Microbial Respiration Research Articles

Suspended particles are hotspots of microbial remineralization in the ocean's twilight zone

The sinking of photosynthetically produced organic carbon from the ocean surface to its interior is a significant term in the global carbon cycle. Most sinking organic carbon is, however, remineralized in the mesopelagic zone (∼100 m–1000 m), thereby exerting control over ocean-atmosphere carbon dioxide (CO2) partitioning and hence global climate. Sinking particles are considered hotspots of microbial respiration in the dark ocean. However, our observations in the contrasting Scotia Sea and the Benguela Current show that >90% of microbial remineralisation is associated with suspended, rather than sinking, organic matter, resulting in rapid turnover of the suspended carbon pool and demonstrating its central role in mesopelagic carbon cycling. A non-steady-state model indicates that temporally variable particle fluxes, particle injection pumps and local chemoautotrophy are necessary to help balance the observed mesopelagic respiration. Temperature and oxygen exert control over microbial respiration, particularly for the suspended fraction, further demonstrating the susceptibility of microbial remineralisation to the ongoing decline in oxygen at mid-ocean depths. These observations suggest a partial decoupling of carbon cycling between non-sinking and fast-sinking organic matter, challenging our understanding of how oceanic biological processes regulate climate.

Temperature sensitivity of microbial respiration of paddy soils amended with rice residues produced under elevated CO2 and warming

Temperature sensitivity of microbial respiration of paddy soils amended with rice residues produced under elevated CO2 and warming

Quantifying the Respiratory Pattern of Rhizosphere Microbial Communities in Healthy and Diseased Tomato Plants Using Carbon Substrates

The sustainable production of tomatoes (Solanum lycopersicum) is important, and this can be achieved by determining the rate of respiration of microbes in the tomato plants' rhizosphere soil. This study aimed at the potential of microbes to utilize carbon substrates embedded in the rhizosphere soil thereby contributing to the healthy nature of the tomato plants. The potential soil physiochemical features and utilization of carbon substrate by soil microorganisms as a result of their respiration to reveal their functions in the ecosystem were evaluated. The soil samples were amassed from the healthy tomato plant rhizosphere, diseased tomatoes, and bulk soil in this study. The physiochemical features and carbon substrate utilization in the bulk soil samples, and rhizosphere samples of powdery diseased, and healthy tomato plants were assessed. The MicroRespTM procedure was used to determine the community-level physiological profiles (CLPP) employing fifteen (15) carbon (C) substrates selected based on their importance to microbial communities embedded in the soil samples. Our results revealed that various physiochemical properties, moisture content, water retention, and C substrates including sugar, amino acid, and carboxylic acid were greater in HR and the substrates were not significantly different (p < 0.05). The study reveals higher soil respiration in HR as a result of the microbial communities inhabiting HR utilizing more of the C-substrates. This investigation contributes to the tomato plant's healthy state as the microbial communities utilized carbon substrate compared to DR after employing the CLPP assays.

Carbonate-hosted manganese deposits and ocean anoxia

Late Devonian (ca. 360 Ma), Early Carboniferous (ca. 330 Ma), and Early Triassic (ca. 250 Ma) manganese deposits in the South China Block support an emerging view that some Mn carbonates form through direct synsedimentary (authigenic) precipitation. These Mn carbonates accumulated on distal shelves and are interbedded with lime mudstone and heterozoan carbonates that accumulated in coastal upwelling environments. Lithofacies, Ce anomalies combined with vanadium, uranium, and molybdenum enrichments indicate that the Mn carbonates were primarily precipitated under anoxic conditions. We provide a robust dataset to clarify the precipitation pathway of these Mn carbonates and explore the implications of using them as proxies of regional shallow water and deep-ocean anoxia. In the studied deposits, Mn calcite encases dolomite rhombs (<10 μm) or aggregates, indicating heterogenous nucleation, which is supported by similar lattice parameters of both minerals with a small lattice mismatch (<2.1%). The presence of micro-sized euhedral rhombs and subhedral aggregates of rhombs, the non-stoichiometric compositions, and characteristic organic matter Raman spectroscopy peaks near the D and G bands in the dolomite nuclei suggest an organogenic origin. Authigenic organogenic dolomite precipitation is interpreted to have preconditioned the sediment with nucleation sites for the subsequent precipitation of Mn carbonates in the shallow seafloor. This is consistent with δ13C values (−2.61‰) of Mn carbonate bulk samples that are slightly lower than coeval seawater (0.31‰, from host rocks), suggesting incorporation of 12C during microbial respiration of sedimentary organic matter during the precipitation of organogenic dolomite and hydrothermal sourced inorganic carbon. The absence of Mn in shallow facies suggests terrestrial input of Mn was minimal. Geochemical and sedimentologic evidence suggests that coastal upwelling delivered manganous anoxic deep waters to the shelves. Eu/Eu⁎ ratios (<1.5) and decoupling of Fe and Mn imply long-range transport of hydrothermal Mn, during which hydrothermal fingerprints were muted through mixing with ambient seawater. The transport of hydrothermal Mn to shelves indicates that the regional deep oceans at the time must have been anoxic, as Mn2+ would be easily oxidized and become insoluble under oxygen-rich conditions, preventing its long-distance transport. This precipitation pathway and depositional model implies that Mn carbonates are a largely unrecognized proxy for tracking ancient oceanic redox fluctuations, particularly during times of well-oxygenated global oceans. Hence, these Mn deposits record at least transient regional deep-ocean oxygen depletion in the generally well-oxygenated Late Paleozoic and Early Triassic oceans. The recognition that this periodic anoxia was broadly coeval with the anoxia-related Hangenberg, Serpukhovian, and Permian-Triassic biotic crises suggests a potential relationship between Mn carbonate accumulation and extinction events.

Influence of urban land use types on ecosystem services in two rapidly urbanizing cities of southwestern Nigeria.

Many ecological functions in cities are based on urban soils. In order to meet the needs of the expanding human population and the ensuing strain on natural resources, it is essential for soil-based ecosystems to function. Approximately 80% of the total urban land use in Akure and Okitipupa, Nigeria, are used for commercial, residential, and agricultural purposes. Thus, we investigated the potential of these three urban land use types (ULUTs) to offer a variety of ecosystem services in the two different cities. Soil properties that serve as proxy indicators for four ecosystem services were measured in the ULUTs: hydraulic conductivity (Kunsat) and available soil water for rainwater retention; soil organic carbon (SOC) stock for carbon storage; soil microbial respiration (SMR) for the capacity to support biological activity; and soil compaction (PR) and total nitrogen (TN) for promoting plant growth. The location and ULUT resulted in distinct ecosystem service provisioning. In comparison to Akure, Okitipupa soils had lower PR (1.0 vs 1.1MPa) but higher Kunsat (36.9 vs 10.3cmh-1), SOC stock (6.9 vs 5.7Mg C ha-1), and SMR levels (35.2 vs 23.6mg CO2-C g-1 soil). Commercial soils exhibited more compaction than residential and agricultural soils but less SOC stock and Kunsat, and TN in both locations. The properties of the urban soils showed that the soils could support a variety of ecosystem services. Different soil properties at the city level led to variations in the potential for ecosystem services in various locations, and these variations were observable in commercial, residential, and agricultural soils. Understanding urban soils would thus necessitate both cross-city comparative studies as well as within-city examinations of the potential for ecosystem services for various urban land use types.

Mapping turnover of dissolved organic carbon in global topsoil

Dissolved organic carbon (DOC), the labile fraction of organic carbon, is a predominant substrate for microbes. Therefore, the turnover of DOC dominates microbial respiration in soils. We compiled a global dataset (1096 data points) of the turnover rates of DOC in 0–30 cm soil profiles and integrated the data with a machine learning algorithm to develop a global map of DOC turnover rate in global topsoil. The global DOC turnover rate in 0–30 cm soil was averaged as 0.0087 day−1, with a considerable variation among biomes. The fastest DOC turnover rate was found in tropical forests (0.0175 day−1) and the lowest in tundra (0.0036 day−1), exhibiting a declining trend from low to high latitudes. The DOC turnover rate is primarily controlled by edaphic and climate factors, as confirmed by the analyses with the structural equation model and the Mental's test. With a machine learning algorithm, we produced global maps of DOC turnover rate at a monthly scale, which were further combined with a global dataset of DOC density to produce monthly maps of carbon mineralization from DOC turnover in topsoil. The annual carbon release from DOC was estimated as 27.98 Pg C year−1 from topsoil across the globe, with the largest contribution from forest biomes, followed by pasture and grassland. Tundra released the least carbon from DOC due to its low turnover rate suppressed by low temperatures. The biome- and global-scale information of DOC turnover rate and carbon release from DOC provide a benchmark for ecosystem models to better project soil carbon dynamics and their contributions to global carbon cycling in the changing environment.

Unknown bacterial species lead to soil CO2 emission reduction by promoting lactic fermentation in alpine meadow on the Qinghai-Tibetan Plateau

Highly variable soil microbial respiration among grasslands has been identified as a major cause of uncertainty in regional carbon (C) budget estimation in the Qinghai-Tibetan Plateau; microbial metabolism mechanisms might explain this variation, but remain elusive. Therefore, we investigated soil CO2 production in incubated soils and detected the associated functional genes at four sampling sites from two major alpine grasslands on the Qinghai-Tibetan Plateau. The results showed that the cumulative CO2 emissions from alpine meadow soils were 71 %–83 % lower than those from alpine steppe soils. Both the enriched genes abundance encoding fermentation and glycolysis (Embden-Meyerhof pathway (EMP)) and the diminished genes encoding tricarboxylic acid cycle (TCA) and phosphate pentose pathway (PPP) explained the CO2 emission reduction in the alpine meadow soils. The EMP: PPP and fermentation: TCA cycle ratios in alpine meadow soils were 1.45- and 1.50-fold higher than those in alpine steppe soils, respectively. Such shifts in metabolic pathways were primarily caused by the increasing dominance of an unknown species of Desulfobacteraceae with high glycolytic potential, carrying a higher abundance of ldh genes during fermentation. These unknown species were promoted by warmer temperatures and higher precipitation in the alpine meadows. Further studies on the unknown species would enhance our understanding and predictability of C cycling in alpine grasslands.

Changes in aggregate-associated carbon and microbial respiration affected by aggregate size, soil depth, and altitude in a forest soil

This study investigates the variations of aggregate-associated organic carbon (OC) and microbial respiration (MR) with respect to aggregate size, soil depth, and land altitude in a forest soil. The research was conducted in Arasbaran forest, East Azerbaijan province, Iran. Four sites were selected at different altitudes: 0–600 m, 600–1200 m, 1200–1800 m, and 1800–2400 m above sea level (a.s.l.), along the north-facing slope of the forest region. Soil samples were collected at five depths: 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm, with three replications for each depth. The soil samples were then fractioned into four aggregate size classes: <0.053 mm, 0.053–0.25 mm, 0.25–2 mm, and >2 mm. Both soil samples and aggregate fractions were analyzed for OC content and MR. The results revealed that OC content and MR in both soil samples and aggregate fractions increased with altitude and decreased with soil depth. Moreover, aggregate-associated OC increased with aggregate size. Specifically, as soil aggregate sizes increased from <0.053 mm to >2 mm at different altitudes, the mean occluded OC content of aggregates increased by approximately four times. Similarly, the mean aggregate-associated MR intensified eight times with the increase in aggregate size. A significant positive correlation was also observed between OC and MR rates of all aggregates. Furthermore, aggregates larger than 2 mm exhibited the highest contribution to the total soil OC storage (47.47–57.22%) and CO2 production rate (20–21%). These findings underscore the critical role of large macro-aggregates (>2 mm) in soil carbon storage and microbial activity, particularly in surface soils at higher altitudes.

Combined effects of salinization and temperature on microbial-mediated oak decomposition and invertebrate consumption

Water salinization is a recognized growing threat to freshwaters, whose consequences on streams’ function, per se or concomitantly with other stressors, are still far from clear. This microcosm study evaluated the combined effect of salinization (0 and 4 g/l NaCl) and temperature (5, 15, and 20 °C) on microbial-mediated oak leaf litter decomposition, with fungal biomass, sporulation, and microbial respiration as microbial descriptors. Invertebrate consumption was also assessed using the common shredder Sericostoma vittatum (Trichoptera, Sericostomatidae). Mass loss was affected by temperature and interaction between salinity and temperature. Under salt conditions, mass loss was higher at 15 °C and reduced (~ 10%) at 20 °C. Microbial activity was lower at 5 °C and higher at 15 and 20 °C, irrespective of salinity. Fungal biomass was affected by both temperature (5 < 20 < 15 °C) and salinity (4 < 0 g/l NaCl), although the interaction between both was not significant. The interaction of both variables affected the production of spores: salt addition strongly reduced sporulation rates at all temperatures despite a significant increase in conidial production with temperature. Invertebrate leaf consumption was significantly reduced only by salinization. Overall, our results seem to indicate that temperature may modulate the effect of salinization (at least at ≥ 4 g/l NaCl) on stream leaf decomposition. While stronger salinization effects may be observed at higher temperatures, a consistent strong inhibition of shredders’ feeding behavior promoted by salt, regardless of temperature, may anticipate important repercussions on streams’ secondary production throughout the year.

Enhancement of bio-S0 recovery and revealing the inhibitory effect on microorganisms under high sulfide loading

Biodesulfurization is a mature technology, but obtaining biosulfur (S0) that can be easily settled naturally is still a challenge. Increasing the sulfide load is one of the known methods to obtain better settling of S0. However, the inhibitory effect of high levels of sulfide on microbes has also not been well studied. We constructed a high loading sulfide (1.55–10.86 kg S/m3/d) biological removal system. 100% sulfide removal and 0.56–2.53 kg S/m3/d S0 (7.0 ± 0.09–16.4 ± 0.25 μm) recovery were achieved at loads of 1.55–7.75 kg S/m3/d. Under the same load, S0 in the reflux sedimentation tank, which produced larger S0 particles (24.2 ± 0.73–53.8 ± 0.70 μm), increased the natural settling capacity and 45% recovery. For high level sulfide inhibitory effect, we used metagenomics and metatranscriptomics analyses. The increased sulfide load significantly inhibited the expression of flavin cytochrome c sulfide dehydrogenase subunit B (fccB) (Decreased from 615 ± 75 to 30 ± 5 TPM). At this time sulfide quinone reductase (SQR) (324 ± 185–1197 ± 51 TPM) was mainly responsible for sulfide oxidation and S0 production. When the sulfide load reached 2800 mg S/L, the SQR (730 ± 100 TPM) was also suppressed. This resulted in the accumulation of sulfide, causing suppression of carbon sequestration genes (Decreased from 3437 ± 842 to 665 ± 175 TPM). Other inhibitory effects included inhibition of microbial respiration, production of reactive oxygen species, and DNA damage. More sulfide-oxidizing bacteria (SOB) and newly identified potential SOB (99.1%) showed some activity (77.6%) upon sulfide accumulation. The main microorganisms in the sulfide accumulation environment were Thiomicrospiracea and Burkholderiaceae, whose sulfide oxidation capacity and respiration were not significantly inhibited. This study provides a new approach to enhance the natural sedimentation of S0 and describes new microbial mechanisms for the inhibitory effects of sulfide.

Redox potential as a soil health indicator – how does it compare to microbial activity and soil structure?

Background and aimsRedox potential is a promising soil health indicator, which integrates the combined effect of chemical oxidation–reduction reactions into a single measurement. However, this method has been tested only on a few soils. The aim of this study was to test redox potential as a soil health indicator, to see if it responds to management practices and to compare it with existing soil health metrics for microbial activity (“CO2burst”) and soil structure.MethodsWe collected 35 soil samples in agricultural fields from a carbon farming trial, where contrasting management practices have been applied to increase carbon stock. The soil samples were dried, rewetted and analyzed for redox and microbial respiration during rewetting. In addition, soil structure, texture and organic matter content was measured. The data was analyzed for correlations between the indicators and for the differences between management and control fields.ResultsRedox was well correlated with microbial activity, structure, and texture. A low redox state was connected to high microbial activity, indicating bioavailable organic matter availability. Soils with good structure had an oxidized redox status, possibly reflecting high gas-transport. The carbon farming practices resulted in lower oxidation, possibly due to build-up of plant residues.ConclusionsThe findings supported the use of redox as a soil health indicator, but highlighted further research needs for identifying the shared mechanisms linking structure, redox and microbial activity. As such, redox can be a low-cost additional measurement to map changes in soil health, but it cannot replace existing structure or microbial activity measurements.

Mechanisms of soil respiration and its temperature sensitivity in black soil farmland

Soil respiration is the process of decomposition of organic matter in soil and microbial metabolism to produce carbon dioxide. In the context of climate warming and degradation of agricultural soil fertility, it becomes crucial to explore the mechanisms of soil respiration to increase carbon sequestration. In this paper, five biochar applications (0, 3.79, 7.58, 11.36, 15.15 t/ha) and two tillage methods (shallow ploughing, deep ploughing) were set up to explore the mechanism of soil respiration and its temperature sensitivity by studying the effects of tillage methods and different amounts of biochar application on soil properties, soil enzyme activities, soil respiration and its temperature sensitivity during the growing season of soybeans in the black soil area. The results showed that soil respiration rate increased with biochar application in the low biochar application range; the opposite trend was observed for high biochar application beyond the threshold (11.36 t/ha). The application of 11.36 t/ha of biochar amount had the strongest promotion effect on soil respiration, reaching 2.42 μmol m−2·s−1 in the shallow ploughing treatment and increasing 0.32 μmol m−2·s−1 in the deep ploughing compared to the shallow ploughing. The application of biochar significantly increased the activity of nitrogen and phosphorus enzymes and had an inhibitory effect on carbon cycle enzymes; the increased activity of nitrogen and phosphorus cycle enzymes provided sufficient substrate for microbial respiration and thus increased soil respiration, and the decrease in the enzymatic reaction of carbon cycle enzymes led to a decrease in temperature sensitivity. The temperature sensitivity of deep ploughing (2.18–2.59) got a more substantial reduction than that of shallow ploughing (2.34–3.53), which indicates that deep ploughing treatments can better reduce the mineralization of organic carbon than shallow tillage. Meanwhile, the temperature sensitivity of soil respiration reached a minimum with the application of 7.58 t/ha of biochar, which was reduced by 16% under deep ploughing treatment compared to the control, 33% under shallow ploughing treatment compared to the control, and also reduced by 27.27% under deep ploughing compared to shallow ploughing, which suggests that the addition of biochar reduces the loss of carbon to a certain extent. This study is important for assessing the effects of tillage practices and biochar combinations on carbon sequestration in agricultural soils in black soil areas.

Adaptations of soil microbes to stoichiometric imbalances in regulating their carbon use efficiency under a range of different grazing intensities

Grazing has a profound impact on the availability of soil resources like carbon (C), nitrogen (N), and phosphorus (P) in grasslands. These changes can potentially make it difficult to meet microbial elemental demands, thus affecting microbial C use efficiency (CUE) and soil C dynamics. Nevertheless, it remains unclear how soil microbes respond to stoichiometric imbalances and their consequent effect on microbial CUE. In this study, we investigated the stoichiometry of soil labile resources, microbial biomass, extracellular enzymes, as well as the microbial community composition and microbial CUE, microbial respiration, microbial quotient (qMB), and soil organic carbon (SOC) changes, at sites with four grazing intensities (no grazing, light, medium, and heavy grazing) in a temperate steppe of northern China. Grazing led to decreased stoichiometric imbalances between soil labile resources and microbial biomass, thereby exacerbating limitations of available C on soil microbes. To alleviate this limitation of C, microbes raised the microbial threshold elemental ratios and microbial biomass, and increased fungi dominance rather than increased activities of C-, N-, and P- acquiring enzymes due to increased microbial own growth. Microbes also improved microbial CUE, qMB, and microbial respiration while decreasing SOC under increasing grazing intensity. These integrated adaptations denote that grazing can reduce SOC which is closely affected by soil microbial C utilization induced by resource change conditions despite the increased microbial biomass contribution to SOC. These findings illustrate the regulation of stoichiometric imbalances in soil C dynamics driven by microbes under grazing and improve our understanding of how stoichiometric changes influences soil C flows in semi-arid grassland.

Comparative genomic analysis reveals electron transfer pathways of Thermoanaerobacterium thermosaccharolyticum: Insights into thermophilic electroactive bacteria

Microbial extracellular respiration is an important energy metabolism on earth, which is significant for the elemental biogeochemical cycle. Herein, extracellular Fe(III) and electrode respiration were confirmed in Thermoanaerobacterium thermosaccharolyticum MJ2. The intra/extracellular electron transfer (IET/EET) mechanism of MJ2 was investigated by comparative genomic analysis for the first time. Morphological characterization and electrochemical properties of anode illustrated that MJ2 generated bio-electricity by forming a biofilm. The respiration chain inhibition and enzyme activity tests showed that hydrogenase with cytochrome c (Cyt-c) was involved in IET of MJ2. Noteworthily, the exogenous Cyt-c increased hydrogenase activity to promote bio-electricity generation by 92.84 %. The Cyt-c gene synteny between MJ2 and another well-known exoelectrogen (Thermincola potens JR) indicated that Cyt-c bound to the outer membrane mediated the formation of biofilm involved in EET of MJ2. This study broadened the understanding of microbial extracellular respiration diversity and provided new insights to explore the electron transfer pathways of exoelectrogens.

Humic acid-dependent respiratory growth of Methanosarcina acetivorans involves pyrroloquinoline quinone.

Although microbial humus respiration plays a critical role in organic matter decomposition and biogeochemical cycling of elements in diverse anoxic environments, the role of methane-producing species (methanogens) is not well defined. Here we report that a major fraction of humus, humic acid reduction enhanced the growth of Methanosarcina acetivorans above that attributed to methanogenesis when utilizing the energy sources methanol or acetate, results which showed both respiratory and fermentative modes of energy conservation. Growth characteristics with methanol were the same for an identically cultured mutant deleted for the gene encoding a multi-heme cytochrome c (MmcA), results indicating MmcA is not essential for respiratory electron transport to humic acid. Transcriptomic analyses revealed that growth with humic acid promoted the upregulation of genes annotated as cell surface pyrroloquinoline quinone (PQQ)-binding proteins. Furthermore, PQQ isolated from the membrane fraction was more abundant in humic acid-respiring cells, and the addition of PQQ improved efficiency of the extracellular electron transport. Given that the PQQ-binding proteins are widely distributed in methanogens, the findings extend current understanding of microbial humus respiration in the context of global methane dynamics.

Dynamics of environmental variables during the incidence of algal bloom in the coastal waters of Gujarat along the northeastern Arabian Sea.

The dynamics of physico-chemical, nutrient, and chlorophyll-a variables were studied in the bloom and non-bloom locations along the off-Gujarat coastal waters to understand the variability in biogeochemistry using multivariate analytical tests. The dissolved oxygen was significantly lower in the bloom stations (3.89 ± 0.44 mgL-1) than in the non-bloom stations (5.50 ± 0.70mg L-1), due to the biological degradation of organic matter in addition to anaerobic microbial respiration. Nutrients (PO4 and NO3) and Chl-a concentrations were recorded higher in the bloom locations at 0.83 ± 0.21µmol L-1, 4.47 ± 0.69µmol L-1, 4.14 ± 1.49mgm-3, respectively. PO4 and NO3 have shown a significantly higher positive correlation of r = 0.73 and r = 0.69 with Chl-a for bloom data than the non-bloom data. The percentage variance contributed by PC1 and PC2 for both bloom and non-bloom locations were estimated at 52.33%. The variable PO4 explains the highest 24.19% variability in PC1, followed by Chl-a (19.89%). The PO4 triggers the bloom formation and also correlates to the higher concentrations of Chl-a in the bloom locations. The bloom concentration ranges from 9553 to 12,235 trichomes L-1. The bloom intensity has shown a significant positive correlation with Chl-a (r = 0.77), NO3 (r = 0.56), and PO4 (r = 0.30), but a negative correlation was noticed with DO (r = - 0.63) and pH (r = - 0.49). The study also initiates a way forward research investigation on ocean-color technologies to identify and monitor blooms and climate change-driven factors for bloom formation. The occurrence of bloom and its influence on fishery resources and other marine biotas will open many research windows in marine fisheries, oceanography, remote sensing, marine biology, and trophodynamics.

Land cover, plant residue and soil microbes as drivers of soil functioning in temperate agricultural lands. A microcosm study

Feedbacks between plants and soil microbes are critical for ecosystem regulation and restoration. Soil microbial diversity is largely dependent on plant diversity, yet these relationships have received little attention at the landscape scale. In agricultural landscapes, the presence of different plant cover types (landscape elements) can modulate these feedbacks by adding spatial heterogeneity through changes in the amount and composition of plant residues. Furthermore, it can also influence the soil biota. Therefore, the more diverse the landscape elements of farmlands, the higher the increase of their heterogeneity. We investigated the microbial catabolic profiles and respiration rates of soils from different plant cover types through the manipulation of plant residues and microbial communities. In individual microcosms, we incubated sterilized soils sampled from five different cover types of a temperate agricultural landscape: Soybean Monocropping, two crop rotations (Rotation and Intensified Rotation) and two uncropped margins: Herbaceous and Woody spontaneous vegetation. We amended them with each of two plant residues: wheat stubble (Wheat) and a mix of spontaneous vegetation (Mix). Soils were also inoculated with each of two soil microbial communities: Soybean Monocropping and Woody margins. We predict that soils treated with the Mix residue and the Woody margins community will show higher catabolic diversity and respiration than those treated with Wheat stubble and Soybean Monocropping community. In turn, we predict that soils from Woody margins, with higher carbon content, will respire more and amplify the effects of plant residue and microbial community. The microbial catabolic profile changed with plant residue and microbial community whereas the microbial respiration changed with cover type. After 30 days of incubation, soils inoculated with Woody margin community sustained higher diversity than those inoculated with Soybean Monocropping community. Conversely, Wheat stubble increased microbial diversity with respect to the Mix, particularly in soils from Woody margins while Mix residue increased the microbial diversity of soils from Soybean Monocropping. Finally, microbial respiration of soils from Woody margins showed the greatest respiration and Soybean Monocropping the lowest, in correlation with their carbon contents. Despite the complex interactions between soil carbon contents and plant residue composition, our results suggest that internal transfers of soil and plant residue between the different landscape elements might contribute to increasing the resilience of agricultural landscapes.

In situ effects of microplastics on the decomposition of aquatic macrophyte litter in eutrophic shallow lake sediments, China

The toxicity of microplastics (MPs) to aquatic organisms has been extensively studied recently. However, few studies have investigated the effects of MPs in sediments on aquatic ecosystem functioning. In the present study, we conducted an in situ experiment to explore the concentration-dependent effects (0.025%, 0.25%, 2.5%) and size-dependent effects (150–300 μm and 500–1000 μm) of polypropylene microplastics (PP MPs) on Vallisneria natans litter decomposition dynamics, in particular, the process associated with macroinvertebrates, microorganisms, as well as microalgae and/or cyanobacteria. The results showed that exposure to high concentrations and large sizes of PP MPs can accelerate leaf litter biomass loss and nutrition release. Moreover, microbial respiration, microalgal and/or cyanobacteria chlorophyll-a were also significantly affected by PP MPs. However, PP MPs have no effect on the abundance of associated macroinvertebrate during the experiment, despite the collection of five macroinvertebrate taxa from two functional feeding groups (i.e., collectors and scrapers). Therefore, our experiment demonstrated that PP MPs may enhance leaf litter decomposition through effected microbial metabolic activity, microalgal and/or cyanobacteria biomass in the sedimentary lake. Overall, our findings highlight that PP MPs have the potential to interfere with the basic ecological functions such as plant litter decomposition in aquatic environments.

Quantifying thermal adaptation of soil microbial respiration

Quantifying the rate of thermal adaptation of soil microbial respiration is essential in determining potential for carbon cycle feedbacks under a warming climate. Uncertainty surrounding this topic stems in part from persistent methodological issues and difficulties isolating the interacting effects of changes in microbial community responses from changes in soil carbon availability. Here, we constructed a series of temperature response curves of microbial respiration (given unlimited substrate) using soils sampled from around New Zealand, including from a natural geothermal gradient, as a proxy for global warming. We estimated the temperature optima ({T}_{{opt}}) and inflection point ({T}_{inf }) of each curve and found that adaptation of microbial respiration occurred at a rate of 0.29 °C ± 0.04 1SE for {T}_{{opt}} and 0.27 °C ± 0.05 1SE for {T}_{inf } per degree of warming. Our results bolster previous findings indicating thermal adaptation is demonstrably offset from warming, and may help quantifying the potential for both limitation and acceleration of soil C losses depending on specific soil temperatures.

Herbicides versus Nitrogen Cycle: Assessing the Trade-Offs for Soil Integrity and Crop Yield—An In-Depth Systematic Review

The interaction of herbicides in the nitrogen cycle and their consequences on soil health and agricultural production are essential topics in agronomic research. In this systematic review article, we have synthesized recent studies on this subject. The results revealed that the indiscriminate use of herbicides can have negative effects on vital processes in the nitrogen cycle, such as reduced enzymatic activity and microbial respiration. Moreover, herbicides alter the soil microbial composition, affecting nitrogen cycling-related activities. Symbiotic nitrogen fixation is also impaired, resulting in a reduction in the population of nitrogen-fixing bacteria and a decrease in the availability of this nutrient in the soil. These effects compromise soil fertility and the release of nitrogen to plants. Therefore, sustainable agricultural practices must be adopted, considering nitrogen cycling efficiency and the preservation of soil and natural resources. This understanding is crucial for guiding appropriate management strategies aimed at minimizing the negative effects of herbicides on the nitrogen cycle and ensuring soil health and agricultural productivity.