Microbial Phospholipid Fatty Acids Research Articles

Effects of Biological Nitrogen Fixation and Nitrogen Deposition on Soil Microbial Communities in Karst Grassland Ecosystems

Diverse exogenous nitrogen (N) sources have a considerable impact on microbial community structure in terrestrial ecosystems. Legume plants and N deposition can relieve N limitations and increase net primary productivity. However, the differences in their effects on soil microbial communities remain unclear. Here, the responses of the soil microbial community to a legume-planting system and simulated N deposition were examined in karst grasslands in Southwest China over five years by analyzing soil microbial phospholipid fatty acids (PLFAs). The experiment included three treatments—legume plant introduction (NL, Indigofera atropurpurea), N deposition (ND, NH4NO3:10 g N m−2 yr−1), and a control with no treatment. The effects of NL and ND on soil microbial community composition differed significantly. ND significantly reduced the biomass of bacteria, actinobacteria, and arbuscular mycorrhizal fungi. NL insignificantly increased the biomass of all microbial groups. However, the total amounts of PLFAs and fungal biomass were significantly higher in NL than in ND. The effect of legume plant introduction on soil microbial community composition was more powerful than that of ND. Overall, the introduction of legume plants is beneficial in terms of increasing the biomass of the soil microbial community and stabilizing the soil microbial community structure in karst grassland ecosystems.

Modulating phytoremediation: How drip irrigation system affect performance of active green wall and microbial community changes

A recent innovation in air phytoremediation is active green walls, which utilises biofiltration technology with airflow from mechanical ventilation. While this novel technology is gaining traction, the influence of irrigation on soil moisture, and subsequently the microbial communities that play a role in air filtration is untested. In this study, the application of drip irrigation techniques in active green walls were investigated for their influence on system performance. A modular green wall system was tested, with tests across 7 different plant species, as well as a substrate only control. Water distribution across the modules, the water-carrying capacity and airflow through the substrate were measured. The microbial community present, which is critical to the phytoremediation process, was quantified by identifying individual microbial phospholipid fatty acids (PLFA) within the substrate. Results demonstrated that the lower-speed drip irrigation reduced water consumption compared to the rapid system, and had generally more uniform moisture distribution. High flow drip irrigation resulted in a water pathway phenomenon, leading to uneven moisture distribution within the green wall, and this effect was accentuated with fibrous root plant species. Drip irrigation did not change microbial community composition across planted modules, apart from increasing fungi by 6%, but did wash out bacteria at the high flow rate used (−56.67%), thus low flow rate irrigation rate is more beneficial for both plant growth and microbial community composition. The current work provides evidence that drip irrigation has considerable effects on both substrate airflow rate and substrate microbial density: both key to system air cleaning performance.

Effects of Tillage Depth and Lime Application on Acidification Reduction and Nutrient Availability in Vertisol Soil

Cropland acidification seriously restricts sustainable agricultural development. The main purpose of this study was to determine whether deeper tilling could alleviate topsoil acidification to improve the quality of arable land. A soil column incubation experiment simulating tillage depths (10 cm, 30 cm and 50 cm) and lime addition was conducted to determine their effects on soil acidification improvement. The changes in soil pH, exchangeable acidity, ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), available phosphorus (AP), and microbial phospholipid fatty acids (PLFA) were analyzed. Tillage depth, lime application, and their interaction all had significant impacts on soil pH. T50 (simulated tillage depth of 50 cm) and T50+Lime (simulated tillage depth of 50 cm plus lime) treatments significantly increased the topsoil pH from 5.41 to 6.35 and 7.12, respectively. T50 treatment significantly reduced the soil exchangeable acid content compared to the T10 treatment. The nutrient accumulation along soil column indicated that the T50 and T50+Lime treatments significantly increased NO3−-N and AP content in the >30–50 cm soil layer. Compared with T30, NO3−-N accumulation in the >30–50 cm soil layers of T50 and T50+Lime treatments was 6.62 and 7.93 times higher, respectively. The accumulation of AP in the >30–50 cm soil layers of the T50 and T50+Lime treatments was 1.33 and 1.54 times higher than in the T30 treatment, respectively. These findings imply tillage up to 50 cm without exogenous materials could be a potential measure to reduce topsoil acidification and increase nutrition availability of >30–50 cm soil layers. Tillage of up to 30 cm combined with lime application confers greater benefits, which would particularly impact crops with shallow root systems. Subsequent field experiments will be conducted to further investigate the efficacy of these strategies in enhancing crop yield.

The fate and biostimulant potential of metal lactates in silt loam soil

AbstractConventional farming practices have negatively impacted micronutrient fertility and overall soil health. Metal lactates are an organic micronutrient amendment that provide both a labile carbon substrate as well as mineral nutrition for plant and microbial growth. To determine the ability of metal lactates to provide readily available micronutrients, Zn, Cu, Mn, Ni, and Co in lactate and chloride salt form were amended to soils and incubated for 28 days. Operationally defined speciation was determined using sequential extraction on samples incubated for 1, 5, or 28 days. The results show a comparable distribution of metals in chloride and lactate form; however, differences were detected in water‐soluble and exchangeable Ni and Zn at each timepoint. For example, in the water exchangeable fraction, there was 2.6%–2.9% less Ni and 0.2%–0.3% less Zn in the metal lactate‐treated soil compared to soil treated with metal chlorides. Furthermore, carbonate‐bound Ni averaged 4.1% and 4% less in metal lactate‐treated soils as compared to metal chloride‐treated soils on days 1 and 5, and Cu decreased 2.9%–3.3% during the treatment period for the lactate‐bound form. Additionally, microbial phospholipid fatty acid (PLFA) was performed and found a stimulatory effect of metal lactates on bacterial biomass with an increase of 12%–18% relative to the metal chloride treatment. Results from this study support the use of metal lactates as a sustainable alternative to conventional fertilizers by providing bioavailable micronutrients for plant nutrition in addition to a labile carbon source to support the growth of microbial populations.

Regulation of soil organic carbon dynamics by microbial communities during reforestation of Chinese fir plantations after clear‐cutting

AbstractReforestation after forest clear‐cutting is an effective measure to increase soil organic carbon (SOC) sequestration; still, the soil C balance under reforestation and the role of microbial communities in that process remain to be determined. Samples of organic (0–2 cm) and mineral (2–10 cm) horizons were collected from the 7‐, 15‐, 20‐, 29‐, and 36‐year‐old forest stands of Chinese fir (Cunninghamia lanceolata) after plantation clear‐cutting in subtropical zone under the condition of phosphorus limitation. Particulate organic carbon (POC), mineral‐associated organic carbon (MAOC), microbial phospholipid fatty acids (PLFAs), and enzymatic activities for C, nitrogen (N), and phosphorus (P) acquisition were analyzed. The lowest contents of POC (10%) and MAOC (13%) in the organic horizon were found in 7‐year‐old stands due to the slow tree regrowth and extensive decomposition of SOC in the first years of forest regrowth. POC (2.0×) and MAOC (0.8×) increases in the organic horizon with forest age were attributed to the stand development and accumulation of above‐ and belowground litter. The organic horizon had a higher POC:MAOC ratio than the mineral (0.7–1.1 vs. 0.2–0.5), indicating lower SOC stability in the first one. The ratio of POC:MAOC increased with the Gram‐positive to Gram‐negative bacteria (G+:G‐) ratio, pointing out that microbial communities developed a specific community structure and substrate utilization strategies of organic matter under plantation restoration. The increase of total PLFAs and the G+:G‐ ratio was closely linked with the microbial C and P limitations, indicating that microorganisms shifted community structure to slow‐growing species and increased their content to cope with the C and P restrictions. In the soils of young plantations, microorganisms were limited by C and P; however, the C limitation was alleviated in the 36‐year‐old plots in the organic horizon due to increased litter input, whereas the P limitation was not. This discrepancy between C and P limitation suppressed the decomposition of litter entering the soil, which was seen in decreased specific activity of C degrading enzymes and led to the accumulation of POC in the organic horizon. Thus, soil C sequestration under reforestation of Chinese fir can be controlled by the amount of litter entering the soil and by metabolic C, N, and P limitations that force microorganisms to shift community structure and change their activity.

Elevated CO2 enhanced the incorporation of 13C-residue into plant but depressed it in the microbe in the tomato (Solanum lycopersicum L.) rhizosphere soils

The translation of plant residue carbon in plant–soil–microbe systems under atmospheric CO2 (aCO2) and elevated CO2 (eCO2) is key to understanding the response of ecosystems to climatic change. Using stable isotope probing technology, we conducted an experiment on 3.5 g·kg−1 tomato 13C-residue (1050 ‰) added to tomato soils to investigate the decomposition and incorporation of 13C-residue under varied CO2 concentrations (aCO2 and eCO2: 400 and 800 μmol·mol−1, respectively). The results showed that the 13C-residue decomposition rate was stimulated by approximately 7.2 % and the 13C amount in plant stems was stimulated by 15.6 % (22.2 vs. 19.2 μg/pot), while the total 13C amount in soil microbial phospholipid fatty acids (PLFAs) was significantly decreased by 16.3 % (541 vs. 646 nmol·g−1), the DNA δ13C in soil microbes decreased by 5.1 % (−27.629 ‰ vs. −26.289 ‰), and soil δ13C decreased by 7.1 % (49.9 ‰ vs. 53.7 ‰) under eCO2. The microbial community structure involved in 13C-residue incorporation was significantly affected by the CO2 concentration. Firmicutes (Caldalkalibacillus 20.4 % and Bacillus 20.4 %) and Actinobacteria (Streptomyces 6.6 %) were the dominant phyla under aCO2 and eCO2, respectively. Proteobacteria (Dyella) were the most depleted microbes under eCO2, whereas almost no genera were found under aCO2. The 13C-residue decomposition rate was positively correlated with soil NO3−-N (r = 0.998, P < 0.05) at t1 (17 days of cultivation under varied CO2 concentrations), and DNA δ13C was positively related with soil pH (r = 0.978, P < 0.05) at t2 (35 days of cultivation under varied CO2 concentrations). Mantel tests showed that the microbial community composition involved in 13C incorporation was significantly correlated with the soil pH under various CO2 conditions (r = 0.879, P < 0.05). These results indicate that eCO2 stimulated the decomposition of 13C-residue and the transportation of 13C to the plant stem, but suppressed the incorporation of 13C into microbes (PLFA and DNA), which were adjusted by the rhizosphere N status and soil pH.

Changes in the content of emerging pollutants and potentially hazardous substances during vermi/composting of a mixture of sewage sludge and moulded pulp

Processing sewage sludge can be problematic due to its potential environmental toxicity. It may contain high concentrations of pharmaceuticals, polycyclic aromatic hydrocarbons, and heavy metals, as well as pathogenic microorganisms. However, it is a good source of organic matter and rich in microbial communities and enzymatic activity. This study deals with composting and vermicomposting of pre-composted mixtures of two different kinds of sewage sludge blended with moulded pulp in an operating composting plant. Of the total number and concentration of pollutants detected in individual piles, a large percentage of them were reduced by the composting process. The composting 2 process resulted in the greatest reduction in contaminating substances--a total of 19 substances by 4.39–90.4%. Some pharmaceuticals accumulated in earthworm bodies during vermicomposting; a total of 11 substances were detected. Atorvastatin showed the highest percentage reduction in compost 2 (90.4%), vermicompost 1 (65.2%) and vermicompost 2 (97.3%). Both composting and vermicomposting appeared to be effective for removal of heavy metals. A higher content of microbial phospholipid fatty acids (PLFAs) was found in composts than vermicomposts. There was a significant reduction in the content of pathogenic microorganisms in both processes, but the reduction in enterococci was not significant.

Drought shifts soil nematode trophic groups and mediates the heterotrophic respiration

Abstract As the most diverse metazoan taxa, soil nematodes serve a diversity of functions in soil food webs and thus can regulate microbial community composition and affect organic matter decomposition and nutrient turnover rates. Because nematodes depend on water films to access food resources, drought can negatively affect nematode–microbial food webs, yet the impacts of drought on nematode diversity and abundance and how these changes may influence food web members and their functions are hardly explored. Here, we coupled research along a drought gradient in arid and semiarid grasslands with a detailed intact plant–soil microcosm experiment to explore the patterns and mechanisms of how drought impacts nematode abundance and carbon footprint, microbial phospholipid fatty acid (PLFA) and heterotrophic soil respiration. Overall, in the field and the microcosm experiments, we found that nematode abundance, carbon footprint and diversity, microbial PLFA and heterotrophic respiration were reduced under drier conditions. In addition, drought altered nematode and microbial community composition, through reducing the nematode channel ratio and increasing the relative fungivorous nematode abundance and the fungal to bacterial ratio. The soil decomposition channel shifted from a bacterial to a fungal pathway in response to drought, indicating decelerated heterotrophic respiration under drought. These results highlight the important contribution of soil nematodes and their associated microbial food web to soil carbon cycling. Our findings underscore the need to incorporate key soil fauna into terrestrial ecosystem model evaluation.

The stable carbon and hydrogen isotopic composition of microbial fatty acids traces microbial metabolism in soils and peats

The compound-specific stable carbon (δ13C) and hydrogen (δ2H) isotopic compositions of microbial fatty acids have been widely used to trace microbial metabolism across a range of mesophilic environments. However, few studies have combined the δ13C and δ2H values of microbial fatty acids. So far none have determined the δ2H of microbial phospholipid fatty acids (PLFAs) in soils or peats, even though these stable isotope combinations could provide new insights into soil microbial metabolism. Here, we measured the δ13C and δ2H values of microbial PLFAs in top soils from peatlands, meadows, and woodlands in the Dajiuhu basin, central China. We observed a significant (p < 0.05) positive correlation between the δ13C and δ2H of microbial PLFAs across the three habitats studied here, indicating that central metabolic pathways affect both carbon and hydrogen isotopic compositions of microbial PLFAs. Moreover, our stable isotope data consistently indicate a relatively conservative metabolic state, which is dominated by expected heterotrophic metabolism. The exception to these observations is PLFAs associated with methanotrophs, as these appear to have decoupled carbon and hydrogen isotopes, providing an additional tool for tracing methanotrophic signals. Our results suggest that the carbon and hydrogen dual isotopic composition of microbial PLFAs can not only provide cross-validation for microbial metabolism in natural environments, but as a combined tool can also provide new insights into the perturbation of soil microbial community metabolism.

Soil biotic associations play a key role in subsoil C mineralization: Evidence from long-term tillage trial in the black soil of Northeast China

Quantifying the potential of soil carbon (C) mineralization improves our understanding of changes in soil health in agricultural ecosystems. Previous studies rarely linked the trait of interactions inherent in soil communities to soil C mineralization rate (Cmin). This study provides field-based evidence of tillage-driven changes in biological associations and their impacts on soil Cmin. Data obtained from a long-term (15 years) conservation tillage field experiment in Northeast China, and showed that the soil Cmin (per unit soil mass) and specific Cmin (per unit soil C) were 79% and 33% higher in topsoil (0–5 cm) and 27% and 24% lower in subsoil (5–20 cm) under no tillage with residue (NT) compared to conventional tillage with residue removal (CT). Meanwhile, in topsoil, NT strengthened biotic associations in June and August; in subsoil, a more complex network was found in CT. In topsoil, soil Cmin was not related to soil biotic associations, but was positively (P < 0.05) correlated with soil organic C (SOC) and certain biotic properties (e.g., MBC (microbial biomass carbon), microbial phospholipid fatty acid (PLFA) biomass and the relative abundance of AMF (arbuscular mycorrhizal fungi) and PP (plant-parasites)). Among them, the increases in SOC under NT exerted a positive effect on soil Cmin directly or indirectly through mediating biotic biomass properties (MBC, the PLFA biomass of all microbial groups and BF biomass). In contrast, in subsoil, soil Cmin was positively (P < 0.05) correlated with soil biotic associations, SOC and the relative abundance of PP. Notably, the increase in soil Cmin value was mainly achieved by strengthening biological associations. These findings provide novel insights into the role of soil biota in C mineralization, highlighting the diverse mechanisms underlying soil Cmin in response to tillage systems at different soil depths.

Phosphorus addition increases microbial necromass by increasing N availability in China: A meta-analysis

Phosphorus (P) is an essential limiting nutrient which has a massive impact on soil organic carbon (SOC) dynamics. However, a general pattern reflecting the response of amino sugars which is an essential component of SOC to P addition in China is unclear. We conducted a meta-analysis using 24 observations in nine research publications to examine the changes in microbial necromass in response to P addition. The results indicated that P addition significantly increased total microbial (total amino sugars, TAS), fungal (glucosamine, GlcN), and bacterial (muramic acid, MurN) necromass. Effect of P addition on amino sugars depends on climate type, ecosystem type, P addition rate and P addition duration. P input can increase galactosamine (GalN), GlcN, and MurN in montane climate, whereas P addition only increased GalN and MurN in continental climates. Also, P addition significantly raised GalN and MurN in forest ecosystems, especially in plantation forests. Low P addition rates (0–50 kg P ha−1 yr−1) had positive effects on GalN and MurN. In addition, the medium P addition time (6–10 years) significantly increased GalN, GlcN, and MurN. We also found that natural log response ratio (lnRR) of soil available nitrogen (N) was positively correlated with lnRR of amino sugars suggesting that P application alleviates N limitation and reduces the uptake of N from microbial necromass leading to increased accumulation of microbial necromass. Unexpectedly, lnRR of microbial phospholipid fatty acids (PLFAs) poorly correlated with lnRR of amino sugars. This may be due to the bias caused by not having enough observations. Limited data set impeded our understanding of whether P-induced increase in amino sugars mainly attributable to increase in PLFAs and underlying mechanisms. Our meta-analysis had important implications on predicting the effect of P addition on amino sugars under different environmental conditions, providing invaluable information for soil fertility enhancement and SOC sequestration.

Microbial responses to soil cooling might explain increases in microbial biomass in winter

In temperate, boreal and arctic soil systems, microbial biomass often increases during winter and decreases again in spring. This build-up and release of microbial carbon could potentially lead to a stabilization of soil carbon during winter times. Whether this increase is caused by changes in microbial physiology, in community composition, or by changed substrate allocation within microbes or communities is unclear. In a laboratory incubation study, we looked into microbial respiration and growth, as well as microbial glucose uptake and carbon resource partitioning in response to cooling. Soils taken from a temperate beech forest and temperate cropland system in October 2020, were cooled down from field temperature of 11 °C to 1 °C. We determined microbial growth using 18O-incorporation into DNA after the first two days of cooling and after an acclimation phase of 9 days; in addition, we traced 13C-labelled glucose into microbial biomass, CO2 respired from the soil, and into microbial phospholipid fatty acids (PLFAs). Our results show that the studied soil microbial communities responded strongly to soil cooling. The 18O data showed that growth and cell division were reduced when soils were cooled from 11 to 1 °C. Total respiration was also reduced but glucose uptake and glucose-derived respiration were unchanged. We found that microbes increased the investment of glucose-derived carbon in unsaturated phospholipid fatty acids at colder temperatures. Since unsaturated fatty acids retain fluidity at lower temperatures compared to saturated fatty acids, this could be interpreted as a precaution to reduced temperatures. Together with the maintained glucose uptake and reduced cell division, our findings show an immediate response of soil microorganisms to soil cooling, potentially to prepare for freezing events. The discrepancy between C uptake and cell division could explain previously observed high microbial biomass carbon in temperate soils in winter.

Mixed-Species Acacia Plantation Decreases Soil Organic Carbon and Total Nitrogen Concentrations but Favors Species Regeneration and Tree Growth over Monoculture: A Thirty-Three-Year Field Experiment in Southern China

Mixed-species plantations of trees with N-fixing species have the potential of promoting forest productivity and soil fertility. However, few studies in the literature have addressed the advantages of mixed-species plantations of leguminous trees over monocultures of leguminous trees based on in situ inventories over a long time period. Here, we monitored the dynamics of tree community composition, vegetation biomass, soil nutrients, and soil microbial phospholipid fatty acids (PLFAs), in an Acacia mangium monoculture plantation during 33 years of development and compared it with a mixed-species plantation of A. mangium associated with 56 native species which were underplanted 14 years after the initial establishment. Leaf N and phosphorus (P) concentrations of three main species in the overstory and understory of the A. mangium monoculture were measured. Our results showed that the soil organic carbon (SOC), total nitrogen (TN), and available phosphorus (AP) concentrations significantly increased over time during the approximately thirty years of A. mangium monoculture plantation, while the disadvantages were associated with new species regeneration and the increment of vegetation biomass. In the A. mangium monoculture plantation, leaf N concentration of A. mangium,Rhodomyrtus tomentosa, and Dicranopteris dichotoma continuously increased from 21 to 31 years, while the leaf P concentration of A. mangium and R. tomentosa decreased. The mixed-species plantations of A. mangium with native tree species had lower SOC and soil TN concentrations, more new tree species recruitment in the understory, and faster vegetation biomass increment than the A. mangium monoculture. However, the PLFAs of soil microbial groups were slightly different between the two types of plantations. We conclude that improved soil N nutrient condition by A. mangium monoculture benefits N absorption by A. mangium, R. tomentosa, and D. tomentosa, while low soil AP limits P absorption by A. mangium and R. tomentosa. Meanwhile, transforming the A. mangium monoculture into a mixed-species plantation via the introduction of multiple native species into the A. mangium monoculture decreases SOC and TN concentrations but the advantages include improving forest regeneration and maintaining forest growth in a long-term sequence. These findings provide useful and practical suggestions for managing forest monocultures of A. mangium in subtropical regions.

Functional redundant soil fauna and microbial groups and processes were fairly resistant to drought in an agroecosystem

Climate change scenarios predict more frequent and intense drought periods for 2071 to 2100 for many regions of the world including Austria. Current and predicted lower precipitation scenarios were simulated at a lysimeter station containing a fertile and less fertile agricultural soil for 9 years. 13C and 15N-labeled green manure was added in year 8 with the aim to analyze how the predicted precipitation regime affects soil fauna and microbial groups and consequently nitrogen (N) and carbon (C) cycling. Among the investigated mesofauna (collembola and oribatida), the abundance and biodiversity of oribatida was significantly reduced by drought, possibly because they mainly represent K-strategist species with low mobility and consequently the need to adapt to long-term adverse environmental conditions. Microbial community composition and microbial biomass, investigated by phospholipid fatty acid (PLFA) analysis, was indistinguishable between the current and the predicted precipitation scenarios. Nonetheless, soil 13C-CO2 emissions and soil water 15N-NO3 data revealed decelerated mineralization of green manure under reduced precipitation in the first 2 weeks, but no effects were observed on soil C sequestration or on 13C incorporation into microbial PLFAs in the following 1.2 years. We found that over a 1-year time period, decomposition was rather driven by plant residue availability than water limitation of microorganisms in the investigated agroecosystem. In contrast, N2O emissions were significantly reduced under drought, and green manure derived 15N accumulated in the soil under drought, which might necessitate the adjustment of future fertilization regimes. The impacts of reduced precipitation and drought were less pronounced in the more fertile agricultural soil, due to its greater buffering capacity in terms of water storage and organic matter and nutrient availability.

Deciphering the effects of genotype and climatic factors on the performance, active ingredients and rhizosphere soil properties of Salvia miltiorrhiza.

Salvia miltiorrhiza Bunge is an important medicinal herb, which is widely cultivated in most parts of China. It has attracted considerable attention because of its pharmacological properties and potential health benefits. We used a field experiment to determine the effects of different genotypes and climatic factors on the performance (plant biomass, morphological parameters), active ingredients, rhizosphere soil physicochemical properties and microbial composition of S. miltiorrhiza at five cultivation locations. The results showed that these parameters were significantly different in the six different genotypes of S. miltiorrhiza from five producing areas. Genotype and soil physicochemical properties were the main factors affecting the growth traits of S. miltiorrhiza, while genotype, climate and soil physicochemical properties were the main factors affecting the content of active components of S. miltiorrhiza. Microbial phospholipid fatty acid analysis showed that the biomass of Gram-positive and Gram-negative bacteria was affected by the genotypes of S. miltiorrhiza plants, while the biomass of arbuscular mycorrhizal fungi, fungi, Gram-positive and Gram-negative bacteria was affected by climate factors. Based on the main results, DS993 was the most suitable genotype for S. miltiorrhiza in the five producing areas from the perspective of comprehensive growth traits and medicinal components, while DS993 and DS2000 were suitable for planting in Shandong province from the perspective of origin. DS996 is not suitable for all of the above production areas. These results are helpful to understand the ecological adaptability of different genotypes of S. miltiorrhiza resources, and to select appropriate S. miltiorrhiza genotypes for specific planting areas, so as to maximize yield and quality.

Microbial Communities as Affected by Clarithromycin Addition in Four Acid Soils (NW Iberian Peninsula)

A laboratory experiment was carried out to investigate the response of the microbial communities in acid agricultural soils located in the NW Iberian Peninsula to the presence of clarithromycin. Four soils, with different organic C content and similar pH, and seven different concentrations of clarithromycin (0.49, 1.95, 7.81, 31.25, 125, 500 and 2,000 mg kg−1 of soil) were used, and microbial estimates were made after 8 and 42 incubation days. The phospholipid fatty acids (PLFA) technique was used to estimate the total microbial biomass and biomass of specific microbial groups as well as the microbial community structure (PLFA pattern). The microbial biomass (total and specific groups) was different in the four studied soils, the lowest values being exhibited by soils with the lowest organic C. The antibiotic addition showed a positive effect on microbial biomass (total and specific groups), especially at the highest dose; the effect being similar or even more accentuated with time passed after the addition (42 days ≥8 days). Principal component analysis (PCA) of the PLFA data carried out with the whole data set showed that the main determining factors of the microbial structure followed the order: soil &amp;gt; time incubation ≥ antibiotic dose. When the PCA was performed individually for each incubation time, the results indicated that microbial communities of the four soils were different. Likewise, for each soil, different microbial communities were observed depending on antibiotic concentration. The microbial biomass and PLFA pattern data were coincidentally showing that the clarithromycin addition favored fungi and G− bacteria more that bacteria and G+ bacteria; the effect being dose-dependent. Our data (microbial biomass, PLFA pattern) also demonstrated that the effect of clarithromycin addition on microbial communities in these four acid agricultural soils persisted even after 42 incubation days.

Soil Microbial Composition and Soil Health of Reverse-Osmosis-Concentrate and Brackish-Groundwater Irrigated Soils in Southern New Mexico

The phospholipid fatty acid method was used to determine the shifts in microbial biomass due to irrigation with reverse-osmosis (RO) concentrate (or highly saline reject water) and brackish groundwater (BGW). In this greenhouse study, RO concentrate and BGW were applied to irrigate pecan trees for 8 months for two consecutive seasons. The objectives of the study were to (i) evaluate how irrigation with RO concentrate and BGW impacts soil microbial composition in pecan rhizospheres using microbial phospholipid fatty acid (PLFA) biomarkers as indicators, and (ii) evaluate its implications on soil health. Three treatments of RO concentrate (EC = 8.0 dS/m), BGW (EC = 4.0 dS/m), and the city of Las Cruces’s water (EC = 0.8 dS/m) as a control were used to irrigate pecan trees. EC, pH, and organic matter (OM%) content of the soil samples were measured, and PLFA biomarkers for the microbial community were determined. Na-, Cl-, and K-ion concentrations were 26.16, 32.54, and 5.93 meq/L in 2017 and 25.44, 24.26, and 5.49 meq/L in 2018, respectively, in RO irrigation pots. For two seasons, gram-positive bacteria were dominant, while gram-negative bacteria were not detected in the second season. PLFA biomarkers of fungi were found among all three treatments in the first season; however, they appeared only with BGW in the second season. Actinomycetes were recorded in the first season while they were not seen in the second season. Increases in soil salinity and microbial shifts could have important implications for soil health. Irrigating with RO and BGW shifted the soil microbial composition; therefore, long-term irrigation with BGW and RO concentrate would be deleterious for pecan production and soil health.

Dynamic response of microbial communities to thermally remediated oil-bearing drilling waste in wheat soil

The primary objective of our study was to mix thermally remediated oil-bearing drilling waste (TRODW) with farmland soil during wheat planting and explore the response of microbial phospholipid fatty acid (PLFA) communities as well as the feasibility of returning TRODW to farmland. Based on environmental protection requirements and the dynamic response of wheat soil, this paper not only provides a method combining multiple models for mutual verification but also provides valuable and exploratory information for the remediation and reuse of oily solid waste.Our research found that salt damage mainly originated from sodium ions and chloride ions that inhibited the development of microbial PLFA communities in the treated soils at the initial stage. When salt damage declined, TRODW improved the levels of phosphorus, potassium, hydrolysable nitrogen and soil moisture, increasing the soil health status and promoting the development of microbial PLFA communities even when the addition ratio reached 10%. Moreover, the influences of petroleum hydrocarbons and heavy metal ions on microbial PLFA community development were not significant. Therefore, when salt damage is controlled effectively and the oil content in TRODW is no more than 3‰, it is potentially feasible to return TRODW to farmland.

Effects of Variation in Tamarix chinensis Plantations on Soil Microbial Community Composition in the Middle Yellow River Floodplain

Floodplains have important ecological and hydrological functions in terrestrial ecosystems, experience severe soil erosion, and are vulnerable to losing soil fertility. Tamarix chinensis Lour. plantation is the main vegetation restoration measure for maintaining soil quality in floodplains. Soil microorganisms are essential for driving biogeochemical cycling processes. However, the effects of sampling location and shrub patch size on soil microbial community composition remain unclear. In this study, we characterized changes in microbial structure, as well as the factors driving them, in inside- and outside-canopy soils of three patch sizes (small, medium, large) of T. chinensis plants in the middle Yellow River floodplain. Compared with the outside-canopy soils, inside-canopy had higher microbial phospholipid fatty acids (PLFAs), including fungi, bacteria, Gram-positive bacteria (GP), Gram-negative bacteria (GN), and arbuscular mycorrhizal fungi. The ratio of fungi to bacteria and GP to GN gradually decreased as shrub patch size increased. Differences between inside-canopy and outside-canopy soils in soil nutrients (organic matter, total nitrogen, and available phosphorus) and soil salt content increased by 59.73%, 40.75%, 34.41%, and 110.08% from small to large shrub patch size. Changes in microbial community composition were mainly driven by variation in soil organic matter, which accounted for 61.90% of the variation in inside-canopy soils. Resource islands could alter microbial community structure, and this effect was stronger when shrub patch size was large. The results indicated that T. chinensis plantations enhanced the soil nutrient contents (organic matter, total nitrogen, and available phosphorus) and elevated soil microbial biomass and changed microbial community composition; T. chinensis plantations might thus provide a suitable approach for restoring degraded floodplain ecosystems.

Biogeochemical properties of blue carbon sediments influence the distribution and monomer composition of bacterial polyhydroxyalkanoates (PHA)

Coastal wetlands are highly efficient ‘blue carbon’ sinks which contribute to mitigating climate change through the long-term removal of atmospheric CO2 and capture of carbon (C). Microorganisms are integral to C sequestration in blue carbon sediments and face a myriad of natural and anthropogenic pressures yet their adaptive responses are poorly understood. One such response in bacteria is the alteration of biomass lipids, specifically through the accumulation of polyhydroxyalkanoates (PHAs) and alteration of membrane phospholipid fatty acids (PLFA). PHAs are highly reduced bacterial storage polymers that increase bacterial fitness in changing environments. In this study, we investigated the distribution of microbial PHA, PLFA profiles, community structure and response to changes in sediment geochemistry along an elevation gradient from intertidal to vegetated supratidal sediments. We found highest PHA accumulation, monomer diversity and expression of lipid stress indices in elevated and vegetated sediments where C, nitrogen (N), PAH and heavy metals increased, and pH was significantly lower. This was accompanied by a reduction in bacterial diversity and a shift to higher abundances of microbial community members favouring complex C degradation. Results presented here describe a connection between bacterial PHA accumulation, membrane lipid adaptation, microbial community composition and polluted C rich sediments.Graphical Geochemical, microbiological and polyhydroxyalkanoate (PHA) gradient in a blue carbon zone.