Phospholipid Fatty Acid Analysis Research Articles

Adaptive multi-paddock grazing increases mineral associated soil carbon in Northern grasslands

Grassland soils play an important role in sequestering carbon (C) and are primarily used for livestock grazing. Grazing management can increase the amount of C stored in soils and the distribution of C in different soil fractions by altering soil microbial community structure, thereby influencing the persistence of soil C over time. Adaptive multi-paddock grazing (AMP), grazing cattle at high stock densities with long periods between grazing events, is considered to enhance grassland sustainability, productivity, and soil C compared to more conventional grazing practices (continuous to slow rotational). However, whether and how AMP grazing might affect the amount of C stored in different soil fractions has received little attention. Soil samples (0–15 cm depth) were collected from 24 ranches in a paired design, where 12 ranches practiced AMP grazing and 12 neighboring ranches practiced conventional grazing. Soil organic C (SOC) and total nitrogen were measured in different soil particle size [fine (<53 µm), medium (53–250 µm) and coarse (>250 µm)], and density [light (>1.6 g cm−3), and heavy (<1.6 g cm−3)] fractions. Soil bacterial and fungal biomass and abundances were obtained from phospholipid fatty acid analysis. Mean weights of soil microaggregates and heavy fractions were higher in soil exposed to AMP grazing, whereas mean weights of macroaggregates and light fractions were higher in conventionally grazed soils. In warmer and drier climatic conditions, SOC in both bulk soils and within various size and density fractions tended to decrease. Soil organic C (both concentration and stock) were significantly higher in the fine soil fractions under AMP management than conventionally grazed grasslands. Given that SOC in fine fractions, is more mineral associated and recalcitrant, our results indicate that AMP grazing increased the size of the stable SOC pool. The increased carbon pool in the fine fraction was associated with greater fungal to bacterial ratios, suggesting a possible biological mechanism for the increase. Overall, the results indicate that AMP grazing may be beneficial for sequestering more stable carbon that helps mitigate the effects of climate change.

The Diversity and Composition of Soil Microbial Communities Differ in Three Land Use Types of the Sanjiang Plain, Northeastern China.

In recent years, the Sanjiang Plain has experienced drastic human activities, which have dramatically changed its ecological environment. Soil microorganisms can sensitively respond to changes in soil quality as well as ecosystem function. In this study, we investigated the changes in soil microbial community diversity and composition of three typical land use types (forest, wetland and cropland) in the Sanjiang Plain using phospholipid fatty acid analysis (PLFA) technology, and 114 different PLFA compounds were identified. The results showed that the soil physicochemical properties changed significantly (p < 0.05) among the different land use types; the microbial diversity and abundance in cropland soil were lower than those of the other two land use types. Soil pH, soil water content, total organic carbon and available nitrogen were the main soil physico-chemical properties driving the composition of the soil microbial community. Our results indicate that the soil microbial community response to the three different habitats is complex, and provide ideas for the mechanism by which land use changes in the Sanjiang Plain affect the structure of soil microbial communities, as well as a theoretical basis for the future management and sustainable use of the Sanjiang plain, in the northeast of China.

Ancient prairies as a reference for soil organic carbon content and microbial community structure

The historic remnant prairies of Missouri display diversity above and below the soil surface and represent the few remaining acres of unconverted grassland habitat in the state. The soil microbiome is foundational to nutrient acquisition, resource partitioning, and ecosystem resilience; therefore, the intact plant-soil interactions of remnant prairies can serve as a reference for microbial community structure and ecosystem services lost due to land conversion. This research was conducted to show the importance of reference soil conditions and the variability that lies therein while contrasting degraded soil ecosystems to provide a standard to which comparable soils should be held. In this study, 35 sites across Missouri representing three prairie management conditions on similar soils and variable climatic conditions were compared to assess differences in the microbial community structure and biomass using phospholipid fatty acid (PLFA) analysis. Surface (0–7.5 cm) soil organic carbon (SOC) content provided a measure of substrate available to support microbial community health. Total microbial biomass, the biomass of individual microbial groups, selected biomarker ratios, and SOC, were significantly different across treatments and highest in remnant prairies apart from Saprophytic fungi and eukaryotes. This study demonstrated that the soil microbial community in reconstructed and restored prairie systems remained significantly diminished in biomass relative to remnant prairies, even after several decades. This study highlights the need to preserve remnant prairies, where soil is in its native state under native flora and abiotic conditions. These results also illustrate the importance of selecting remnant systems as the ecological reference standard for prairie lands.

Soil carbon dynamics in drained prairie pothole wetlands

Drainage leads to trade-offs between crop production efficiency and wetland conservation, with complex impacts on ecosystem services. In North America’s Prairie Pothole Region, wetland drainage is widespread, often to increase the available land for cultivation, prevent crop loss due to flooding, and manage soil salinity. Wetlands are known for providing key ecosystem services such as improved water quality, flood mitigation, and carbon storage. There is limited research on how changes to soil hydrology and soil redistribution through wetland drainage can impact soil carbon storage and persistence in this region. This research evaluates factors that contribute to soil carbon storage in drained prairie pothole wetland based on 33 drained wetlands in Saskatchewan, Canada. These analyses showed regional differences in the response of soil carbon storage to drainage that are driven by environmental factors such as annual precipitation, temperature, and wetland permanence. We observed increasing soil carbon storage from the Dark Brown to Black soil zones, as well as with longer wetland pond permanence. The sampling depth used for calculating soil carbon storage was especially important when comparing geographically across the soil zones as the Black soil zone had greater soil carbon stored at depth. Soil carbon was also intensively monitored over 2 years following installation of surface drainage across a wetland complex (8 drained wetlands) where water was partially directed to a consolidation wetland. We further assessed changes in soil carbon dynamics and protection from microbial decomposition based on three soil organic matter fractions, ATR-FTIR for organic matter functional groups, and phospholipid fatty acid analysis to understand the microbial community abundance and structure. After 2 years following drainage, ephemeral wetlands with short pond permanence were found to be most sensitive to drainage and the only wetland class with decreases in soil carbon. The temporary and seasonal wetland classes showed no significant differences in soil carbon content but there were changes in the organic matter with depth due to soil redistribution during drainage implementation. Jointly, this research provides region-specific estimates of soil carbon storage in drained prairie pothole wetlands that can be used to inform wetland soil carbon management in cultivated fields.

Bacterial and fungal communities in sub-Arctic tundra heaths are shaped by contrasting snow accumulation and nutrient availability.

Climate change is affecting winter snow conditions significantly in northern ecosystems but the effects of the changing conditions for soil microbial communities are not well-understood. We utilized naturally occurring differences in snow accumulation to understand how the wintertime subnivean conditions shape bacterial and fungal communities in dwarf shrub-dominated sub-Arctic Fennoscandian tundra sampled in mid-winter, early, and late growing season. Phospholipid fatty acid (PLFA) and quantitative PCR analyses indicated that fungal abundance was higher in windswept tundra heaths with low snow accumulation and lower nutrient availability. This was associated with clear differences in the microbial community structure throughout the season. Members of Clavaria spp. and Sebacinales were especially dominant in the windswept heaths. Bacterial biomass proxies were higher in the snow-accumulating tundra heaths in the late growing season but there were only minor differences in the biomass or community structure in winter. Bacterial communities were dominated by members of Alphaproteobacteria, Actinomycetota, and Acidobacteriota and were less affected by the snow conditions than the fungal communities. The results suggest that small-scale spatial patterns in snow accumulation leading to a mosaic of differing tundra heath vegetation shapes bacterial and fungal communities as well as soil carbon and nutrient availability.

Microbial mechanisms of organic matter mineralization induced by straw in biochar-amended paddy soil

Combined straw and straw-derived biochar input is commonly applied by farmland management in low-fertility soils. Although straw return increases soil organic matter (SOM) contents, it also primes SOM mineralization. The mechanisms by which active microorganisms mineralize SOM and the underlying factors remain unclear for such soils. To address these issues, paddy soil was amended with 13C-labeled straw, with and without biochar (BC) or ferrihydrite (Fh), and incubated for 70 days under flooded conditions. Compound-specific 13C analysis of phospholipid fatty acids (13C-PLFAs) allowed us to identify active microbial communities utilizing the 13C-labeled straw and specific groups involved in SOM mineralization. Cumulative SOM mineralization increased by 61% and 27% in soils amended with Straw + BC and Straw + Fh + BC, respectively, compared to that with straw only. The total PLFA content was independent of the straw and biochar input. However, 13C-PLFAs contents increased by 35–82% after biochar addition, reflecting accelerated microbial turnover. Compared to that in soils without biochar addition, those with biochar had an altered microbial community composition-increased amounts of 13C-labeled gram-positive bacteria (13C-Gram +) and fungi, which were the main active microorganisms mineralizing SOM. Microbial reproduction and growth were susceptible to nutrient availability. 13C-Gram + and 13C-fungi increased with Olsen P but decreased with dissolved organic carbon and NO3-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{NO}}_{3}^{ - }$$\\end{document} contents. In conclusion, biochar acts as an electron shuttle, stimulates iron reduction, and releases organic carbon from soil minerals, which in turn increases SOM mineralization. Gram + and fungi were involved in straw decomposition in response to biochar application and responsible for SOM mineralization.Graphical

Parental material and climate jointly determine the biomass and diversity of soil microbial communities along an elevational gradient on a subtropical karst mountain

AbstractAimClimate is widely understood to determine elevational patterns of soil microbial communities, whereas the effects of parental material are uncertain. Changes in the composition of parental materials along elevational transects could also affect soil microbial communities by influencing soil pH and nutrient availability. Here, we aim to illustrate the combined effects of climate and parental material on the biomass and composition of soil microbial communities along an elevational transect.LocationA subtropical forest on a karst mountain (Mt. Jinfo), China.TaxonBacteria and Fungi.MethodsWe use phospholipid fatty acid analysis (PLFA) and DNA amplicon high‐throughput sequencing to determine biomass and diversity patterns of soil microbial communities along a subtropical elevational gradient with contrasting parental materials (limestone and clasolite).ResultsWe observed that the microbial communities were more diverse (α‐diversity) and productive (biomass) on limestone than on clasolite. Additionally, we found that parental material played a role in shaping the composition (β‐diversity) of soil microbial communities along the elevational gradient. The impact of climate on soil microbial communities was found to be significant, albeit relatively weak. Structural equation models provided evidence for both direct and indirect effects of climate and parental material on microbial biomass and α‐diversity along the elevational gradient. Notably, the changes in soil pH, influenced by both parental material and climate, were identified as a key factor driving these effects.Main ConclusionsOur results underline the importance of both climate and parental material variations in space‐for‐time studies investigating soil microbial communities along elevational gradients.

Farm‐level variability in soil biological health indicators in Michigan is dependent on management and soil properties

AbstractSoil biology is vital for maintaining productivity, enhancing soil health, and creating resilient agroecosystems. However, many questions remain on how microbial communities are impacted by different soil properties and management practices, especially on grower‐managed fields. This study examined soil biological health properties (0–15 cm) and field history data from 310 grower‐managed fields within Michigan between Fall 2019 and Spring 2021. The objectives were to evaluate the impact of soil texture, tillage, and crop diversity on microbial populations and examine the relationship between soil health indicators and microbial community. Phospholipid fatty acid analysis was used to estimate total microbial abundance and composition of broad taxonomic groups like bacteria, fungi, arbuscular mycorrhizal fungi, actinomycetes, and eukaryotes. Other soil health indicators measured were organic carbon, permanganate oxidizable carbon, potentially mineralizable nitrogen, phosphorus, calcium, potassium, magnesium, and water‐stable aggregation. Soil texture did not significantly influence microbial community except for actinomycetes, which were significantly higher in fine‐textured soils. Tillage had the largest influence on microbial communities, with significantly lower values for all microbes in tilled compared to no‐till fields. Crop diversity had a minimal impact, affecting only arbuscular mycorrhizal fungi and eukaryote populations. All measured soil health indicators were positively associated with microbial populations except for phosphorous, which had a negative correlation (r = −0.56 to −0.66). Overall, we conclude that tillage is the dominant driver of soil biological health on grower‐managed fields across Michigan. Consequently, adoption of no‐till management practices where possible can help restore soil health and long‐term sustainability in agroecosystems.

Microbial strategies for phosphorus acquisition in rice paddies under contrasting water regimes: Multiple source tracing by 32P and 33P

Microbial acquisition and utilization of organic and mineral phosphorus (P) sources in paddy soils are strongly dependent on redox environment and remain the key to understand P turnover and allocation for cell compound synthesis. Using double 32/33P labeling, we traced the P from three sources in a P-limited paddy soil: ferric iron-bound phosphate (Fe-P), wheat straw P (Straw-P), and soil P (Soil-P) in microbial biomass P (MBP) and phospholipids (Phospholipid-P) of individual microbial groups depending on water regimes: (i) continuous flooding or (ii) alternate wetting and drying.32/33P labeling combined with phospholipid fatty acid analysis allowed to trace P utilization by functional microbial groups. Microbial P nutrition was mainly covered by Soil-P, whereas microorganisms preferred to take up P from mineralized Straw-P than from Fe-P dissolution. The main Straw-P mobilizing agents were Actinobacteria under alternating wetting and drying and other Gram-positive bacteria under continuous flooding. Actinobacteria and arbuscular mycorrhiza increased P incorporation into cell membranes by 1.4–5.8 times under alternate wetting and drying compared to continuous flooding. The Fe-P contribution to MBP was 4–5 times larger in bulk than in rooted soil because (i) rice roots outcompeted microorganisms for P uptake from Fe-P and (ii) rhizodeposits stimulated microbial activity, e.g. phosphomonoesterase production and Straw-P mineralization. Higher phosphomonoesterase activities during slow soil drying compensated for the decreased reductive dissolution of Fe-P. Concluding, microbial P acquisition strategies depend on (i) Soil-P, especially organic P, availability, (ii) the activity of phosphomonoesterases produced by microorganisms and roots, and (iii) P sources – all of which depend on the redox conditions. Maximizing legacy P utilization in the soil as a function of the water regime is one potential way to reduce competition between roots and microbes for P in rice cultivation.

Shifts in microbial community composition and metabolism correspond with rapid soil carbon accumulation in response to 20 years of simulated nitrogen deposition

Anthropogenic nitrogen (N) deposition and fertilization in boreal forests frequently reduces decomposition and soil respiration and enhances C storage in the topsoil. This enhancement of the C sink can be as strong as the aboveground biomass response to N additions and has implications for the global C cycle, but the mechanisms remain elusive. We hypothesized that this effect would be associated with a shift in the microbial community and its activity, and particularly by fungal taxa reported to be capable of lignin degradation and organic N acquisition. We sampled the organic layer below the intact litter of a Norway spruce (Picea abies (L.) Karst) forest in northern Sweden after 20 years of annual N additions at low (12.5 kg N ha−1 yr−1) and high (50 kg N ha−1 yr−1) rates. We measured microbial biomass using phospholipid fatty-acid analysis (PLFA) and ergosterol measurements and used ITS metagenomics to profile the fungal community of soil and fine-roots. We probed the metabolic activity of the soil community by measuring the activity of extracellular enzymes and evaluated its relationships with the most N responsive soil fungal species. Nitrogen addition decreased the abundance of fungal PLFA markers and changed the fungal community in humus and fine-roots. Specifically, the humus community changed in part due to a shift from Oidiodendron pilicola, Cenococcum geophilum, and Cortinarius caperatus to Tylospora fibrillosa and Russula griseascens. These microbial community changes were associated with decreased activity of Mn-peroxidase and peptidase, and an increase in the activity of C acquiring enzymes. Our results show that the rapid accumulation of C in the humus layer frequently observed in areas with high N deposition is consistent with a shift in microbial metabolism, where decomposition associated with organic N acquisition is downregulated when inorganic N forms are readily available.

Comparison of cover crop termination methods for small-scale organic vegetable production: effect on soil fertility and health

Termination methods and the timing of the termination of the cover crops are critical factors determining the efficacy of cover crops in improving soil fertility and quality. We hypothesized that different termination methods will produce varying quantities of organic residue which will affect microbial diversity and thereby nutrient cycling and availability. The objective of this study was to compare termination methods (roller-crimper, flail mowing, rotary mowing, sickle bar mowing, and occultation using black tarps) for fall-grown cover crop combination (hairy vetch-cereal rye) under organic vegetable production. Field experiments were carried out in three consecutive years (2018–2021) and soil samples were collected from 0 to 15 cm and processed for analysis. Soil organic matter content, nutrients, health parameters, enzymes, and microbial diversity were measured. Flail mowing significantly enhanced the potentially mineralizable nitrogen, available phosphorus, and active carbon. Total Phospholipid Fatty Acid (PLFA) analysis showed a 24% increase for flail mowed, 17% for rotary mowed, and 15% for sickle bar mowed termination methods. There was a significant increase in active carbon content which ranged from 38.9% (rotary mowed), 25.4% (sickle bar mowed), 23.5% (flail mowed), 16.4% for crimper rolled method, and with 2.8% (occultation) respectively. Individual termination methods had varying effects on select enzyme activities. Results indicated that integrating cover crops has the potential to modify soil microbial community structure and increase soil enzyme activities. In this study, flail mowing appeared to be a good method for managing cover crops of choice in terms of soil microbial functionality and fertility.

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.

An assessment of soil microbial community environmental stress in alpine marginal ecosystems using microbial indicators

Alpine marginal ecosystems above the natural tree line are considered to be the most vulnerable habitats for maintaining local biodiversity. The soil microbial community is crucial for ecosystem stability and function. However, our comprehension of the overall soil microbial community in alpine marginal ecosystems remains limited, particularly regarding environmental stress. We selected the Baima Mountain National Nature Reserve (BMNNR) in the northwest Yunnan provinces as our study area and collected soil samples from three different depth layers, in alpine marginal ecosystems. The phospholipid fatty acid (PLFA) analysis method was utilized to evaluate alterations in soil microbial communities. The results showed that: (1) the PLFA content gradually decreased with increasing soil depth; (2) on the whole, the variations in PLFA across alpine marginal ecosystems were obviously, the highest in alpine meadow (AM) and the lowest in alpine screes (AS); (3) the site effect exerted a greater direct influence than microhabitat effect and elevation (0–5 cm, 32 %, 16 % and 9 %, respectively; 20–40 cm, 46 %, 29 % and 0 %, respectively), with the direct impact of elevation decreasing as soil depth increased (0–5 cm, 5–20 cm and20-40 cm, 9 %, 1 % and 0 %, respectively); and (4) the ratio of cyclopropyl to precursors (Cy:Pre) in all communities was > 0.1, indicating that the soil microbial community was under environmental stress. This study demonstrates the potential of PLFA analysis to profile soil microbial communities and their stress status under field conditions and also provides a better understanding of the correlation between soil microbial communities and the function and health of alpine marginal ecosystems.

Composts of diverse green wastes improve the soil biological quality, but do not alleviate drought impact on lettuce (Lactuca sativa L.) growth

AbstractIntense soil cultivation and climate change have detrimental effects on soils. Solutions are needed to improve the biological quality and water holding capacity of agricultural soils. A greenhouse experiment was conducted to investigate the interactive effect of compost application and drought stress on a soil/plant system in order to determine the improvement of soil quality and plant growth and the alleviation of drought stress. Lettuce (Lactuca sativa L.) was grown under greenhouse conditions in a sandy soil with sufficient mineral fertilizer application to test the effect of five compost types (three made from municipal garden and park wastes with differing nutrient contents, one from municipal household waste, and one from farm plant residues) applied at 30 Mg ha−1 dry weight, with which we compared soil quality and plant growth to soil without compost application. Treatment pots were irrigated or subjected to drought conditions during the last 14 days of lettuce growth. Assays of potential N mineralization during 28 days, dehydrogenase and β‐glucosidase activities, and a phospholipid fatty acid (PLFA) analysis were performed to assess effects on soil biological quality. Gas exchange, leaf relative water content, biomass, nitrogen accumulation, and root tip growth of lettuce were measured to investigate compost and drought stress effects on lettuce physiology. All composts improved indices of soil biological quality significantly, except for fungal abundance, relative to soil without compost. The greatest increase was obtained from farm compost, which significantly increased potential nitrogen (N) mineralization and soil enzyme activities of β‐glucosidase and dehydrogenase by factors of 4, 2, and 43, respectively. Furthermore, soil with farm compost generally showed a higher abundance of soil microbial organisms compared with soil without compost, which could be related to its high cellulose and hemicellulose contents. The lowest abundance of microbial organisms was generally found in soil with garden and park waste compost with a medium nutrient content, which could be related to its low organic matter content. The beneficial effect of compost on soil biological quality did not lead to improved lettuce growth, which suggests that soil biological quality (ameliorated by compost application) is not important for a fast‐growing crop, such as lettuce, that is sufficiently fertilized. Drought stress reduced aboveground lettuce biomass, root tip growth, and the abundance of most soil microbial groups significantly, but compost in soil did not alleviate these negative effects. In conclusion, the farm compost made from grass–clover, straw, and vegetable residues is superior to garden and park waste and household waste composts in terms of beneficial effects on soil biological quality. Compost clearly improved soil biological quality, but did not influence lettuce's response to drought stress. The knowledge gained in this study is useful for producing tailor‐made compost with desired effects of improved soil biological quality.

Investigating the Climate Mitigation Performance of A Green Roof System in the Flint Hills Ecoregion, USA

Rooftop green infrastructure enhances sustainable urban development by reducing atmospheric CO2 as carbon is sequestered in plants and substrates. However, it is uncertain what substrate types, depths, and plant combinations sequester the greatest amounts of carbon in green roofs across different ecoregions, including the U.S. Great Plains. This research sought to evaluate carbon sequestration potential of two experimental green roof beds of 10 cm (4 in) and 20 cm (8 in) and two substrate types in Manhattan, Kansas, USA. Microbial and root biomass and their interactions were measured as early indicators of changes in soil organic carbon (SOC). Soil and root biomass samples were taken from beds of two depths with two substrates (K and R) and three plant communities (all sedum, sedum and grass, and native grasses and forbs) for a total of 48 plots. Microbial biomass was measured by phospholipid fatty acids (PLFA) analysis in 2019 and root biomass in 2020. Root biomass and microbial biomass was greater in native grass in shallower beds. Shallower beds can partially offset the need for deeper beds and should perform well in mitigating climate change if beds are irrigated during very dry periods.

Biodegradation of aliphatic polyurethane foams in soil: Influence of amide linkages and supramolecular structure

Polyurethane (PU) foams are classified as physically nonrecyclable thermosets. The current effort of sustainable and eco-friendly production makes it essential to explore methods of better waste management, for instance by modifying the structure of these frequently used polymers to enhance their microbial degradability. The presence of ester links is known to be a crucial prerequisite for the biodegradability of PU foams. However, the impact of other hydrolysable groups (urethane, urea and amide) occurred in PU materials, as well as the supramolecular structure of the PU network and the cellular morphology of PU foams, is still relatively unexplored.In this work, fully aliphatic PU foams with and without hydrolyzable amide linkages were prepared and their aerobic biodegradation was investigated using a six-month soil burial test. Besides the variable chemical composition of the PU foams, the influence of their different supramolecular arrangement and cellular morphologies on the extent of biodegradation was also evaluated. Throughout the soil burial test, the release of carbon dioxide, and enzyme activities of proteases, esterases, and ureases were measured. At the same time, phospho-lipid fatty acids (PLFA) analysis was conducted together with an assessment of microbial community composition achieved by analysing the genetic information from the 16S rRNA gene and ITS2 region sequencing.The results revealed a mineralization rate of 30–50 % for the PU foams, indicating a significant level of degradation as well as indicating that PU foams can be utilized by soil microorganisms as a source of both energy and nutrients. Importantly, microbial biomass remained unaffected, suggesting that there was no toxicity associated with the degradation products of the PU foams. It was further confirmed that ester linkages in PU foam structure were easily enzymatically cleavable, while amide linkages were not prone to degradation by soil microorganisms. In addition, it was shown that the presence of amide linkages in PU foam leads to a change in the supramolecular network arrangement due to increased content of hard segments, which in turn reduces the biodegradability of PU foam. These findings show that it is important to consider both chemical composition and supramolecular/macroscopic structure when designing new PU materials in an effort to develop environmentally friendly alternatives.

Beyond PLFA: Concurrent extraction of neutral and glycolipid fatty acids provides new insights into soil microbial communities

The analysis of phospholipid fatty acids (PLFAs) is one of the most common methods used to quantify the abundance, and analyse the community structure, of soil microbes. The PLFA extraction method can yield two additional lipid fractions—neutral lipids and glycolipids—which potentially hold additional, valuable information on soil microbial communities. Yet its quantitative sensitivity on complete neutral lipid (NLFA) and glycolipid fatty acid (GLFA) profiles has never been validated. In this study we tested (i) if the high-throughput PLFA method can be expanded to concurrently extract complete NLFA and GLFA profiles, as well as sterols, (ii) whether taxonomic specificities of signature fatty acids are retained across the three lipid fractions in pure culture strains, and (iii) whether NLFAs and GLFAs allow soil-specific fingerprinting to the same extent as PLFA analysis. By adjusting the polarity of chloroform with 2% ethanol for solid phase extraction, pure lipid standards were fully fractionated into neutral lipids, glycolipids, and phospholipids. Sterols eluted in the neutral lipid fraction, and a betaine lipid co-eluted with phospholipids. We found consistent taxonomic specificities of fatty acid markers across the three lipid fractions by analysing pure culture extracts representative of soil microbes. Fatty acid profiles from soil extracts, however, showed stronger differences between PLFAs, NLFAs, and GLFAs than between soil types. This indicates that PLFAs and NLFAs signify different community properties (biomass vs. carbon storage, putatively), and that GLFAs are sensitive markers for community traits which behave differently than PLFAs. Although we consistently found high abundances of characteristic sterols in fungal extracts, the PLFA extraction method only yielded miniscule amounts of ergosterol from soil extracts. We argue that concomitant measurement of fatty acid profiles from all three lipid fractions is a low-effort and potentially information-rich addition to the PLFA method, and discuss its applicability for soil microbial community analyses.

No-till annual wheat increases plant productivity, soil microbial biomass, and soil carbon stabilization relative to intermediate wheatgrass in a Mediterranean climate

As interest in the production of perennial grain crops increases, it is critical to quantify differences in above ground biomass (AGB) productivity and soil carbon stabilization potential between annual and perennial grain crops, and to understand the factors determining these relationships. This study measured the effects of crop type and nitrogen (N) fertilization on AGB, soil microbial biomass, and soil carbon while controlling for the effect of tillage in rainfed annual and perennial grain crops in a Mediterranean climate. AGB and associated soil samples from tilled annual wheat (Triticum aestivum), no-till annual wheat, and intermediate wheatgrass [Kernza ® (Thinopyrum intermedium)] (IWG) were collected annually across three years under various N fertilization rates. We quantified AGB yields, soil microbial biomass (via phospholipid fatty acid analysis), permanganate oxidizable carbon (POXC) and mineralizable soil carbon (MinC). Across N rates and years, IWG yielded approximately 25% less AGB than tilled and no-till annual wheat (p ≤ 0.001). The lack of soil disturbance in no-till wheat and IWG contributed foremost to greater soil microbial biomass in the topsoil by year three of the experiment (p < 0.1). Crop type and the associated AGB productivity had the greatest influence on whether microbial communities trended toward stabilizing versus mineralizing soil carbon. More specifically, higher soil carbon stabilization processes were primarily driven by the increased plant productivity of tilled and no-till annual wheat compared to IWG. Within the annual wheat systems, lack of tillage also contributed to soil carbon stabilization, but primarily in the top 30 cm of soil. Compared to the other treatments, no-till annual wheat resulted in 25% (IWG) and 36% (tilled annual wheat) greater soil microbial biomass in the top 30 cm by the final year of the experiment and had higher soil carbon stabilization potential than IWG at 0–15 and 15–30 cm and tilled annual wheat at 0–15 cm across time (p ≤ 0.01). This was achieved by matching tilled annual wheat in aboveground biomass productivity and IWG in lack of soil disturbance. Results from this study suggest that no-till annual wheat is better suited than tilled annual wheat or IWG to increase soil microbial biomass and soil carbon stabilization in shallow soil, while maintaining stable aboveground biomass yields over time in a Mediterranean climate.

Organic fertilizers incorporation increased microbial necromass accumulation more than mineral fertilization in paddy soil via altering microbial traits

Long-term fertilization is considered as the most effective practice in organic C accrual in intensively managed paddy soils. However, the contribution and mechanism of microbial necromass C for soil organic C accrual, and the effective incremental component in paddy soils under the different fertilization remain unclear. To address the knowledge gap, we collected soils from a 31-year long-term fertilization paddy field including no fertilization (control), mineral fertilizers alone (NPK), mineral fertilizers plus rice straw incorporation (NPK + S), and mineral fertilizers plus manure incorporation (NPK + M). Living microbial biomass and their necromass were quantified by the biomarker analysis of phospholipid fatty acids and amino sugars, respectively. Results showed that the three fertilization treatments significantly increased the bacterial and fungal biomass in both 0–10 and 10–20 cm layers, which were universally greatest in NPK + M. The microbial necromass C was little affected by 31-year mineral fertilization; however, mineral combined organic fertilizers incorporation greatly stimulated microbial necromass C accumulation. Besides, soil treated with NPK + M showed 3.55 ± 0.12 g kg−1 higher accumulation of microbial necromass C than NPK + S, because manure application increased the abundance of Gram-positive r-strategy bacteria (mainly Firmicutes and Actinobacteria), and enriched filamentous fungi (Ascomycota). Compared to the control, the increase in the microbial necromass C contribution to SOC was lowest in NPK and highest in NPK + M, mainly derived from the variation in the contribution of bacterial necromass. Consequently, this study suggested long-term mineral combined manure application in subtropical paddy fields could effectively increase soil C sequestration by strengthening microbial necromass accumulation. Bacterial and fungal necromass C accrual was closely associated with living microbial biomass and their community structure. Given the C sequestration potential of manure in paddy soil, as the crucial resource of livestock and poultry waste in this region, it should be incorporated into subtropical agricultural ecosystems.

Earthworm-invaded boreal forest soils harbour distinct microbial communities

Abstract. Earthworm invasion in North American forests has the potential to greatly impact soil microbial communities by altering soil physicochemical properties, including structure, pH, nutrient availability, and soil organic matter (SOM) dynamics. While most research on the topic has been carried out in northern temperate forests, little is known about the impact of invasive earthworms on soil microbial communities in hemiboreal and boreal forests, characterized by a slower decay of organic matter (OM). Earthworm activities can increase OM mineralization, altering nutrient cycling and biological activity in a biome where low carbon (C) and nitrogen (N) availability typically limits microbial and plant growth. Here, we characterized and compared microbial communities of earthworm-invaded and non-invaded soils in previously described sites across three major soil types found in the Canadian (hemi)boreal forest using a space-for-time approach. Microbial communities of forest floors and surface mineral soils were characterized using phospholipid fatty acid (PLFA) analysis and metabarcoding of the 16S rRNA gene for bacteria and archaea and of the internal-transcriber-spacer-2 (ITS2) region for fungi. In forest floors, the effects of earthworm invasion were minor. In mineral soil horizons, earthworm invasion was associated with higher fungal biomass and greater relative abundance of ectomycorrhizal fungi. Oligotrophic bacteria (Acidobacteriota and Chloroflexi) were less abundant in invaded mineral soils, where Gram(+) : Gram(−) ratios were also lower, while the opposite was observed for the copiotrophic Bacteroidota. Additionally, earthworm-invaded mineral soils harboured higher fungal and bacterial species diversity and richness. Considering the important role of soil microbial communities for ecosystem functioning, such earthworm-induced shifts in their community composition are likely to impact nutrient cycling, as well as vegetation development and forest productivity at a large scale, as the invasion progresses in these (hemi)boreal systems.