Niche and interspecific associations of dominant plant species in antimony mining ecological damaged site in Nandan, Guangxi, China.

In order to provide a guide for plant selection of ecological restoration at antimony (Sb) mining ecological damaged sites, species composition, importance value, niche, and interspecific associations of tree, shrub, and herb layers were examined at Sb mining site in Nandan City, Guangxi, China. The results showed that 23 vascular plant species were recorded at the Sb mining ecological damaged site, belonging to 22 genera and 13 families, primarily Gramineae, Cyperaceae, Fabaceae, and Asteraceae. The highest importance values for trees, shrubs, and herbs were observed in Rhus chinensis (56.7%), Coriaria nepalensis (56.3%), and Eremochloa ciliaris (44.0%), which were characterized by fairly large niche widths of 1.58, 1.32 and 1.57, respectively. The highest niche overlap values were found between R. chinensis and Triadica sebifera in the tree layer, and between Thysanolaena latifolia and Bidens pilosa in the herb layer, with the value of 0.68 and 0.99, respectively. Shrub layer exhibited a lower range of niche overlap (0.30-0.42), suggesting significant niche differentiation among different species. In the tree and shrub layers, most species showed insignificantly negative associations, the proportion was 83.3% and 66.7%, respectively, indicating that the plant community was not stable. Herb layer generally exhibited significantly positive correlations, with 52.4% of species pairs showing positive correlation, indicating weak resource competition among species. Overall, plant community at Sb mining ecological damaged site was unstable. In the process of ecological restoration, trees and shrubs that can adapt to the conditions and have positive associations should be prioritized in species selection, such as R. chinensis, C. lanceolata, C. nepalensis, and B. nivea. This will promote vegetation positive succession, rehabilitate the ecosystem and ensure sustainable development at Sb mining ecological damaged sites.

Drought-responsive WRKY transcription factor genes IgWRKY50 and IgWRKY32 from Iris germanica enhance drought resistance in transgenic Arabidopsis.

Drought greatly affects the growth and development of garden plants and affects their ornamental value. WRKY transcription factors make up one of the largest transcription factor families in plants and they play an important role in the plant response to drought stress. However, the function of the WRKY gene in response to drought stress in Iris germanica, which is commonly used in landscaping, has not been studied. In this study, we isolated two WRKY transcription factor genes from Iris germanica, IgWRKY50 and IgWRKY32, which belong to Group II and Group III of the WRKY family, respectively. IgWRKY50 and IgWRKY32 could be induced by PEG-6000, high temperature and ABA in Iris germanica. IgWRKY50 and IgWRKY32 could quickly respond to drought and they peaked at 3 h after PEG-6000 treatment (19.93- and 23.32-fold). The fusion proteins IgWRKY50-GFP and IgWRKY32-GFP were located in the nucleus of mesophyll protoplasts of Arabidopsis. The overexpression of the IgWRKY50 and IgWRKY32 genes improved the osmotic tolerance of transgenic Arabidopsis, mainly exhibited by the transgenic plants having a higher germination rate and a longer total root length on 1/2 MS medium containing mannitol. Under PEG-6000 stress, the transgenic plants had higher stomatal closure than the wild type (WT). Under natural drought stress, the water loss rate of the isolated leaves of transgenic Arabidopsis was lower than that of WT, the contents of proline (Pro) and soluble protein (SP) and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the transgenic plants were higher, but the content of malondialdehyde (MDA) was lower. Furthermore, the expression of several stress-related genes (RD29A, DREB2A, PP2CA, and ABA2) was significantly increased in IgWRKY50- and IgWRKY32- overexpressing transgenic Arabidposis plants after drought treatment. These results suggest that IgWRKY50 and IgWRKY32, as two positive regulators, enhance the drought resistance of transgenic Arabidopsis by mediating the ABA signal transduction pathway. IgWRKY50 and IgWRKY32 can be used as candidate genes for molecular breeding of drought resistance in Iris.

Nitrogen and sulfur fertilizers promote the absorption of lead and cadmium with Salix integra Thunb. by increasing the bioavailability of heavy metals and regulating rhizosphere microbes.

Fertilization is an effective agronomic strategy to improve the efficiency of phytoextraction by Salix integra Thunb. However, the specific effects of the simultaneous application of nitrogen (N) and sulfur (S) fertilizers in the rhizosphere remain unclear. We investigated the bioavailability of lead (Pb) and Cadmium (Cd) along with the microbial metabolic functions and community structure in the rhizosphere soil of S. integra after the application of N (0, 100, and 200 kg·ha-1·year-1) and S (0, 100, and 200 kg·ha-1·year-1) fertilizers for 180 days. The simultaneous application of N and S fertilizers significantly enhanced the absorption of Pb and Cd by S. integra, whereas this effect was not observed for the single application of N or S fertilizer. The contents of acid-soluble Pb and Cd in the rhizosphere soil significantly increased after either single or combined fertilize applications. The microbial metabolic activity was enhanced by the N and S fertilizers, whereas the microbial diversity markedly decreased. The metabolic patterns were mainly affected by the concentration of N fertilizer. The dominant fungi and bacteria were similar under each treatment, although the relative abundances of the dominant and special species differed. Compared to the N200S100 and N200S200 treatments, the N100S100 and N100S200 treatments resulted in fewer pathogenic fungi and more rhizosphere growth-promoting bacteria, which promoted phytoremediation by S. integra. Redundancy analysis indicated that the pH and nitrate content were the key factors affecting the structure of the microbial community. Collectively, the results suggest interactive effects between N and S fertilizers on the rhizosphere soil, providing a potential strategy for plant-microbial remediation by S. integra.

Inoculation With Indigenous Rhizosphere Microbes Enhances Aboveground Accumulation of Lead in Salix integra Thunb. by Improving Transport Coefficients.

The application of plant-microbial remediation of heavy metals is restricted by the difficulty of exogenous microbes to form large populations and maintain their long-term remediation efficiency. We therefore investigated the effects of inoculation with indigenous heavy-metal-tolerant rhizosphere microbes on phytoremediation of lead (Pb) by Salix integra. We measured plant physiological indexes and soil Pb bioavailability and conducted widespread targeted metabolome analysis of strains to better understand the mechanisms of enhance Pb accumulation. Growth of Salix integra was improved by both single and co-inoculation treatments with Bacillus sp. and Aspergillus niger, increasing by 14% in co-inoculated plants. Transfer coefficients for Pb, indicating mobility from soil via roots into branches or leaves, were higher following microbial inoculation, showing a more than 100% increase in the co-inoculation treatment over untreated plants. However, Pb accumulation was only enhanced by single inoculation treatments with either Bacillus sp. or Aspergillus niger, being 10% greater in plants inoculated with Bacillus sp. compared with uninoculated controls. Inoculation mainly promoted accumulation of Pb in aboveground plant parts. Superoxide dismutase and catalase enzyme activities as well as the proline content of inoculated plants were enhanced by most treatments. However, soil urease and catalase activities were lower in inoculated plants than controls. Proportions of acid-soluble Pb were 0.34 and 0.41% higher in rhizosphere and bulk soil, respectively, of plants inoculated with Bacillus sp. than in that of uninoculated plants. We identified 410 metabolites from the microbial inoculations, of which more than 50% contributed to heavy metal bioavailability; organic acids, amino acids, and carbohydrates formed the three major metabolite categories. These results suggest that both indigenous Bacillus sp. and Aspergillus niger could be used to assist phytoremediation by enhancing antioxidant defenses of Salix integra and altering Pb bioavailability. We speculate that microbial strains colonized the soil and plants at the same time, with variations in their metabolite profiles reflecting different living conditions. We also need to consider interactions between inocula and the whole microbial community when applying microbial inoculation to promote phytoremediation.

Pollen morphology of different species of Iris barbata and its systematic significance with scanning electron microscopy methods.

Forty-eight cultivars of Iris barbata were used as research materials, and observations of their pollen morphologies were made using scanning electron microscopy (SEM). The pollen of I. barbata consisted of a single grain, which was subspheroidal or subprolate and boat-shaped in equatorial view and oval or nearly round in polar view. The pollen was symmetrical or radially symmetrical on both sides, and there were five types of germination furrows: monocolpate, dicolpate, monocolpate-colpoidal, 2-syncolpate, and parasyncolpate. The exine ornamentation was mostly crass-reticulate and occasionally verrucate or pilate. Variation in the equatorial axis length of I. barbata pollen was the lowest, and variation in pollen morphology was stable. Q-type cluster analysis was conducted using seven indexes: polar axis length (P), equatorial axis length (E), P/E, mesh diameter (D), net ridge width (W), D/W, and germination furrow width (WG). The 48 cultivars were divided into three groups. Three dwarf cultivars were clustered in one group, and the degree of evolution of this group was higher than that of the other two groups. This paper systematically describes the characteristics of I. barbata for the first time, and thus provides important palynological insights into the classification and cross-breeding of I. barbata.