摘要：
Dissolved organic matter (DOM) can clearly reflect composting components changes, thus it is supposed to indicate the humification process during composting. To demonstrate this, three compost mixtures and two techniques were arranged. DOM evolution was detected by three spectral techniques. X-ray diffraction (XRD) showed that the crystal structure substances decreased gradually during the composting, including cellulose, struvite, sylvine, quartz, and calcite; Specifically, the struvite was found, which was conducive to the fixation of nitrogen and phosphorus. Fourier transform infrared spectroscopy (FTIR) and three-dimensional fluorescence spectroscopy (3D-EEM) further showed that pig manure-based mixtures, added cabbage, and windrow composting are beneficial to sugar, protein, fulvic acid, and soluble microbial by-products decompose and humic acids produce. This process was closely related to the change of physical-chemical parameters (temperature; pH; moisture content; and NH4+-N content) and maturity index (C/N ratio, E4/E6 and GI). Therefore, DOM evolution could quickly reflect the maturity process of compost. In subsequent research, the quantitative analysis of DOM components can be considered to modify DOM spectral parameters, or to build a model, so as to achieve rapid evaluation of compost maturity.
通讯机构：
[Si Luo] C;College of Resources and Environment, Hunan Agricultural University, Changsha, People’s Republic of China
关键词：
Cadmium and arsenic;Straw return;Soil;Speciation;Bioavailability;Bacterial community
摘要：
PurposeStraw return is a common agronomic practice for improving soil fertility and sustaining crop productivity. This paper considers the potential impacts of contaminated straw return on the availability of metal(loid)s and on microbial activity in paddy soils. MethodsCadmium (Cd) and arsenic (As) co-contaminated soils were collected and incorporated with contaminated rice straw (RS) or coupled with straw-decomposing microbial inoculants (SD), and were incubated for 75 days under laboratory-controlled conditions. ResultsThe results showed that addition of straws (both RS and SD) increased soil total Cd and As concentrations by 0.07-0.11 and 1.83-1.89 mg & BULL;kg(-1), respectively. In contrast to the control treatment (no straws, CK), RS and SD treatments significantly increased soil-available As concentrations throughout the incubation period, whereas available Cd concentrations decreased from day 10 to day 45. A remarkable rise in all Cd fractions was observed in the straw-applied treatments compared with CK. The easily soluble, Ca-associated and residual fractions of As were decreased and changed into Al-associated and Fe-oxyhydroxides As fractions. Compared with RS treatment, applying SDMIs accelerated the decomposition process of the straw and the transformation of Cd and As, and increased the richness and diversity of the bacterial community. Based on redundancy analysis, pH and dissolved organic carbon (DOC) were identified as the most important controlling factors for redistribution of Cd and As fractions during straw decomposition. ConclusionsThese results highlight that we should be cautious when returning co-contaminated rice straw to paddy fields, as this practice may increase the risk of more As production. SDMI utilization is an effective strategy to immobilize Cd, but it may enhance the availability of As.
摘要：
Long-term consumption of tea with high fluoride (F) content has a potential threat to human health. The application of different amounts of biochar to reduce F accumulation in tea leaves has been little studied. In this study, a pot experiment was conducted to investigate the effect of biochar amounts (0, 0.5%, 2.5%, 5.0%, 8.0%, and 10.0%, w/w) on tea F content during the tea plant growth. Changes in tea quality, soil F fraction, and soil properties caused by biochar and the relationship with tea F accumulation were also considered. The results showed that the application of biochar amendment significantly reduced water-soluble F contents in tea leaves compared to CK (without biochar), especially in the 8.0% treatment (72.55%). Overall, biochar contributed to improving tea polyphenols and caffeine, but had no significant impact on free amino acids and water leachate. Compared with CK, 5.0-10.0% biochar significantly increased soil water-soluble F content due to the substitution of F- with OH- under high pH. Additionally, biochar applied to tea garden soil was effective in decreasing the soil exchangeable aluminum (Ex-Al) content (46.37-91.90%) and increasing the soil exchangeable calcium (Ca2+) content (12.02-129.74%) compared to CK, and correlation analysis showed that this may help reduce F enrichment of tea leaves. In general, the application of 5.0-8.0% biochar can be suggested as an optimal application dose to decrease tea F contents while simultaneously improving tea quality.
摘要：
Accurate prediction of heavy metal accumulation in soil ecosystems is crucial for maintaining healthy soil environments and ensuring high-quality agricultural products, as well as a challenging scientific task. In this study, we constructed a dataset containing 490 sets of multidimensional environmental covariate data and proposed prediction models for heavy metal concentrations (HMC) in a soil-rice system, EL-HMC (including RF-HMC and GBM-HMC), based on Random Forest (RF) and Gradient Boosting Machine (GBM) ensemble learning (EL) techniques. To reasonably evaluate the effectiveness of each model, Multiple linear and Bayesian regressions were selected as benchmark models (BM), and mean absolute error (MAE), root mean square error (RMSE), and determination coefficient R(2) were selected as evaluation indicators. In addition, sensitivity and spatial autocorrelation (SAC) analyses were used to examine the robustness of the model. The results showed that the R(2) values of RF-HMC and GBM-HMC for modeling available cadmium (Cd) concentrations in soil were 0.654 and 0.690, respectively, with an average increase of 48.0% compared to the BMs. The R(2) values of RF-HMC and GBM-HMC for predicting Cd, lead (Pb), chromium (Cr), and mercury (Hg) concentrations in rice ranged from 0.618 to 0.824 and 0.645 to 0.850, respectively, with an average increase of 58.2% compared with the BMs. The corresponding MAEs and RMSEs of RF-HMC and GBM-HMC had low error levels. Sensitivity analysis of the input features and the SAC of the prediction bias showed that the EL-HMC models have excellent robustness. Therefore, the EL technology-based prediction models for HMCs proposed herein are practical and feasible, demonstrating better accuracy and stability than the traditional model. This study verifies the application potential of EL technology in pollution ecology and provides a new perspective and solution for sustainable management and precise prevention of heavy metal pollution in farmland soil at the regional scale.
通讯机构：
[Huilin Yang; Zinan Luo; Dengwang Liu] C;College of Resources and Environment, Hunan Agriculture University, Changsha, Hunan, China<&wdkj&>College of Agriculture, Hunan Agricultural University, Changsha, Hunan, China<&wdkj&>Arid Land Crop Research Institute, Hunan Agricultural University, Changsha, Hunan, China<&wdkj&>College of Agriculture, Hunan Agricultural University, Changsha, Hunan, China<&wdkj&>Arid Land Crop Research Institute, Hunan Agricultural University, Changsha, Hunan, China
摘要：
Peanut is vulnerable under waterlogging stress, and it is important to explore efficient agronomic practices to reduce adverse effects induced by waterlogging stress. In this study, the effects of waterlogging stress on plant morphology, physiological and biochemical characters in peanut seedlings were studied. It was founded waterlogging stress posted adverse effects on plant growth and development and triggered the activities of antioxidant enzymes and osmotic adjustment substances to improve the plant tolerance under stress. It was also found that exogenous calcium fertilization could significantly improved root growth and development under stress. Moreover, higher dose of calcium fertilizer (1600 mg/kg) showed better performance on improving waterlogging tolerance than lower dose one (800 mg/kg) in peanut seedlings. This study explored positive effects of exogenous calcium on recovering damages especially in roots caused by waterlogging stress, providing a theoretical guidance in agronomic practice to improve waterlogging tolerance, and laying a foundation for agronomic practice when further discovering molecular mechanisms in response to waterlogging stress.
摘要：
Cadmium (Cd) pollution in agricultural soils has been a worldwide problem that threatens eco-environmental sustainability and exerts a negative influence on plant growth. The effects of nitrification inhibitors (NIs)—namely, dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP)—on Cd phytoavailability have been reported in some studies, but the underlying mechanisms driving the changes in Cd uptake and accumulation in rice (Oryza sativa L.) seedlings are not well understood. Here, rice seedlings were transplanted into Cd-contaminated paddy soil, treated with urea and NIs (DCD or DMPP), and cultivated for 21days. Pot experiments showed that NIs treatments significantly inhibited the ammoxidation process and increased the rhizospheric pH, thereby reducing the DTPA-extracted Cd concentration in soil and decreasing Cd accumulation in rice tissues. Besides, hydroponic culture experiments were performed to explore the impacts of NIs on Cd uptake and translocation in rice seedlings and identify the underlying mechanisms. It was found that adding urea combined with NIs weakened Cd uptake by rice roots through supplying a large amount of NH4+. Furthermore, NIs applications significantly limited net Cd2+ influx and down-regulated the transcription of Cd uptake-related genes in roots via increasing NH4+, thereby decreasing the movement of Cd2+ into roots and Cd accumulation in rice. However, DMPP treatments also promoted Cd root-to-shoot translocation, likely due to the DMPP-induced increase in the expression of the OsHMA2 and OsNRAMP1 genes. Our results suggested that the application of appropriate ratios of NIs and nitrogen fertilizer can inhibit Cd uptake and accumulation in rice. • Cd accumulation in rice was driven by multiple factors through NIs application. • Cd uptake in rice was mainly affected by NIs altering soil pH and Cd availability. • N forms was also regulated by NIs thus influencing Cd uptake in rice. • Urea + DMPP inhibited the expressions of NRAMP5 in rice roots. • Urea + DMPP elevated Cd translocation by promoting the HMA2 and NRAMP1 transcription.
摘要：
Soil microbial communities play essential roles in degraded soil ecosystems. The “emergent trait” indices (e.g., microbial biomass C and N, and enzyme activity) and specific soil microbiota associations have been intensively studied, but the responses of soil microbial composition and network complexities to land-use changes remain unclear. Using amplicon sequencing of 16S rRNA genes and internal transcribed spacer (ITS) regions, we assessed the response ratio of soil microbial genomic diversity, community structure, and network parameters to primary evergreen broadleaved forest (control) conversion to conifer plantations, orchards, sloping tillage, and paddy fields. Agricultural lands had a higher soil bacterial and lower fungal diversity than primary forest. Overall, primary forest conversion reduced microbial network complexity, except in the sloping tillage. Moreover, land-use changes shifted the microbial community composition by either decreasing or increasing the relative abundance of dominant and putative keystone associations. The mean response ratio (indicator response percentage to primary forest conversion) of the microbial index to the land-use change varied depending on the soil microbial alpha diversity, network topological parameters, and dominant and putative keystone associations. Alterations in soil microbial diversity, composition, and network complexity were related to reduced soil resource availability following land-use change. Our study suggested that primary forest conversion to agricultural lands did not always negatively influences soil microbial diversity, composition, network complexity, and putative keystone associations. In addition, specific soil microbial associations showed highly sensitive to land-use change.
摘要：
Several mechanisms have been proposed to explain NH4+ toxicity. However, the core information about the biochemical regulation of plants in response to NH4+ toxicity is still lacking. In this study, the tissue NH4+ concentration is an important factor contributing to variations in plant growth even under nitrate nutrition and NH4+ tolerance under ammonium nutrition. Furthermore, NH4+ led to the reprogramming of the transcriptional profile, as genes related to trehalose-6-phosphate and zeatin biosynthesis were downregulated, whereas genes related to nitrogen metabolism, camalexin, stilbenoid and phenylpropanoid biosynthesis were upregulated. Further analysis revealed that a large number of genes, which enriched in phenylpropanoid and stilbenoid biosynthesis, were uniquely upregulated in the NH4+- tolerant ecotype Or-1. These results suggested that the NH4+-tolerant ecotype showed a more intense response to NH4+ by activating defense processes and pathways. Importantly, the tolerant ecotype had a higher (NH4+)-N-15 uptake and nitrogen utilization efficiency, but lower NH4+, indicating the tolerant ecotype maintained a low NH4+ level, mainly by promoting NH4+ assimilation rather than inhibiting NH4+ uptake. The carbon and nitrogen metabolism analysis revealed that the tolerant ecotype had a stronger carbon skeleton production capacity with higher levels of hexokinase, pyruvate kinase, and glutamate dehydrogenase activity to assimilate free NH4+, Taken together, the results revealed the core mechanisms utilized by plants in response to NH4+, which are consequently of ecological and agricultural importance.
通讯机构：
[Vladimir Matichenkov] H;Hunan University of Finance and Economics, Changsha, China<&wdkj&>Institute Basic Biological Problems Russian Academy of Sciences, Pushchino, Russia
摘要：
Remediation of CdAs co-contaminated soils has long been considered a difficult problem to solve, as Cd and As have distinctly different metallic characters. Amending contaminated soils with traditional single passivation materials may not always work well in the stabilization of both Cd and As. Here, we reported that analog soil organo-ferrihydrite composites made with either living or non-living organics (bacterial cells or humic acid) could achieve stabilization of both Cd and As in contaminated soils. BCR and Wenzel sequential extractions showed that organo-ferrihydrite, particularly at 1wt% loading, shifted liable Cd and As to more stable phases. Organo-ferrihydrite amendments significantly (p<0.05) increased soil urease, alkaline phosphatase and catalase enzyme activities. With organo-ferrihydrite amendments, the bioavailable fraction of Cd decreased to 35.3% compared with the control (65.1%), while the bioavailable As declined from 29.4% to 12.4%. Soil pH, microbial community abundance and diversity were almost unaffected by organo-ferrihydrite. Ferrihydrite and organo fractions both contributed to direct Cd-binding, while the organo fraction probably maintained the Fe-bound As via lowering ferrihydrite phase transformation. Compared to pure ferrihydrite, organo-ferrihydrite composites performed better not only in reducing liable Cd and As, but also in maintaining soil quality and ecosystem functions. This study demonstrates the applications of organo-ferrihydrite composites in eco-friendly remediation of CdAs contaminated soils, and provides a new direction in selecting appropriate soil amendments.
摘要：
Fe-Mn binary oxides have superior catalytic and oxidation performance, and calcined layered double hydroxides (LDOs) have stably dispersed metals and a large specific surface area. Combining the advantages of both, MgFeMn-LDOs were prepared by co-precipitation and calcination, and applied to monovalent thallium (Tl(I)) removal in aqueous. MgFeMn-LDOs before and after Tl(I) adsorption were characterized by scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS), X-ray Diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The adsorbent has abundant active sites and oxygen-containing groups, and a high specific surface area (76.77m2/g). Its removal efficiency of Tl(I) was more than 96% under a broad pH, and showed high selectivity under the conditions of coexisting Na+, Ca2+, Mg2+, and EDTA. The calculated maximum adsorption capacities by the Langmuir and Freundlich model are 135.3 mg/g at 293 K. The adsorption kinetic fitted the pseudo-second-order model and the adsorption process was spontaneous and endothermic. The excellent Tl(I) adsorption of MgFeMn-LDOs is mainly dominated by surface complexation, oxidation, coprecipitation, and electrostatic adsorption. The high Tl(I) adsorption capacity, selectivity, and wide pH working range of MgFeMn-LDOs is beneficial to practical application.
摘要：
BACKGROUND: A growing number of researches indicated the association between plasma trace elements and blood lipids. However, the potential interaction and dose-response relationship were less frequently reported. METHODS: In this study, a total of 3548 participants were recruited from four counties in Hunan Province, South China. Demographic characteristics were collected by face-to-face interviews and inductively coupled plasma mass spectrometry (ICPMS) was used to determine the levels of 23 trace elements in plasma. We applied a fully adjusted generalized linear regression model (GLM) and a multivariate restricted cubic spline (RCS) to estimate the correlation, dose-response relationship and possible interaction between 23 trace elements and four blood lipid markers. RESULTS: The results indicated positive dose-response relationships of plasma (66)zinc with triglycerides (TG) and low density lipoprotein cholesterol (LDL-C), plasma (78)selenium with LDL-C and total cholesterol (TCH), and plasma (59)cobalt with high-density lipoprotein cholesterol (HDL-C). There was a negative dose-response relationship between (59)cobalt and LDL-C. Further analysis found that (66)zinc and (59)cobalt had an antagonistic effect on the risk of increased LDL-C level. CONCLUSIONS: This study added new evidence for the potential adverse effects of (66)Zn and (78)Se on blood lipids, and provided new insight into the threshold value setting for metals as well as the intervention strategy for dyslipidemia.
摘要：
Cadmium (Cd) is one of the dominant metal pollutants present in the aquatic environment that affects ion homeostasis, oxidative stress (OS) and immune responses of aquatic organisms. Given the physicochemical similarities between Cd(2+) and calcium (Ca(2+)) ions, their antagonism may facilitate the mitigation of Cd-induced toxicity. To better understand the role of Ca in protecting against Cd-induced toxicity in teleosts, juvenile grass carp were exposed to Cd (measured concentration 3μg/L) and a gradient of Ca concentrations (measured concentration 1.5mg/L, 2.5mg/L, 3.0mg/L, and 3.5mg/L in the control (CTL) group, low calcium (LCA) group, medium calcium (MCA) group, and high calcium (HCA) group, respectively) for 30 days. Inductively coupled plasma mass spectrometry (ICP-MS) data analyses showed that simultaneous exposure to Ca impaired the accumulation of Cd in all tested tissues. Besides, Ca addition maintained the plasma ion (Na(+), K(+), Cl(-)) homeostasis, alleviated Cd-induced oxidative stress (OS), and regulated the activities and transcriptional levels of ATPase. Furthermore, transcriptional heatmap analysis demonstrated that several indicator genes for OS and calcium signaling pathway were found to be significantly modulated by Ca addition. This work delineates a protective effect of Ca against Cd-induced toxicity in grass carp, providing new insight into the possible solutions to Cd pollution issues in aquaculture industry.
摘要：
Sulfate affects the transformation of arsenic (As) in soil and its absorption by plant roots. However, the influence of sulfate and irrigation interactions on the mobility of As in the soil-rice system remains poorly understood. To address this gap, we conducted a pot experiment with varying sulfate levels and irrigation modes to examine their effects on rice As translocation, soil As forms, iron plaque formation, and microorganisms involved in As transformation. The addition of exogenous sulfate significantly reduced grain As levels by a maximum of 60.1%, 46.7%, and 70.5% under flooding (F), flooding-moist alternate (FM), moist (M) conditions, respectively. However, the changes in soil available As did not fully correspond to grains As content. Soil available As was only reduced by sulfate under the FM treatment, which limited grains As accumulation under this condition. The reduction in grains As content under F and M conditions was mainly attributed to sulfate-induced increases in soil pH, which in turn inhibited As translocation and promoted iron plaque formation. Additionally, both irrigation mode and sulfate fertilization independently or interactively influenced the abundance of Sulfuritalea, Koribacter, Geobacter, and Sulfuriferula, thereby affecting the As forms in soil through the Fe/S redox process. Specifically, under F and FM conditions, SO(4)(2-)-S inhibited Geobacter but stimulated Fe-oxidizing bacteria, possibly resulting in increased As bound to Fe/Mn oxides (As-F3). Under M condition, SO(4)(2-)-S levels regulated As adsorption and release through the participation of Fe/S cycle bacteria, specifically influencing the adsorbed As fraction (As-F2). Therefore, the addition of SO(4)(2-)-S hindered As translocation to grains by promoting As sequestration in the iron plaque and facilitating microbe-mediated As immobilization through the Fe/S cycle, which was dependent on soil moisture. These results can be used as a guide for sulfur fertilizer application under different soil moisture with the goal of minimizing rice grain As.
关键词：
energy sorghum;phytoremediation;Cd;regeneration cropping system
摘要：
Planting energy sorghum to remove soil cadmium (Cd) has been selected as an effective phytoremediation method in subtropical farmland in China in recent years. Nevertheless, the effects of energy sorghum species and cropping systems on Cd removal by energy sorghum are still not fully understood. In the present work, biomass sorghum (BS) and sweet sorghum (SS) were planted for screening varieties and comparing the applicability of cropping systems to remove Cd from contaminated soils through batch field experiments. The results indicated that BS had a higher plant height (4.70–75.63%), lower water content in the shoot (4.78–13.49%), greater dry biomass yield (13.21–125.16%), and stronger Cd removal (average 45.71%) compared with SS. Significant differences (p < 0.05) were observed in the agronomic traits and Cd accumulation of energy sorghums with genetic regulation of varieties. Pearson correlation coefficients analysis and the structural equation model (SEM) showed that plant height was the crucial agronomic parameter affecting the dry biomass yield, and Cd concentration in the stem was the key factor for evaluating the Cd extraction ability of energy sorghums, which indirectly determined the removal of Cd by energy sorghum together. Furthermore, the regeneration cropping system was the most suitable because of the adaptation to climatic conditions of energy sorghums in subtropical regions of China, and its Cd removal efficiency increased by more than 49% compared with double cropping and single cropping systems, respectively. Our study provides valuable information for the phytoremediation of Cd-contaminated soil in Chinese subtropical farmland.
通讯机构：
[Yang Yang] C;College of Resources and Environment, Hunan Agricultural University, Changsha 410128, China<&wdkj&>Hunan Provincial Key Laboratory of Rural Ecosystem Health in Dongting Lake Area, Changsha 410128, China
摘要：
Identifying suitable plants for phytoremediation of Cd (cadmium) contaminated agricultural soil is critical. In this study, whether chicory (Cichorium intybus L.) qualified as an ideal accumulator for phytoremediation was investigated. The hydroponic and pot experiments showed that Cd concentration in chicory leaves exceeded 100mgkg(-1) (BCF >1, TF >1) with 40mgkg(-1) Cd in pot; No significant effects on chicory growth, leaf protein and physiological and biochemical aspects when treated with ≤20μM or 40mgkg(-1) Cd, because chicory could relieve Cd toxicity by increasing activities of photoprotection mechanisms, the reactive oxygen species scavenging system and concentrations of functional groups in plant tissues. In field experiment, 16.2 and 26.6t ha(-1) of chicory leaves was harvested in winter and summer, respectively. The highest Cd concentration in leaves was close to 25.0mgkg(-1) (BCF >1, TF >1) from the acid soil with 0.980mgkg(-1) Cd. Over 320gha(-1) Cd was extracted from soil by harvesting chicory leaves both in winter and summer, with 9.24% and 12.9% of theoretical phytoremediation efficiency. Therefore, chicory can be as an ideal Cd-accumulator for phytoremediation of slight-to-moderate Cd-contaminated agricultural soil in any season.
摘要：
This review aims to provide a holistic synopsis of the current state of the art knowledge on caproic acid pro-duction via anaerobic fermentation from the perspectives of microbes and metabolic pathway. The pure bacterial isolations with ability of caproic acid synthesis were summarized for metabolic identification and syntrophic potentials. Compared with single bacterium, mixed microflora with caproic acid production capacity is more conducive to caproic acid recovery and stability of the fermentation system. The anaerobic fermentation influ-encing factors, such as pH, temperature, electron donor and acceptor, hydrogen partial pressure, and competition between microbes were discussed. It is found that these factors essentially affect the performance of microbes causing system fluctuation thus decreased caproic acid production. Facing with the immature caproic acid separation technology, were compared from the prospect of application and electrodialysis was proposed as the mainstream technology in future. Simultaneously, it is believed that in-situ separation strategy can improve the yield and purity of caproic acid. Targeting on a large scale caproic acid production through anaerobic fermen-tation, it is also necessary to strengthen the research on the synergy and competition between microbes in the process of anaerobic fermentation, and to establish a readiness caproic acid separation technology. This work is expected to contribute to the goal of carbon summit and carbon neutrality.
通讯机构：
[Hui Fu] E;Ecology Department, College of Resources & Environments, Hunan Provincial Key Laboratory of Rural Ecosystem Health in Dongting Lake Area, Hunan Agricultural University, Changsha, People’s Republic of China
摘要：
Functional traits of individuals and not just species can regulate ecological interactions with biotic and abiotic environments, yet how individual-level functional diversity (FDind) mediates the environmental effects on community properties (e.g., interaction patterns, connectivity and productivity) remains largely unexplored. Here, we assembled 4432 individuals from 30 macrophyte species across 26 lakes in south China and measured six functional traits -shoot height, specific leaf area, lamina thickness, leaf dry mass content, stem diameter and stem dry mass content-for each individual. We estimated FDind for macrophyte community in each plot using trait probability density framework. Path analysis revealed that functional richness promoted negative interactions (the absolute value of negative: positive cohesion as proxy of community interaction patterns) and thus community productivity at lower total phosphorus (TP) and shallower water, while functional divergence/redundancy reduced negative interaction and thus community productivity at shallower water, lower TP and higher altitude. Functional evenness decreased community productivity at higher TP and deeper water. Functional dissimilarity reduced community connectivity (total cohesion) and thus community productivity at deeper water and higher altitude. Our results highlight that FDind could modify the environmental effects (from local to regional) on the interaction patterns, network connectivity and productivity of macrophyte community.
