along roadside. Four different wild plant species, i.e., Acacia nilotica L., Calotropis procera L., Ricinus communis L., and Ziziphus mauritiana L. were selected for the study. Leaf samples of these species were collected from four different sites, i.e., Control, New Lahore, Nawababad and Fatehabad. Leaf samples were analyzed to determine Pb2+, Zn2+, Ni2+, Mn2+ and Fe3+ accumulation. The A. nilotica, Z. mauritiana and C. procera accumulated significant amount of Pb at New Lahore site. Similarly, R. communis and A. nilotica accumulated higher amounts of Mn, Zn and Fe at Nawababad and New Lahore sites compared to the rest of the species. Nonetheless, Z. mauritiana accumulated higher amounts of Ni at all sites compared with the other species included in the study. Soil surface contributed towards the uptake of heavy metals in leaves; therefore, wild plant species should be grown near the roadsides to control heavy metals pollution. Results revealed that wild plants growing along roadsides accumulate significant amounts of heavy metals. Therefore, these species could be used to halt the vehicular pollution along roadsides and other polluted areas.

Can the Application of Municipal Sewage Sludge Compost in the Aided Phytostabilization Technique Provide an Effective Waste Management Method?

(1) Background: sewage sludge is a by-product of wastewater treatment, which needs to be managed appropriately, e.g., in composting processes. The application of municipal sewage sludge composts (MSSCs) as a soil amendment is a potential way to effectively manage sewage sludge. (2) Methods: this paper presents the results of a vegetation pot experiment undertaken to assess the suitability of Dactylis glomerata L. and MSSC in the aided phytostabilization technique when applied on soils from an area effected by industrial pressure; this is characterized by high levels of heavy metal (HM). The contents of HMs in the test plant (the roots and above-ground parts), as well as in the soil and MSSC, were determined via an atomic spectrometry method. (3) Results: the application of MSSC positively contributed to an increased production of plant biomass and an increase in the pH in the soil. Concentrations of Cu, Cd, Pb, Zn, and Cr were higher in the roots than in the above-ground parts of Dactylis glomerata L. The addition of MSSC contributed most significantly to the considerable reduction in Ni, Pb, and Zn contents in the soil after the experiment. (4) Conclusions: MSSC can support the phytostabilization of soils contaminated with high levels of HMs.