Total Phospholipid Fatty Acid Content Research Articles

Insights from Fertilization and Cultivation Management for Interpreting the Variations in the Quantity and Quality of Dissolved Organic Carbon and Microbial Community Structure on Purple Soil Sloping Farmland in Southwest China

It is crucial to comprehend how fertilization and cultivation management alter the composition of dissolved organic carbon (DOC) and microbial communities to regulate the biogeochemical cycling of soil nutrients and mitigate adverse impacts on soil–water quality. Based on 15 years of long-term field trials conducted in purple soil on farmland with a slope of 15° in southwestern China, the following five treatments were examined: CK (no fertilizer was applied), T1 (NPK plus organic manure and downslope cultivation), T2 (NPK and downslope cultivation), T3 (1.5-fold NPK and downslope cultivation), and T4 (NPK and contour cultivation). Soil samples were obtained from summer maize at two soil depths (0–10 and 10–20 cm) and from rhizospheric soil, and the changes in the DOC content, UV–visible (UV–Vis) absorptivity, and phospholipid fatty acids (PLFAs) were assessed. Our results revealed a significant change in the DOC content following fertilization, especially in T1, as it was 136.0%, 179.4%, and 132.2% higher, respectively, than that in CK at the 0–10 and 10–20 cm depths and rhizospheric soil. Fertilization decreased the UV–Vis absorptivity variables of DOC (i.e., SUVA254, SUVA260, SUVA400, SUVA465, SUVA665, and C:C ratio) and raised the E4:E6 ratio (fulvic acid to humic acid in DOC), regardless of T2 and T3 at the 10–20 cm depth and in the rhizospheric soil compared with those in CK, respectively. Fertilization significantly increased the total PLFA content and selected microbial groups relative to CK. Among the treatments, T1 significantly increased the total PLFA content by 50.6%, 59.0%, and 46.2%, respectively, relative to CK, at the 0–10 and 10–20 cm depths and in the rhizospheric soil. The microbial community structure in contour cultivation (T4) was significantly greater than in downslope cultivation (T2). Random forest analysis (RFA) revealed that SOC and DOC were likely the primary variables for regulating the total PLFAs in the examined soil. Partial least squares path modeling (PLS-PM) further indicated that the DOC content and the ratio of E4:E6 among DOC compositions had greater effects on the soil microbial community structure in the examined soil. These observations suggested that long-term fertilization and cultivation management are effective approaches to regulating the soil microbial community structure by altering the composition of DOC in sloping farmland.

Main soil microbial groups assessed by phospholipid fatty acid analysis of temperate alley agroforestry systems on crop- and grassland

The phospholipid fatty acid (PLFA) composition of soils was analysed at three poplar-based silvo-arable systems and at one willow-based silvo-grassland alley agroforestry system in Central Germany. The objective was to analyse tree row effects on the PLFA composition of main fungal and main bacterial groups. The fungal groups were BAM (Basidiomycota + Ascomycota + Mucoromycota) and AMF (Arbuscular Mycorrhizal Fungi). The bacterial groups were Gram-negative, Firmicutes, and Actinobacteria. The total PLFA content varied between 53 and 170 nmol g−1 soil. Total PLFA and microbial biomass carbon (MBC) showed a strong linear relationship, which resulted in a mean MBC/total PLFA ratio of 4.2 μg nmol−1. AMF contributed on average 4 mol% and the fungal BAM group 10 % to total PLFA. Gram-negative bacteria contributed on average 37 mol%, Firmicutes 23 mol%, and Actinobacteria 6 mol% to total PLFA. The presence of poplar or willow trees increased the mean total PLFA content in comparison with the alleyways by 30 %. Especially the mean contribution of fungal PLFA to total PLFA showed a significant +7.0 mol% increase in the tree row compared with the alleyways, exclusively caused by the BAM group (+7.6 mol%), whereas the contribution of the AMF PLFA linearly decreased from the middle of the alleyway to the tree row at all sites. Within the alleyways, the Gram-negative/Firmicutes PLFA ratio showed a significant decline from the 1 m up to the 24 m distance samples at sites Dornburg and Forst. Despite a decrease of AMF in tree rows, agroforestry tree rows led to a rapid increase in fungi, most likely due to the promotion of ecto-mycorrhizal fungi.

Effect of electrokinetic process on in situ stabilization and detoxification of arsenic-contaminated soil with high content of calcium

Owing to the high risk of human exposure to arsenic-contaminated soil, reducing its toxicity is essential. This study used the electrokinetic (EK) process with iron-rich electrodes to synchronously achieve the accumulate, stabilize and detoxify soil arsenic. Changes in arsenic valence, leaching toxicity, and microbial communities related to toxicity were comprehensively considered. The results demonstrated that arsenic was mainly transported toward the anode and accumulated by electromigration owing to the negatively charged arsenic anions under EK conditions. The cathode approaching effectively promote arsenic movement to the anode; the largest As(T) transportation rate of 30.61% was achieved near the cathode (S4). The transportation ratio of As(III) was 1.84 times more than that of As(V). The As(III) content and leaching toxicity of soil arsenic in all treatments decreased after applying the EK process. In particular, the anode approaching effectively elevated the average ratios of soil As(III) oxidation and stabilization to 37.88% and 61.73%, respectively. Correspondingly, the total phospholipid fatty acid content increased substantially after EK treatment and showed a pollution stress elimination effect. The electrokinetic effect can essentially cause highly active and easily migrated arsenic to accumulate near the anode and middle sections. The electric field mediated iron mineralization and stabilized arsenic by oxidizing As(III) and reacting with newly formed iron-rich phases (S). Meanwhile, the electric field regulated the form of soil calcium from CaCO3 to CaSO4 and caused calcium-bound arsenic to change to a more stable form. According to these results, in situ stabilization and detoxification of arsenic-contaminated soil can be realized by the EK process, avoiding stabilizer addition and excavation.

Rewetting the hyper-arid Atacama Desert soil reactivates a carbon-starved microbial decomposer community and also triggers archaeal metabolism

Extreme environmental conditions make soils of the hyper-arid Atacama Desert one of the most hostile habitats for life on the planet. During the short intervals of moisture availability that occur, it remains unresolved how soil microorganisms physiologically respond to such dramatic environmental changes. Therefore, we simulated a precipitation event – without (H2O) and with (H2O + C) labile carbon (C) supplementation – and investigated the responses in microbial communities (using phospholipid fatty acids (PLFAs) and archaeal glycerol dialkyl glycerol tetraether (GDGTs)) and physiology (by means of respiration, bacterial and fungal growth and C-use efficiency (CUE)) during a five-day incubation. We demonstrated that bacterial and fungal growth does occur in these extreme soils following rewetting, albeit at 100–10,000-fold lower rates compared to previously studied soil systems. C supplementation increased levels of bacterial growth and respiration responses by 5- and 50-fold, respectively, demonstrating a C-limited microbial decomposer community. While the microbial CUE following rewetting was c. 14 %, the addition of labile C during rewetting resulted in a substantial reduction (c. 1.6 %). Consistent with these interpretations, the PLFA composition clearly shifted from saturated towards more unsaturated and branched PLFAs, which could arise from (i) a physiological adaptation of the cell membrane to changing osmotic conditions or (ii) a community composition shift. Significant increases in total PLFA concentrations were solely found with H2O + C addition. Contrary to other recent studies, we found evidence for a metabolically active archaeal community in these hyper-arid soils upon rewetting. We conclude that (i) microorganisms in this extreme soil habitat can be activated and grow within days following rewetting, (ii) available C is the limiting factor for microbial growth and biomass gains, and (iii) that an optimization of tolerating the extreme conditions while maintaining a high CUE comes at the expense of very poor resource-use efficiency during high resource availability.

Sediment microbial community structure, enzymatic activities and functional gene abundance in the coastal hypersaline habitats

Salt marsh vegetation, mudflat and salt production are common features in worldwide coastal areas; however, their influence on microbial community composition and structure has been poorly studied and rarely compared. In the present study, microbial community composition (phospholipid fatty acid (PLFA) profiling and 16S rRNA gene sequencing (bacterial and archaeal)) and structure, enzymatic activities and abundance of functional genes in the sediments of salt ponds (crystallizer, condenser and reservoir), mudflat and vegetated mudflat were determined. Enzyme activities (β-glucosidase, urease and alkaline phosphatase) were considerably decreased in saltpan sediments because of elevated salinity while sediment of vegetated mudflat sediments showed the highest enzyme activities. Concentrations of total microbial biomarker PLFAs (total bacterial, Gram-positive, Gram-negative, fungal and actinomycetes) were the highest in vegetated mudflat sediments and the lowest in crystallizer sediments. Nonmetric-multidimensional scaling (NMDS) analysis of PLFA data revealed that the microbial community of crystallizer, mudflat and vegetated mudflat was significantly different from each other as well as different from condenser and reservoir. The most predominant phyla within the classified bacterial fractions were Proteobacteria followed by Firmicutes, Bacteroidetes and Planctomycetes, while Euryarchaeota and Crenarchaeota phyla dominated the classified archaeal fraction. Cyanobacterial genotypes were the most dominant in the condenser. Mudflat and vegetated mudflat supported a greater abundance of Bacteroidetes and Actinobacteria, respectively. The results of the present study suggest that salt ponds had significantly decreased the microbial and enzyme activities in comparison to mudflat and vegetated mudflat sediments due to very high salinity, ionic concentrations and devoid of vegetation. The present study expands our understanding of microbial resource utilization and adaptations of microorganisms in a hypersaline environment.

Bacteria not fungi drive soil chemical quality index in banana plantations with increasing years of organic fertilizer application.

Maintaining or improving soil chemical quality is critical for sustainable agricultural productivity and environmental safeguards. Organic fertilizer application, a common agricultural practice in banana cultivation, is often associated with greater microbial biomass and activity, which are linked to improvements in soil chemical quality. However, the effect of the duration of organic fertilizer application on soil chemical quality and whether it is microbially driven still needs to be investigated. We collected soil samples from banana plantations consistently applying organic fertilizers for 1 (Y1), 4 (Y4), 7 (Y7) and 10 (Y10) years. Soil chemical quality is expressed as total data set (TDS) and minimum data set (MDS) based on chemical indicators, and soil microorganisms are characterized by phospholipid fatty acid (PLFA). Based on TDS and MDS, the soil chemical quality indices in Y7 and Y10 treatments were significantly higher than that in Y1 and Y4 treatments. Soil total PLFA concentrations and the proportional abundance of fungi and arbuscular mycorrhizal fungi increased with prolonged banana cultivation. Total PLFA concentrations were significantly positive correlation with the soil chemical quality index. Soil gram-positive bacteria (G+), bacteria, protozoa and ratio of G+ to gram-negative bacteria (G-) were major drivers of soil chemical quality. The organic fertilizer application can significantly improve soil chemical quality, which is regulated by soil bacteria. Regular application of organic fertilizers is important in promoting soil quality and soil biological properties need to be incorporated into the assessment of soil health in banana plantations. © 2022 Society of Chemical Industry.

Interaction of soil microbial communities and phosphorus fractions under long-term fertilization in paddy soil

Understanding the impact of biological activities on the soil phosphorus (P) distribution under long-term fertilizer application can facilitate better soil P fertility management. Therefore, the primary objectives of this study were to investigate the effect of long-term (since 1981) fertilizer application on the soil P fractions and microbial community and to evaluate correlations between the microbial community structure and P distribution. The following treatments were implemented in a long-term field trial: no fertilization (CK), inorganic N and K (NK), inorganic P and K (PK), inorganic N, P and K (NPK) and manure+NPK (MNPK) fertilization. The study showed that the soil pH, soil organic carbon and total and available N and P concentrations were considerably higher in the MNPK treatment than in the CK treatment. The soil microbial biomass C, N and P concentrations were also significantly higher in the MNPK treatment than in the CK treatment. Among fertilization treatments, the β-1,4-glucosidase, α-1,4-glucosidase, urease, acid phosphatase and phosphodiesterase activities were the highest in the MNPK treatment. Compared to inorganic fertilization, the MNPK treatment increased the labile soil P fractions and decreased the residual soil P concentration. Continuous fertilization significantly affected the soil microbial composition. The total phospholipid fatty acid (PLFA) concentrations in the NK, PK, NPK and MNPK treatments were 23.3, 43.1, 48.7 and 87.7% higher, respectively, than in the CK treatment. A significant correlation was observed between the microbial community and soil P fractions. Moreover, the aggregated boosted tree (ABT) model showed that among the various soil biochemical properties, the total PLFA concentration was the factor that most influenced the active P pool, accounting for 35.4% of the relative influence of all soil biochemical properties examined. These findings reveal that combined manure and inorganic fertilizer application is a better approach than applying inorganic fertilizer alone for sustaining long-term P fertility by mediating soil biological activity.

Subsoiling tillage with straw incorporation improves soil microbial community characteristics in the whole cultivated layers: A one-year study

The subsoiling tillage managements have been recommended to remediate subsoil compaction and maintain crop production. These practices can improve soil properties and fertility due to soil loosening and straw incorporation, and further affect soil microbial community characteristics. However, the response of soil microbial community structure to subsoiling tillage managements is still poorly understood. The objective of this study was to examine the effects of tillage practices (conventional tillage, CT; subsoiling tillage, ST; subsoiling tillage with straw incorporation, STS) on soil microbial community characteristics. Topsoil (0–20 cm) and subsoil (20–35 cm) samples were taken from a 360–day in−situ field experiment in northeast China. Microbial community characteristics were determined by the phospholipid fatty acid (PLFA) method. The contents of subsoil bacterial PLFAs and fungal PLFAs were lower in the ST treatment than those in the other treatments within 60–360 days, and gram−positive (G+) bacteria were more abundant in the subsoil of ST treatment than those in the subsoil of STS treatment. In contrast to the other treatments, the STS treatment had the larger total PLFAs content and the higher ratio of fungal to bacterial PLFAs (F/B) in the subsoil during the whole incubation period, and fungi played a dominant role in straw degradation of subsoil. Compared with the other treatments, the STS treatment had a lower cyclopropyl to precursors (cy/pre) ratio in the subsoil on the 30th day, suggesting that the STS treatment provided more K2SO4−extractable organic carbon (EOC) and some available nutrients (nitrogen, potassium and phosphorous) for soil microbes. The STS treatment relative to the other treatments increased the bacterial PLFAs and fungal PLFAs contents in the topsoil, which were associated with the increase in the EOC/SOC ratio. Accordingly, STS practice had a great potential for improving subsoil and topsoil microbial community characteristics.

Impact of N-fertilization and peanut shell biochar on soil microbial community structure and enzyme activities in a Typic Haplustoll under different management practices

The application of biochar with N-fertilizer is one of the most attractive practices for increasing soil quality and fertility. However, few studies have examined the combined effects of peanut biochar and urea on soil microbial community structure and function. Phospholipid fatty acid (PLFA) analysis and various enzyme activities were used to monitor microbial community structure and function in a 20-week incubation experiment. Different rates of biochar (0, 1, and 3% dry wt. soil) and N-fertilizers (with or without urea addition at 0.2 g kg−1) were applied to a Typic Haplustoll under conventional (CV) and conservation (CS) land management practices. A pristine forest soil (CK) was also included as control. Overall, the lowest microbial activity and abundance of microbial PLFA bioindicators were recorded under CV, confirming that conservation management may improve soil quality. Our study also indicated that the effect of biochar and management practices on the microbial community structure was more significant than that of urea. Particularly under both CS and CK, biochar tended to increase glucosidase, glucuronidase, and phosphomonoesterase activities, being on average 65%, 43%, and 85% significantly higher in biochar 3% than in the control treatment, respectively. Thus, we found a strong correlation between soil macronutrients and enzymes such as glucosidase and urease. Although total PLFA content was poorly affected, biochar addition increased some individual PLFA biomarkers, suggesting that both the biochar rates (1% and 3%) may increase Gram-negative bacteria and fungal populations. Regardless of biochar addition, urea application significantly increased urease activity. We also found a positive correlation between fungal PLFAs (VAM and total fungi) and urease activity, indicating that biochar tended to increase fungal biomass. The combined application of biochar and urea to soil under appropriate management may thus be a feasible and effective strategy for improving soil microbial quality.

Changes in soil microbial community during shrub encroachment process in the Inner Mongolia grassland of northern China

This study attempted to elucidate the characteristics of the soil microbial community during the grass-to-shrub transition process and to identify underlying factors influencing changes in the soil microbial community with increasing intensity of shrub encroachment. In this study, evaluations were conducted on three states (grass-dominated, grass-shrub mixed and shrub-dominated states) of the shrub-encroached grassland. In each state, the landscape consists of shrub patches and grass patches, therefore the soils were sampled under the shrub patches and the grass patches respectively. The composition and biomass of the soil microorganisms were quantified by the phospholipid fatty acid (PLFA) method. The results indicated that as shrub encroachment increased, the contents of soil total PLFAs, total bacteria, fungi, actinomycetes and G− bacteria increased under the shrub patches. And the contents of total PLFAs, total bacteria, fungi, actinomycetes, and G− bacteria first decreased and subsequently increased under the grass patches from grass-dominated state to shrub-dominated state. The soil PLFAs were mostly distributed in the soil depth 40 cm under the shrub patches but were primarily in the soil layer 20 cm under the grass patches. Soils under the shrub patches had greater contents of total PLFAs, total bacteria, actinomycetes and Gram-positive bacteria (G+) than did soils under the grass patches. Soil water and belowground biomass were significantly correlated with the concentrations of total PLFAs, bacteria, fungi, G+, G−, actinomycetes, G−/G− and fungi/bacteria (F/B). Additionally, the aboveground biomass (AB) of C. microphylla L. of the shrub patches and AB of S. krylovii of the grass patches were both significantly correlated with the concentration of G−/G+. There were significant positive correlations between the belowground biomass (BB) and total PLFAs, bacteria, G+ bacteria, G− bacteria and actinomycetes. The contents of soil sand and silt, organic matter, total N, total P, available P and NO−3-N were significantly correlated with the concentrations of total PLFAs, bacteria, fungi, G+, G−, actinomycetes, and G−/G+. The findings of this study highlight that shrub encroachment significantly affect the microorganism biomass and the community composition. The inherent characteristics of the plants and the soil physicochemical properties are the main factors for the change of microbial community during the processes of shrub encroachment.

Temperature sensitivity of CO2 efflux in soils from two alpine elevation levels with distinct bedrock types

Predicted increase in climate warming will affect soil organic carbon (SOC) dynamics in vulnerable cold alpine environments. In contrast to freeze and thaw cycles, less is known about the effects of temperature regimes in the range between 2 and 10 °C on SOC availability to soil microorganisms. For this reason, CO2 efflux, extracellular enzyme activities and microbial communities were measured in an incubation experiment with three temperature treatments: (T1) continuous 10 °C, (T2) cooled down to 2 °C, and (T3) rewarmed from 2 to 10 °C. Two forest soils at low elevation and two grassland soils at high elevation were taken from two sites with distinct bedrock types (limestone at Hochschwab, gneiss and schist at Rauris). The CO2 efflux did not differ significantly between the elevation levels at the two sites. In the continuous warm treatment T1, the relative decline in CO2 efflux was stronger in the two Rauris than in the two Hochschwab soils during the 0–123 days period. In the cooling treatment T2, the cumulative ΣCO2C efflux of the Hochschwab soils was lowered by 32% and that of the Rauris soils by only 19% compared with T1 during the 30–123 days period. In the rewarming treatment T3, the ΣCO2 efflux was on average 33% higher than that of treatment T1 during the 91–123 days period, ranging from +8% to +62%. Phospholipid fatty acid (PLFA) composition and extracellular enzyme activities were not markedly affected by incubation time or temperature treatments. The differences in bedrock properties had stronger effects on the ΣCO2 efflux, enzyme activities as well as total PLFA content and composition than elevation level or vegetation. Other, largely unknown factors control the rewarming effects on the mobilisation of a labile SOC pool.

Linkages between ecoenzymatic stoichiometry and microbial community structure under long-term fertilization in paddy soil: A case study in China

This study investigated relationships between ecoenzymatic stoichiometry and microbial community structure under long-term (38-years) combined organic and inorganic fertilization. Experiment was initiated in 1982 and seven fertilization treatments were studied that included: CK (no fertilizer), NPK (inorganic N, P and potassium fertilizers), NPM (inorganic N, P fertilizers and manure), NKM (inorganic N, K fertilizers and manure), PKM (inorganic P, K fertilizers and manure), NPKM (inorganic N, P, K fertilizers and manure) and M (manure) treatments. We analyzed soil and microbial biomass of C, N and P, enzyme activities related to C, N and P, and their effects on the microbial community structure in the top layer (0–20 cm) of the paddy soil. The results showed that combined application of manure and inorganic fertilizers significantly increased soil C, N, P contents, extracellular enzyme activities and total phospholipid fatty acid (PLFA) concentration, compared to the NPK and CK treatments. Fertilization treatments significantly changed microbial biomass stoichiometry. Among all fertilization treatments, highest microbial biomass C:N, C:P ratio and N:P ratios were 10.2, 36.0 and 3.59, respectively, under the PKM treatment. Soil C, N and P-cycling enzyme activities were highest under the NPKM treatments. Soil C:N showed positive and soil C:P ratio showed negative relationships with microbial biomass C:N and C:P ratios, respectively. Soil total PLFA concentration was highest under NPKM treatment. The order of individual PLFAs concentrations in all fertilization treatments was: Gram negative bacteria > Gram positive bacteria > Actinomycetes > AM fungi > Fungi> Eukaryotes > anaerobes. Soil organic C, total N, soil N:P and microbial N:P ratios were positively correlated with total PLFA concentration. While, soil C:N and microbial biomass C:N ratios were negatively correlation with total PLFA and individual microbial community structure. Our results suggested that ecoenzymatic stoichiometry and microbial community structure are very sensitive to combined long-term organic and inorganic fertilization that can affect the nutrient acquisition and cycling in agroecosystem.

Response of Soil Microbial Communities to Warming and Clipping in Alpine Meadows in Northern Tibet

In order to explore responses of soil microbial communities among different alpine meadows under warming and clipping, soil microorganisms of three alpine meadow sites (low altitude: 4313 m, alpine steppe meadow, 30°30′ N, 91°04′ E; mid-altitude: 4513 m, alpine steppe meadow, 30°31′ N, 91°04′ E; and high altitude: 4693, alpine Kobresia meadow, 30°32′ N, 91°03′ E) were measured using the phospholipid fatty acid (PLFA) method. Both warming and clipping significantly reduced PLFA content and changed the community composition of soil microbial taxa, which belong to bacterial and fungal communities in the alpine Kobresia meadow. Warming significantly reduced the soil total PLFA content by 36.1% and the content of soil fungi by 37.0%; the clipping significantly reduced the soil total PLFA content by 57.4%, the content of soil fungi by 49.9%, and the content of soil bacteria by 60.5% in the alpine Kobresia meadow. Only clipping changed the total fungal community composition at a low altitude. Neither clipping nor warming changed the microbial community composition at a moderate altitude. Soil temperature, soil moisture, and pH were the main factors affecting soil microbial communities. Therefore, the effects of warming and clipping on soil microbial communities in alpine meadows were related to grassland types and soil environmental conditions.

Soil microbiome-induced changes in the priming effects of 13C-labelled substrates from rice residues

Knowledge gap exists to understand the soil CO2 emission and microbial group response to substrates of whole plant residues and derived biochar. We used 13C-labelled substrates (rice straw, roots and biochar) to track influences of their decomposition on soil priming effect (PE) and phospholipid fatty acid (PLFA) composition during one-year incubation. Organic substrates at 1% (w/w) level increased soil pH, available nitrogen (AN) and available phosphorus (AP), especially during the first 45 days of incubation. After incubation, 44% of the added straw was mineralized to 13CO2, followed by roots (~35%) and biochar (~5%). Straw and roots amendment caused positive PE during 4–360 day of the incubation, where a lowest value of 41.9 mg C kg−1 was observed. Biochar amendment caused negative PE during 56–150 day of the incubation, where a largest value of −99.0 mg C kg−1 was observed. Analysis of 13C-labelled PLFA enabled the differentiation of microbial groups during substrates utilization. Gram positive bacteria (G+) and general bacteria groups were dominated in co-metabolizing both the native soil organic carbon (SOC) and substrates after straw and roots amendment. Gram negative bacteria (G−), especially identified by PLFA biomarkers cy17:0 and cy19:0, preferentially utilizes the 13C-labelled biochar but not promoting soil priming effect. Soil pH, SOC, AN and AP all explained changes of total and 13C-labelled PLFA contents (>75%, p < .05). Evidences showed that biochar is best in sequestering soil C pool, followed by straw and roots, and soil microbial groups in utilization of organic substances mediated SOC mineralization.

Fingerprinting ambient air to understand bioaerosol profiles in three different environments in the south east of England

Molecular and chemical fingerprints from 10 contrasting outdoor air environments, including three agricultural farms, three urban parks and four industrial sites were investigated to advance our understanding of bioaerosol distribution and emissions. Both phospholipid fatty acids (PLFA) and microbial volatile organic compounds (MVOC) profiles showed a different distribution in summer compared to winter. Further to this, a strong positive correlation was found between the total concentration of MVOCs and PLFAs (r = 0.670, p = 0.004 in winter and r = 0.767, p = 0.001 in summer) demonstrating that either chemical or molecular fingerprints of outdoor environments can provide good insights into the sources and distribution of bioaerosols. Environment specific variables and most representative MVOCs were identified and linked to microbial species emissions via a MVOC database and PLFAs taxonomical classification. While similar MVOCs and PLFAs were identified across all the environments suggesting common microbial communities, specific MVOCs were identified for each contrasting environment. Specifically, 3,4-dimethylpent-1-yn-3-ol, ethoxyethane and propanal were identified as key MVOCs for the industrial areas (and were correlated to fungi, Staphylococcus aureus (Gram positive bacteria) and Gram negative bacteria, R = 0.863, R = 0.618 and R = 0.676, respectively) while phthalic acid, propene and isobutane were key for urban environments (correlated to Gram negative bacteria, fungi and bacteria, R = 0.874, R = 0.962 and R = 0.969 respectively); and ethanol, 2-methyl-2-propanol, 2-methyl-1-pentene, butane, isoprene and methyl acetate were key for farms (correlated to fungi, Gram positive bacteria and bacteria, R = 0.690 and 0.783, R = 0.706 and R = 0.790, 0.761 and 0.768). The combination of MVOCs and PLFAs markers can assist in rapid microbial fingerprinting of distinct environmental influences on ambient air quality.

Seasonal Change in Microbial Diversity and Its Relationship with Soil Chemical Properties in an Orchard

This study aimed to determine the microbial diversity at different soil depths (0–5 and 5–20 cm) in a subtropical orchard during different seasons (i.e., spring, summer and autumn) to advance knowledge of the roles of microbes in orchard ecosystem balance. In tracking experiments conducted in an orchard (established in 1996), the phospholipid fatty acid (PLFA) biomarker method was employed to determine the soil microbial system. The total PLFA concentration did not vary significantly between soil depths but changed between seasons. It peaked in the summer at 258.97 ± 23.48 μg g soil-1 from 0–5 cm and at 270.99 ± 58.94 μg g soil-1 from 5–20 cm. A total of 33 microbial fatty acid biomarkers were observed and identified in the sampled soil. The quantities of PLFAs for 29 microbial groups varied significantly between seasons, except for 15:0 iso 3OH, 15:1 iso G, 16:0 2OH, and 17:0 iso 3OH. The bacterial PLFAs and fungal and actinomycetic PLFAs in the orchard soil collected in summer were significantly more abundant than those collected in the spring or autumn (P < 0.01). The number of soil microorganism species (richness) and the Simpson and Shannon-Wiener indexes were all highest in summer. The total PLFAs, bacterial PLFAs, fungal PLFAs, actinomycetic PLFAs, richness, and Simpson and Shannon-Wiener indexes were all significantly negatively correlated with soil pH, total organic carbon (TOC), total nitrogen (TN) and the cation exchange capacity (CEC) (P < 0.05).

Intercropping of kura clover (Trifolium ambiguum M. Bieb) with prairie cordgrass (Spartina pectinata link.) enhanced soil biochemical activities and microbial community structure

Optimizing the use of N fertilization is the major factor for establishing perennial grasses to enhance the biomass production and soil health under marginally yielding croplands. A study was conducted to investigate the influence of N fertilization and intercropping of kura clover (Trifolium ambiguum M. Bieb) (KC) with prairie cordgrass (PCG) (Spartina pectinata Link.) on soil biochemical activities and microbial community structure. The fertilization treatments included four N levels: 0, 75, 150, and 225 kg N ha−1, and the grass-legume intercropping system included one grass (PCG) and one legume (KC) (PCG-KC). Data showed that soil microbial biomass C (MBC) was 90 and 55% higher with PCG-KC than the PCG-225N and PCG-75N, respectively. Enzyme activities associated with life processes of microorganisms and release of mineral nutrients from organic matter were the highest in PCG-KC, and were comparable to that observed under medium to high N fertilization. The results indicated that PCG-KC intercropping could sustainably provide soil health benefits compared to the N fertilization. The PCG-KC combination led to an increase in total PLFA (phospholipid fatty acid) and total bacterial PLFA concentration relative to the PCG-0N, PCG-75N and PCG-225N. The PCG-KC also had the highest glomalin-related soil protein content (11.9 mg g−1) indicating high abundance of Arbuscular mycorrhizal fungi crucial for P nutrition. Further, N deficiency as well as high N fertilization appear to reduce the abundance of N-fixing bacteria as indicated by the presence of nifH amplicons. In summary, PCG-KC intercropping yielded comparable or more desirable soil microbial community structure and enzymatic activities compared to the N fertilization. Considering the cost and negative impact of N fertilization on the environment, intercropping KC with PCG can be desirable for improving soil health of marginally yielding croplands.

The responses of soil organic carbon mineralization and microbial communities to fresh and aged biochar soil amendments

AbstractWhile biochar soil amendment has been widely proposed as a soil organic carbon (SOC) sequestration strategy to mitigate detrimental climate changes in global agriculture, the SOC sequestration was still not clearly understood for the different effects of fresh and aged biochar on SOC mineralization. In the present study of a two‐factorial experiment, topsoil samples from a rice paddy were laboratory‐incubated with and without fresh or aged biochar pyrolyzed of wheat residue and with and without crop residue‐derived dissolved organic matter (CRM) for monitoring soil organic matter decomposition under controlled conditions. The six treatments included soil with no biochar, with fresh biochar and with aged biochar treated with CRM, respectively. For fresh biochar treatment, the topsoil of a same rice paddy was amended with wheat biochar directly from a pyrolysis wheat straw, the soil with aged biochar was collected from the same soil 6 years following a single amendment of same biochar. Total CO2 emission from the soil was monitored over a 64 day time span of laboratory incubation, while microbial biomass carbon and phospholipid fatty acid (PLFA) were determined at the end of incubation period. Without CRM, total organic carbon mineralization was significantly decreased by 38.8% with aged biochar but increased by 28.9% with fresh biochar, compared to no biochar. With CRM, however, the significantly highest net carbon mineralization occurred in the soil without biochar compared to the biochar‐amended soil. Compared to aged biochar, fresh biochar addition significantly increased the total PLFA concentration by 20.3%–33.8% and altered the microbial community structure by increasing 17:1ω8c (Gram‐negative bacteria) and i17:0 (Gram‐positive bacteria) mole percentages and by decreasing the ratio of fungi/bacteria. Furthermore, biochar amendment significantly lowered the metabolic quotient of SOC decomposition, thereby becoming greater with aged biochar than with fresh biochar. The finding here suggests that biochar amendment could improve carbon utilization efficiency by soil microbial community and SOC sequestration potential in paddy soil can be enhanced by the presence of biochar in soil over the long run.

Functional Soil Organic Matter Fractions, Microbial Community, and Enzyme Activities in a Mollisol Under 35 Years Manure and Mineral Fertilization

Fertilization is a worldwide practice to maintain and increase crop productivity and improve soil quality in agricultural ecosystems. The interactive mechanisms of long-term fertilization affecting the functional soil organic matter (SOM) fractions, microbial community, and enzyme activities are unclear. We investigated the effects of manure and mineral fertilization on six SOM fractions (non-protected, physically, chemically, biochemically, physical-chemically, and physical-biochemically protected), microbial community structure, and enzyme activities based on a 35-year fertilization experiment. The combined application of manure and mineral fertilizers (NPKM) increased the soil organic carbon (SOC) and total nitrogen (TN) in the biochemically (28.6–43.9%) and physically (108–229%) protected fractions, compared to their content in the unfertilized soil (CK). The total phospholipid fatty acid content, Gram(−) bacteria, and actinomycetes, as well as the activities of α-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, β-1,4-xylosidase, and cellobiohydrolase were highest under NPKM fertilization. The protected SOM fractions (physical, biochemical, physical-chemical, and physical-biochemical) were closely related to microbial community composition (accounting for 67.6% of the variance). Bacteria were sensitive to changes in the physically and biochemically protected fractions, whereas fungi responded more to the changes in the chemically protected fraction. In summary, long-term mineral and organic fertilization has a strong effect on microbial communities and activities through the changes in the functional SOM fractions.

Influence of slope aspect on the microbial properties of rhizospheric and non-rhizospheric soils on the Loess Plateau, China

Abstract. Slope aspect is an important topographic factor in the micro-ecosystem environment, but its effect on the microbial properties of grassland rhizospheric soil (RS) and non-rhizospheric soil (NRS) remain unclear. A field experiment was conducted at the Ansai Research Station on the Loess Plateau in China to test the influence of slope aspects (south-facing, north-facing, and northwest-facing slopes, all with Artemisia sacrorum as the dominant species) on RS and NRS microbial biomass carbon (MBC) contents, phospholipid fatty acid (PLFA) contents, and the rhizospheric effect (RE) of various microbial indices. Soil samples were collected from the three slope aspects, including rhizospheric and non-rhizospheric region, and analyzed to determine the various related microbial indices. The results showed that MBC content differed significantly among the slope aspects in RS but not in NRS, and the RE for MBC content in the south-facing slope was larger than that in the north-facing slope. RS total, bacterial, and Gram-positive bacterial PLFA contents in the south-facing slope were significantly lower than those in the north- and northwest-facing slopes, and RS Gram-negative bacterial (G−) and actinomycete PLFA contents in the south-facing slope were significantly lower than those in the north-facing slope. In contrast, NRS total, bacterial, and G− PLFA contents in the north-facing slope were significantly higher than those in the south- and northwest-facing slopes, and NRS fungal and actinomycete PLFA contents in the north- and south-facing slopes were significantly higher than those in the northwest-facing slope. RE for all PLFA contents except fungal in the northwest-facing slope were higher than those in the south-facing slope. Slope aspect significantly but differentially affected the microbial properties in RS and NRS, and the variable influence was due to an evident RE for most microbial properties.