Nitrogen addition alleviated sexual differences in responses to cadmium toxicity by regulating the antioxidant system and root characteristics, and inhibiting Cd translocation in mulberry seedlings

Exogenous Hydrogen sulfide attenuates cadmium toxicity to Chrysanthemum (Chrysanthemum indicum) by modulating glutathione synthesis and cadmium adsorption capacity in the cell wall

Soil cadmium (Cd) contamination leads to plant toxicity and poses a risk to human health both directly and indirectly through the food chain. Hydrogen sulfide (H2S), a novel gaseous signaling molecule, has been shown to enhance plant tolerance to various abiotic stresses. In this study, the potential of H2S in mitigating Cd toxicity in chrysanthemum (Chrysanthemum indicum) was investigated through physiological, biochemical and transcriptomic analyses. Results showed that the application of exogenous H2S resulted Cd accumulation in the roots by 21.15 %, while reducing Cd in the aboveground parts by 13.21 %. It was further found that H2S increased the pectin and hemicellulose content by 50.09 % and 49.79 %, respectively, through the regulation of cell wall polysaccharide synthesis-related genes, leading to changes in root functional group content and cell wall adsorption capacity for cadmium ions (Cd2+). Additionally, H2S also promoted the synthesis of GSH and PCs by regulating the expression of genes related to sulfur metabolism, chelating free Cd2+ in the cytoplasm, and reducing their harmful effects on the organelles. It was also found that exogenous H2S may have regulated the expression of transporter proteins by modulating the expression of transcription factors (MYB, AP2/ERF, and WRKY), thereby affecting the uptake, transport, and accumulation of Cd2+. In conclusion, exogenous H2S reduced the free Cd2+ content in the cytoplasm by promoting the adsorption of Cd2+ in the root cell walls and facilitating the synthesis of GSH and PCs in the cells, which in turn alleviated the toxic effects of Cd2+ on chrysanthemum.

Nitrogen deposition mitigates ozone-induced stress in Quercus aliena: Transcriptomic and metabolomic perspectives

Ozone (O3) pollution poses an increasingly serious threat to forest ecosystems. To investigate the effects of O3 exposure on Quercus aliena and elucidate its defense mechanisms, we exposed Q. aliena to O3 and monitored its responses using physiological, transcriptomic, and metabolomic analyses. The results revealed that after 84 days of O3 exposure, the malondialdehyde (MDA) and proline contents in Q. aliena leaves significantly increased, while catalase (CAT) activity and soluble sugar content significantly decreased. Notably, N addition markedly alleviated O3-induced oxidative stress. Integrated transcriptomic and metabolomic analyses revealed that N addition under O3 stress modulated metabolic pathways associated with flavonoid biosynthesis and amino acid metabolism. Specifically, O3 and N treatment increased the levels of rhoifolin, afzelechin, apigenin, luteoloside, kaempferol, and trifolin, while reducing the levels of phloretin, butin, cyanidin, taxifolin, myricetin, 2'-hydroxydaidzein, laricitrin, quercetin, prunin, luteolin, eriodictyol, quercitrin, and dihydromyricetin. Additionally, the co-treatment elevated the concentrations of L-glutamine, arginine, and ornithine, along with the levels of enzymes closely related to their synthesis, such as glnA (Uni0006561, Uni0006562, Uni0077758, Uni0101990), GSH (Uni0086646, Uni0101788), GSS (Uni0037737), and GCLC (Uni0034253). This study elucidates the metabolic alterations in Q. aliena under combined O3 and N treatments, highlighting changes in flavonoid biosynthesis and amino acid metabolism pathways. Using a multi-omics approach, we provide comprehensive insights into the responses of Q. aliena to O3 stress and N addition, offering significant implications for the management and conservation of forest ecosystems under environmental stress.

Nitrogen Deposition Effects on Invasive and Native Plant Competition: Implications for Future Invasions

Nitrogen (N) deposition has increased dramatically in recent decades, which is significantly affecting the invasion and growth of exotic plants. Whether N deposition leads to invasive alien species becoming competitively superior to native species remains to be investigated. In the present study, an invasive species (Oenothera biennis L.) and three co-occurring native species (Artemisia argyi Lévl. et Vant., Inula japonica Thunb., and Chenopodium album L.) were grown in a monoculture (two seedlings of the same species) or mixed culture (one seedling of O. biennis and one seedling of a native species) under three levels of N deposition (0, 6, and 12 g∙m^-2∙year^-1). Nitrogen deposition had no effect on soil N and P content. Nitrogen deposition enhanced the crown area, total biomass, leaf chlorophyll content, and leaf N to phosphorus ratio in both invasive and native plants. Oenothera biennis dominated competition with C. album and I. japonica due to its high resource acquisition and absorption capacity (greater height, canopy, leaf chlorophyll a to chlorophyll b ratio, leaf chlorophyll content, leaf N content, leaf mass fraction, and lower root-to-shoot ratio). However, the native species A. argyi exhibited competitive ability similar to O. biennis. Thus, invasive species are not always superior competitors of native species; this depends on the identities of the native species. High N deposition enhanced the competitive dominance of O. biennis over I. japonica by 15.45% but did not alter the competitive dominance of O. biennis over C. album. Furthermore, N deposition did not affect the dominance of O. biennis or A. argyi. Therefore, the species composition of the native community must be considered when preparing to resist future biological invasions. Our study contributes to a better understanding of the invasion mechanisms of alien species under N-loading conditions.

A Dark Septate Endophyte Improves Cadmium Tolerance of Maize by Modifying Root Morphology and Promoting Cadmium Binding to the Cell Wall and Phosphate

Dark septate endophytes (DSEs) can improve the performance of host plants grown in heavy metal-polluted soils, but the mechanism is still unclear. A sand culture experiment was performed to investigate the effects of a DSE strain (Exophiala pisciphila) on maize growth, root morphology, and cadmium (Cd) uptake under Cd stress at different concentrations (0, 5, 10, and 20 mg·kg^-1). The results indicated that the DSE significantly improved the Cd tolerance of maize, causing increases in biomass, plant height, and root morphology (length, tips, branch, and crossing number); enhancing the Cd retention in roots with a decrease in the transfer coefficient of Cd in maize plants; and increasing the Cd proportion in the cell wall by 16.0-25.6%. In addition, DSE significantly changed the chemical forms of Cd in maize roots, resulting in decreases in the proportions of pectates and protein-integrated Cd by 15.6-32.4%, but an increase in the proportion of insoluble phosphate Cd by 33.3-83.3%. The correlation analysis revealed a significantly positive relationship between the root morphology and the proportions of insoluble phosphate Cd and Cd in the cell wall. Therefore, the DSE improved the Cd tolerance of plants both by modifying root morphology, and by promoting Cd binding to the cell walls and forming an insoluble phosphate Cd of lower activity. These results of this study provide comprehensive evidence for the mechanisms by which DSE colonization enhances Cd tolerance in maize in root morphology with Cd subcellular distribution and chemical forms.

Dissolved organic matter-assisted phytoremediation potential of cotton for Cd-contaminated soil: a relationship between dosage and phytoremediation efficiency

Dissolved organic matter (DOM) is a novel Cd-contaminated soils amendment for phytoremediation. However, the phytoremediation efficiency for different DOM doses has been insufficiently investigated. In this study, we investigated the effect of five DOM doses (v/w, 0%, 1%, 2%, 4% and 8%) on the phytoremediation efficiency of cotton in Cd-contaminated soil through pot experiment. The results showed that bioavailable Cd concentrations and organic matter in the soil increased with the increased of DOM dosage. The DOM dose increased the chlorophyll content, photosynthesis, and the total biomass of cotton. In addition, the DOM application increased the Cd content in cotton roots and changed the Cd uptake in cotton shoots, increasing shoot Cd extraction efficiency by 8.53-20%. Simultaneously, soil Cd phytoextraction efficiency significantly increased. Furthermore, applying a 1% DOM dose resulted in safeguarding fibre biomass and maximising the efficiency of shoot extraction. Redundancy analysis showed that the Mn content in leaves is critical for increasing cotton biomass, anti-oxidation competence and phytoremediation efficiency under 1% DOM dose. In conclusion, DOM enhanced cotton remediation in Cd-contaminated soils and applying DOM at 1% was a suitable choice for Cd-contaminated soils.

Enhanced cadmium phytoremediation capacity of poplar is associated with increased biomass and Cd accumulation under nitrogen deposition conditions

Nitrogen (N) deposition plays a significant role in soil cadmium (Cd) phytoremediation, and poplar has been considered for the remediation of contaminated soil because of its enormous biomass and strong Cd resistance. To reveal the underlying physiological and root phenotypic mechanisms of N deposition affecting Cd phytoextraction in poplar, we assessed root phenotypic characteristics, Cd absorption and translocation, chlorophyll fluorescence performance, and antioxidant enzyme activities of a clone of Populus deltoides × P. nigra through combined greenhouse Cd and N experiments. Our results showed that Cd significantly changed the root phenotype by reducing root length, tip number, and diameter. Cd also caused the peroxidation of lipids, damaged the photosystem II (PSII) reaction centre, and reduced photosynthetic capacity, resulting in a decrease in biomass accumulation in poplar. The N60 (60 kg N·ha^-1·yr^-1) and N90 (90 kg N·ha^-1·yr^-1) treatments promoted the net photosynthetic rate of poplar by increasing the activity of antioxidant enzymes and proline content and repairing the PSII reaction centre, thus increasing the biomass accumulation of poplar exposed to Cd stress. Simultaneously, the N60 and N90 treatments might have increased Cd uptake from the soil by upregulating total root length, root tips, and fine root length. Cd mainly accumulated in roots and stems but not in leaves. The N30 (30 kg N·ha^-1·yr^-1) treatment had no obvious effects on these parameters compared with the single Cd treatment. Consequently, our study suggested that adequate N can improve biomass and Cd accumulation to enhance the phytoremediation capacity of poplar for Cd, which might be related to the improvement of leaf physiological defence and the change in root phenotypic characteristics.

Effects of Red Mud on Cadmium Uptake and Accumulation by Rice and Chemical Changes in Rhizospheres by Rhizobox Method

Red mud (RM), a byproduct of aluminum production, is used as amendments to increase the pH and reduce the available Cd in soil, but the effects of RM treatments on rice and rhizosphere chemistry changes at different radial-oxygen-loss (ROL) rates and developmental stages remain unclear. To address this concern, a rhizobox trial was conducted to investigate the effect of 0%, 0.5%, and 1.0% RM, on Cd accumulation by rice cultivars differing in ROL rate (‘Zheyou12’ (ZY12), ‘Qianyou1’ (QY1), and ‘Chunjiangnuo2’ (CJN2)) at two growth stages (tillering and bolting). The results showed that mobility factors of Cd in the soil were decreased significantly at both stages. The Cd mobility factor (MF) of CJN2 was decreased by 33.01% under 1% RM treatment at bolting stage. The pH value was increased by 0.39–0.53 units at two stages. RM contains large amounts of metals, which can increase soil iron (Fe) and manganese (Mn) concentrations, reduce redox potential, and transform the available Cd into Fe/Mn oxide-bound Cd. In addition, the Fe plaque further increased to inhibit the transformation of Cd. These changes reduced the available Cd in the soil and further decreased Cd absorption by rice. With the increase in RM concentration, the shoot and root biomass increased, and Cd accumulation in the plant significantly decreased. Compared with that under 0% RM treatment, the shoot Cd concentrations of ZY12, QY1, and CJN2 under 1% RM treatment at the bolting stage decreased by 27.59%, 36.00%, and 46.03%, respectively. The relative Cd accumulation ability of the three rice cultivars was CJN2 < QY1 < ZY12. The ROL promotes Fe plaque formation on the root surface. The Fe plaque is an obstacle or buffer between Cd and rice, which can immobilize Cd in Fe plaque and further reduce Cd absorption by rice. The addition of RM, in combination with a high-ROL rice cultivar, is a potential strategy for the safe production of rice on Cd-contaminated soils.