Aeration increases soil bacterial diversity and nutrient transformation under mulching-induced hypoxic conditions

Stratified Effects of Tillage and Crop Rotations on Soil Microbes in Carbon and Nitrogen Cycles at Different Soil Depths in Long-Term Corn, Soybean, and Wheat Cultivation

Understanding the soil bacterial communities involved in carbon (C) and nitrogen (N) cycling can inform beneficial tillage and crop rotation practices for sustainability and crop production. This study evaluated soil bacterial diversity, compositional structure, and functions associated with C-N cycling at two soil depths (0-15 cm and 15-30 cm) under long-term tillage (conventional tillage [CT] and no-till [NT]) and crop rotation (monocultures of corn, soybean, and wheat and corn-soybean-wheat rotation) systems. The soil microbial communities were characterized by metabarcoding the 16S rRNA gene V4-V5 regions using Illumina MiSeq. The results showed that long-term NT reduced the soil bacterial diversity at 15-30 cm compared to CT, while no significant differences were found at 0-15 cm. The bacterial communities differed significantly at the two soil depths under NT but not under CT. Notably, over 70% of the tillage-responding KEGG orthologs (KOs) associated with C fixation (primarily in the reductive citric acid cycle) were more abundant under NT than under CT at both depths. The tillage practices significantly affected bacteria involved in biological nitrogen (N2) fixation at the 0-15 cm soil depth, as well as bacteria involved in denitrification at both soil depths. The crop type and rotation regimes had limited effects on bacterial diversity and structure but significantly affected specific C-N-cycling genes. For instance, three KOs associated with the Calvin-Benson cycle for C fixation and four KOs related to various N-cycling processes were more abundant in the soil of wheat than in that of corn or soybean. These findings indicate that the long-term tillage practices had a greater influence than crop rotation on the soil bacterial communities, particularly in the C- and N-cycling processes. Integrated management practices that consider the combined effects of tillage, crop rotation, and crop types on soil bacterial functional groups are essential for sustainable agriculture.

A comparative evaluation of biochar and Paenarthrobacter sp. AT5 for reducing atrazine risks to soybeans and bacterial communities in black soil

Application of biochar and inoculation with specific microbial strains offer promising approaches for addressing atrazine contamination in agricultural soils. However, determining the optimal method necessitates a comprehensive understanding of their effects under similar conditions. This study aimed to evaluate the effectiveness of biochar and Paenarthrobacter sp. AT5, a bacterial strain known for its ability to degrade atrazine, in reducing atrazine-related risks to soybean crops and influencing bacterial communities. Both biochar and strain AT5 significantly improved atrazine degradation in both planted and unplanted soils, with the most substantial reduction observed in soils treated with strain AT5. Furthermore, bioaugmentation with strain AT5 outperformed biochar in enhancing soybean growth, photosynthetic pigments, and antioxidant defenses. While biochar promoted higher soil bacterial diversity compared to strain AT5, the latter selectively enriched specific bacterial populations. Additionally, soil inoculated with strain AT5 displayed a notable increase in the abundance of key genes associated with atrazine degradation (trzN, atzB, and atzC), surpassing the effects observed with biochar addition, thus highlighting its effectiveness in mitigating atrazine risks in soil.

Synergistic mitigation of atrazine-induced oxidative stress on soybeans in black soil using biochar and Paenarthrobacter sp. AT5

Atrazine, a widely used herbicide in modern agriculture, can lead to soil contamination and adverse effects on specific crops. To address this, we investigated the efficacy of biochar loaded with Paenarthrobacter sp. AT5 (an atrazine-degrading bacterial strain) in mitigating atrazine's impact on soybeans in black soil. Bacterially loaded biochar (BBC) significantly enhanced atrazine removal rates in both unplanted and planted soil systems. Moreover, BBC application improved soybean biomass, photosynthetic pigments, and antioxidant systems while mitigating alterations in metabolite pathways induced by atrazine exposure. These findings demonstrate the effectiveness of BBC in reducing atrazine-induced oxidative stress on soybeans in black soil, highlighting its potential for sustainable agriculture.

Rhizosphere Ventilation Effects on Root Development and Bacterial Diversity of Peanut in Compacted Soil

Soil compaction is one of the crucial factors that restrains the root respiration, energy metabolism and growth of peanut (Arachis hypogaea L.) due to hypoxia, which can be alleviated by ventilation. We therefore carried out a pot experiment with three treatments: no ventilation control (CK), (2) ventilation volumes at 1.2 (T1), and 1.5 (T2) times of the standard ventilation volume (2.02 L/pot). Compared to no-ventilation in compacted soil, ventilation T1 significantly increased total root length, root surface area, root volume and tips at the peanut anthesis stage (62 days after sowing), while T2 showed a negative impact on the above-mentioned root morphological characteristics. At the podding stage (S2, 95 days after sowing), both ventilation treatments improved root morphology, especially under T1. Compared to CK, both ventilation T1 and T2 decreased the activities of enzymes involving the anaerobic respiration, including root lactate dehydrogenase, pyruvate decarboxylase and alcohol dehydrogenase. The activities of antioxidant enzymes of root superoxide dismutase, peroxidase and catalase also decreased at S1, while superoxide dismutase and peroxidase significantly increased under T1 at S2. The ventilation of compacted soil changed soil nitrogen-fixing bacterial communities, with highest bacterial alpha diversity indices under T1. The Pearson correlation analyses indicated a positive relationship between the relative abundance of Bradyrhizobiaceae and root activity, and between unclassified_family of Rhizobiales and the root surface area, while Enterobacteriaceae had a negative impact on the root nodule number. The Pearson correlation test showed that the root surface, tips and activity positively correlated with root superoxide dismutase and peroxidase activities. These results demonstrate that soil ventilation could enhance plant root growth, the diversity and function of soil nitrogen-fixing bacterial communities. The generated results from this present study could serve as important evidence in alleviating soil hypoxia caused by compaction.

Effects of Aerated Drip Irrigation on the Soil Nitrogen Distribution, Crop Growth, and Yield of Chili Peppers

In order to study the soil nitrogen (N) distribution pattern in the root zone of chili peppers under aerated drip irrigation (ADI) conditions and analyze the relationship between soil N distribution and crop growth, two irrigation methods (conventional drip irrigation and ADI) and three N levels (0, 140, and 210 kg hm-2) were set up in this experiment. Soil samples were collected by the soil auger method at the end of different reproductive periods, and the uniformity coefficient of soil N in the spatial distribution was calculated by the method of Christiansen's coefficient. The growth status and soil-related indices of pepper were determined at each sampling period, and the relationships between soil N distribution and chili pepper growth were obtained based on principal component analysis (PCA). The results showed that the spatial content of soil nitrate-N (NO3--N) fluctuated little during the whole reproductive period of chili peppers under ADI conditions, and the coefficient of uniformity of soil NO3--N content distribution increased by 5.29~37.63% compared with that of conventional drip irrigation. The aerated treatment increased the root length and surface area of chili peppers. In addition, the ADI treatments increased the plant height, stem diameter, root vigor, and leaf chlorophyll content to some extent compared with the nonaerated treatment. The results of PCA showed that the yield of chili peppers was positively correlated with the uniformity coefficient of soil NO3--N, root vigor, and root length. ADI can significantly improve the distribution uniformity of soil NO3--N and enhance the absorption and utilization of N by the root system, which in turn is conducive to the growth of the crop, the formation of yields, and the improvement of fruit quality.

Effects of aeration treatments on root and rhizome growth parameters of Phyllostachys violascens (Lei bamboo) under intensive cultivation: A field study

Aeration through underground tunneling in mulched Phyllostachys violascens (Lei bamboo) forests can improve soil quality. Nevertheless, the effect of soil ventilation on the growth of bamboo roots and rhizomes at different distances, directions and depths of the forest are still unclear. In a field experiment, four treatments including organic mulching without aeration (MNA), organic mulching with aeration (MA), non-mulched with aeration (NMA), and non-mulched and non-aeration treatment (control) were set up to investigate the effects of soil aeration treatment on bamboo root and rhizome growth at different depths and radii distances from the bamboo trunk in both perpendicular (PD) and horizontal (HD) aeration directions. The results show that root and rhizome quantity and quality decreased vertically and linearly in the soil layers and this trend was more significant in the PD direction and near the trunk. MA treatment induced the most significant effects on the determined root and rhizome growth parameters. At 10 cm depth, the number of rhizomes in CK was 70.8 %, 77.1 %, and 18.8 % higher than that in MA, NMA, and MNA plots, respectively. However, fewer rhizomes appeared in CK and MNA plots at 20 and 30 cm depths relative to 10 cm while the number was increased by 149 % in MA and 151 % NMA plots at 20 cm. This suggest that in CK and MNA plots, soil hypoxia and soil acidification were prevalent which inhibited rhizome growth by inducing rhizome up-floating and preventing root elongation, respectively. Also, the root morphological parameters including lengths, surface areas, and volumetric areas were significantly increased in MA and MNA treatments compared to the control and NMA. For example, root length, surface area, and volumetric area in MA were increased by 56 %, 44.9 %, and 28.3 % while that in MNA increased by 40 %, 55.8 %, and 81.0 % compared with roots from the control plot. This study provides both a theoretical and practical guide for improving soil quality and bamboo growth under intensive management using aeration treatment.

Impact of Aerated Drip Irrigation and Nitrogen Application on Soil Properties, Soil Bacterial Communities and Agronomic Traits of Cucumber in a Greenhouse System

Root hypoxia stress and soil nutrient turnover have been related to reduced crop productivity. Aerated drip irrigation (ADI) can effectively enhance crop productivity and yield. However, the response of the soil bacterial community to different irrigation water dissolved oxygen (DO) concentrations remains elusive due to the extreme sensitivity of microorganisms to environmental variations. We investigated the effects of aerated irrigation with different concentrations of DO on soil properties and agronomic performance of cucumber, as well as the contribution of the bacterial community. We performed experiments on cucumber cultivation in Shouguang, China, including different irrigation methods (ADI: O2-10 and O3-20 mg L-1, non-aerated groundwater: O1-5 mg L-1) and nitrogen (N) application rates: 240 and 360 kg N ha-1. ADI (particularly O2) significantly improved soil properties, root growth, cucumber yields, and irrigation water use efficiency (IWUE), and appropriate DO concentrations reduced N fertilizer application and increased crop yields. Furthermore, these changes were associated with bacterial community diversity, aerobic bacteria abundance, and consolidated bacterial population stability within the network module. Environmental factors such as soil respiration rate (Rs), DO, and NO3--N have significant effects on bacterial communities. The FAPROTAX results demonstrated enhanced nitrification (Nitrospira) and aerobic nitrite oxidation by soil bacteria under ADI, promoting the accumulation of effective soil N and improved soil fertility and crop yield. Appropriate DO concentration is conducive to the involvement of soil bacterial communities in regulating soil properties and cucumber growth performance, which are vital for the sustainable development of facility agriculture.

Effects of Root Zone Aeration on Soil Microbes Species in a Peach Tree Rhizosphere and Root Growth

The oxygen content in the root zone considerably affects the growth and development of peach trees. However, few studies have been conducted on the effects of the oxygen content in the root zones of peach trees on soil microbes and root growth. Four-year-old Ruiguang 33/Prunus persica (L.) Batsch trees were used to study the effects of root-zone aeration on soil microbes in a peach orchard, as well as on the soil nutrient contents, peach tree root systems, and plant potassium-to-nitrogen ratios. The results showed that the root-zone aeration substantially increased the soil oxygen content in the root zone and changed the soil microbial community structure. Compared with the control, the relative abundances of soil nitrogen-fixing microorganisms (Beta proteobacteria and Bradyrhizobium elkanii) and potassium-solubilizing microorganisms (Bacillus circulans) under the root-zone aeration conditions were greatly enhanced. Root-zone aeration increased the soil's alkaline nitrogen content, available potassium content, and organic matter content, as well as the number and thickness of new white roots of peach trees, and root activity was increased significantly. At the same time, root-zone aeration changed the relative contents of total potassium and total nitrogen in the plants and considerably increased the potassium-nitrogen ratio in the shoots. The results indicate that aeration in the root zone can change the soil microbial community structure, increase the abundances of nitrogen-fixing and potassium-solubilizing microorganisms, and increase the plant potassium-to-nitrogen ratio, which are conducive to peach fruit quality.

An efficient anoxic/aerobic/aerobic/anoxic process for domestic sewage treatment: From feasibility to application

In this paper, the anoxic/aerobic/aerobic/anoxic (AOOA) process was proposed using fixed biofilms in a continuous plug-flow multi-chamber reactor, and no sludge reflux operation was performed during the 190 days of operation. The reactor volume ratio of 1.5:2:1.5:1 (A/O/O/A) with the dissolved oxygen (DO) concentration of 2 mg L⁻¹ in the aerobic zone was the optimal condition for reactor operation. According to the results obtained from the treatment of real domestic sewage, when the hydraulic retention time (HRT) was 6 h, the effluent of the reactor could meet the discharge standard even in cold conditions (13°C). Specifically, the elemental-sulfur-based autotrophic denitrification (ESAD) process contributed the most to the removal of total inorganic nitrogen (TIN) in the reactor. In addition, the use of vibration method was helpful in removing excess sludge from the biofilms of the reactor. Overall, the AOOA process is an efficient and convenient method for treating domestic sewage.

Legacy effect of microplastics on plant-soil feedbacks

Microplastics affect plants and soil biota and the processes they drive. However, the legacy effect of microplastics on plant-soil feedbacks is still unknown. To address this, we used soil conditioned from a previous experiment, where Daucus carota grew with 12 different microplastic types (conditioning phase). Here, we extracted soil inoculum from those 12 soils and grew during 4 weeks a native D. carota and a range-expanding plant species Calamagrostis epigejos in soils amended with this inoculum (feedback phase). At harvest, plant biomass and root morphological traits were measured. Films led to positive feedback on shoot mass (higher mass with inoculum from soil conditioned with microplastics than with inoculum from control soil). Films may decrease soil water content in the conditioning phase, potentially reducing the abundance of harmful soil biota, which, with films also promoting mutualist abundance, microbial activity and carbon mineralization, would positively affect plant growth in the feedback phase. Foams and fragments caused positive feedback on shoot mass likely via positive effects on soil aeration in the conditioning phase, which could have increased mutualistic biota and soil enzymatic activity, promoting plant growth. By contrast, fibers caused negative feedback on root mass as this microplastic may have increased soil water content in the conditioning phase, promoting the abundance of soil pathogens with negative consequences for root mass. Microplastics had a legacy effect on root traits: D. carota had thicker roots probably for promoting mycorrhizal associations, while C. epigejos had reduced root diameter probably for diminishing pathogenic infection. Microplastic legacy on soil can be positive or negative depending on the plant species identity and may affect plant biomass primarily via root traits. This legacy may contribute to the competitive success of range-expanding species via positive effects on root mass (foams) and on shoot mass (PET films). Overall, microplastics depending on their shape and polymer type, affect plant-soil feedbacks.