The Salinity Survival Strategy of Chenopodium quinoa: Investigating Microbial Community Shifts and Nitrogen Cycling in Saline Soils.

Quinoa is extensively cultivated for its nutritional value, and its exceptional capacity to endure elevated salt levels presents a promising resolution to the agricultural quandaries posed by salinity stress. However, limited research has been dedicated to elucidating the correlation between alterations in the salinity soil microbial community and nitrogen transformations. To scrutinize the underlying mechanisms behind quinoa's salt tolerance, we assessed the changes in microbial community structure and the abundance of nitrogen transformation genes across three distinct salinity thresholds (1 g·kg-1, 3 g·kg-1, and 6 g·kg-1) at two distinct time points (35 and 70 days). The results showed the positive effect of quinoa on the soil microbial community structure, including changes in key populations and its regulatory role in soil nitrogen cycling under salt stress. Choroflexi, Acidobacteriota, and Myxococcota were inhibited by increased salinity, while the relative abundance of Bacteroidota increased. Proteobacteria and Actinobacteria showed relatively stable abundances across time and salinity levels. Quinoa possesses the ability to synthesize or modify the composition of keystone species or promote the establishment of highly complex microbial networks (modularity index > 0.4) to cope with fluctuations in external salt stress environments. Furthermore, quinoa exhibited nitrogen (N) cycling by downregulating denitrification genes (nirS, nosZ), upregulating nitrification genes (Archaeal amoA (AOA), Bacterial amoA (AOB)), and stabilizing nitrogen fixation genes (nifH) to absorb nitrate-nitrogen (NO3-_N). This study paves the way for future research on regulating quinoa, promoting soil microbial communities, and nitrogen transformation in saline environments.

The influences of soil sulfate content on the transformations of nitrate and sulfate during the reductive soil disinfestation (RSD) process.

The transformations and products of sulfate (SO42-) and nitrate (NO3-), especially the influences of SO42- content on the transformations during RSD process, are unclear. In this study, a series of soil SO42- contents (from 333 to 3000 mg S kg-1) were prepared before RSD treatment. The results indicated that nearly all the cumulative NO3- (>98.6%) was removed and not affected by the soil SO42- content. The 15N recovery results showed that 0.57-1.24% and 2.94-4.59% of NO3- translated into ammonium (NH4+) and organic N, respectively, and high SO42- contents stimulated the processes of NO3- dissimilatory reduction and NO3- immobilization. The soluble SO42- contents decreased by 397-922 mg S kg-1, but the contents of total sulfur, sulfide, and sulfate precipitation varied slightly after RSD, indicating that the decreased SO42- was mainly immobilized into organic sulfur in all soils. In addition, a fraction of decreased SO42- was adsorbed to the soil with a relatively high SO42- content. The leaching of SO42- was high (42.9-602 mg S kg-1) during the RSD process, and the leaching amounts increased with increasing soil SO42- content. In terms of the gases emitted from the transformations of NO3- and SO42-, the cumulative emissions of nitrous oxide (N2O) and six sulfurous gases (hydrogen sulfide, carbonyl sulfide, carbon disulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide) were in the ranges of 17.1-21.2 mg N kg-1 and 7.78-23.5 µg S kg-1, respectively, during the whole RSD process. The emissions of sulfurous gases were inhibited by high soil SO42- content, but the N2O emissions were unaffected. In conclusion, the soil SO42- content influenced the transformations of NO3- and SO42- during RSD process, and the SO42- leaching and N2O emissions might threaten the environment which should be concerned.

Impacts on soil microbial characteristics and their restorability with different soil disinfestation approaches in intensively cropped greenhouse soils.

The different impacts, especially on soil physicochemical and microbial characteristics, among disinfestation methods based on different principles (including physical, chemical, and biological) have not been illustrated well. Here, we used steam sterilization, dazomet fumigation, and reductive soil disinfestation (RSD) methods representative of physical, chemical, and biological soil disinfestation, respectively, to disinfest seriously degraded greenhouse soils before watermelon cultivation in one season. Compared with the control, RSD significantly decreased the soil nitrate content by 85.9% and the electrical conductivity by 52.0% and increased the soil pH to 7.44. Although all three soil disinfestations significantly decreased the abundance of the pathogen Fusarium oxysporum by 83.0-99.2%, their impacts on soil microbial characteristics were variable. Briefly, steam sterilization significantly changed multiple bacterial and fungal properties. Dazomet fumigation impacted mainly fungal properties, such as abundance, diversity, and community structure, but RSD significantly decreased bacterial diversity and altered the bacterial community structure. Although the differences mentioned above got smaller after watermelon cultivation, the plant performances differed dramatically in different soils. The largest plant biomass, fruit ratio, and yield were found in the RSD-treated soil, whereas the lowest fruit ratio and yield were found in the steam-sterilized soil. The soil nitrate content, electrical conductivity, bacterial diversity and community structure, and some specific microbial agents, such as Aspergillus, Cladosporium, and Pseudomonas, were correlated with plant performance. RSD is a promising soil disinfestation strategy to support plant growth in intensively cultivated greenhouse soils with serious problems, such as acidification, salinization, and pathogen accumulation.

Response of denitrification in paddy soils with different nitrification rates to soil moisture and glucose addition.

Denitrification is one of the most important N loss pathways in paddy soil. The nitrification rate is a key natural feature for controlling denitrification N loss in paddy soil. However, the relationship between nitrification and denitrification under different conditions in paddy soil remains unknown. By using 15N tracing, we investigated the response of denitrification loss to soil moisture and glucose addition in six paddy soils, whose net nitrification rates ranged from 0.36 mg N kg-1 day-1 to 5.72 mg N kg-1 day-1. The soils were amended with or without glucose to simulate root exudates at rates of 100 mg kg-1 of soil and incubated under either 60% water holding capacity (WHC) or flooded (2 cm depth) at 25 °C for 15 days. Denitrification loss was calculated by the unrecovered 15NH4+. The results showed that the soil nitrification rate significantly affected the N recovery form and denitrification loss of the applied 15N. NH4+ was the main recovered N form of the applied 15N in soil with a low nitrification rates. Denitrification losses were higher in the high nitrification rate soil than soil with low nitrification rate in all treatments. The correlation between denitrification and nitrification rates was well fit by Michaelis-Menten kinetics during the incubation, irrespective of soil moisture and glucose addition, and the R2 ranged from 0.801 to 0.977 (P < 0.05). Glucose addition did not stimulate denitrification under either 60% WHC or flooded conditions. The results showed that nitrification rate, rather than labile organic supply, controlled denitrification in paddy soil.

Deciphering differences in the chemical and microbial characteristics of healthy and Fusarium wilt-infected watermelon rhizosphere soils.

Plant health is determined by the comprehensive effect of soil physicochemical and biological properties. In this study, we compared the chemical properties and microbiomes of the rhizosphere soils of healthy, Fusarium oxysporum-infected, and dead watermelon plants and attempted to assess their potential roles in plant health and Fusarium wilt expression. The rhizosphere soils were collected from watermelon plants grown in a greenhouse under the same field management practices, and various soil microbial and chemical characteristics were analyzed. The rhizosphere soil of healthy plants had the lowest abundance of F. oxysporum and pH and the highest contents of ammonium (NH4+) and nitrate (NO3-). The relative content of hemicellulose was decreased in the rhizosphere soil of F. oxysporum-infected plants. The differences in soil microbial compositions among the watermelons at the three health statuses were obvious, and their microbiomes changed gradually along with plant health status. The microbiome in the rhizosphere soil of healthy plants had the highest relative abundances of potential antagonists and the lowest relative abundances of potential pathogens. The specific microbial composition together with some chemical properties of the rhizosphere soil of healthy plants might be responsible for inhibiting Fusarium wilt expression.

Effect of liming on sulfate transformation and sulfur gas emissions in degraded vegetable soil treated by reductive soil disinfestation.

Reductive soil disinfestation (RSD), namely amending organic materials and mulching or flooding to create strong reductive status, has been widely applied to improve degraded soils. However, there is little information available about sulfate (SO4(2-)) transformation and sulfur (S) gas emissions during RSD treatment to degraded vegetable soils, in which S is generally accumulated. To investigate the effects of liming on SO4(2-) transformation and S gas emissions, two SO4(2-)-accumulated vegetable soils (denoted as S1 and S2) were treated by RSD, and RSD plus lime, denoted as RSD0 and RSD1, respectively. The results showed that RSD0 treatment reduced soil SO4(2-) by 51% and 61% in S1 and S2, respectively. The disappeared SO4(2-) was mainly transformed into the undissolved form. During RSD treatment, hydrogen sulfide (H2S), carbonyl sulfide (COS), and dimethyl sulfide (DMS) were detected, but the total S gas emission accounted for <0.006% of total S in both soils. Compared to RSD0, lime addition stimulated the conversion of SO4(2-) into undissolved form, reduced soil SO4(2-) by 81% in S1 and 84% in S2 and reduced total S gas emissions by 32% in S1 and 57% in S2, respectively. In addition to H2S, COS and DMS, the emissions of carbon disulfide, methyl mercaptan, and dimethyl disulfide were also detected in RSD1 treatment. The results indicated that RSD was an effective method to remove SO4(2-), liming stimulates the conversion of dissolved SO4(2-) into undissolved form, probably due to the precipitation with calcium.

[Effects of strong reductive approach on remediation of degraded facility vegetable soil].

High application rate of chemical fertilizers and unreasonable rotation in facility vegetable cultivation can easily induce the occurrence of soil acidification, salinization, and serious soil-borne diseases, while to quickly and effectively remediate the degraded facility vegetable soil can considerably increase vegetable yield and farmers' income. In this paper, a degraded facility vegetable soil was amended with 0, 3.75, 7.50, and 11.3 t C x hm(-2) of air-dried alfalfa and flooded for 31 days to establish a strong reductive environment, with the variations of soil physical and chemical properties and the cucumber yield studied. Under the reductive condition, soil Eh dropped quickly below 0 mV, accumulated soil NO3(-) was effectively eliminated, soil pH was significantly raised, and soil EC was lowered, being more evident in higher alfalfa input treatments. After treated with the strong reductive approach, the cucumber yield in the facility vegetable field reached 53.3-57.9 t x hm(-2), being significantly higher than that in un-treated facility vegetable field in last growth season (10.8 t x hm(-2)). It was suggested that strong reductive approach could effectively remediate the degraded facility vegetable soil in a short term.