Functional carbon nanodots improve soil quality and tomato tolerance in saline-alkali soils

Spd-CDs-driven respiratory burst oxidase homolog/polyamine oxidase-dependent H2O2 signaling molecule engineering for salt tolerance in tomato

Carbon dots, are now considered safe, environment-friendly materials. Spermidine carbon dots (Spd-CDs) have been used as new agrochemicals for abiotic stress, but in-depth studies of salt stress remain scarce. Here, foliar application of Spd-CDs improved salt stress tolerance in tomatoes, and the beneficial effects were concentration-dependent. Tomato seedlings supplied with Spd-CDs (3.0 mg/L) had a greater height, a higher maximum quantum yield of PSII, and a higher net photosynthetic rate than controls after being exposed to 120 mM NaCl for 7 d. Molecular evidence showed that Spd-CDs promoted H2O2 molecule production by inducing the expression of respiratory burst oxidase homolog 1 (rboh1) and polyamine oxidase 5 (pao5), thus causing H2O2 molecule production and conferring resistance to salt stress. The role of RBOH1- and PAO5-dependent H2O2 molecule generation was evaluated by manipulating endogenous H2O2 levels and in rboh1 and pao5 mutants. Spd-CDs-meditated H2O2 regulation of salt tolerance could be articulated by reducing iron deficiency, maintaining ion homeostasis, and reducing root-to-shoot Na+ loading. Overall, the ROS signal molecule produced by RBOH1 and PAO5 protein was involved in the control of salt tolerance by Spd-CDs. These findings demonstrate that Spd-CDs are an effective and durable strategy to improve plant performance under salt stress, and to increase food security and quality.

Revisiting the role of light signaling in plant responses to salt stress

As one of the grave environmental hazards, soil salinization seriously limits crop productivity, growth, and development. When plants are exposed to salt stress, they suffer a sequence of damage mainly caused by osmotic stress, ion toxicity, and subsequently oxidative stress. As sessile organisms, plants have developed many physiological and biochemical strategies to mitigate the impact of salt stress. These strategies include altering root development direction, shortening the life cycle, accelerating dormancy, closing stomata to reduce transpiration, and decreasing biomass. Apart from being a prime energy source, light is an environmental signal that profoundly influences plant growth and development and also participates in plants' response to salt stress. This review summarizes the regulatory network of salt tolerance by light signals in plants, which is vital to further understanding plants' adaptation to high salinity. In addition, the review highlights potential future uses of genetic engineering and light supplement technology by light-emitting diode (LED) to improve crop growth in saline-alkali environments in order to make full use of the vast saline land.

Synergistic promotion mechanism and structure-function relationship of nonmetallic atoms doped carbon nanodots driving Tagetes patula L. to remediate cadmium-contaminated soils

Phytoremediation is an economical and effective strategy to remove cadmium (Cd) from polluted environments. To improve its efficiency, nanotechnology has been proposed to collaborate with hyperaccumulators in the remediation of Cd-polluted soils. However, the intricate structure-function relationship and the underlying regulatory mechanisms by which nanomaterials regulate Cd migration and conversion within the soil-plant system remained unrevealed. In this study, functional carbon nanodots (FCNs) were modified by doping with nitrogen and (or) sulfur elements. The synthesized nonmetallic atoms-doped FCNs were utilized to investigate their structure-function relationship and the regulatory mechanisms underlying their role in the phytoremediation of Cd-polluted soils by Tagetes patula L. FCNs-based nanomaterials can regulate the migration and bioaccumulation of Cd in the soil-plant system, which exhibits an obvious structural dependency. Specifically, the synergistic application of sulfur doped FCNs and Tagetes patula L. had the highest Cd removal efficiency of 53.2 %, which was 20.1 % higher than Tagetes patula L. alone. The uptake and migration of Cd in the soil-plant system are regulated by FCNs-based nanomaterials through both direct and indirect mechanisms, involving interfacial reactions, plant physiology regulation and environmental influence. This study not only sheds light on the fate of FCNs-based nanomaterials and Cd in the soil-plant system, but also provides innovative nanotools for reinforcing phytoremediation efficiency in contaminated soils.

Functional carbon nanodots enhance tomato tolerance to zinc deficient soils: Mechanisms and structure-function relationships

Zinc (Zn) deficiency is a global problem disorder affecting both crops and humans. Herein, modified functional carbon nanodots (MFCNs) with various structures and characteristics were developed to regulate tomato yields and Zn migration in plant-soil systems affected by Zn deficiency through structure-function relationships. Sulfur-doped FCNs (S-FCNs), nitrogen-doped FCNs (N-FCNs), and nitrogen‑sulfur co-doped FCNs (N,S-FCNs) were hydrothermally modified using FCNs as precursors. Their regulatory effects on tomatoes growing in Zn-deficient alkaline soils were studied in pot culture experiments. Specifically, 8 mg kg-1 of FCNs and S-FCNs improved tomato yields by 132 % and 108 %, respectively, compared with the control. However, N-FCNs and N,S-FCNs showed no significant effect on yield compared with the control (P < 0.05). Moreover, the application of FCNs or S-FCNs significantly improved fruit quality and nutritional value, including Zn content (by 26.3 % and 22.0 %, respectively) and naturally occurring antioxidants (by 3.37- and 2.08-fold for lycopene, 1.31- and 1.18-fold for flavonoids, and 2.28- and 1.89-fold for phenolics, respectively; P < 0.05). Although N-FCNs and N,S-FCNs increased Zn contents, they inhibited the synthesis of naturally occurring antioxidants in fruits. Zn bioaccessibility, uptake, and transportation in plant-soil systems were regulated by MFCNs through both direct and indirect mechanisms, including ionic reactions, plant physiology, and environmental effects. MFCNs regulated plant tolerance to Zn deficiency not only by affecting root activity, redox homeostasis, micronutrient balance, chelator synthesis, genetic expression, and plant photosynthesis but also by influencing rhizosphere soil properties and the microbial environment. Based on their dual role as "plant growth regulators" and "soil conditioners", MFCNs may have general applicability in agriculture. This study highlights the behavior of MFCNs in plant-soil systems, providing innovative nanotools for enhancing Zn availability, crop stress resistance and environmental preservation in sustainable agriculture.

Phosphogypsum with Rice Cultivation Driven Saline-Alkali Soil Remediation Alters the Microbial Community Structure

The improvement of saline-alkali land plays a key role in ensuring food security and promoting agricultural development. Saline soils modifies the response of the soil microbial community, but research is still limited. The effects of applying phosphogypsum with rice cultivation (PRC) on soil physicochemical properties and bacterial community in soda saline-alkali paddy fields in Songnen Plain, China were studied. The results showed that the PRC significantly improved the physicochemical properties of soil, significantly reduced the salinity, increased the utilization efficiency of carbon, nitrogen, and phosphorus, and significantly increased the activities of urease and phosphatase. The activities of urease and phosphatase were significantly correlated with the contents of total organic carbon and total carbon. A redundancy analysis showed that pH, AP, ESP, HCO3-, and Na+ were dominant factors in determining the bacterial community structure. The results showed that PRC could improve soil quality and enhance the ecosystem functionality of soda saline-alkali paddy fields by increasing nutrient content, stimulating soil enzyme activity, and regulating bacterial community improvement. After many years of PRC, the soda-alkali soil paddy field still develops continuously and healthily, which will provide a new idea for sustainable land use management and agricultural development.

Exploring the mechanism of nano-selenium treatment on the nutritional quality and resistance in plum plants

The impact of emerging stressors, such as pesticides and heavy metals, on the nutritional quality, resistance, and antioxidant systems of crops is the subject of intense monitoring. Due to its low toxicity and biocompatibility, nano-selenium (nano-Se) increases antioxidant capacity more effectively than selenium (Se). However, the protective mechanism of nano-Se in plum trees is still unknown when subjected to long-term abiotic stress. In this study, nano-Se foliar application enhanced the fruit's fresh weight and diameter and plant growth and development by increasing the content of trace elements (Zn and Se) and amino acids (Try, Phe, Pro, and Arg) in leaves and fruits. Compared to the control, nano-Se treatment dramatically improved the plant's antioxidant system, resulting in a substantial increase in SOD (44.3 %), POD (24.3 %), and CAT (95.6 %) levels. It also increased IAA (118.8 %), total flavonoids (23.0 %), total phenols (15.8 %), rutin (37.7 %), quercetin (146.8 %), and caffeic acid (19.8 %) contents by regulating phenylpropane metabolic pathways. Targeted amino acid analysis indicated that nano-Se biofortification greatly enhanced the levels of His (60.7 %), Ser (123.5 %), Thr (105.7 %), Val (202.1 %), Ile (236.2 %), Leu (84.0 %), Tyr (235.0 %), and Phe (164.7 %). The non-target metabolomics results showed that nano-Se treatment stimulated plum growth and nutrition by boosting phenylpropane metabolism and amino acid production. Therefore, nano-Se can improve the quality and resistance of plums by regulating both the primary and secondary metabolic pathways of plants and enhancing the antioxidant capacity. This investigation provides a reference for extrapolating the positive effects of nano-Se on crop quality to other plant species.

Carbon Nanodot-Microbe-Plant Nexus in Agroecosystem and Antimicrobial Applications

The intensive applications of nanomaterials in the agroecosystem led to the creation of several environmental problems. More efforts are needed to discover new insights in the nanomaterial-microbe-plant nexus. This relationship has several dimensions, which may include the transport of nanomaterials to different plant organs, the nanotoxicity to soil microbes and plants, and different possible regulations. This review focuses on the challenges and prospects of the nanomaterial-microbe-plant nexus under agroecosystem conditions. The previous nano-forms were selected in this study because of the rare, published articles on such nanomaterials. Under the study's nexus, more insights on the carbon nanodot-microbe-plant nexus were discussed along with the role of the new frontier in nano-tellurium-microbe nexus. Transport of nanomaterials to different plant organs under possible applications, and translocation of these nanoparticles besides their expected nanotoxicity to soil microbes will be also reported in the current study. Nanotoxicity to soil microbes and plants was investigated by taking account of morpho-physiological, molecular, and biochemical concerns. This study highlights the regulations of nanotoxicity with a focus on risk and challenges at the ecological level and their risks to human health, along with the scientific and organizational levels. This study opens many windows in such studies nexus which are needed in the near future.

Physiological, molecular, and environmental insights into plant nitrogen uptake, and metabolism under abiotic stresses

Nitrogen (N) as an inorganic macronutrient is inevitable for plant growth, development, and biomass production. Many external factors and stresses, such as acidity, alkalinity, salinity, temperature, oxygen, and rainfall, affect N uptake and metabolism in plants. The uptake of ammonium (NH4 +) and nitrate (NO3 -) in plants mainly depends on soil properties. Under the sufficient availability of NO3 - (>1 mM), low-affinity transport system is activated by gene network NRT1, and under low NO3 - availability (<1 mM), high-affinity transport system starts functioning encoded by NRT2 family of genes. Further, under limited N supply due to edaphic and climatic factors, higher expression of the AtNRT2.4 and AtNRT2.5T genes of the NRT2 family occur and are considered as N remobilizing genes. The NH4 + ion is the final form of N assimilated by cells mediated through the key enzymes glutamine synthetase and glutamate synthase. The WRKY1 is a major transcription factor of the N regulation network in plants. However, the transcriptome and metabolite profiles show variations in N assimilation metabolites, including glycine, glutamine, and aspartate, under abiotic stresses. The overexpression of NO3 - transporters (OsNRT2.3a and OsNRT1.1b) can significantly improve the biomass and yield of various crops. Altering the expression levels of genes could be a valuable tool to improve N metabolism under the challenging conditions of soil and environment, such as unfavorable temperature, drought, salinity, heavy metals, and nutrient stress.

The intrinsic and extrinsic mechanisms regulated by functional carbon nanodots for the phytoremediation of multi-metal pollution in soils

Functional carbon nanodots (FCNs) were currently demonstrated to regulate plant behavior in the agricultural and environmental areas. However, their regulation mechanisms on the interactions of plant-soil system during phytoremediation remain unrevealed. Here, Solanum nigrum L. was employed to explore the intrinsic and extrinsic mechanisms regulated by FCNs in the phytoremediation of Cd-Pb co-contaminated soils. The mediation of FCNs on metal removal and plant growth showed a hormesis manner, wherein the maximum induction effect was contributed by 15 mg kg-1 FCNs. Cd/Pb removal were enhanced by 8.5% and 31.6%, respectively. Moreover, FCNs reallocate metal distribution in plant by immobilized metals in roots and suppressed metal translocation to leaves. Improving plant growth (by 82.8% for root), stimulating plant hormesis, and activating plant detoxification pathways are the intrinsic mechanism for the phytoremediation smartly regulated by FCNs. Notably, FCNs induced soil enzyme activities that associated with soil nutrients recycling, up-regulated the microbial diversity and the soil immune system, and regulated S. nigrum L. to recruit beneficial microbials in the rhizosphere. The above-mentioned comprehensive improvement of soil micro-environment is the extrinsic mechanism regulated by FCNs. This study provides new insights to evaluate the interactions of nanomaterials with plant-soil system under soil contamination.

Preparation of Salicylic Acid-Functionalized Nanopesticides and Their Applications in Enhancing Salt Stress Resistance

Soil salinization is one of the global ecological and environmental problems that are tremendously threatening to the sustainable development of agriculture and food supply. In this work, a facile strategy was proposed to enhance the salt stress resistance of plants by preparing salicylic acid (SA)-functionalized mesoporous silica nanocarriers loaded with emamectin benzoate (EB). The obtained nanopesticides demonstrated a particle size of less than 300 nm. As an endogenous plant hormone, the grafting of SA in this nanopesticide system improved the uptake and translocation of pesticides in cucumber plants by 145.06%, and the applications of such nanopesticides enhanced the salt stress resistance of plants. This phenomenon was accounted for by the SA-functionalized nanopesticides increasing the superoxide dismutase and peroxidase activities (640 and 175%, respectively) and reducing the malondialdehyde content (54.10%), correspondingly alleviating the accumulation of reactive oxygen species and cell damage in plants. The above results were also confirmed by Evans blue staining and NBT staining experiments on cucumber leaves. In addition, these nanopesticides exhibited high insecticidal toxicity, and they also demonstrated biosafety toward nontarget organisms due to their sustained release property. Therefore, this work developed a biosafe SA-functionalized nanopesticide system, and these newly developed nanopesticides have potential in the agricultural field for enhancing salt stress resistance of plants.

Efficacy of Carbon Nanodots and Manganese Ferrite (MnFe2O4) Nanoparticles in Stimulating Growth and Antioxidant Activity in Drought-Stressed Maize Inbred Lines

Despite being the third most-consumed crop, maize (Zea mays L.) is highly vulnerable to drought stress. The predominant secondary metabolite in plants is phenolic acids, which scavenge reactive oxygen species to minimize oxidative stress under drought stress. Herein, the effect of carbon nanodots (CND) and manganese ferrite (MnFe2O4) nanoparticles (NP) on the drought stress tolerance of maize has been studied. The experimental results revealed that the highest leaf blade length (54.0 cm) and width (3.9 cm), root length (45.2 cm), stem diameter (11.1 mm), root fresh weight (7.0 g), leaf relative water content (84.8%) and chlorogenic (8.7 µg/mL), caffeic (3.0 µg/mL) and syringic acid (1.0 µg/mL) contents were demonstrated by CND-treated (10 mg L-1) inbred lines (GP5, HW19, HCW2, 17YS6032, HCW3, HCW4, HW7, HCW2, and 16S8068-9, respectively). However, the highest shoot length (71.5 cm), leaf moisture content (83.9%), shoot fresh weight (12.5 g), chlorophyll content (47.3), and DPPH free radical scavenging activity (34.1%) were observed in MnFe2O4 NP-treated (300 mg L-1) HF12, HW15, 11BS8016-7, HW15, HW12, and KW7 lines, respectively. The results indicate that CND and MnFe2O4 NP can mitigate drought stress effects on different accessions of the given population, as corroborated by improvements in growth and physio-biochemical traits among several inbred lines of maize.

Bioremediation of phenanthrene in saline-alkali soil by biochar- immobilized moderately halophilic bacteria combined with Suaeda salsa L

Polycyclic aromatic hydrocarbon (PAH) contaminated saline-alkali soil is commonly salinized and hardened, which leads to low self-purification efficiency, making it difficult to reuse and remediate. In this study, pot experiments were conducted to investigate remediation of PAH contaminated saline-alkali soil using biochar-immobilized Martelella sp. AD-3, and Suaeda salsa L (S. salsa). Reduction in phenanthrene concentration, PAH degradation functional genes, and the microbial community in the soil were analyzed. The soil properties and plant growth parameters were also analyzed. After a 40-day remediation, the removal rate of phenanthrene by biochar-immobilized bacteria combined with S. salsa (MBP group) was 91.67 %. Additionally, soil pH and electrical conductivity (EC) reduced by 0.15 and 1.78 ds/m, respectively. The fresh weight and leaf pigment contents increased by 1.30 and 1.35 times, respectively, which effectively alleviated the growth pressure on S. salsa in PAH-contaminated saline-alkali soil. Furthermore, this remediation resulted in abundance of PAH degradation functional genes in the soil, with a value of 2.01 × 10³ copies/g. The abundance of other PAH degraders such as Halomonas, Marinobacter, and Methylophaga in soil also increased. Furthermore, the highest abundance of Martelella genus was observed after the MBP treatment, indicating that strain AD-3 has a higher survival ability in the rhizosphere of S. salsa under the protection of biochar. This study provides a green, low-cost technique for remediation of PAH-contaminated saline-alkali soils.

Ecotoxicological evaluation of functional carbon nanodots using zebrafish (Danio rerio) model at different developmental stages

Considering functional carbon nanodots (FCNs) are potential to be applied in many areas, their risk and toxicity to organisms are imperative to be evaluated. Thus, this study conducted acute toxicity test of zebrafish (Danio rerio) at embryonic and adult stage to estimate the toxicity of FCNs. Results show that the toxic effects of FCNs and nitrogen doped FCNs (N-FCNs) at their 10% lethal concentration (LC₁₀) values on zebrafish are expressed in developmental retardation, cardiovascular toxicity, renal damage and hepatotoxicity. There are interactive relationships between these effects, but the main reason should be ascribed to the undesirable oxidative damage induced by high doses of materials, as well as the biodistribution of FCNs and N-FCNs in vivo. Even so, FCNs and N-FCNs can promote the antioxidant activity in zebrafish tissues to cope with the oxidative stress. FCNs and N-FCNs are not easy to cross the physical barriers in zebrafish embryos or larvae, and can be excreted from intestine by adult fish, which proves their biosecurity to zebrafish. In addition, because of the differences in physicochemical properties, especially nano-size and surface chemical property, FCNs show higher biosecurity to zebrafish than N-FCNs. The effects of FCNs and N-FCNs on hatching rates, mortality rates and developmental malformations are dose-dependent and time-dependent. The LC₅₀ values of FCNs and N-FCNs on zebrafish embryo at 96 hpf are 1610 mg/L and 649 mg/L, respectively. According to the Acute Toxicity Rating Scale of the Fish and Wildlife Service, the toxicity grades of FCNs and N-FCNs are both defined as "practically nontoxic", and FCNs are "Relatively Harmless" to embryos because their LC₅₀ values are above 1000 mg/L. Our results prove the biosecurity of FCNs-based materials for future practical application.

Isolation and screening of phosphorus solubilizing bacteria from saline alkali soil and their potential for Pb pollution remediation

The high pH and salinity of saline alkali soil not only seriously restrict the growth of crops, but also aggravate the pollution of heavy metals. The fixation of heavy metals and the regulation of pH by phosphorus solubilizing microorganisms may become a new way to repair heavy mental and improve saline alkali soil. In this study, a saline-alkali resistant bacteria (CZ-B1, CGMCC No: 1.19458) was screened from saline-alkali soil, and its tolerance to salt/alkali/lead stress was investigated by shaking flask experiment. The strain was identified as Bacillus amyloliquefaciens by morphology and 16S rRNA gene sequence analysis. The optimum growth temperature of CZ-B1 is about 35°C-40℃. The maximum salt stress and pH that it can tolerance are 100 g/L and 9 respectively, and its tolerance to Pb²⁺ can reach 2000 mg/L. The phosphorus release amount of CZ-B1 to Ca₃(PO₄)₂ within 72 h is 91.00-102.73 mg/L. The phosphate solubilizing index in PVK agar medium and NBRIP agar medium are more than 2, which can be defined as phosphate solubilizing bacteria. Moreover, the dissolution of CZ-B1 to phosphorus is mainly attributed to tartaric acid, citric acid and succinic acid in inorganic medium. In addition, the removal rate of Pb²⁺ by CZ-B1 can reach 90.38% for 500 mg/L. This study found that CZ-B1 can immobilize Pb through three biological mechanisms (organic acid, extracellular polymers and mineralization reaction). The release of succinic acid (10.97 g/L) and citric acid (5.26 g/L) may be the main mechanism to promote the mineralization reaction of CZ-B1 (phosphate and oxalate) and resistance to Pb stress. In addition, the high enrichment of Pb²⁺ by EPS can increase the rate of extracellular electron transfer and accelerate the mineralization of CZ-B1. The screening and domestication of saline-tolerant phosphorus-solubilizing bacteria not only help to remediate Pb contamination in saline soils, but also can provide P element for plant growth in saline soil.

Mechanisms of plant saline-alkaline tolerance

Saline-alkaline soil affects crop growth and development, thereby suppressing the yields. Human activities and climate changes are putting arable land under the threat of saline-alkalization. To feed a growing global population in limited arable land, it is of great urgence to breed saline-alkaline tolerant crops to cope with food security. Plant salt-tolerance mechanisms have already been explored for decades. However, to date, the molecular mechanisms underlying plants responses to saline-alkaline stress have remained largely elusive. Here, we summarize recent advances in plant response to saline-alkaline stress and propose some points deserving of further exploration.

Sugar-terminated carbon-nanodots stimulate osmolyte accumulation and ROS detoxification for the alleviation of salinity stress in Vigna radiata

In recent times, nanotechnology has emerged as an efficient tool to manage the adverse effect of environmental stresses on plants. In this connection, carbon-nanodots (CNDs) have been reported to ameliorate the negative impacts of salinity stress. Further, surface modification of CNDs is believed to augment their stress-alleviating potential, however, very little has been known about the potential of surface-functionalized CNDs. In this purview, two sugar (trehalose and glucose) terminated CNDs (CNPT and CNPG) have been synthesized and assessed for their stress-alleviating effects on Vigna radiata (a salt-sensitive legume) seedlings subjected to different concentrations of NaCl (0, 50, and 100 mM). The synthesized CNDs (CNPT and CNPG) exhibited a hydrodynamic size of 20-40 nm and zeta potential of up to - 22 mV with a 5-10 nm core. These water-soluble nanomaterials exhibited characteristic fluorescence emission properties viz. orange and greenish-yellow for CNPT and CNPG respectively. The successful functionalization of the sugar molecules on the CND cores was further confirmed using FTIR, XRD, and AFM. The results indicated that the application of both the CNDs improved seed germination, growth, pigment content, ionic and osmotic balance, and most importantly, the antioxidant defense which decreased ROS accumulation. At the same time, CNPT and CNPG exhibited no toxicity in the Allium cepa root tip bioassay. Therefore, it can be concluded that sugar-terminated CNDs improved the plant responses to salinity stress by facilitating sugar uptake to the aerial part of the seedlings.