Effect of Auxin on Cadmium Toxicity-Induced Growth Inhibition in Solanum lycopersicum.

Auxins play crucial regulatory roles in plants coping with cadmium (Cd) stress. However, the regulatory mechanism by which auxins alleviate Cd toxicity in tomato seedlings remains unclear. Here, we demonstrate that exposure to Cd stress leads to dynamic changes in the auxin response in tomato roots, characterized by an initial increase followed by a subsequent weakening. Under Cd stress, tomato seedlings show primary root- and hypocotyl-growth inhibition, accompanied by the accumulation of Cd and reactive oxygen species (ROS) in the roots. The exogenous application of 1-naphthylacetic acid (NAA) does not mitigate the inhibitory effect of Cd toxicity on primary root growth, but it does significantly enhance lateral root development under Cd stress. Auxin transport inhibitors, such as 1-N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenoic acid (TIBA), aggravate the growth inhibition of primary roots caused by Cd stress. Additionally, lateral root development was inhibited by NPA. However, applying auxin synthesis inhibitors L-kynurenine (kyn) and yucasin alleviated the tomato root growth inhibition caused by Cd stress; between them, the effect of yucasin was more pronounced. Yucasin mitigates Cd toxicity in tomato seedlings by reducing Cd2+ absorption and auxin accumulation, strengthening ROS scavenging, and reducing cell death in roots. These observations suggest that yucasin potentially mitigates Cd toxicity and improves the tolerance of tomato seedlings to Cd stress.

Selenium-Containing Organic Fertilizer Application Affects Yield, Quality, and Distribution of Selenium in Wheat.

This study was designed to investigate the effect on wheat yield of applying organic fertilizers (OF) with five different selenium (Se) concentrations. The mineral nutrients, cadmium (Cd) content, and the distribution of Se in wheat plants were also measured. The results showed that wheat yields reached a maximum of 9979.78 kg ha-1 in Mengcheng (MC) County and 8868.97 kg ha-1 in Dingyuan (DY) County, Anhui Province, China when the application amount of selenium-containing organic fertilizer (SOF) was up to 600 kg ha-1. Among the six mineral nutrients measured, only the calcium (Ca) content of the grains significantly increased with an increase in the application amount of SOF in the two regions under study. Cd content showed antagonistic effects with the Se content of wheat grains, and when the SOF was applied at 1200 kg ha-1, the Cd content of the grains was significantly reduced by 30.1% in MC and 67.3% in DY, compared with under the Se0 treatment. After application of SOF, the Se content of different parts of the wheat plant ranked root > grain > spike-stalk > glume > leaf > stem. In summary, SOF application at a suitable concentration could increase wheat yields and significantly promote the Ca content of the grains. Meanwhile, the addition of Se effectively inhibited the level of toxic Cd in the wheat grains.

Different ratios of raw material triggered composting maturity associated with bacterial community co-occurrence patterns.

Exploring the ecological function of potential core bacteria for high-efficiency composting can provide a fundamental understanding of the role of composting bacterial communities. Mushroom residue and kitchen garbage at different ratios (N1: 1/1, N2: 1/2) of dry weight were tested to investigate the key ecological role of the core bacteria responsible for producing mature compost. N1 had a peak temperature of 75.0 °C which was higher than N2 (68.3 °C). Other key composting parameters (carbon to nitrogen ratio (C/N) and germination index (GI)) also indicated that N1 achieved higher compost maturity. Rice seedlings experiments also further validated this conclusion. Putative key bacterial taxa (Thermobifida, Luteimonasd, Bacillus, etc.) were positively associated with the GI, indicating a substantial contribution to composting maturity. Co-occurrence network analysis revealed the ecological function of potentially beneficial core bacteria promoted cooperation among the bacterial community. The putative core bacteria in N1 may affect composting efficiency. Our findings reveal the mechanism of potential core bacteria throughout the compost maturity phases.

The addition of sawdust reduced the emission of nitrous oxide in pig manure composting by altering the bacterial community structure and functions.

Although composting, a measure to dispose agricultural waste, is widely accepted and applied, specific knowledge of microbially driven effects on nitrous oxide (N2O) emissions during composting remains limited. Here, we monitored the impact of sawdust on N2O emissions during pig manure composting. The results suggested that adding sawdust to the compost improved the compost temperature and reduced N2O emissions. The addition of sawdust significantly altered the bacterial community structure and enhanced community turnover during the composting process. The addition of sawdust significantly reduced the relative abundance of denitrification and ureolysis, while increasing the relative abundance of nitrogen fixation. Specifically, adding sawdust may reduce N2O emissions by reducing the relative abundance of Salinithrix, Truepera, Azomonas, Iamia, Silanimonas, Phycisphaera, and Gp21 during the thermophilic and mature phases of the composting period.

Patterns of fungal community succession triggered by C/N ratios during composting.

Accumulating evidence indicates that the functional rather than taxonomic composition of microbial communities is closely correlated to local environmental factors. While composting is a widely accepted practice, specific knowledge of how fungal functional groups interact during the composting process remains limited. To address this, the impact of the initial C/N ratio of composting material on fungal community was analyzed in order to reveal the succession of functional diversity. Compared with the raw materials, the final composting product significantly reduced the relative abundances of plant and animal pathogens. Abundances of plant and animal pathogens, as well as dung saprotrophs, were negatively correlated with compost maturity, while abundances of wood saprotrophs exhibited positive correlations. Specific OTUs that showing highly abundant in each treatment were expected to compete for environmental preferences (niches) and/or interact with each other in positive (facilitative) ways. OTU2 (wood saprotroph) exhibiting the highest occurrence was negatively related to OTU7 (animal pathogen) and OTU4 (plant pathogen) during the mesophilic phase. Taken together, high-efficiency composting is represented as pattern variations of fungal community with a process of gradual decline of plant and animal pathogens as well as dung saprotrophs.

Microbial community composition turnover and function in the mesophilic phase predetermine chicken manure composting efficiency.

The aim of this work was to study the influence of inoculation with microbial inoculants (MI) or mature compost (MC) by comparing the resultant composting efficiency with that in a noninoculated (CK) treatment. MI and MC application both accelerated the composting process according to fluorescence excitation-emission matrix (EEM) detection and germination index testing. Bacterial and fungal community composition both differed significantly over the composting period. However, the turnover of the initial bacterial community played a significant role in the composting process, and the key operational taxonomic units (OTUs) of MI (OTU_26, Thermicanus) and MC (OTU_48, Tepidimicrobium) showed significant explanatory power for the formation of humic acid-like and fulvic acid-like substances, respectively, during the stage of composting. Thus, our results indicate that microbial inoculation accelerates the composting process by stimulating key resident microbes in the initial stage.

Enzymatic activities triggered by the succession of microbiota steered fiber degradation and humification during co-composting of chicken manure and rice husk.

The carbon to nitrogen ratio (C/N) is well known for its importance in the composting process, however the fiber degradation and humification associated with enzymatic activity and microbial variation derived from different C/N ratios are poorly studied. Here, we designed two treatments of chicken manure with 15% (initial C/N ratio 9.61) and 50% (initial C/N ratio 17.3) rice husk to adjust the moisture of mixtures for turning feasibly by towable fertilizer turner in industrial level. Compared to the C/N ratio 9.61, the suitable C/N ratio of 17.3 significantly enhanced the composting efficiency and the final germination index (23.7%). Moreover, the suitable C/N ratio increased the relative abundance of Bacilli, which played an important role during the mesophilic and thermophilic phases. Bacilli abundance was related to cellulose and ß-glycosidase activities, thus improved fiber degradation and humification. This study not only seeks a swift method in industrial level to process chicken manure but also provides insight into the enzymatic activity of microbial community related to high-efficient composting.

Key extracellular enzymes triggered high-efficiency composting associated with bacterial community succession.

A consortium of key bacterial taxa plays critical roles in the composting process. In order to elucidate the identity and mechanisms by which specific bacterial species drive high-efficiency composting, the succession of key bacterial consortia and extracellular enzymes produced during the composting process were monitored in composting piles with varying initial C/N ratios. Results showed that C/N ratios of 25 and 35 enhanced composting efficiency through elevated temperatures, higher germination indices, enhanced cellulose and hemicellulose degradation, and higher cellulase and dehydrogenase activities. The activities of cellulase and ß-glucosidase, cellulase and protease, and cellulase and ß-glucosidase exhibited significant relationships with bacterial community composition within the mesophilic, thermophilic, and mature phases, respectively. Putative key taxa, linked to a higher composting efficiency, such as Nonomuraea, Desemzia, Cellulosimicrobium, Virgibacillus, Clostridium, and Achromobacter, exhibited significantly positive relationships with extracellular enzyme activities, suggesting a significant contribution to these taxa to the development of composting maturity.