Amendment-driven soil health restoration through soil pH and microbial robustness in a Cd/Cu-combined acidic soil: A ten-year in-situ field experiment.

Soil health arguably depends on biodiversity and has received wide attention in heavy-metal (HM) contaminated farmland remediation in recent years. However, long-term effects and mechanisms of soil amendment remain poorly understood with respect to soil microbal community. In this in-situ field study, four soil amendments (attapulgite-At, apatite-Ap, montmorillonite-M, lime-L) at three rates were applied once only for ten years in a cadmium (Cd)-copper (Cu) contaminated paddy soil deprecated for over five years. Results showed that after ten years and in compared with CK (no amendment), total Cd concentration and its risk in plot soils were not altered by amendments (p > 0.05), but total Cu concentration and its risk were significantly increased by both Ap and L, especially the former, rather than At and M (p < 0.05), through increased soil pH and enhanced bacterial alpha diversity as well as plant community. Soil microbial communities were more affected by amendment type (30%) than dosage (11%), microbial network characteristics were dominated by rare taxa, and soil multifunctionality was improved in Ap- and L-amended soils. A structural equation model (SEM) indicated that 57.3% of soil multifunctionality variances were accounted for by soil pH (+0.696) and microbial network robustness (-0.301). Moreover, microbial robustness could be potentially used as an indicator of soil multifunctionality, and Ap could be optimized to improve soil health in combined with biomass removal. These findings would advance the understanding of soil microbial roles, especially its network robustness, on soil multifunctionality for the remediation of metal contaminated soils and metal control management strategies in acidic soils. ENVIRONMENTAL IMPLICATION: Farmland soil contamination by heavy metals (HMs) has been becoming a serious global environmental challenge. However, most studies have been conducted over the short term, leading to a gap in the long-term remediation efficiency and ecological benefits of soil amendments. For the successful deployment of immobilization technologies, it is critical to understand the long-term stability of the immobilized HMs and soil health. Our study, to the best of our knowlege, is the first to state the long-term effects and mechanisms of soil amendments on soil health and optimize an effective and eco-friendly amendment for long-term Cd/Cu immobilization.

Insights into Adaptive Regulation of the Leaf-Petiole System: Strategies for Survival of Water Lily Plants under Salt Stress.

The water lily (Nymphaea tetragona) is an ancient angiosperm that belongs to the Nymphaeaceae family. As a rooted floating-leaf plant, water lilies are generally cultivated in fresh water, therefore, little is known about their survival strategies under salt stress. Long-term salt stress causes morphological changes, such as the rapid regeneration of floating leaves and a significant decrease in leaf number and surface area. We demonstrate that salt stress induces toxicity soon after treatment, but plants can adapt by regenerating floating leaves that are photosynthetically active. Transcriptome profiling revealed that ion binding was one of the most-enriched GO terms in leaf-petiole systems under salt stress. Sodium-transporter-related genes were downregulated, whereas K+ transporter genes were both up- and downregulated. These results suggest that restricting intracellular Na+ importing while maintaining balanced K+ homeostasis is an adaptive strategy for tolerating long-term salt stress. ICP-MS analysis identified the petioles and leaves as Na-hyperaccumulators, with a maximum content of over 80 g kg-1 DW under salt stress. Mapping of the Na-hyperaccumulation trait onto the phylogenetic relationships revealed that water lily plants might have a long evolutionary history from ancient marine plants, or may have undergone historical ecological events from salt to fresh water. Ammonium transporter genes involved in nitrogen metabolism were downregulated, whereas NO3--related transporters were upregulated in both the leaves and petioles, suggesting a selective bias toward NO3- uptake under salt stress. The morphological changes we observed may be due to the reduced expression of genes related to auxin signal transduction. In conclusion, the floating leaves and submerged petioles of the water lily use a series of adaptive strategies to survive salt stress. These include the absorption and transport of ions and nutrients from the surrounding environments, and the ability to hyperaccumulate Na+. These adaptations may serve as the physiological basis for salt tolerance in water lily plants.

Anthocyanin metabolism in Nelumbo: translational and post-translational regulation control transcription.

BACKGROUND: Lotus (Nelumbo Adans.) is used as an herbal medicine and the flowers are a source of natural flavonoids. 'Da Sajin', which was firstly found in the plateau area, is a natural mutant in flower color with red streamers dyeing around white petals. RESULTS: The LC-MS-MS results showed that eight anthocyanin compounds, including cyanidin 3-O-glucoside, cyanidin 3-O-galactoside, malvidin 3-O-galactoside, and malvidin 3-O-glucoside, were differentially enriched in red-pigmented tissues of the petals, whereas most of these metabolites were undetected in white tissues of the petals. Transcriptome profiling indicated that the relative high expression levels of structural genes, such as NnPAL, NnF3H, and NnANS, was inconsistent with the low anthocyanin concentration in white tissues. Members of the NnMYB and NnbHLH transcription factor families were presumed to play a role in the metabolic flux in the anthocyanin and proanthocyanidin biosynthetic pathway. The expression model of translational initiation factor, ribosomal proteins and SKP1-CUL1-F-box protein complex related genes suggested an important role for translational and post-translational network in anthocyanin biosynthesis. In addition, pathway analysis indicated that light reaction or photo destruction might be an important external cause for floral color determination in lotus. CONCLUSIONS: In this study, it is supposed that the natural lotus mutant 'Da Sajin' may have originated from a red-flowered ancestor. Partial loss of anthocyanin pigments in petals may result from metabolic disorder caused by light destruction. This disorder is mainly regulated at post translation and translation level, resulting in a non-inherited phenotype. These results contribute to an improved understanding of anthocyanin metabolism in lotus, and indicate that the translational and post-translational regulatory network determines the metabolic flux of anthocyanins and proanthocyanidins under specific environmental conditions.

Linking ecological niches to bacterial community structure and assembly in polluted urban aquatic ecosystems.

Introduction: Bacterial communities play crucial roles in the functioning and resilience of aquatic ecosystems, and their responses to water pollution may be assessed from ecological niches. However, our understanding of such response patterns and the underlying ecological mechanisms remains limited. Methods: In this study, we comprehensively investigated the effects of water pollution on the bacterial structure and assembly within different ecological niches, including water, sediment, submerged plant leaf surfaces, and leaf surfaces, using a 16S high-throughput sequencing approach. Results: Ecological niches had a greater impact on bacterial community diversity than pollution, with a distinct enrichment of unique dominant phyla in different niches. This disparity in diversity extends to the bacterial responses to water pollution, with a general reduction in α-diversity observed in the niches, excluding leaf surfaces. Additionally, the distinct changes in bacterial composition in response to pollution should be correlated with their predicted functions, given the enrichment of functions related to biogeochemical cycling in plant surface niches. Moreover, our study revealed diverse interaction patterns among bacterial communities in different niches, characterized by relatively simply associations in sediments and intricate or interconnected networks in water and plant surfaces. Furthermore, stochastic processes dominated bacterial community assembly in the water column, whereas selective screening of roots and pollution events increased the impact of deterministic processes. Discussion: Overall, our study emphasizes the importance of ecological niches in shaping bacterial responses to water pollution. These findings improve our understanding of the complicated microbial response patterns to water pollution and have ecological implications for aquatic ecosystem health.

Abundant Allelochemicals and the Inhibitory Mechanism of the Phenolic Acids in Water Dropwort for the Control of Microcystis aeruginosa Blooms.

In recent years, with the frequent global occurrence of harmful algal blooms, the use of plant allelopathy to control algal blooms has attracted special and wide attention. This study validates the possibility of turning water dropwort into a biological resource to inhibit the growth of harmful Microcystis aeruginosa blooms via allelopathy. The results revealed that there were 33 types of allelopathic compounds in the water dropwort culture water, of which 15 were phenolic acids. Regarding water dropwort itself, 18 phenolic acids were discovered in all the organs of water dropwort via a targeted metabolomics analysis; they were found to be mainly synthesized in the leaves and then transported to the roots and then ultimately released into culture water where they inhibited M. aeruginosa growth. Next, three types of phenolic acids synthesized in water dropwort, i.e., benzoic, salicylic, and ferulic acids, were selected to clarify their inhibitory effects on the growth of M. aeruginosa and their mechanism(s) of action. It was found that the inhibitory effect of phenolic acids on the growth of M. aeruginosa increased with the increase of the exposure concentration, although the algae cells were more sensitive to benzoic acid than to salicylic and ferulic acids. Further study indicated that the inhibitory effects of the three phenolic acids on the growth of M. aeruginosa were largely due to the simultaneous action of reducing the number of cells, damaging the integrity of the cell membrane, inhibiting chlorophyll a (Chl-a) synthesis, decreasing the values of F0 and Fv/Fm, and increasing the activity of the antioxidant enzymes (SOD, POD, and CAT) of M. aeruginosa. Thus, the results of this study indicate that both culture water including the rich allelochemicals in water dropwort and biological algae inhibitors made from water dropwort could be used to control the growth of noxious algae in the future.

Effects of simulated Cd deposition on soil Cd availability, microbial response, and crop Cd uptake in the passivation-remediation process of Cd-contaminated purple soil.

Atmospheric deposition of heavy metals such as Cd is a threat to ecosystems and food safety. Our knowledge is still limited about the effectiveness of remediation process for Cd-contaminated agro-soils under atmospheric Cd deposition. In this study, eight soil amendments were used in a Cd-contaminated purple soil to investigate their impacts on soil Cd availability, microbial response, and Cd uptake by mustard and corn plants via simulating the atmospheric Cd deposition under laboratory incubation and greenhouse conditions. Results showed that the simulated atmospheric Cd deposition increased the soil high-risk Cd (HR, exchangeable and carbonate Cd) and decreased soil medium-risk Cd fraction (MR, bound to Fe/Mn oxide and organic Cd), and the largest direct effects on crop Cd uptakes were 0.94 and 0.66 for mustard and corn based on the path-coefficient analysis, respectively. Generally, Cd deposition led to decreasing soil microbial biomass carbon, populations of bacteria, fungi and actinomycetes, and enzyme activities of urease, catalase, sucrase, and acid phosphatase whereas increasing soil microbial biomass nitrogen. Compared with control and lime treatments, an organic-inorganic combined preparation (OCP) appeared to be effective for remediation of the Cd-contaminated purple soil due to its potential to increase the HR-Cd and reduce both MR-Cd and crop Cd uptake, as accompanied by its neutral effects on soil bacterial alpha diversity and community structure. Results also indicated that application of nitrogen fertilizers should be considered for remediation of the Cd-contaminated soils as nitrogen inputs were demonstrated to promote soil health under elevated Cd condition.

Nutrients resorption and stoichiometry characteristics of different-aged plantations of Larix kaempferi in the Qinling Mountains, central China.

Elucidating the stoichiometry and resorption patterns of multiple nutrients is of essential importance to holistically understanding plant nutrition and biogeochemical cycling. Although many studies on ecological stoichiometry have been carried out, surprisingly few of them were simultaneously done on the investigation of both nutrient resorption efficiency and stoichiometry for different-aged plantations of a perennial tree. Here, both green and senesced leaf samples were collected from four Larix kaempfer plantations aged of 8, 15, 22, and 32 years in the Qinling Mountains to examine nutrients resorption efficiency and stoichiometry characteristics. The results suggested that the nutrient concentrations of N, P, K, Ca, Mg, Al, and Fe in both green and senesced leaves of L. kaempferi (a deciduous conifer tree) did not show a regular change trends along the plantation ages in the Qinling Mountains. The concentrations of the most nutrients examined, except for Fe, in the green leaves were relatively lower than or close to the required physiological concentrations, suggesting a relative limitation of multiple nutrients exists in L. kaempferi for its above-ground biomass growth. The rank order of resorption efficiencies of four key nutrients (N, P, K, and Mg) was K (80.89%) > N (67.42%) > P (65.34%) > Mg (41.16%), whereas the nutrient Ca and Fe tended to accumulate in senesced leaves. Overall, the nutrient resorption efficiency of all examined elements did not exhibit a regular trend corresponding to the change of the plantation ages in L. kaempferi, but it was positively related to the nutrient concentrations in green leaves. The mean C:N and C:P ratios in the green and senesced leaves were significantly higher than those reported globally (on average). By contrast, the N:P ratio, at <14, was not only much lower than that reported for both China's flora and globally (on average), but it did suggest that the N nutrient limits growth of L. kaempferi in these plantations. Taken together, the results of this study are of substantial interest and value to forest managers and for the sustainable development of the Qinling forest ecosystems.

Gene Expression Profile in the Long-Living Lotus: Insights into the Heat Stress Response Mechanism.

Lotus (Nelumbo Adans) is an aquatic perennial plant that flourished during the middle Albian stage. In this study, we characterized the digital gene expression signatures for China Antique lotus under conditions of heat shock stress. Using RNA-seq technology, we sequenced four libraries, specifically, two biological replicates for control plant samples and two for heat stress samples. As a result, 6,528,866 to 8,771,183 clean reads were mapped to the reference genome, accounting for 92-96% total clean reads. A total of 396 significantly altered genes were detected across the genome, among which 315 were upregulated and 81 were downregulated by heat shock stress. Gene ontology (GO) enrichment of differentially expressed genes revealed protein folding, cell morphogenesis and cellular component morphogenesis as the top three functional terms under heat shock stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis led to the identification of protein processing in endoplasmic reticulum, plant-pathogen interactions, spliceosome, endocytosis, and protein export as significantly enriched pathways. Among the upregulated genes, small heat shock proteins (sHsps) and genes related to cell morphogenesis were particularly abundant under heat stress. Data from the current study provide valuable clues that may help elucidate the molecular events underlying heat stress response in China Antique lotus.