Aerobic Soil Research Articles

Isotopic seasonality of fluvial-derived greenhouse gases implies active layer deepening

Abstract Climate change in the northern circumpolar regions is rapidly thawing organic-rich permafrost soils, releasing substantial dissolved CO2 and CH4 into fluvial systems. This mobilization impacts local ecosystems and global climate feedback loops, playing a crucial role in the Arctic carbon cycle. Here, we analyze the stable carbon (δ13C) and radiocarbon (F14C) isotopic composition of dissolved CO2 and CH4 in the Sagavanirktok and Kuparuk River watersheds on the North Slope, Alaska. By examining spatial and seasonal variations in these isotopic signatures, we identify patterns of carbon release and transport along the river continuum. We find consistent CO2 isotopic signatures across the fluvial continuum, reflecting a mixture of geogenic and biogenic sources integrated throughout the watershed. Bayesian mixing models further demonstrate a systematic depletion in 13C and 14C signatures of dissolved CO2 sources from spring to fall, indicating increasing contributions of aged carbon as the active layer deepens seasonally. This seasonal deepening allows percolating groundwater to access deeper, older soil horizons, transporting CO2 produced by aerobic and anaerobic soil respiration to streams and rivers. In contrast, we observe no clear relationships between the 13C and 14C compositions of dissolved CH4 and landscape properties. Given the reduced solubility of CH4, which facilitates outgassing and limits its transport in aquatic systems, the isotopic signatures are likely indicative of localized contributions from streambeds, adjacent water saturated soils, and lake outflows. Our study demonstrates that dissolved greenhouse gases are sensitive indicators of the release of old carbon from thawing permafrost and serve as early warning signals for permafrost carbon feedback. It establishes a crucial baseline for understanding their role in regional carbon cycling and Arctic environmental change.

Nitrosotalea devaniterrae gen. nov., sp. nov. and Nitrosotalea sinensis sp. nov., two acidophilic ammonia oxidising archaea isolated from acidic soil, and proposal of the new order Nitrosotaleales ord. nov. within the class Nitrososphaeria of the phylum Nitrososphaerota.

Two obligately acidophilic, mesophilic and aerobic soil ammonia-oxidising archaea were isolated from a pH 4.5 arable sandy loam (UK) and pH 4.7 acidic sulphate paddy soil (PR China) and designated strains Nd1T and Nd2T, respectively. The strains shared more than 99 % 16S rRNA gene sequence identity and their genomes were both less than 2 Mb in length, sharing 79 % average nucleotide identity, 81 % average amino acid identity and a DNA G+C content of approximately 37 mol%. Both strains were chemolithotrophs that fixed carbon dioxide and gained energy by oxidising ammonia to nitrite, with no evidence of mixotrophic growth. Neither strain was capable of using urea as a source of ammonia. Both strains were non-motile in culture, although Nd1T does possess genes encoding flagella components and therefore may be motile under certain conditions. Cells of Nd1T were small angular rods 0.5-1 µm in length and grew at pH 4.2-5.6 and at 20-30 °C. Cells of Nd1T were small angular rods 0.5-1 µm in length and grew at pH 4.0-6.1 and at 20-42 °C. Nd1T and Nd2T are distinct with respect to genomic and physiological features and are assigned as the type strains for the species Nitrosotalea devaniterrae sp. nov. (type strain, Nd1T=NCIMB 15248T=DSM 110862T) and Nitrosotalea sinensis sp. nov. (type strain, Nd2T=NCIMB 15249T=DSM 110863T), respectively, within the genus Nitrosotalea gen. nov. The family Nitrosotaleaceae fam. nov. and order Nitrosotaleales ord. nov. are also proposed officially.

Numerical Simulation on Cathodic Protection Potential Distribution Along Horizontal Directional Drilling Pipe

ABSTRACTEvaluating the cathodic protection (CP) effectiveness of horizontal directional drilling (HDD) pipe is a significant technical challenge, due to the feasibility of testing only in shallow buried areas at entry/exit extremities, and not in deeply buried areas or the crossing section of the pipe. Numerical simulation provides a method to evaluate the CP effectiveness of HDD pipes. To improve the accuracy of potential distribution along the HDD pipe, it is necessary to adopt appropriate boundary conditions of the HDD pipe and accurate holiday models of coating. A specialized deep well polarization test device was designed and employed in the field to obtain the actual polarization characteristics as the boundary condition of the HDD pipe at buried depths ranging from 2 to 25 m. The result revealed that the polarization characteristics of HDD pipe in various depths were different and the potential distribution of the actual situation was greatly different from the potential distribution of the shallow aerobic soil. The potential distribution along the HDD pipe was analyzed in two types of holiday models. The results could be used as a reference for the CP effectiveness evaluation of HDD pipes.

Increased N2O emissions from aerobic soil with warming is mainly attributable to increased mineralization of organic nitrogen: An incubation study

Increased N2O emissions from aerobic soil with warming is mainly attributable to increased mineralization of organic nitrogen: An incubation study

Development of a new test design to investigate the degradation of pesticides in soil under sunlight conditions

Pesticides applied to soil surface are subject to photodegradation if the parent molecule is sensitive to UV-light absorption. Photodegradation studies are therefore mandatory for the registration of plant protection products to provide data on the degradation rate and on the nature of photoproducts formed. In general, sunlight is simulated in these studies with xenon lamps, e.g., a Suntest® device. Surface application on very thin soil layers followed by direct irradiation is common practice, but the control of the boundary conditions, i.e. soil temperature and moisture, to maintain the structure and viability of the soil is challenging. A homogeneous and stable soil microclimate is crucial to compare the degradation data of the test item from the irradiated soil samples to the dark controls as well as to the results from the aerobic soil metabolism study. After trying different scale-up test systems with the UV-sensitive herbicide imazamox as comparative test item, a new soil photolysis test system was developed which is manageable in the laboratory and enables a more favorable management of the boundary conditions, especially with regard to the soil moisture and temperature. For this, the solar simulator SolarConstant® 1200, equipped with metal halide lamps Radium HRI-TS 1000W/D/S/PRO, was installed by Atlas Ametek (Germany) in a temperature controllable walk-in incubation chamber with aluminum racks and reflectors to minimize diffuse light and to maintain a homogenous temperature of 22(± 1)°C within the irradiated soil. Borosilicate glass vessels with an inner diameter of 10 cm and a maximum height of 9 cm, covered by quartz glass, were used for the incubation of the applied soil under light. Contrary to the imazamox degradation half-lives obtained with the Suntest® test system, where an unusual slower degradation was observed under light compared to the dark controls, the results from the new SolarConstant® study design showed the expected faster degradation under light. Hence, it can be concluded that the experimental boundary conditions of the new test system are more suitable to maintain the viablity of the irradiated soil. Since no adjustments of the soil water content were needed, compared to daily water adjustments for thin soil layers incubated under a Suntest®, drying–wetting cycles are eliminated and microbial-induced soil processes are maintained.

Nitrogen and phosphorus mineralization dynamics in human excreta-derived fertilizers

Growing interest in human-excreta derived fertilizers requires more information on their agronomic relevance. In this study, we measured the nitrogen (N) and phosphorus (P) mineralization from fresh urine, stored urine, urine-enriched biochar prepared with either fresh or stored urine, and feces-derived compost application in a 90-day aerobic loam soil incubation. Soils were extracted for available N at days 0, 5, 10, 20, 30, 60, and 90, while soils were extracted for four biologically relevant P pools at days 0, 30, 60, and 90. We found that N in urine applied alone was immediately bioavailable, supplying nearly all the 200 kg-N ha-1 applied, while urine-enriched biochar supplied approximately half of the N applied. Feces-derived compost application led to a slow release of mineral N. Feces-derived compost application stimulated substantial native soil P mining, while urine-P was likely rapidly immobilized. These results are relevant to container-based sanitation and other source-separated sanitation endeavors, and researchers and producers interested in human excreta-derived fertilizers. Future research should explore, among other things, different urine-enriched biochar preparations and the co-application of urine-based fertilizers and feces-derived compost.

Toxicokinetics of selenate in earthworm sub-tissues and potential bio-accessibility assessment of earthworm-derived selenium

Selenium (Se) pollution is mainly caused by anthropogenic activities, and the resulting biosecurity concerns have garnered significant attention in recent years. Using one-compartmental toxicokinetic (TK) modelling, this study explored the kinetic absorption, sub-tissue distribution, and elimination processes of the main Se species (selenate, Se(VI)) in the cultivated aerobic soil of the earthworm Eisenia fetida. The bio-accessibility of earthworm-derived Se was assessed using an in vitro simulated gastrointestinal digestion test to evaluate its potential trophic risk. The results demonstrated that Se accumulated in the pre-clitellum (PC) and total tissues (TT) of earthworms in a time- and dose-dependent manner. The highest Se levels in the PC, post-clitellum (PoC), and TT were 70.54, 57.93, and 64.26 mg/kg during the uptake phase, respectively. The kinetic Se contents in the earthworms PC and TT were consistent with the TK model but not with PoC. The earthworm TT exhibited a faster uptake (Kus = 0.83–1.02 mg/kg/day) and elimination rate of Se (Kee = 0.044–0.049 mg/kg/day), as well as a shorter half-life time (LT1/2 = 15.88–14.22 days) than PC at low soil Se levels (≤5 mg/kg). Conversely, the opposite trend was observed with higher Se concentrations (10 and 20 mg/kg). These results are likely attributable to the tissue specificity and concentration of the toxicant. Earthworms PC and TT exhibited a higher kinetic Se accumulation factor (BAFk) than steady-state BAF (BAFss), with values ranging from 8 to 24 and 3–13, respectively. Furthermore, the bio-accessibility of earthworm-derived Se to poultry ranged from 66.25 % to 84.35 %. As earthworms are at the bottom of the terrestrial food chain, the high bio-accessibility of earthworm-derived Se poses a potential risk to predators. This study offers data support and a theoretical foundation for understanding the biological footprint of soil Se and its toxicological impacts and ecological hazards.

The coupling of carbon and energy fluxes reveals anaerobiosis in an aerobic soil incubation with a Bacillota-dominated community

Soil microorganisms rely on coupled fluxes of carbon and energy to fuel their maintenance, to switch from dormancy to activity and to grow under dynamically changing conditions in microhabitats. To identify the principles underlying this coupling, we measured heat and CO2 release from soil after glucose addition along with estimates of microbial biomass and community composition. The results revealed bi-directional deviations of the ratio of heat to CO2 release (Calorespirometric Ratio, CR) that are inconsistent with theoretical predictions for aerobic respiration, which is commonly assumed to be the major metabolic pathway in incubation experiments. Moreover, the microbial community was dominated by members of the Bacillota, whose relative abundance increased from 4 percent to 65 percent in 18 h. To interpret these findings, we developed a dynamic model of carbon and energy fluxes during the microbial growth on glucose. The model simulates aerobic respiration as well as anaerobic fermentation pathways to lactate, acetate and propionate depending on the time-varying availability of O2. Simulations captured the observed temporal CR pattern and suggested a gradual depletion of O2 and a shift to anaerobic pathways as the main driver. This interpretation is consistent with the dominance of Bacillota, many members of which are well adapted to anaerobic conditions. Our results highlight the potential of the joint analysis of matter and energy fluxes in combined experimental and modeling approaches and indicate the presence of facultative anaerobiosis under common experimental conditions, which could confer a competitive advantage to certain microbial taxa during growth on labile substrate.

The effect of white grub (Maladera Verticalis) larvae feeding on rhizosphere microbial characterization of aerobic rice (Oryza sativa L.) in Puer City, Yunnan Province, China

BackgroundRhizosphere microorganisms are vital in plants’ growth and development and these beneficial microbes are recruited to the root-zone soil when experiencing various environmental stresses. However, the effect of white grub (Maladera verticalis) larvae feeding on the structure and function of rhizosphere microbial communities of aerobic rice (Oryza sativa L.) is unclear.ResultsIn this study, we compared physicochemical properties, enzyme activities, and microbial communities using 18 samples under healthy and M. verticalis larvae-feeding aerobic rice rhizosphere soils at the Yunnan of China. 16 S rRNA and ITS amplicons were sequenced using Illumina high throughput sequencing. M. verticalis larvae feeding on aerobic rice can influence rhizosphere soil physicochemical properties and enzyme activities, which also change rhizosphere microbial communities. The healthy and M. verticalis larvae-feeding aerobic rice rhizosphere soil microorganisms had distinct genus signatures, such as possible_genus_04 and Knoellia genera in healthy aerobic rice rhizosphere soils and norank_f__SC − I−84 and norank_f__Roseiflexaceae genera in M. verticalis larvae-feeding aerobic rice rhizosphere soils. The pathway of the metabolism of terpenoids and polyketides and carbohydrate metabolism in rhizosphere bacteria were significantly decreased after M. verticalis larvae feeding. Fungal parasite–wood saprotroph and fungal parasites were significantly decreased after M. verticalis larvae feeding, and plant pathogen–wood saprotroph and animal pathogen–undefined saprotroph were increased after larvae feeding. Additionally, the relative abundance of Bradyrhizobium and Talaromyces genera gradually increased with the elevation of the larvae density. Bacterial and fungal communities significantly correlated with soil physicochemical properties and enzyme activities, respectively.ConclusionsBased on the results we provide new insight for understanding the adaptation of aerobic rice to M. verticalis larvae feeding via regulating the rhizosphere environment, which would allow us to facilitate translation to more effective measures.

Spatial distribution of volatile organic compounds in contaminated soil and distinct microbial effect driven by aerobic and anaerobic conditions

The vertical distribution of 35 volatile organic compounds (VOCs) was investigated in soil columns from two obsolete industrial sites in Eastern China. The total concentrations of ΣVOCs in surface soils (0–20 cm) were 134–1664 ng g−1. Contamination of VOCs in surface soil exhibited remarkable variability, closely related to previous production activities at the sampling sites. Additionally, the concentrations of ΣVOCs varied with increasing soil depth from 0 to 10 m. Soils at depth of 2 m showed ΣVOCs concentrations of 127–47,389 ng g−1. Among the studied VOCs, xylene was the predominant contaminant in subsoils (2 m), with concentrations ranging from n.d. to 45,400 ng g−1. Chlorinated alkanes and olefins demonstrated a greater downward migration ability compared to monoaromatic hydrocarbons, likely due to their lower hydrophobicity. As a result, this vertical distribution of VOCs led to a high ecological risk in both the surface and deep soil. Notably, the risk quotient (RQ) of xylene in subsoil (2 m, RQ up to 319) was much higher than that in surface soil. Furthermore, distinct effects of VOCs on soil microbes were observed under aerobic and anaerobic conditions. Specifically, after the 30-d incubation of xylene-contaminated soil, Ilumatobacter was enriched under aerobic condition, whereas Anaerolineaceae was enriched under anaerobic condition. Moreover, xylene contamination significantly affected methylotrophy and methanol oxidation functions for aerobic soil (t-test, p < 0.05). However, aromatic compound degradation and ammonification were significantly enhanced by xylene in anaerobic soil (t-test, p < 0.05). These findings suggest that specific VOC compound has distinct microbial ecological effects under different oxygen content conditions in soil. Therefore, when conducting soil risk assessments of VOCs, it is crucial to consider their ecological effects at different soil depths.

A statistical model predicts N mineralization of various organic amendments for paddy fields

ABSTRACT To predict the mineralization of nitrogen(N) in organic amendments in paddy fields, we applied data obtained from incubation experiments under waterlogged conditions by a hierarchical Bayesian model using acid-detergent-soluble organic N (ADSON) as a model input. Each of 20 organic amendments (6 cattle manure composts, 3 swine manure composts, 3 poultry manure composts, 2 oil cakes, 2 rice brans, 1 fish meal, 1 sludge fertilizer, and 2 mixed commercial organic fertilizers) was mixed with paddy soil, and the N mineralization curves obtained after 1, 2, 4, 8, and 12 weeks of waterlogging were incorporated into the model to obtain values of the model parameters k i , α1, and Q 10. All model parameters converged with a mean absolute error (MAE) of 0.044 g N kg−1, a root mean square error (RMSE) of 0.060 g N kg−1, and a model efficiency (EF) of 0.96. These values were comparable to or slightly better than those of a previous model for upland soil conditions. Most of the observed values were within the 95% Bayesian prediction interval, indicating that the model performed well with the observed data. Although it is generally believed that livestock manure composts decompose more slowly than organic fertilizers such as oil cake, the livestock manure composts had a large value of the rate constant k i , presumably because of the initial rapid decomposition of the small amounts of organic N present in them. In paddy fields, the soil conditions are aerobic between the application of organic amendments and water entry. In such a case, we propose the use of the upland field model to predict the mineralization of organic N during the period of aerobic soil conditions and of this study’s model during the period of waterlogging, subtracting the amount of already mineralized N from the parameters N in and ADSON. The model devised here is expected to be useful for fertilization design in organic agriculture and in the reduction of the use of inorganic fertilizer.

Structural and Functional Characterization of a Gene Cluster Responsible for Deglycosylation of C-glucosyl Flavonoids and Xanthonoids by Deinococcus aerius

Plant C-glycosylated aromatic polyketides are important for plant and animal health. These are specialized metabolites that perform functions both within the plant, and in interaction with soil or intestinal microbes. Despite the importance of these plant compounds, there is still limited knowledge of how they are metabolized. The Gram-positive aerobic soil bacterium Deinococcus aerius strain TR0125 and other Deinococcus species thrive in a wide range of harsh environments. In this work, we identified a C-glycoside deglycosylation gene cluster in the genome of D. aerius. The cluster includes three genes coding for a GMC-type oxidoreductase (DaCGO1) that oxidizes the glucosyl C3 position in aromatic C-glucosyl compounds, which in turn provides the substrate for the C-glycoside deglycosidase (DaCGD; composed of α+β subunits) that cleaves the glucosyl-aglycone C–C bond. Our results from size-exclusion chromatography, single particle cryo-electron microscopy and X-ray crystallography show that DaCGD is an α2β2 heterotetramer, which represents a novel oligomeric state among bacterial CGDs. Importantly, the high-resolution X-ray structure of DaCGD provides valuable insights into the activation of the catalytic hydroxide ion by Lys261. DaCGO1 is specific for the 6-C-glucosyl flavones isovitexin, isoorientin and the 2-C-glucosyl xanthonoid mangiferin, and the subsequent C–C-bond cleavage by DaCGD generated apigenin, luteolin and norathyriol, respectively. Of the substrates tested, isovitexin was the preferred substrate (DaCGO1, Km 0.047 mM, kcat 51 min−1; DaCGO1/DaCGD, Km 0.083 mM, kcat 0.42 min−1).

The specific molecular signature of dissolved organic matter extracted from different arctic plant species persists after biodegradation

Dissolved organic matter (DOM) is a small but very reactive pool of organic matter (OM) in the environment. Its role is related to its composition, which depends on its source. In soils, vegetation is the main source of DOM, and biodegradation is the main regulating mechanism. This study aims to characterise DOM produced by contrasted arctic vegetation species and their biodegradation products.The water-extractable organic matter (WEOM) was produced from C. stellaris (lichen), E. vaginatum (sedge), A. polifolia (dwarf evergreen shrub) and B. nana (deciduous dwarf shrub). The WEOM were inoculated with a common aerobic heterotrophic soil bacteria (P. aureofaciens) and incubated for 7 days. During the experiment, WEOM was characterised through a wide range of analytical methods (TOC, UV–Vis absorbance, high-performance ion chromatography and HRMS Orbitrap).The results showed bacteria consumed a significantly greater proportion of WEOM produced by C. stellaris than by A. polifolia and B. nana at the end of the experiment (p < 0.05). Furthermore, the number of features in WEOM decreased for C. stellaris and E. vaginatum, whereas it increased for B. nana. These findings shed light on the species-specific biodegradation processes that rely on the initial composition of DOM, specifically influenced by the vegetation's capacity to produce recalcitrant compounds. Furthermore, our results emphasised that even though bacterial activity greatly impacted molecular characteristics, the WEOM produced by different vegetation species maintained their distinct molecular signatures. As a result, it can be inferred that the DOM found in natural environments directly reflects the relevant vegetation cover despite the strong influence of biogeochemical processes on DOM molecular composition. This should be considered when developing models to assess the influence of climate change on vegetation cover composition and its subsequent effects on DOM dynamics in soil and surface waters.

Mineralization and residue characteristics of chloramphenicol in aerobic soils: evidence from a carbon-14 study.

Chloramphenicol, a broad-spectrum antibiotic employed for controlling bacterial infections, presents an intriguing aspect in terms of its environmental fate in soils. 14C-labeled chloramphenicol was used to explore its mineralization and residue characteristics in three distinct agricultural soils in China. The findings revealed a nuanced pattern in the fate of 14C-chloramphenicol, with notable variations among the different soils under investigation. The chloramphenicol extract residue exhibited a reduction of 18.04% in sandy clay soil, 23.04% in clay loam soil, and 21.73% in loamy clay soil. Notably, the mineralization rate in sandy clay soil was 25.22% surpassed that in the other two soils, particularly during the initial stages of incubation. Over time, the diminishing extract residue underwent conversion into minerals and bound residue. The formation rate of bound residue was increased from 44.59 to 53.65% after adding 10% manure, suggesting that chloramphenicol easily binds with soils rich in organic matter. The bound residue is predominantly localized in the humin fraction across all soils. Additionally, the sterilized soil experiments indicated the pivotal role of microorganisms in influencing the fate of chloramphenicol under the specified experimental conditions. In conclusion, this study offers valuable insights into the environmental dynamics of chloramphenicol in soils, emphasizing the importance of soil composition, organic matter content, and microbial activity. The findings contribute to a scientific understanding of the environmental safety implications associated with chloramphenicol usage.

Arsenite and arsenate stress differently affect auxin distribution in rice roots and brassinosteroids restore it sustaining root system plasticity

Rice is a worldwide cultivated crop that serves as an important source of food for the human population, but it is also the simplest route for arsenic (As) contamination of the food chain. The As inorganic forms, arsenate [As(V)] and arsenite [As(III)], are the highly toxic As species found in the soil and the most easily absorbed by the roots. The absorption of As(V) prevails in aerobic soils while that of As(III) is favored in anaerobic soils. As(V) is converted to As(III) in the roots, although small amounts of As(V) also remain in the plant organs. The root system is the first target of the action of both As forms. The mechanisms of action of As(V) and As(III) are still widely unknown. Understanding them is essential for selecting rice genotypes with a lower capacity of As uptake and transport to the caryopses, thus improving food safety. Auxin is the phytohormone necessary for the development and plasticity of the root system, and its action is modulated by endogenous/exogenous brassinosteroids (BRs), mainly under stress conditions. The research aim was to deepen the knowledge of the mechanisms triggered by As(III) or As(V) in rice roots with particular attention to the role played by the interaction between auxin transport and BRs. We show that As(III) is the main As species present in rice roots regardless of the As(III) or As(V) forms supplied to the growing medium. Arsenic alters auxin distribution in both adventitious and lateral roots, but strongly in the latter ones. The application of an exogenous BR, the 24-epibrassinolide (eBL), combined with As(III) or As(V) strongly increases the expression of the OsPIN2 and OsAUX1 genes involved in auxin transport, thus contributing to restore the correct auxin distribution altered by As, and mainly by As(III), with higher effects on the LRs. Moreover, eBL increases the antioxidant activity in the roots in the presence of As, but only when combined with As(V).

Influence of vegetation on soil organic nitrogen composition and mineralization in a subtropical wetland

Studies have investigated the role of litter type on soil organic nitrogen (SON) mineralization and the resulting chemical composition in aerobic soils; however, the role of anaerobic conditions have been limitedly explored. We determined the SON chemical composition and N mineralization rate with depth of two different vegetation types (emergent aquatic vegetation, EAV and submerged aquatic vegetation, SAV) and prevailing flooded soil conditions in a subtropical treatment wetland. The treatment wetland provided similar water quality and climate conditions across the vegetation types. Three soil depths were sampled, the surficial floc, recently accreted soil, and soil present before constructing the treatment wetland. The surficial floc material created from emergent plants exhibited a mean total carbon (TC) and total N (TN) of 364 g C kg−1 and 27 g N kg−1 vs 185 g C kg−1and 12 g N kg−1 for submerged plants. Despite these differences, there were no significant differences in the proportion of N that was soil organic nitrogen (SON). Mean extractable ammonium was lower (95 mg N kg−1) in SAV systems and may be due to increased pH (~9) during the day compared to EAV systems (207 mg N kg−1). For the chemical composition, the N-associated aromatics comprised 4.8% of the SON in SAV areas compared with just 1.6% for EAV, which suggests an increased SON recalcitrance in SAV created floc. The difference in EAV and SAV chemical composition may be important for the long-term storage of SON and future studies should focus on additional environmental factors that favor the formation of stable recalcitrant SON.

Influence of Drip Irrigation and Fertigation Levels on Physiological Characters and Yield of Aerobic Rice (Oryza sativa L.)

Background: Water shortage is becoming severe in many rice growing areas in the world. Conventional method of irrigation, which not only consumes huge water, but also causes severe water and nutrient losses under anaerobic condition. Introduction of aerobic rice, growing high yielding rice in non-puddled and non-flooded aerobic soil with the support of external inputs like supplementary irrigation, manures and fertilizers can reduced water use and increase rice production. Methods: Study on different levels of drip irrigation and fertigation on physiological characters and yield of aerobic rice was conducted during summer 2022 and 2023 at research farm of wetland in Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu. The experiment was laid out in randomized complete block design with thirteen treatments, replicated thrice. Result: The findings revealed that drip fertigation @ 100% PE up to 30 DAS+150% PE up to 60 DAS+200% PE up to 90 DAS with 125% RDF (25% through NF+75% through WSF) resulted significantly higher leaf area index (5.84 and 5.95), chlorophyll index (SPAD) (41.5 and 42.3) and grain yield (4315.9 and 4446.1 kg ha-1) respectively than all other treatments during both summer 2022 and 2023. However, significantly lower leaf area index (2.70 and 2.91), chlorophyll content (31.9 and 32.2) and yield (2301.0 and 2364.8 kg ha-1) observed with fertigation at 50% PE up to 30 DAS+100% PE up to 60 DAS+150% PE up to 90 DAS with 75% RDF (75% through NF+25% through WSF), respectively in summer 2022 and 2023.

Soil-borne disease suppressiveness after short and long term application of fermented, composted or fresh organic amendment treatments in arable soils

Soil-borne diseases can cause significant crop losses and should be tackled sustainably in agroecosystems. Increasing the capacity of soils to suppress the effects of soil-borne diseases (soil suppressiveness) is an important tool in sustainable crop production. Soil suppressiveness can be improved by adding organic amendments to the soil for multiple years, but the effects can vary greatly depending on the processing method of the organic amendment (composted, fermented, or fresh material) and the time since application. To test these impacts we conducted two bioassays using the Lepidium savitum (cress) – Pythium ultimum model system. We tested the disease suppression capacity of sandy arable soil from a field experiment where fresh plant material, compost, or Bokashi (fermented amendment), all originating from the same plant material had been applied for two consecutive years across 10 field sites subject to conventional farming. In addition, the effect of short term application on soil suppressiveness was tested right after applying the same organic amendments to control arable sandy soil from 2 sites from the field experiment. Field sites strongly differed in cress growth independent of the organic amendment treatments. Absence of field effects in the sterilized soil and their soil chemical characteristics suggested differences in inherent soil pathogen load between the field sites. Focussing on sites with low inherent pathogen load we found no significant impact of long term organic amendment application on either cress weight or soil suppressiveness. However, short term application of Bokashi did significantly promote soil suppressiveness. This effect can likely be attributed to the increased metabolic activity of the soil's microorganisms in response to Bokashi, which contains more easily decomposable compounds as compared to the other soil amendments, together with Bokashi microorganisms that survive the fermentation and are activated in the aerobic soil condition. Our results suggest that Bokashi could promote the suppression of soil-borne diseases by stimulating the locally adapted soil microbiome but the longevity of this effect requires further field tests.

Strigolactone GR24-mediated mitigation of phosphorus deficiency through mycorrhization in aerobic rice

Strigolactones (SLs) are a new class of plant hormones that play a significant role in regulating various aspects of plant growth promotion, stress tolerance and influence the rhizospheric microbiome. GR24 is a synthetic SL analog used in scientific research to understand the effects of SL on plants and to act as a plant growth promoter. This study aimed to conduct hormonal seed priming at different concentrations of GR24 (0.1, 0.5, 1.0, 5.0 and 10.0 µM with and without arbuscular mycorrhizal fungi (AMF) inoculation in selected aerobic rice varieties (CR Dhan 201, CR Dhan 204, CR Dhan 205, and CR Dhan 207), Kasalath-IC459373 (P-tolerant check), and IR-36 (P-susceptible check) under phosphorus (P)-deficient conditions to understand the enhancement of growth and priming effects in mycorrhization. Our findings showed that seed priming with 5.0 µM SL GR24 enhanced the performance of mycorrhization in CR Dhan 205 (88.91 %), followed by CR Dhan 204 and 207, and AMF sporulation in CR Dhan 201 (31.98 spores / 10 gm soil) and CR Dhan 207 (30.29 spores / 10 g soil), as well as rice growth. The study showed that the highly responsive variety CR Dhan 207 followed by CR Dhan 204, 205, 201, and Kasalath IC459373 showed higher P uptake than the control, and AMF treated with 5.0 µM SL GR24 varieties CR Dhan 205 followed by CR Dhan 207 and 204 showed the best performance in plant growth, chlorophyll content, and soil functional properties, such as acid and alkaline phosphatase activity, soil microbial biomass carbon (MBC), dehydrogenase activity (DHA), and fluorescein diacetate activity (FDA). Overall, AMF intervention with SL GR24 significantly increased plant growth, soil enzyme activity, and uptake of P compared to the control. Under P-deficient conditions, seed priming with 5.0 µM strigolactone GR24 and AMF inoculum significantly increased selected aerobic rice growth, P uptake, and soil enzyme activities. Application of SLs formulations with AMF inoculum in selected aerobic rice varieties, CR Dhan 207, CR Dhan 204, and CR Dhan 205, will play an important role in mycorrhization, growth, and enhancement of P utilization under P- nutrient deficient conditions.

Niche-specification of aerobic 2,4-dichlorophenoxyacetic acid biodegradation by tfd-carrying bacteria in the rice paddy ecosystem.

This study aimed for a better understanding of the niche specification of bacteria carrying the tfd-genes for aerobic 2,4-dichlorphenoxyacetic acid (2,4-D) degradation in the rice paddy ecosystem. To achieve this, a dedicated microcosm experiment was set up to mimic the rice paddy system, with and without 2,4-D addition, allowing spatial sampling of the different rice paddy compartments and niches, i.e., the main anaerobic bulk soil and the aerobic surface water, surface soil, root surface and rhizosphere compartments. No effect of 2,4-D on the growth and morphology of the rice plant was noted. 2,4-D removal was faster in the upper soil layers compared to the deeper layers and was more rapid after the second 2,4-D addition compared to the first. Moreover, higher relative abundances of the 2,4-D catabolic gene tfdA and of the mobile genetic elements IncP-1 and IS1071 reported to carry the tfd-genes, were observed in surface water and surface soil when 2,4-D was added. tfdA was also detected in the root surface and rhizosphere compartment but without response to 2,4-D addition. While analysis of the bacterial community composition using high-throughput 16S rRNA gene amplicon sequencing did not reveal expected tfd-carrying taxa, subtle community changes linked with 2,4-D treatment and the presence of the plant were observed. These findings suggest (i) that the surface soil and surface water are the primary and most favorable compartements/niches for tfd-mediated aerobic 2,4-D biodegradation and (ii) that the community structure in the 2,4-D treated rice paddy ecosystem is determined by a niche-dependent complex interplay between the effects of the plant and of 2,4-D.