Potential roles of iron nanomaterials in enhancing growth and nitrogen fixation and modulating rhizomicrobiome in alfalfa (Medicago sativa L.)

Two-phase remediation of extreme textured soils: Integrating stabilized sludge and plant-assisted strategies for enhanced water-nutrient supply and nitrogen fixation

The continuous degradation of soil texture has severely suppressed soil productivity. Here, we present a two-phase remediation strategy aimed at improving extreme textured soils (ETS), specifically clay (CL) and sandy (SA) soils, by integrating stabilized sludge (SS) amendment and nitrogen-fixing plant (alfalfa) cultivation. In Phase I, the application of SS improved soil texture, as indicated by the optimized mechanical composition and aggregate structure. Water-stable aggregates contributed to organic carbon accumulation by protecting particulate organics. In addition, the improved aggregate spatial arrangement enhanced water dynamics. In Phase II, alfalfa cultivation restructured the diazotroph community via plant-rhizobium symbiosis, upregulating nitrogenase genes (nifKDH) and boosting nitrogen fixation. The synergy between SS and alfalfa established a resilient microbial ecosystem, offering a sustainable solution for ETS remediation and efficient sludge utilization, addressing both environmental and resource management goals.

Asymbiotic Nitrogen Fixation in the Phyllosphere of Urban Green Spaces

Biological nitrogen fixation (BNF) is an important source of nitrogen in ecosystems. Compared to symbiotic nitrogen-fixing microorganisms, free-living diazotrophic bacteria have a broader distribution and greater diversity, demonstrating greater potential for application. Leaf surfaces constitute one of the largest microbial reservoirs on Earth, harboring a variety of free-living diazotrophic bacteria, contributing significantly to plant N acquisition and growth. The distribution patterns, abundance, diversity, and the environmental variables affecting the asymbiotic nitrogen fixation (ANF) rates of free-living diazotrophic bacteria of non-leguminous plants in urban green spaces were investigated using high-throughput sequencing of nifH gene amplicons and the acetylene reduction method. Both green space type and plant species significantly impact ANF rates and nifH gene abundance in the phyllosphere, with green space type having a more pronounced effect. Leaf metal elements iron (Fe), molybdenum (Mo), and the free-living diazotrophic bacteria of the genus Skermanella collectively influence the ANF rates in the phyllosphere of urban green spaces. Linear regression analysis revealed that metal elements Fe, Mo, and potassium (K) in the leaves were significantly positive correlated with the diversity of the free-living diazotrophic bacteria and the abundance of the N-fixing gene nifH. The alpha diversity and symbiotic network structure of the free-living diazotrophic bacterial community in the phyllosphere indicated a significant negative correlation between human disturbance and environmental perturbation and the biodiversity and network complexity of these bacteria. This study provides a crucial foundation for understanding the nitrogen-fixing functions of microbes in urban ecosystems and their contributions to the nitrogen cycle.

Eco-safe potential of FITC-tagged nFeO in enhancing alfalfa-rhizobia symbiosis and salt stress tolerance via physicochemical and ultrastructural modifications

Salt stress severely limits global crop productivity by disrupting ionic balance, physiological processes, and cellular ultrastructure, particularly in salt-sensitive forages like alfalfa (Medicago sativa L). Addressing this issue requires environmentally feasible and innovative strategies. This study investigated the comparative potential of Nano-FeO and FeSO4 (30 mg kg-1) soil supplements with rhizobium on alfalfa salt tolerance employing morphological, physicochemical, and cellular approaches. The results demonstrated that FITC-nFeO and rhizobium significantly reduced Na+ uptake, enhanced K+ accumulation, and improved the Na+/K+ ratio in alfalfa roots and shoots relative to FeSO4. Scanning electron microscopy illustrated that FITC-nFeO ameliorated root ultracellular structure and leaf stomatal functionality, facilitating improved gaseous exchange characteristics and photosynthetic performance. Confocal laser scanning microscopy confirmed FITC-tagged nFeO adhesion to roots, supported by transmission electron microscopy findings of preserved chloroplast ultrastructure under FITC-nFeO and rhizobium application. FITC-nFeO also mitigated oxidative damage of ROS, as evidenced by reduced hydrogen peroxide, electrolyte leakage, and thiobarbituric acid reactive substances (TBARS) content, through enhanced antioxidant enzyme activities. Overall, in comparison to FeSO4, FITC-nFeO with rhizobium retrieved the salt-induced damages in alfalfa by promoting morpho-physiological and ultracellular integrity. This study highlights the role of nanotechnology in enhancing the resilience of forages on salt-contaminated soils, paving the way for eco-friendly remediation strategies.

Preharvest and Postharvest Applications of Fe-Based Nanomaterials: A Potent Strategy for Improving Pepper Storage

Nanomaterials (NMs) hold significant potential for enhancing agricultural production, extending the shelf life, and maintaining the quality of postharvest vegetables and fruits. In this study, after foliar spraying with 1, 10, and 50 mg of L-1 Fe-P NMs at different stages (seedling, flowering, and fruit stage), the pepper plant growth was significantly improved. In particular, the foliar application of 10 mg of L-1 Fe-P NMs during the flowering stage was found to be an optimal cultivation approach to promote the growth, yield, and freshness of peppers. Compared with the control group, Fe-P NMs increased net photosynthetic rate, plant height, and fruit number by 132.7%, 40.4%, and 265.7%, respectively. The applied Fe-P NMs, at the flowering stage, altered the capsaicin metabolic pathway, upregulating the genes for the synthesis of total phenols, flavonoids, lignans, and capsaicinoids. Consequently, these metabolites, which are beneficial for maintaining the freshness of pepper fruits, were increased. Furthermore, Fe-P NMs at the flowering stage downregulated the abundance of rot-causing microorganisms (Enterobacter and Chryseobacterium) and upregulated beneficial microorganisms (Pseudomonas, Arthrobacter, Sphingobacterium, and Paenibacillus) to change the microbial community structure. This ultimately created a micro-ecological environment conducive to the preservation of pepper fruits. For comparison, during pepper fruit storage, dipping and spraying with Fe-P NM suspensions effectively delayed weight loss and enhanced the growth of beneficial bacteria. Nevertheless, the effect was less pronounced than preharvest foliar application. This study provides insights into the pre- or postharvest application of NMs for improving the preservation performance of pepper fruits.

Impact of iron oxide nanoparticles on cadmium toxicity mitigation in Brassica napus

Cadmium (Cd) contamination greatly hinders plant productivity. Nanotechnology offers a promising solution for Cd phytotoxicity. The novelty of this study lies in the limited research on the effects of nanoiron (Fe3O4NPs) in regulating Cd toxicity in oilseed crops. This study examined how Fe3O4NPs regulated the Cd-exposure in B. napus. Foliar spray of 10 mg L-1 Fe3O4NPs was applied to 50 μM Cd-stressed B. napus seedlings via leaf exposure in hydroponic system. Under Cd stress, Fe3O4NPs decreased the Cd-accumulation (25-37%) due to adsorption followed by more root Cd-immobilization, and increased the plant height (23-31%) and biomass (17-24%). These findings were directly correlated with better photosynthetic activity (chlorophylls, gas exchanges and photosynthetic efficiency), leaf stomata opening and nutrients accumulation (20-29%). Subcellular localization revealed that Fe3O4NPs enhanced the binding capacity of cell wall for Cd to hinder its entry into cell organalles and facilitated vacoular sequestration. Additionally, Fe3O4NPs decreased the oxidative stress (21-33%) and peroxidation of lipids (24-31%) by regulating the genes-associated to superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, glutathione reductase, reduced glutathione, phytochelation, chlorophyll synthesis and Cd-transporters. Fe3O4NPs protected plant roots from Cd-induced cell structural damages and cell death. Among studied parameters, ZD 635 exhibited greater tolerance to Cd stress when compared to ZD 622 cultivar. Findings revealed that Fe3O4NPs effectively mitigate Cd toxicity by improving the photosynthesis, antioxidant defense mechanisms, cellular protection, nutrients accumulation and limiting Cd accumulation. This research offers a benchmark for the practical applicability of Fe3O4NPs to enhance the quality of canola production in Cd-contaminated soils.

Rhizobacteria protective hydrogel to promote plant growth and adaption to acidic soil

Endophytic plant growth promoting rhizobacteria (PGPRs) could replace chemical fertilizers in sustainable agriculture. Unfortunately, they are susceptible to harsh environmental conditions. Here, we proposed a polymeric hydrogel (PMH) consisting of carboxymethyl chitosan, sodium alginate, and calcium chloride for loading and protecting endophytic PGPR. This hydrogel can load endophytic PGPRs to not only boost its growth-promoting efficiency, but also help them adapt more effectively to environments. Using endophytic PGPR Ensifer C5 as model bacteria and Brasscia napus as host, we demonstrate that the PMH facilitate the colonization of endophytic PGPRs in the apical and lateral root primordia regions. Further analysis indicates that the PMH modulate suberin deposition of the endodermal cell layers and regulate the accumulation of auxin at the root tip. Meanwhile, PMH enhances the antioxidant capacity and disease resistance properties of plants by increasing the content of arachidonic acid metabolism intermediates in the plant. Importantly, the combination of PMH and endophytic PGPRs increases the yields of B. napus by approximately 30% in the field. Furthermore, PMH attenuates the loss of endophytic PGPR activity in the acidic environments. Overall, this microbial encapsulation strategy is a promising way to protect fragile endophytic microorganisms, providing attractive avenues in sustainable agriculture.

Assessing the efficacy of different nano-iron sources for alleviating alkaline soil challenges in goji berry trees (Lycium barbarum L.)

Alkalinity is a significant environmental factor affecting crop production, which is exacerbated by the current climate change scenario. In alkaline soils, iron availability is severely reduced due to its low solubility at high pH levels and bicarbonate concentrations, which hinders plant iron absorption by rendering it inactive. In modern agriculture, green-synthesized nanoparticles have attracted considerable attention due to their environmental compatibility, cost-effectiveness, and enhanced potential for foliar uptake. This study explores the effects of various iron sources and concentrations, including FeSO4.7H2O, Fe-EDDHA, Nano-Fe, and green-synthesized nano-Fe, at three concentrations (0, 0.25, and 0.5 g L- 1) on the growth, physiological, biochemical parameters, and nutrient uptake of goji berry. The evaluated parameters included leaf area, fresh and dry weight of leaves and fruits, chlorophyll a, b, and a/b ratio, carotenoids, total soluble sugar in leaves and fruits, catalase, guaiacol peroxidase, ascorbate peroxidase enzymes, and the concentrations of nutrient elements (N, P, K, Ca, Mg, Cu, Mn, Zn, and Fe). Results demonstrated that increasing iron concentrations led to enhanced fresh and dry weights of leaves and fruits, with the highest values recorded at 0.5 g L⁻¹ of all iron sources. Nano-Fe significantly boosted fresh and dry weight of leaves, resulting in a 4.95 to 4.84-fold increase compared to the control. The highest fresh (1.267 g) and dry (0.815 g) fruit weights were observed at 0.5 g L⁻¹ of green-synthesized nano-Fe. Regarding photosynthetic pigments, the chlorophyll a/b ratio peaked at 1.62 mg g⁻¹ FW under the 0.5 g L⁻¹ green-synthesized nano-Fe treatment, while the control exhibited the lowest ratio (1.31 mg g⁻¹ FW). A similar trend was observed in nutrient uptake, with the highest leaf iron content (0.189 mg g⁻¹ DW) recorded in the 0.5 g L⁻¹ nano-Fe treatment, and the lowest (0.116 mg g⁻¹ DW) in the control. Although iron concentration positively influenced most traits, it led to a decline in zinc and manganese levels. Overall, these results highlight the potential of green-synthesized nano-Fe as an efficient, cost-effective iron source for improving vegetative growth, photosynthetic pigment levels, and nutrient uptake in goji berries grown in alkaline soils.

Multifaceted impacts of nanoparticles on plant nutrient absorption and soil microbial communities

With the growth of the global population and the increasing scarcity of resources, the sustainability and efficiency improvement of agricultural production have become urgent needs. The rapid development of nanotechnology provides new solutions to this challenge, especially the application of nanoparticles in agriculture, which is gradually demonstrating its unique advantages and broad prospects. Nonetheless, various nanoparticles can influence plant growth in diverse manners, often through distinct mechanisms of action. Beyond their direct effects on the plant itself, they frequently alter the physicochemical properties of the soil and modulate the structure of microbial communities in the rhizosphere. This review focuses intently on the diverse methods through which nanoparticles can modulate plant growth, delving deeply into the interactions between nanoparticles and plants, as well as nanoparticles with soil and microbial communities. The aim is to offer a comprehensive reference for the utilization of functionalized nanoparticles in the agricultural sector.

Genome-wide identification and expression analysis of ferric reductase oxidase (FRO) genes in Gossypium spp. reveal their crucial role in iron homeostasis under abiotic and biotic stress

Ferric Reductase Oxidase (FRO) genes are pivotal in iron uptake and homeostasis in plants, yet they are not studied in cotton. Here, we identify and analyze 65 FRO homologs (21 GhFRO, 21 GbFRO, 11 GaFRO, 12 GrFRO) across four Gossypium species (G. hirsutum, G. barbadense, G. arboreum, G. raimondii). FRO exhibit conserved ferric reductase activity and conserved domain structures; Ferric_reduct (PF01794), FAD_binding_8 (PF08022), and NAD_binding_6 (PF08030) across species. Physicochemical properties and subcellular localization analysis provided insights into FRO proteins' functional characteristics, mainly localized to the plasma membrane. Phylogenetic analysis delineates 11 groups, indicating both conserved and divergent evolutionary patterns. Gene structure analysis unveils varying exon-intron compositions. Chromosomal localization shows distribution across A and D genomes, suggesting evolutionary dynamics. Synteny analysis reveals paralogous and orthologous gene pairs subjected to purifying selection. The cis-regulatory elements analysis implicates diverse regulatory mechanisms. Expression profiling highlights dynamic regulation across developmental stages, abiotic and biotic stress conditions. GhFRO interacts with Ca++-dependent protein kinases-10/28-like (CDPKs10/28-like) and metal transporter Natural resistance-associated macrophage protein 6 (Nramp6) to regulate metal ion transport and iron homeostasis. The three-dimensional protein structure prediction suggests potential ligand-binding sites in FRO proteins. Moreover, qRT-PCR analysis of selected eight GhFROs in leaves treated with stress elicitors, MeJA, SA, NaCl, and PEG for 1h, 2h, 4h, and 6h revealed significant downregulation. Overall, this comprehensive study provides insights into FRO gene diversity, evolution, structure, regulation, and function in cotton, with implications for understanding plant iron homeostasis and stress responses.

O-Carboxymethyl chitosan nanoparticles: A novel approach to enhance water stress tolerance in maize seedlings

Water stress, a significant abiotic stressor, significantly hampers crop growth and yield, posing threat to food security. Despite the promising potential of nanoparticles (NPs) in enhancing plant stress tolerance, the precise mechanisms underlying the alleviation of water stress using O-Carboxymethyl chitosan nanoparticles (O-CMC-NPs) in maize remain elusive. In this study, we synthesized O-CMC-NPs and delved into their capacity to mitigate water stress (waterlogging and drought) in maize seedlings. Structural characterization revealed spherical O-CMC-NPs with a size of approximately 200 nm. These NPs accumulated near the seed embryo and root tip, resulting in a substantial increase in fresh and dry weights. The application of O-CMC-NPs to water-stressed maize seedlings remarkedly elevated the chlorophyll content and activity of various antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO). The malondialdehyde (MDA) content was significantly reduced compared to the untreated control. Additionally, the expression of stress-responsive genes, such as ZmSOD, ZmCAT, ZmPOD, ZmTIFY, ZmACO, ZmPYL2, ZmNF-YC12, and ZmEREB180, were significantly upregulated in the O-CMC-NPs treated seedlings. These findings unveil the novel role of O-CMC-NPs in enhancing plant stress tolerance, suggesting their potential application in safeguarding maize seedlings under water stress conditions and facilitating the recovery from oxidative damage.

Exploring the Structure and Substance Metabolism of a Medicago sativa L. Stem Base

The stem base of alfalfa is a critical part for its overwintering, regeneration, and yield. To better understand the specificity and importance of the stem base, we analyzed the structure, metabolic substances, and transcriptome of the stem base using anatomical techniques, ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS), and RNA sequencing (RNA-seq), and compared it with stems and roots. The anatomical structure shows that the ratio of xylem to phloem changes at the base of the stem. A total of 801 compounds involved in 91 metabolic pathways were identified from the broadly targeted metabolome. Transcriptome analysis revealed 4974 differentially expressed genes (DEGs) at the stem base compared to the stem, and 5503 DEGs compared to the root. Comprehensive analyses of differentially accumulated compounds (DACs) and DEGs, in the stem base vs. stem, identified 10 valuable pathways, including plant hormone signal transduction, zeatin biosynthesis, α-Linolenic acid metabolism, histidine metabolism, carbon metabolism, carbon fixation in photosynthetic organisms, pentose phosphate pathway, galactose metabolism, and fructose and mannose metabolism. The pathways of plant hormone signal transduction and carbon metabolism were also identified by comparing the stem base with the roots. Taken together, the stem base of alfalfa is the transition region between the stem and root in morphology; in terms of material metabolism, its growth, development, and function are regulated through hormones and sugars.

Iron-containing nanominerals for sustainable phosphate management: A comprehensive review and future perspectives

Adsorption, which is a quick and effective method for phosphate management, can effectively address the crisis of phosphorus mineral resources and control eutrophication. Phosphate management systems typically use iron-containing nanominerals (ICNs) with large surface areas and high activity, as well as modified ICNs (mICNs). This paper comprehensively reviews phosphate management by ICNs and mICNs in different water environments. mICNs have a higher affinity for phosphates than ICNs. Phosphate adsorption on ICNs and mICNs occurs through mechanisms such as surface complexation, surface precipitation, electrostatic ligand exchange, and electrostatic attraction. Ionic strength influences phosphate adsorption by changing the surface potential and isoelectric point of ICNs and mICNs. Anions exhibit inhibitory effects on ICNs and mICNs in phosphate adsorption, while cations display a promoting effect. More importantly, high concentrations and molecular weights of natural organic matter can inhibit phosphate adsorption by ICNs and mICNs. Sodium hydroxide has high regeneration capability for ICNs and mICNs. Compared to ICNs with high crystallinity, those with low crystallinity are less likely to desorb. ICNs and mICNs can effectively manage municipal wastewater, eutrophic seawater, and eutrophic lakes. Adsorption of ICNs and mICNs saturated with phosphate can be used as fertilizers in agricultural production. Notably, mICNs and ICNs have positive and negative effects on microorganisms and aquatic organisms in soil. Finally, this study introduces the following: trends and prospects of machine learning-guided mICN design, novel methods for modified ICNs, mICN regeneration, development of mICNs with high adsorption capacity and selectivity for phosphate, investigation of competing ions in different water environments by mICNs, and trends and prospects of in-depth research on the adsorption mechanism of phosphate by weakly crystalline ferrihydrite. This comprehensive review can provide novel insights into the research on high-performance mICNs for phosphate management in the future.

Nano molybdenum trioxide-mediated enhancement of soybean yield through improvement of rhizosphere soil molybdenum bioavailability for nitrogen-fixing microbial recruitment

Molybdenum (Mo) plays a pivotal role in the growth and nitrogen-fixing process of plants mediated by rhizobia. However, the influence of nano‑molybdenum trioxide (MoO3NPs) on soybean growth, rhizosphere bioavailable Mo, and nitrogen-fixing microorganisms remains underexplored. Here, we report that compared with that of ionic Mo and bulk MoO3, the utilization of MoO3NPs (specifically NPs0.05 and NPs0.15) significantly boosted the available Mo content in the rhizosphere soil throughout the seedling (by 21.64 %-101.38 %), podding (by 54.44 %-68.89 %), and mature stage (by 34.41 %-to 45.71 %) of soybean growth. Furthermore, both NPs0.05 and NPs0.15 treatments maintained consistently higher levels of acid-extractable Mo, reducible Mo, and oxidizable Mo across these stages, which facilitated stable conversion and supply of bioavailable Mo. Within the rhizosphere soil, NPs0.05 and NPs0.15 treatments resulted in the highest relative abundance of Rhizobiales and Bradyrhizobium genera, and significantly promoted the colonization of nitrogen-fixing microorganisms, thereby increasing the content of nitrate nitrogen (NO3--N) by 8.69 % and 7.72 % and ammonium nitrogen (NH4+-N) by 44.75 % and 17.55 %, respectively. Ultimately, these effects together contributed to 107.17 % and 84.00 % increment in soybean yield by NPs0.05 and NPs0.15 treatments, respectively. In summary, our findings underscore the potential of employing MoO3NPs to promote plant growth and maintain soil nitrogen cycling, indicating distinct advantages of MoO3NPs over ionic Mo and bulk MoO3.

Enhancing iron content and growth of cucumber seedlings with MgFe-LDHs under low-temperature stress

The development of cost-effective and eco-friendly fertilizers is crucial for enhancing iron (Fe) uptake in crops and can help alleviate dietary Fe deficiencies, especially in populations with limited access to meat. This study focused on the application of MgFe-layered double hydroxide nanoparticles (MgFe-LDHs) as a potential solution. We successfully synthesized and characterized MgFe-LDHs and observed that 1-10 mg/L MgFe-LDHs improved cucumber seed germination and water uptake. Notably, the application of 10 mg/L MgFe-LDHs to roots significantly increased the seedling emergence rate and growth under low-temperature stress. The application of 10 mg/L MgFe-LDHs during sowing increased the root length, lateral root number, root fresh weight, aboveground fresh weight, and hypocotyl length under low-temperature stress. A comprehensive analysis integrating plant physiology, nutrition, and transcriptomics suggested that MgFe-LDHs improve cold tolerance by upregulating SA to stimulate CsFAD3 expression, elevating GA3 levels for enhanced nitrogen metabolism and protein synthesis, and reducing levels of ABA and JA to support seedling emergence rate and growth, along with increasing the expression and activity of peroxidase genes. SEM and FTIR further confirmed the adsorption of MgFe-LDHs onto the root hairs in the mature zone of the root apex. Remarkably, MgFe-LDHs application led to a 46% increase (p < 0.05) in the Fe content within cucumber seedlings, a phenomenon not observed with comparable iron salt solutions, suggesting that the nanocrystalline nature of MgFe-LDHs enhances their absorption efficiency in plants. Additionally, MgFe-LDHs significantly increased the nitrogen (N) content of the seedlings by 12% (p < 0.05), promoting nitrogen fixation in the cucumber seedlings. These results pave the way for the development and use of LDH-based Fe fertilizers.

Assessing the growth dynamics of alfalfa varieties (Medicago sativa cv. Bilensoy 80 and Nimet) response to varied carbon dioxide (CO2) concentrations

Rising atmospheric CO2 levels drive greenhouse effects, elevating temperatures, and diminishing water accessibility in semi-arid regions, affecting agriculture. Alfalfa contributes to climate change mitigation by sequestering carbon, enhancing soil fertility and carbon storage, reducing synthetic nitrogen fertilizer use, preventing soil erosion, supplying high-quality livestock feed, and serving as a bioenergy source. This research examined the effects of elevated CO2 levels in climate change scenarios (600, 800, and 1000 ppm, with control at 400 ppm) on two alfalfa varieties, Medicago sativa cv. Nimet and Bilensoy-80. The experiments were conducted in specialized Climate Change Simulation Greenhouses, allowing control of CO2, water, and temperature variables. Results revealed a positive relationship between higher CO2 concentrations and increased photosynthesis (P ≤ 0.001), promoting the plant growth leaf area (P ≤ 0.001), yields and both leaf (P ≤ 0.05) and stem dry biomass (P ≤ 0.001). At 1000 ppm CO2, a saturation point was reached, halting further photosynthesis. This down-regulation was linked to decreased intercellular CO2 levels, which expedited chlorophyll and breakdown and potentially induced leaf senescence. High CO2 levels led to greater biomass, as anticipated. However, total protein levels, a forage quality indicator, initially decreased with high CO2 concentrations (up to 1000 ppm) due to an inverse relationship with shoot yield. Surprisingly, the 1000 ppm CO2 concentration mitigated this protein reduction in both alfalfa varieties.

Utilization of phosphogypsum and red mud in alfalfa cultivation

In this work, the utilization of phosphogypsum (PG), a waste coming from the manufacture of phosphate fertilizers, as fertilizer for alfalfa (Medicago sativa L.) crops was investigated using pot experiments. The objective of this study was to evaluate the effects of both phosphogypsum and red mud (RM) in two soils representative of the pasture production area in Southern Spain. The morpho-physiological parameters of biomass, plant height, number of stems and number of leaves, as well as the chemical parameters of soil content, were measured. High doses of PG inhibited seed germination in some treatments. In addition, the treatment substrate (2550 g soil + 50 g kg-1 PG + 100 g kg-1 RM) also affected seed germination, possibly due to the large amount of RM. The application of PG and RM to the soil increased the availability of important nutrients for alfalfa, such as phosphorus (P), calcium (Ca2+) and magnesium (Mg2+). The results demonstrate that the treatment with PG significantly improved the uptake of P in alfalfa.

Integrated physiological and transcriptomic analyzes reveal the duality of TiO2 nanoparticles on alfalfa (Medicago sativa L.)

Alfalfa (Medicago sativa L.) is a feed crop due to its rich nutrition and high productivity. The utilization of titanium oxide nanoparticles (TiO2 NPs) brings benefits to agricultural production but also has potential hazards. To investigate the duality and related mechanism of TiO2 NPs on alfalfa, its different doses including 0, 50, 100, 200, 500, and 1000 mg L- 1 (CK, Ti-50, Ti-100, Ti-200, Ti-500, and Ti-1000) were sprayed on leaves. The results showed that greater doses of TiO2 NPs (500 and 1000 mg L-1) negatively affected the physiological parameters, including morphology, biomass, leaf ultrastructure, stomata, photosynthesis, pigments, and antioxidant ability. However, 100 mg L-1 TiO2 NPs revealed an optimal positive effect; compared with the CK, it dramatically increased plant height, fresh weight, and dry weight by 22%, 21%, and 41%, respectively. Additionally, TiO2 NPs at low doses significantly protected leaf tissue, promoted stomatal opening, and enhanced the antioxidant system; while higher doses had phytotoxicity. Hence, TiO2 NPs are dose-dependent on alfalfa. The transcriptomic analysis identified 4625 and 2121 differentially expressed genes (DEGs) in the comparison of CK vs. Ti-100 and CK vs. Ti-500, respectively. They were mainly enriched in photosynthesis, chlorophyll metabolism, and energy metabolism. Notably, TiO2 NPs-induced phytotoxicity on photosynthetic parameters happened concurrently with the alterations of the genes involved in the porphyrin and chlorophyll metabolism and carbon fixation in photosynthetic organisms in the KEGG analysis. Similarly, it affected the efficiency of alfalfa energy transformation processes, including pyruvate metabolism and chlorophyll synthesis. Several key related genes in these pathways were validated. Therefore, TiO2 NPs have positive and toxic effects by regulating morphology, leaf ultrastructure, stomata, photosynthesis, redox homeostasis, and genes related to key pathways. It is significant to understand the duality of TiO2 NPs and cultivate varieties resistant to nanomaterial pollution.