Soil Phospholipid Fatty Acid Research Articles

Water Management-Mediated Changes in the Rhizosphere and Bulk Soil Microbial Communities Alter Their Utilization of Urea-Derived Carbon.

As one of the most important fertilizers in agriculture, the fate of urea-derived nitrogen (urea-N) in agricultural ecosystems has been well documented. However, little is known about the function of urea-derived carbon (urea-C) in soil ecosystems, especially which soil microorganisms benefit most from the supply of urea-C and whether the utilization of urea-C by the rhizosphere and bulk soil microorganisms is affected by irrigation regimes. To address this, a soil pot experiment was conducted using 13C-labeled urea to investigate changes in the composition of the rhizosphere and bulk soil microbial communities and differences in the incorporation of urea-derived C into the rhizosphere and bulk soil phospholipid fatty acids (PLFA) pool under flooded irrigation (FI) and water-saving irrigation (CI). Our results suggest that the size and structure of the rhizosphere and bulk soil microbial communities were strongly influenced by the irrigation regime. The CI treatment significantly increased the total amount of PLFA in both the rhizosphere and bulk soil compared to the FI treatment, but it only significantly affected the abundance of Gram-positive bacteria (G+) in the bulk soil. In contrast, shifts in the microbial community structure induced by irrigation regimes were more pronounced in the rhizosphere soil than in the bulk soil. Compared to the FI treatment, the CI treatment significantly increased the relative abundances of the G+ and Actinobacteria in the rhizosphere soil (p < 0.05). According to the PLFA-SIP, most of the labeled urea-derived C was incorporated into 16:1ω7c, 16:0 and 18:1ω7c under both treatments. Despite these general trends, the pattern of 13C incorporation into the PLFA pool differed between the treatments. The factor loadings of individual PLFAs suggested that 18:1ω7c, 16:1ω7c and 16:1ω5c were relatively enriched in urea-C in the bulk soil, while 17:1ω8c, i16:0 and 16:0 were relatively enriched in urea-C in the rhizosphere soil under different irrigation regimes. The loadings also confirmed that 10-me16:0, cy17:0 and cy19:0 were relatively enriched in urea-C under the CI treatment, whereas 14:0, a15:0 and 15:0 were relatively enriched in urea-C under the FI treatment. These results are helpful not only in revealing the interception mechanism of urea-C in soil but also in understanding the functions of key microbes in element cycles.

Input of high-quality litter reduces soil carbon losses due to priming in a subtropical pine forest

To date, it is unclear how differences in litter quality affect soil organic matter (SOM) decomposition through a phenomenon called 'priming effects' (PEs), especially for low-fertility forest soils under field conditions. Here, the effects of low- and high-quality leaf litter on PE and microbial metabolism of litter-derived carbon (C) were explored in a low-fertility pine (Pinus massoniana) plantation. A 185-day in situ incubation experiment was carried out by adding two 13C-labeled leaf litters to the pine soil—a low-quality (high lignin: nitrogen ratio) litter sourced from pine and a broadleaved species Schima superba produced high-quality (low lignin: nitrogen ratio) litter. To determine the key microbial groups contributing to PEs, the abundance of 13C-labeled litter enrichment in soil phospholipid fatty acids (13C-PLFAs) was quantified. We found that high-quality litter decomposed more rapidly than low-quality litter, with both litter-derived CO2 efflux reaching a plateaued level during the experimental period. Low-quality litter induced net positive PEs, while high-quality litter induced net negative PEs during the litter decomposition processes. The 13C-PLFAs results showed that bacterial groups governed the negative PEs induced by high-quality litter, whereas fungal communities targeted the positive PEs induced by low-quality litter. Random forest model and variation partitioning analysis demonstrated that the direction and magnitude of PEs were driven by litter-induced changes in key microbial groups rather than the structure of the microbial community. Our results demonstrate that microorganisms preferentially utilized litter-derived C in high-quality litter treatment and SOM in low-quality litter treatment, respectively. In contrast to low-quality litter, adding high-quality litter promoted the microbial metabolism of litter-derived C, reducing SOM decomposition (strong negative PEs). Taken together, this study provides isotope-based suggestions for the improvement of degraded pine forests—introducing tree species that produce high-quality litter may benefit soil C sequestration by reducing soil C losses due to PE in nutrient-poor pine forests.

Effects of Soil Microbiological Properties on the Fractional Distribution and Stability of Soil Organic Carbon under Different N Addition Treatments

Soil organic carbon (SOC) fractions are influenced by inputs of nitrogen (N) from globally rising N deposition; however, the mechanisms of how soil microbiological properties are influenced by N deposition and its impact on the fractional distribution and stability of SOC remain unclear. In this study, we assessed the effects on SOC fraction distribution and stability from four aspects of soil microbiological properties: soil microbial biomass (SMB), soil microbial activity, structure diversity, and functional diversity of soil microbial community in a Pinus tabuliformis plantation, which received four N addition levels (0 g N m−2 y−1 (N0), 3 g N m−2 y−1 (N3, low N addition), 6 g N m−2 y−1 (N6, mid-N addition), and 9 g N m−2 y−1 (N9, high N addition)) for 2 years. The N inputs did significantly affect some soil microbiological properties, like SMB, soil phospholipid fatty acid (PLFA), and soil microbial functional diversity. Mid- and high N addition decreased the richness (HPLFA) and evenness (EPLFA) index of the soil microbial community, from 3.24 to 2.91 and 0.93 to 0.87, respectively. In addition, the low N addition promoted the carbon management index (CMI) to 141.35, i.e., higher than the CMIs in the mid- and high-level treatments. The SOC stability also showed significant differences among N addition treatments, and SOC could be the most stable at the mid-N addition level. Regarding the effects of the four soil microbiological attributes on the CMI and stability, SMB and soil respiration positively impacted the CMI, but did not significantly affect the stability. In addition, EPLFA had positive effects, but EBIOLOG had negative effects on CMI and lability. Our findings indicate that soil microbiological properties are essential in SOC fractional distributions and stability. Further identification and study of soil microbial species used to change SOC fractions would help to clarify the detailed mechanisms involved.

Accumulation of Labile P Forms and Promotion of Microbial Community Diversity in Mollisol with Long-Term Manure Fertilization

Soil phosphorus (P) can be divided into inorganic P (Pi) and organic P (Po). Microorganisms play essential roles in soil P transformation. However, there are many ways to detect P transformation, and the relationship between P forms and microorganisms under long-term fertilization is largely unclear. In this study, soil P forms were analyzed by a chemical sequential fractionation method and solution 31P nuclear magnetic resonance (31P-NMR) technique. Phospholipid fatty acid (PLFA) contents were measured by gas chromatography as the characterization of soil microbial community structures. The objective was to determine the changes of soil P forms and associated microbial community composition in mollisol with long-term fertilization. We sampled soil from a field experiment with 26-year-old continuous maize (Zea mays L.) cropping in Northeastern China. Three fertilization treatments were selected as chemical fertilization (NPK), NPK with crop straw (NPKS), and NPK with manure (NPKM). As shown in 31P-NMR spectra, orthophosphate accounted for 62.8–85.8% of total extract P. Comparison to NPK and NPKS treatments, NPKM application notably increased the concentrations of Po, Olsen-P, orthophosphate, orthophosphate monoester, and total P. Soil P fractions including resin-Pi, NaHCO3-P, NaOH-P, and HCl-P, especially Pi fractions, were enhanced by NPKM. The amounts of total PLFAs and PLFAs in bacteria, Gram-positive (G+) and Gram-negative (G−) bacteria, actinomycetes, and fungi were high in NPKM-treated soil. The percentages of PLFAs in bacteria and fungi in total soil PLFAs were 56.8% and 9.7%, respectively, which did not show any significant difference among the treatments. NPKM increased the proportions (%) of PLFAs in G+ bacteria, and NPKS increased the proportions (%) of G− bacteria in total PLFAs. The composition of soil microbial community was found to be significantly affected by soil total carbon and pH. There was a close relationship between HCl-Pi, NaHCO3-Po, orthophosphate, and pyrophosphate with anaerobe, aerobes, and G+. Manure addition directly increased soil available P concentrations, and indirectly acted through the alterations of anaerobe, aerobes, and G+. It is concluded that long-term NPKM application would lead to the accumulation of labile P and moderately labile P in mollisol through the activity of soil microbes.

Rapid biodegradation of atrazine by a novel Paenarthrobacter ureafaciens ZY and its effects on soil native microbial community dynamic.

An atrazine-utilizing bacterium, designated as ZY, was isolated from agricultural soil and identified as Paenarthrobacter ureafaciens. The P. ureafaciens ZY demonstrated a significant degradation capacity of atrazine, with the degradation efficiency of 12.5 mg L-1 h-1 in liquid media (at pH 7, 30°C, and the atrazine level of 100 mg L-1). The P. ureafaciens ZY contained three atrazine-degrading genes (i.e., trzN, atzB, and atzC) could metabolize atrazine to form cyanuric acid, which showed lower biotoxicity than the parent atrazine as predicted by Ecological Structure Activity Relationships model. A laboratory-scale pot experiment was performed to examine the degradation of atrazine by P. ureafaciens ZY inoculation and investigate its effects on the native microbial communities. The results exhibited that the P. ureafaciens ZY was conductive to the degradation of atrazine, increased the total soil phospholipid fatty acids at the atrazine level of 50, 70, and 100 mg kg-1. By using high-throughput sequencing analysis, Frateuria, Dyella, Burkholderia-Caballeronia-Paraburkholderia were considered as the most important indigenous atrazine-degrading microorganisms due to their relative abundances were positively correlated with the atrazine degradation rate. In addition, P. ureafaciens ZY also increased the abundance of atrazine-degrading genus Streptomyces and Bacillus, indicating that there may be a synergic relationship between them in the process of atrazine degradation. Our work provides a new insight between inoculums and native microorganisms on the degradation of atrazine.

The Characteristics of Dissolved Organic Matter and Soil Microbial Communities in the Soils of Larix principis-rupprechtii Mayr. Plantations in the Qinling Mountains, China

Soil microorganisms and dissolved organic matter (DOM) play vital roles in nutrient cycling and maintaining plant diversity. The aim of this study was to clarify the relationship between DOM component characteristics and microbial community structure in the soil of Larix principis-rupprechtii Mayr. plantations. We quantified the responses of the soil microbial and DOM characteristics to stand age in a plantation forest ecosystem using phospholipid fatty acid (PLFA) analyses, ultraviolet-visible spectroscopy, and fluorescence spectroscopy. Three humic-like components and a fulvic-like component were identified from the soil samples, and humic-like substances were the dominant component of the soil DOM of the stands of different ages. The fluorescence index showed that the sources of soil DOM in the stands of different ages throughout the growth stages may be mostly plant residues, with very little contribution from microbial sources. Furthermore, the results demonstrated that stand age and growth season had a significant effect on the contents of the soil PLFA biomarkers of L. principis-rupprechtii Mayr. Additionally, significantly higher contents of different species of soil PLFA biomarkers were observed in the young forest (17a) than in the sapling forest (7a) and half-mature forest (27a), suggesting that stand age differences in the quality and quantity of larch litter and soil physicochemical characteristics affect the microbial community structure. Redundancy analysis (RDA) showed that changes in the soil DOM quality and components that were driven by growth season and stand age were the major drivers of variations in the soil microbial community structure in the study region. Overall, the seasonal variations in DOM quality and components may contribute to the variability of soil microorganisms, and the soil microbial responses to tree age will depend upon the provisioning of these resources.

Effects of Mulching and Slow-release Fertilizer Application Reduction on Soil Microbial Community Structure in Rapeseed Field Under Two Different Rainfall Conditions

In order to investigate the effects of furrow and ridge rainwater harvesting, straw mulching, and reduced and slow-release fertilizer on soil microbial community structure of rapeseed, a two-year field study was conducted in rainy (2016-2017) and drought (2017-2018) seasons, which included three cultivation patterns:1 conventional flat planting, 2 straw mulching, and 3 ridge-furrow rainfall harvesting system and four fertilization patterns:1 conventional fertilization (100% of the amount), 2 reduced slow-release fertilizer Ⅰ (80% of the amount), 3 reduced slow-release fertilizer Ⅱ (60% of the amount), and 4 no fertilizer. The results indicated that it was rainy in 2016-2017, with seasonal drought during the nutritional growth stage in 2017-2018. The two technologies (straw mulching+80% slow-release fertilizer, J80 and ridge-furrow rainfall harvesting system+80% slow-release fertilizer, M80) were beneficial to boost the soil microbial activity. J80 and M80 increased the microbial biomass carbon by 9.94% and 10.32% and microbial biomass nitrogen by 2.38% and 1.19%, respectively, compared with that of the local cultivation pattern under two different climate conditions. The total amount of microbial phospholipid fatty acid (PLFA) decreased by 30.75% in the rainy year compared with that in the drought year, and mulching technology could effectively increase the total amount of soil PLFA. The PLFA contents of soil bacteria and fungi in the rainy year were 33.67% and 53.21%, respectively, lower than those in the drought year. However, the PLFA content of actinomycetes increased by 13.04%. Microbial communities were sensitive to abnormal precipitation. The bacteria/fungi ratio increased in rainy weather. The drought climate heighted the ratio of straight chain saturated fatty acid/straight chain monounsaturated fatty acid and straight chain monounsaturated fatty acid/cyclopropane acid. In conclusion, adopting the optimal cultivation technologies can stabilize the soil microenvironment under abnormal precipitation, relieve water and nutrient stress, and provide an effective means for rapeseed sustainable development.

Adaptive multi-paddock grazing increases soil nutrient availability and bacteria to fungi ratio in grassland soils

Grasslands are used extensively for grazing livestock, and variation in grazing management may affect the soil microbial community and ecosystem functions, such as nutrient cycling, in grasslands. In particular, adaptive multi-paddock (hereafter ‘multi-paddock’) grazing is considered a regenerative grazing management practice that can improve the sustainability of grasslands. However, little is known about how multi-paddock grazing affects the soil microbial community, which plays an importance role in global biogeochemical cycling. In this study, grassland soils were collected from 15 ranch pairs located across the Canadian prairie, where, in each pair, one ranch practiced multi-paddock grazing while the other practiced conventional grazing (varying from continuous to slow to fast rotational grazing). We used soil phospholipid fatty acid (PLFA) profiles to quantify microbial functional groups, and measured microbial biomass C and soil properties. Our data show that microbial PLFA abundances and microbial biomass C was not different between the two grazing systems. However, multi-paddock grazing resulted in lower ratios of microbial biomass C: N (MBC:MBN), fungi: bacteria (F:B) and Gram-positive: Gram-negative bacteria in grassland soils compared to conventional grazing. Further investigation of specific management metrics revealed that MBC:MBN and F:B ratios were most affected by cattle stocking rate and stocking density, respectively. Thus, there is potential to affect soil function by altering the composition of soil microbial communities through multi-paddock grazing.

Crop\u2013livestock integration enhanced soil aggregate-associated carbon and nitrogen, and phospholipid fatty acid

Integrated crop–livestock (ICL) production enhances diversification and provides ecosystem benefits by improving nutrient cycling and energy efficiency, thus, increasing overall farm productivity. However, a detailed study is needed to understand the influence of crop diversification and grazing animals on soil aggregation and associated carbon (C) and nitrogen (N), and microbial properties, especially compared with a grazed native pasture. We investigated the soil aggregate size distribution and associated C and N fractions, glomalin-related soil protein, and soil phospholipid fatty acid (PLFA) to understand the collective influence of livestock grazing of crop residue and cover crops (CC) and compared it with native pasture and non-grazed traditional production systems. The study was conducted in South Dakota at four different locations consisting of three long-term (> 30 years) on-farm sites: 1 (Salem), 2 (Bristol), 3 (Bristol) with three treatments that included ICL (corn, Zea Mays L.-soybean, Glycine max L.-oats, Avena sativa L.-CC with cattle grazing); natural ecosystem (NE) or native pasture; and control (CNT) (corn–soybean-without grazing or CC). Experimental site 4 (Beresford) with study duration of 3-year consisted of oats, oats with CC, oats with CC + grazing, and grazed pasture mix. Soil samples were collected from 0 to 5 cm depth at all four sites in summer 2019. Data showed that at sites 1 and 2, ICL had significantly (P ≤ 0.5) greater fractionation of 0.053–0.25 mm and > 4 mm aggregates compared with NE and CNT. At site 1, ICL showed significantly higher soil organic carbon (SOC, 36–49%) and higher nitrogen (33–44%) in > 4 mm aggregates than NE and CNT. At site 2, ICL had 32–41% higher SOC than NE and CNT for 0.25–0.5 mm aggregates. At site 1, NE enhanced total phospholipid fatty acid (PLFA), total bacterial biomass, gram (+), gram (−) bacteria than CNT, however, it did not vary significantly than ICL. Grazed pasture mix at site 4 had higher total PLFA (40.81 nmol g−1 soil) than the other treatments. The principal components 1 and 2 accounted for 33% and 22% of the variation, respectively, where the majority of the microbial compositions and aggregate-associated C and N were influenced by ICL and NE compared with corn–soybean without grazing or short-term oats/CC/grazing treatments. Integrated crop–livestock system and NE enhanced C and N concentrations in macroaggregates as well as in microaggregates. It is concluded that ICL and NE systems are sustainable prospects in enhancing overall soil health. Integrating crop and livestock improved physicochemical and microbial properties compared to the traditional corn–soybean system.

Impacts of short-term tillage and crop residue incorporation managements on soil microbial community in a double-cropping rice field

Soil microbial community were usually reconsidered as a sensitive indicator in soil quality and soil environment change of paddy field. However, the effects of different tillage and crop residue incorporation managements on soil bacterial community under the double-cropping rice cropping system were still need to further investigated. Therefore, the impacts of different tillage and crop residue incorporation managements on soil bacterial community under the double-cropping rice cropping system in southern of China were studied by using phospholipid fatty acids (PLFAs) profile method in the present paper. The experiment included four different tillage treatments: rotary tillage without crop residue input as a control (RTO), no-tillage with crop residue retention (NT), rotary tillage with crop residue incorporation (RT), and conventional tillage with crop residue incorporation (CT). Compared with RTO treatment, grain yield of rice with NT, RT and CT treatments increased by 1.21%, 3.13% and 6.40%, respectively. This results showed that soil aC15:0, C16:0, iC17:0, C19:0c9, 10 fatty acids with CT and RT treatments were higher than that of RTO treatment, while soil C16:1ω6c and C18:1ω9t fatty acids with NT treatment were higher than that of RTO treatment, respectively. Soil G+ and G− bacteria PLFAs contents with CT treatment were higher than that of NT, RT and RTO treatments, while the value of soil G+/G− bacteria PLFAs with NT treatment were higher than that of CT, RT and RTO treatments. This results indicated that Richness and McIntosh indices with CT treatment were significantly higher than that of RTO treatment. Principal component analysis (PCA) results showed that the first and second principal components (PC1 and PC2) were explained 93.2% of total variance with all tillage treatments. Except C12:0, C14:0 2OH and C18:2ω6, all unsaturated and cyclopropyl PLFAs contents were belong to PC1. PC1 and PC2 were explained 88.4% of total variance with all tillage treatments. There had significantly positive correlation between soil Richness, Shannon indices and soil PLFAs, G+ bacteria, G− bacteria, fungi contents. As a result, it were benefit practices for increasing soil bacterial community structure in the double-cropping rice field of southern China by combined application of rotary, conventional tillage with crop residue incorporation managements.

Cropping management in a livestock-pasture-crop integration modifies microbial communities, activity, and soil health score.

Understanding indicators of soil health is crucial for developing agricultural systems that are sustainable and climate resilient. Labile soil carbon (C), microbial properties, and nutrient status are all incorporated into the Haney Soil Health Tool with the goal of summarizing several indicators into one index. Monthly soil samples from an integrated crop-livestock system in Central Texas were collected from 2017 to 2019. Fields represented a range of management practices, including cover crops, no-till, rotational grazing, and a native prairie remnant. Soil samples were analyzed for total C, water-soluble C, macro- and micronutrient content and bioavailability, and phospholipid fatty acids (PLFAs). Microbial activity was determined via a 24-h CO2 incubation. Soil health score, C, and PLFAs were well correlated with each other. The greatest total PLFA (219.5nmol g-1 soil) and organic C (54.3g kg-1 soil) were found in the native prairie, and the lowest were found in the unfertilized continuous-corn system (60.5nmol PLFAs g-1 soil and 24.0g organic C kg-1 soil). Of all agroecosystems, the perennial grazing system (soil health score, 24.7) was most similar to the native prairie (soil health score, 27.4), having high soil C and a large microbial community. Of the row cropping systems, the no-till system approached the perennial systems better than the conventional till and unfertilized conventional till (soil health score, 11.1 vs. 8.0 and 5.3, respectively). This study highlights the value of perennial grass grazing in agroecosystems and appropriate best management practices. Expanding this analysis to other sites may provide additional insight.

Interaction between ciliate and plant growth promoting bacteria influences the root structure of rice plants, soil PLFAs and respiration properties

Plant growth and productivity depend on the complex and dynamic interaction between the plant roots and soil microorganisms. At present, the research on rhizosphere associated microbes is largely focused on bacteria and fungi; whereas the interaction of soil protists with plants and other microbes remains unexplored. The present study aimed to investigate the interactive impact of a ciliate (Kreyellidae, C5) and two plant growth-promoting bacteria (PGPB) i.e., Pseudomonas sp. (Ps) and Enterobacter sp. (Ec), on the growth of rice plants, soil microbial community composition and soil chemical properties. It was observed that the protist-PGPB interaction significantly modified the root structure leading to an enhanced outgrowth of lateral roots (272.08%–380.41%) and seminal roots (190.40%–250.45%), in addition to an increase in the primary root length (p < 0.05). The phospholipid fatty acid (PLFA) analysis indicated a striking shift in the overall soil microbial communities, especially in the Gram negative bacterial community and fungi, which were found to be decreased in treatments due to the presence of a predator. The combined ciliate-bacterial treatments further increased the microbial carbon biomass to 223.59% and 310.57% as compared to control and PGPB treatments respectively. A similar enhancement of dehydrogenase enzyme activity was observed in soil samples of rice plants on combined treatments. In contrast, the alkaline phosphatase and fluorescein diacetate enzyme activities were recorded to be more in soil samples treated with PGPB. The combined treatment of rice plants also enhanced the uptake of N and P moderately, as compared to PGPB treated plants. The colony-forming unit and most probable number were found to be significantly higher in PGPB treated soil and combined treatments (Tukey's HSD, p < 0.05). In conclusion, this is the first study that demonstrates significant modification of root structure and increased nutrient uptake by rice plants through interaction between ciliate and PGPB.

Phospholipid fatty acids in soil\u2014drawbacks and future prospects

The current opinion and position paper highlights (1) correct assignation of indicator phospholipid fatty acids (PLFA), (2) specificity and recycling of PLFA in microorganisms, and (3) complete extraction and detection of PLFA. The straight-chain PLFA 14:0, 15:0, 16:0, and 17:0 occur in all microorganisms, i.e., also in fungi and not only in bacteria. If the phylum Actinobacteria is excluded from the group of Gram-positive bacteria, all remaining bacteria belong to the bacterial phylum Firmicutes, which should be considered. The PLFA 16:1ω5 should be used as an indicator for the biomass of arbuscular mycorrhizal fungi (AMF) as there is no experimental evidence that they occur in marked amounts in Gram-negative bacteria. Fungal PLFA should embrace the AMF-specific 16:1ω5. In the presence of plants, ergosterol should be used instead of the PLFA 18:2ω6,9 and 18:1ω9 as fungal indicators for Mucoromycotina, Ascomycota, and Basidiomycota. The majority of indicator PLFA are not fully specific for a certain microbial group. This problem might be intensified by recycling processes during decomposition to an unknown extent. Soil handling and extraction conditions should be further optimized. The reliability and accuracy of gas chromatographic separation need to be regularly checked against unintentional variations. PLFA analysis will still be of interest over the next decades as an important independent control of DNA-based methods.

Response of potato yield, soil chemical and microbial properties to different rotation sequences of green manure-potato cropping in North China

Continuous cropping of potato (Solanum tuberosum L.) can result in soil degradation and yield decline. These negative effects could be alleviated by crop rotation. Green manure-potato rotation is being proposed as an alternative that can sustain high yield and soil quality in potato production system. However, the mechanisms by which biotic and abiotic factors are affected by different cropping sequences remain unclear. A 12-year green manure (G)-potato (P) rotation experiment was conducted to explore the response of potato yield, soil chemistry properties, and microbial community composition to different rotation sequences in North China, the cropping sequence treatment included 2-year of green manure and 1-year of potato (P1G2), 1-year of green manure and 2-year of potato (P2G1), and continuous cropping potato (P3), with a rotation period of 3-year. The content of NH4+-N (AN), organic matter (OM), available potassium (AK), total phospholipid fatty acids (PLFAs), and bacterial PLFAs in soil, and potato yield were higher in P1G2 compared with those in P2G1 and P3, while the ratio of fungal to bacterial biomarkers was decreased significantly than that in P3. Soil dominant bacterial phyla Bacteroidetes, Gemmatimonas, Proteobacteria, and Nitrospirae presented higher abundance in P1G2 relative to those in P2G1 and P3; however, phyla Actinobacteria decreased significantly in P1G2 than other two treatments. The beneficial microflora Sphingomonas, Haliangium, Gemmatimonas, and Pseudogymnoascus increased significantly in P1G2 over P2G1 and P3, and the pathogenic fungal Fusarium, Stagonosporopsis, Alternaria, and Lectera showed higher abundance in P3 than P1G2 and P2G1. The redundant analysis showed that soil AN, OM, AP, and AK were positively correlated with dominant flora of bacteria and fungi in P1G2, and were negatively correlated with dominant flora of bacteria and fungi in P3. Partial least squares path modeling revealed that the conversion of cropping sequences had a direct positive effect on the fungal community rather than the bacterial community. Overall, the rotation cropping combined green manure and potato attained higher potato yield by maintaining higher soil fertility and healthy ecosystem, we also gave a suggestion on rotation sequences combined yield and economic benefits of potato.

Pyrolysis-assisted transesterification for accurate quantification of phospholipid fatty acids: Application to microbial community analysis in 1000-years paddy soil chronosequence

Phospholipid fatty acids (PLFAs) are widely used to assess soil microbial community and metabolic activity in variousenvironmentalsamples. However, the transesterification of phospholipids into PLFAs still utilize homogeneous acid/alkaline catalyst, which may increase environment risk. This study developedand validated an accurate method for the determination of PLFAs in soil utilizing pyrolysis-assisted transesterification with diatomaceous earth. The thermolysis behavior of phospholipids, optimal pyrolysis conditions, tolerance against impurities, and recyclability of porous material were evaluated. Under optimal conditions, the transesterification can complete in only 8 min, with high impurity tolerance. The repeatability (relative standard deviation (RSD) between 2.59% and 12.12%), reproducibility (RSD between 5.22% and 16.22%), and linearity (r between 0.9259 and 0.9999) were excellent. This method was applied to analyze the PLFAs to evaluate microbial community of 1000-years paddy soil chronosequences and the relationships among soil chemical properties, enzyme activities and microbial community composition. Soil microbial biomass PLFAs increased significantly over time followed by slight fluctuation at 60–1000 years, but the ratios of soil fungal to bacterial and gram-positive to gram-negative PLFAs remained constant. In addition to soil total N and organic matter, soil enzyme activities related to N cycling metabolism also positively significantly influenced microbial communities. Overall, the developed PLFAs method using pyrolysis-assisted transesterification was environmentally friendly, efficient, accurate, stable, and suitable alternative to acid/alkaline transesterification of phospholipids.

Variations in soil microbial communities in the sedge-dominated peatlands along an altitude gradient on the northern slope of Changbai Mountain, China

The mechanisms that shape soil microbes in peatlands along the altitude gradient remain unresolved due to limited data and inconsistent findings along different vertical vegetation belts from investigations. In this study, we present results of soil phospholipid fatty acids (PLFAs) profiles from an altitude gradient survey (300–1500 m) in Changbai Mountain aimed at determining the elevational patterns of soil microbial communities and their driving forces in the sedge-dominated peatlands. The results showed that the total microbial lipid biomass in the sedge-dominated peatlands increased with altitude. However, there were no obvious trends with altitude in ratios of the fungi to bacteria (F/B), the Gram positive bacteria to Gram negative bacteria (G+/G-), and the bacteria to actinomycetes (B/ACT). Redundancy analysis indicated that the dissolved organic carbon (DOC) explained most variation in soil microbial groups, while mean annual temperature (MAT) explained most variation in microbial community structure. Variation partitioning analysis revealed that climatic factors had greater influences on soil microbial community structure than soil physical and chemical properties, and 53% of the total variance was explained by MAT, mean annual precipitation (MAP) and their combined effects. This finding challenges the prevailing view that local soil properties, but not climate, control soil microbial community structure along the altitude gradient, and enhances our understanding of the role of soil microbes as carbon pumps in sedge-dominated peatlands in the process of global warming.

High C-and N-based soil fertility and microbial associations sustain the plant biodiversity of the campo rupestre in Brazil

The campo rupestre vegetation in the Serra do Rola Moça State Park (PESRM) grows on ironstone outcrops, forming vegetation islands where plant species establish belowground interactions. This area is circumscribed by several mining companies and, for mined land rehabilitation purpose, we assessed plant species composition, plat-microbial associations, and soil fertility patterns in a preserved campo rupestre. Aside from high plant biodiversity, we found elevated soil fertility in relation to soil CEC (~18 cmol/dm3), organic matter (~115 g/Kg), soil C (~ 53.3 g/Kg), humic (~12.5 g/Kg) and fulvic (~8.9 g/Kg) acids, soil N (~4 g/kg) and a low C:N ratio (~12). The overall nutrient levels were higher than or comparable to those of other preserved sites in Brazil. The prevalent legume Mimosa calodendron, hosting N-fixing and plant growth-promoting bacteria in its nodules, was considered an N source to the soil, as evidenced by the elevated leaf N content and the greater depletion of leaf δ15N compared to other families. However, leaf N was parsimoniously distributed among biogeochemical islands and within different plant species and families, which was attributed to a common mycorrhizal network (CMN) formed by arbuscular (AMF) and orchid mycorrhizal fungi (OMF), suggested by general root mycorrhizal colonisation and soil phospholipid fatty acid (PLFA) analyses. We revealed that a high C- and N-based soil fertility constitutes a natural pattern of fertility, which is maintained by below-ground associations and is sufficient to sustain plant biodiversity. For rehabilitation purposes, this natural soil fertility of preserved sites should be maintained by integrating the biogeochemical relations involving plant communities and microbial associations.

Studying greenhouse gas emissions through interactions between phospholipid fatty acid content and soil properties of alpine grassland soil in Northern Tibet, China

This study aimed to gain a better understanding of the carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes due to soil microbial community and soil physicochemical factors in Northern Tibet, China. We selected five types of grassland soils, incubated them under controlled temperature and humidity conditions, and analyzed the relationship between soil greenhouse gas (GHG) emissions and soil phospholipid fatty acids (PLFAs), soil bulk density, pH, soil organic carbon (SOC), dissolved organic carbon total nitrogen (TN), and total inorganic nitrogen content. The results showed that GHG emissions varied across different types of alpine grassland soils. The highest GHG fluxes occurred in alpine meadows, while the lowest fluxes occurred in alpine deserts, which could be explained based on the soil nutrient contents, including SOC and TN. In total, 23 microbial biomarker PLFAs were extracted from five types of alpine grassland soils to model the relationships between PLFAs and GHG emissions (or absorption) using backward regression analysis, over a three-month incubation experiment. Bacterial groups were responsible for CO2 emissions, while the initial quantities of bacteria and the fungi: bacteria ratio influence N2O emissions. Soils were the CH4 sink, and CH4 amount was influenced by the initial quantities of methane-oxidizing bacterial biomarkers (18:1ω5c) in Northern Tibet. Therefore, our findings showed that the microbial community structure and soil properties jointly explains the variation in soil GHG fluxes under specific environmental condition.

Organic carbon, total nitrogen, and microbial community distributions within aggregates of calcareous soil treated with biochar

Soil aggregate exerts an important part in carbon turnover as well as soil nutrients. Biochar (BC) has considerable potential as a soil amendment in enhancing the levels of soil total organic carbon (TOC) and total nitrogen (TN), as well as the microbial activity. However, it remains largely unclear about whether BC plus chemical fertilisers have synergistic effect on the soil properties within aggregates. In the present study, the 2-year field experiment was performed for examining distributions of TOC, TN, and microbial community compositions in the aggregate fractions in calcareous soil fertilised with BC and/or chemical fertilisers. The treatments comprised the application of no fertiliser (CK), chemical fertilisers (NPK), biochar (BC), and biochar plus chemical fertilisers (BC+NPK). Our study suggested that the BC+ NPK treatment evidently enhanced the stability of aggregates (MWD) compared to other treatments. Compared with CK and NPK treatments, all BC-amended treatments elevated the TOC level in bulk soil and within each aggregate fraction by 12.99–126.40%, of which, 2–0.25 mm fraction displayed the largest increase. Similar increases in the TN level by 23.95–52.66% were observed in bulk soil and within 2–0.25 mm fraction. Moreover, all NPK-amended treatments significantly elevated the total PLFAs in bulk soil and within each fraction compared with CK. The BC+ NPK treatments dramatically elevated the relative fungal abundance and fungi/bacteria ratio in bulk soil and within > 2 mm fraction relative to CK and NPK treatments, similar increases were observed in the 2–0.25 mm fraction following the application of BC alone. In addition, the 2–0.25 mm fraction showed the greatest levels of TN, TOC, C/N ratio, along with total phospholipid fatty acids (PLFAs). Redundancy analysis (RDA) revealed that the soil TN content is the primary parameter that affects microbial community compositions within aggregates. The present study indicated that the application of BC in combination with NPK fertilisers can serve as an efficient approach to improve soil structure and micro-ecological environment, as well as to enhance TOC and N storage in the aggregate fractions of calcareous soil.

Keystone species affect the relationship between soil microbial diversity and ecosystem function under land use change in subtropical China

AbstractSoil microbial diversity affects soil chemical cycling and ecosystem function. However, how highly connected keystone species regulate associated microbial structure and function (of the whole community and of specialized species), irrespective of their abundance under land use change, remains unresolved.Here, we identified the relationship between microbial diversity [soil phospholipid fatty acid (PLFA) richness and composition, and ammonia‐oxidizing archaea and bacteria (AOA and AOB) communities] with both a broad (i.e. microbial respiration) and specialized function (i.e. nitrification rate) in a woodland, shrubland and adjacent cropland in subtropical China.Microbial respiration was significantly positively related to the microbial richness, but negatively correlated with the keystone species richness across different land use types. The relationships between biodiversity and the broad ecosystem function varied with land use, with a stronger relationship in the afforested land compared with in the cropland. In contrast to the broad function, land use did not significantly affect the specialized function, but the specialized function was positively related to AOA richness in the cropland. Additionally, the specialized function was predominately driven by the keystone species composition in AOA and AOB communities and indirectly regulated by soil environmental factors (particularly soil temperature) across land uses.Overall, our results provide direct experimental insight into the mechanisms underlying the role of the keystone species in regulating below‐ground ecosystem functions under land use change. In particular, our findings reveal that the broad function is maintained by the niche compensation effect, while the specialized function is maintained by the identity effect.A freePlain Language Summarycan be found within the Supporting Information of this article.