Fungal Phospholipid Fatty Acid Research Articles

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.

Long-term fertilization affects microbial necromass accumulation by regulating nutrient and enzymatic stoichiometry in a calcareous Fluvisol

Microbial necromass accumulation through rhizodeposition plays a critical role in increasing the stable soil organic carbon pool, which is greatly affected by fertilization. However, the legacy effects of long-term fertilization on microbial necromass accumulation remain unclear. Here, we selected a calcareous Fluvisol treated with no fertilizer (Ctrl), P and K fertilizers (PK), N and K fertilizers (NK), and N, P and K fertilizers (NPK) for 34 years and conducted a 12-week microcosm experiment with simulated daily rhizodeposition to disentangle the legacy effects of long-term fertilization on microbial necromass accumulation. We measured soil C, N and P contents and C-, N- and P-acquiring extracellular enzyme activities and analyzed phospholipid fatty acids (PLFAs) and amino sugars to indicate microbial biomass and necromass, respectively. We found that compared with the Ctrl and NK treatments, the PK and NPK treatments significantly decreased the C:N and C:P ratios and the net accumulation of microbial necromass but significantly increased the ratios of C- to N- and C- to P-acquiring enzyme activities and the fungal PLFAs abundance in soils. The net accumulation of microbial necromass was positively correlated with soil nutrient stoichiometry (mainly the C:N and C:P ratios) but negatively correlated with soil enzymatic stoichiometry (mainly the ratios of C- to N- and C- to P-acquiring enzyme activities) and the fungal to bacterial PLFA ratio. Taken together, these results suggest that long-term fertilization has legacy effects on microbial necromass accumulation and that fertilization-induced changes in nutrient and enzymatic stoichiometry regulate microbial necromass accumulation through rhizodeposition in the calcareous Fluvisol.

Long‐term grazing intensity by reindeer alters the response of the soil micro‐food web to simulated climate change in subarctic tundra

Top–down control by nematodes over soil microorganisms – considered to be stronger over bacteria than over fungi – may dampen microbial responses to global changes in tundra. To test whether large grazers alter the responses of belowground trophic networks to global changes, we employed factorial warming and nitrogen fertilization treatments in adjacent sites with different reindeer grazing intensities for the past 50 years. Lightly grazed tundra is dominated by dwarf shrubs and a more fungal‐based microbial community, while in heavily grazed tundra the high reindeer densities during autumn migration have induced a shift into graminoids and a more bacterial‐based microbial community. We analysed the soil micro‐food web (i.e. the nematode density, trophic structure and species composition) as well as fungal, bacterial and total phospholipid fatty acids (PLFAs) after four growing seasons of warming and fertilization both before and during reindeer migration. We predicted that bacterivore densities are higher and fungivore densities lower under heavy than light grazing (i.e. nematode populations before migration reflect grazing effects via the base of the food web), whereas reindeer migration induces a negative impact on nematode densities under heavy grazing (disturbance by trampling is the driving factor). We further predicted that nematodes negate treatment effects on microbial biomass to a stronger extent in the bacterial‐based heavily grazed tundra than in the fungal‐based lightly grazed tundra. Fungivore densities were higher under light than under heavy grazing, but nematodes did not respond to trampling. Warming increased fungivores and the fungal PLFAs irrespective of grazing and timing but, under heavy grazing, it increased bacterivores while the bacterial PLFAs remained steady. Fertilization increased carnivores and influenced nematode species composition, diversity and maturity interactively with warming. Our data suggest that large grazers affect tundra soil nematodes via bottom–up effects through microbial community composition and biomass, which in turn may alter the strength of their top–down control over soil bacteria under climate warming.

The effect of prescribed fires on abiotic and biotic factors in the southern region of Puerto Rico

Field fires can modify soil nutrient cycling and alter soil microbial communities (SMC), although the latter is not well understood. In the southern region of Puerto Rico, field fires have become a significant problem during the dry season. To mimic the effects of a field fire, we performed prescribed fires on a hillside at the Juana Díaz Agricultural Experiment substation in October 2015 and March 2017. A complete randomized block design was established in Yauco soil (Typic calciustolls) that included the following treatments: negative control (unburned), positive control (burned plots, no remediation), mulching treatment (burned plots remediated with Leucaena spp. mulch), and surfactant treatment (burned plots remediated with a surfactant). In the first burning (2015), soil samples were collected before burning and at 30, 180, and 420 days after burning (DAB). In the second burning (2017), soil samples were collected at 30, 90, and 270 DAb. soil physicochemical properties and microbial community structure were assessed using phospholipid fatty acid (PLFA) analysis. Overall, burning increased soil exchangeable Ca2+ (except after 30 DAB in the second burning) and decreased exchangeable K+ when compared to unburned soils. compared to unburned plots, total fungal PLFA was significantly lower in burned plots with or without mulch and surfactant treatments, and total bacterial PLFA did not differ between burned and unburned plots after 30 days. Total microbial biomass was significantly (P<0.05) higher in mulch and surfactant treated burned soil compared to unburned and burned plots without treatment after 90 DAB (2017) and 420 (2015) DAB. The use of mulch and surfactant treatments in prescribed burning fields increased microbial communities 90 DAB. This study emphasizes short-term changes in microbial communities and suggests they are highly resilient to disturbances after prescribed fires.

Variations in diversity, composition, and species interactions of soil microbial community in response to increased N deposition and precipitation intensity in a temperate grassland

BackgroundGlobal climate change has resulted in precipitation regimes exhibiting an increasing trend in rainfall intensity but a reduction in frequency. In addition, nitrogen (N) deposition occurs simultaneously in arid and semi-arid regions. Microbial biomass, diversity, composition, and species interactions are key determinants of ecological functions. We examined the effects of changes in precipitation intensity and N addition on the soil bacterial and fungal communities in a semi-arid grassland in Inner Mongolia, China.MethodsThe microbial biomass (bacterial PLFAs and fungal PLFAs) was determined through phospholipid fatty acid (PLFA) analysis, and microbial diversity (Shannon index and evenness index) was determined with high-throughput sequencing (16S and ITS). Species interactions were determined using a molecular ecological network analysis. The relationships between microbial community (bacterial community and fungal community) and environmental variables were examined by Mantel tests.ResultsWe found that N addition decreased fungal PLFA under moderate, high, and extreme precipitation intensity treatments and increased fungal community complexity under the high precipitation intensity treatment. Furthermore, N addition increased bacterial diversity under moderate and high precipitation intensity treatments. N addition caused greater environmental stress to the fungal community, which was dominated by deterministic processes.ConclusionsThe effects of N deposition on soil bacterial and fungal communities were altered by precipitation intensity. The changes in soil bacterial and fungal communities were different, implying that composition and functional traits adapt differently to projected global changes at a regional scale.

Effect of two broad-spectrum fungicides on the microbial communities of a soil subjected to different degrees of water erosion

The impact of both fungicide and water erosion on soil microbial communities has been little studied, and far less in subhumid-dry climates. To help fill this knowledge gap, we evaluated the influence of two broad-spectrum fungicides applied to soil subjected to different degrees of water erosion on microbial population and function. Soil samples were taken from an experimental site under three water erosion levels: an agricultural land subjected to minimum water erosion by terrace farming (MIN), an agricultural land subjected to moderate water erosion without terrace farming (MOD), and a land with no water erosion control treatment (non-eroded, NON). Three dosages of both carbendazim and iprodione were applied to microcosms, and the responses of microbial community and function were examined after 30-day exposure. Phospholipid fatty acid (PLFA) analysis, soil enzyme activities, and microbial abundances estimated by quantitative real-time PCR (qPCR) were used to evaluate the impact of carbendazim and iprodione fungicides applied at three dosages on microbial community structure and enzyme activities. The lowest values of fluorescein diacetate hydrolase (FDA), dehydrogenase, urease, and glucosidase activities were registered in soil under moderate erosion, while the highest ones were observed in non-eroded soils. Both carbendazim and iprodione decreased C- and P-related activities, even when those fungicides were applied at field rate doses. Thus, phosphomonoesterase, glucosidase, and xylosidase in soil treated with fungicides applied at recommended field rate decreased by 46 %, 61 %, and 34 % compared to soil without fungicide application. The lowest values of PLFA biomarkers for Gram-positive bacteria, Gram-negative bacteria, and arbuscular mycorrhizal fungi were registered in soils treated with the highest dose of both carbendazim and iprodione. Thus, Gram-positive bacteria, Gram-negative bacteria, arbuscular mycorrhizal fungi, and fungal PLFA biomarkers in soils without fungicide application were about 36 %, 3 %, 47 %, and 82 % higher than those soils treated with the highest doses of fungicides, respectively. In addition, the highest doses of fungicide application tended to greater decrease total PLFAs in both non-eroded and minimum eroded compared to moderate eroded soils. Similarly, the response of bacterial and fungal populations to fungicide treatment was more pronounced in non-eroded soils than in eroded soils. This study illustrates how the interactions between fungicides and water erosion levels affect soil enzyme activities, microbial abundances, and microbial community structure in agroecosystems.

Nonlinear effects of biochar on greenhouse gas emissions and soil microbial community composition under intensive vegetable production in South China

Biochar amendment in agroecosystems is proposed to mitigate the greenhouse (GHG) emissions and enhance multiple ecosystem services. However, it remains unclear whether and how various biochar amendment rates can influence soil microbial communities linking with GHG mitigation. In a two-year field experiment with five biochar amendment rates (0, 10, 20, 30 and 40 Mg ha−1), we determined cumulative GHG emissions, soil physiochemical properties and soil microbial community composition base one total phospholipid fatty acids (PLFA) under intensive vegetable production from Ultisols in southern China. Results showed that biochar amendment significantly decreased cumulative N2O emissions by 40–66 % during the whole study period (p < 0.01), whereas effects on CH4 emissions were inconsistent across the two study years. In addition, biochar amendment significantly decreased PLFAs and fungi/bacteria ratio by 4–31 % and 12–39 %, respectively. Annual global warming potential (GWP) was effectively reduced by biochar amendment, and random forest analysis showed that soil pH, C/N, humic acid (HA) and fungal PLFAs exhibited the highest mean predictor importance. The nonlinear correlations between the biochar amendment rate and GHG emissions mainly caused by soil pH, and the 20 Mg ha−1 biochar amendment rate was recommended because it produced the lowest GWP with the lowest economic costs. These findings demonstrated that various biochar amendment rates can differently alter GHG emissions and microbial properties under intensive vegetable production, which can provide new insights on optimal biochar amendment rates for GHG mitigation in agricultural production in China.

Changes in vineyard soil parameters after repeated application of organic-inorganic amendments based on spent mushroom substrate

The changes of physicochemical and biochemical parameters of a silty loam (S1) and sandy loam (S2) vineyard soils added with spent mushroom substrate (SMS) or SMS composted with ophite (OF) as rock dust (SMS + OF) were studied. Two doses of SMS or SMS + OF (25 and 100 Mg ha−1) were applied for two consecutive years (2020–2021) and changes of soil physicochemical parameters, and dehydrogenase activity (DHA), respiration (RES), microbial biomass (BIO), and the phospholipid fatty acids (PLFAs) profile were assayed on a temporal basis. The results showed an increase in soil organic carbon (OC) content, total and mineralised N, P, and K, especially when the highest SMS dose was applied to soils. Repeated application caused OC content over time up to 2.3 times higher than initial content in the silty loam soil. This increase was not observed in sandy soil, possibly due to a higher bioavailability of OC, as indicated by the evolution of extractable humic acid/fulvic acid pools. In both soils, all biochemical parameters increased after amendment, being favoured both by the OC and by the presence of OF. Significant positive correlations were found between DHA, RES and BIO, and OC content especially in the first part and then levelled off after the second dose application. Total bacterial or fungal PLFAs patterns reflected the variation of BIO by SMS application. The higher growth of fungi vs. bacterial community in amended soils was recorded after the first SMS application, although the opposite effect occurred after the second application, with similar results in both soils. The findings indicate that the application of SMS or SMS + OF in vineyard soils could be an appropriate agronomic management practice for maintaining soil sustainability, although doses and application times of these amendments should first be evaluated depending on soil texture.

Elevated ozone decreases the multifunctionality of belowground ecosystems.

Elevated tropospheric ozone (O3 ) affects the allocation of biomass aboveground and belowground and influences terrestrial ecosystem functions. However, how belowground functions respond to elevated O3 concentrations ([O3 ]) remains unclear at the global scale. Here, we conducted a detailed synthesis of belowground functioning responses to elevated [O3 ] by performing a meta-analysis of 2395 paired observations from 222 publications. We found that elevated [O3 ] significantly reduced the primary productivity of roots by 19.8%, 16.3%, and 26.9% for crops, trees and grasses, respectively. Elevated [O3 ] strongly decreased the root/shoot ratio by 11.3% for crops and by 4.9% for trees, which indicated that roots were highly sensitive to O3 . Elevated [O3 ] impacted carbon and nitrogen cycling in croplands, as evidenced by decreased dissolved organic carbon, microbial biomass carbon, total soil nitrogen, ammonium nitrogen, microbial biomass nitrogen, and nitrification rates in association with increased nitrate nitrogen and denitrification rates. Elevated [O3 ] significantly decreased fungal phospholipid fatty acids in croplands, which suggested that O3 altered the microbial community and composition. The responses of belowground functions to elevated [O3 ] were modified by experimental methods, root environments, and additional global change factors. Therefore, these factors should be considered to avoid the underestimation or overestimation of the impacts of elevated [O3 ] on belowground functioning. The significant negative relationships between O3 -treated intensity and the multifunctionality index for croplands, forests, and grasslands implied that elevated [O3 ] decreases belowground ecosystem multifunctionality.

Contrasting Effect of Thinning and Understory Removal on Soil Microbial Communities in a Subtropical Moso Bamboo Plantation

Thinning and understory clearance are among the two most popular forest management practices carried out to improve stand productivity in subtropical plantations. Unfortunately, studies have not fully explored the single and combination effect of thinning and understory clearance on soil microbial properties. By conducting a field manipulation experiment in a subtropical moso bamboo (Phyllostachys edulis) plantation in Southern China, we assessed the effects of thinning, understory clearance, and their combination on soil microbial phospholipid fatty acids (PLFAs) three years after treatments were first applied. We also examined the changes in soil properties after thinning and/or understory clearance. Thinning decreased soil fungal and bacterial PLFAs, and consequently soil total microbial PLFAs due to the increased soil NH4+-N, and NO3−N concentrations. Understory clearance decreased soil pH and soil water content resulting in increased soil fungal PLFAs and the ratio of soil fungal to bacterial (F:B). In addition, thinning and understory clearance caused apparent interactive effects on soil total microbial PLFAs and bacterial PLFAs, and the negative influence of thinning on soil total microbial and bacterial PLFAs were partly compensated by understory clearance. These results suggest the contrasting and interactive effect of thinning and understory clearance should be considered to assess the changes of soil microbial community and ecological processes in subtropical moso bamboo (Phyllostachys edulis) plantations in southern China.

Meta-analysis of the impacts of phosphorus addition on soil microbes

Soil microbes play a crucial role in myriad ecological processes in terrestrial ecosystem. With increasing nitrogen (N) loading, phosphorus (P) may become more limiting for soil microbes and these processes. However, it remains unclear to what extent P addition impacts soil microbial communities and respiration at global scale, especially under different N loadings. Therefore, we used a global meta-analysis to examine the effects of phosphorus addition on soil microbes based on 2293 paired observations from 129 studies in the world. Overall, P addition increased significantly total as well as fungal, bacterial, and actinomycete (ACT) phospholipid fatty acids (PLFAs), together with Gram+ bacteria (G+) and Gram- bacteria (G-) abundance regardless of N input or not. The increments were more pronounced under higher P addition rate or places with higher mean annual temperature or mean annual precipitation. Moreover, the fungi: bacteria ratio significantly decreased along elevational gradients. Furthermore, higher P addition frequency tended to have significantly more ACT PLFAs, as well as higher G+:G-, but significantly lower fungi: bacteria ratio (F:B). However, the responses of P addition on bacterial PLFAs and F:B were larger in forest than grassland, and cropland and varied with P fertilizer forms. In addition, the responses of soil organic carbon (SOC) contents was positively correlated with those of microbial biomass carbon (MBC) and bacterial PLFAs, and all these three parameters, in addition to fungal PLFAs, correlated positively with the response of soil respiration (Rs). Our results suggest that phosphorus addition had globally positive effects on soil microbes with different N loadings, and the positive effects of soil microbial abundance tended to promote heterotrophic respiration (Rh) and Rs. These results deepen our understanding of soil microbial community structure and function dynamics under increasing P deposition. They also provide extensive evidences and bases for parameterization of soil carbon cycling models incorporating microbial responses under global climate change.

Effects of land use on soil microbial community structure and diversity in the Yellow River floodplain

Abstract Soil microorganisms and their diversity are important bioindicators of soil carbon and nutrient cycling. Land use type is a major determining factor that influences soil microbial community composition in floodplain ecosystems. However, how the structure and diversity of soil microbial communities respond to specific changes in land use, as well as the main drivers of these changes, are still unclear. This study was conducted in the Yellow River floodplain to examine the effects of land use type on soil microbial communities. Four land use types (shrubland, farmland, grassland and forest) were selected, wherein shrubland served as the baseline. We measured soil microbial structure and diversity using phospholipid fatty acids (PLFAs). Land use type significantly affected total, bacterial and fungal PLFAs, and the gram-positive/negative bacterial PLFAs. Compared with shrubland, peanut farmland had higher total and bacterial PLFAs and forest had higher fungal PLFAs. Soil pH and phosphorus were the predominate drivers of microbial PLFAs, explaining 37% and 26% of the variability, respectively. Soil total nitrogen and nitrate nitrogen were the main factors increasing microbial community diversity. Peanut farmland had the highest soil carbon content, soil carbon stock, total PLFAs and microbial diversity, suggesting that farmland has great potential as a carbon sink. Our findings indicated that peanut farmland in the Yellow River floodplain is critical for maintaining soil microbial communities and soil carbon sequestration.

Soil nutrients and nutrient ratios influence the ratios of soil microbial biomass and metabolic nutrient limitations in mountain peatlands

Soil microbes regulate the storage of carbon (C) in peatlands, which is facilitated by nutrients. To date, few researchers have examined the spatial distribution of soil microbial biomass, microbial community structure, and their metabolic nutrient limitations in mountain peatlands at different altitudes. This study aimed to improve the knowledge of how and why soil microbial biomass and their metabolic nutrient limitations varied with altitude. We investigated the phospholipid fatty acids (PLFAs) and enzymatic stoichiometry in surface (0–20 cm) and subsurface (20–50 cm) soil from peatlands with different types of vegetation in the Changbai Mountains. Overall, the soil microbial PLFAs were higher in the sedge-dominated peatlands than in the shrub/Sphagnum-dominated peatlands. The soil microbial PLFAs in the sedge-dominated peatlands were elevated at high altitudes but decreased with altitude in the shrub/Sphagnum-dominated peatlands. The soil fungal/bacterial ratios (F/B) in the surface soil increased with altitude in the sedge-dominated peatlands but not in the shrub/Sphagnum-dominated peatlands. The Gram-positive/Gram-negative bacteria ratios (G+/G−) in the surface soil decreased with altitude in the sedge-dominated and shrub/Sphagnum-dominated peatlands. The soil F/B ratios were higher, but the G+/G− ratios were lower in the shrub/Sphagnum-dominated peatlands than in the sedge-dominated peatlands. The soil pH and nutrient ratios explained most of the differences in soil bacterial and fungal PLFAs, respectively. However, the total nutrients of soil were the primary regulators of soil F/B and G+/G−. The soil microbial activities suffered from C- and phosphorus (P)- limitations in the mountain peatlands. The limitations were worse in the shrub/Sphagnum-dominated peatlands than in the sedge-dominated peatlands. The P limitations were greater at high altitude than at low altitude in both types of peatlands. The C and P limitations on soil microbial metabolism were primarily controlled by soil physical properties and nutrient ratios, respectively.

Characteristics of Microbial Utilization for Crop Residue-Derived C in Paddy and Upland Soils

Two typical subtropical agricultural soils, a flooded paddy soil and its adjacent upland, were collected and then incubated with or without 13C-labeled crop residue (maize straw) for 40 days. During the incubation, the mineralization rate of the crop residue was monitored, and the 13C incorporated into fungal and bacterial phospholipid fatty acid (PLFA) was quantified. At the early stage (0.25-1 days), the mineralization rate of crop residue was faster in paddy soil than that in upland soil, whereas the opposite trend was observed from 2 to 20 days. At the late stage (21-40 days), the mineralization rate was similar in both soils. At the end of incubation, 11% of the total crop residue was mineralized in paddy soil, which was about half of that in upland soil (20%). Although paddy soil had a higher amount of microbial biomass (indicated by total PLFA), the total amounts of 13C-PLFA were comparable in both soils, and the enrichment ratio (proportion of 13C to total C in PLFA) was lower in paddy soil than that in upland soil. This indicated that the microbial community in paddy soil was less active in the uptake of crop residue C than that in upland soil. During the incubation, the residue-derived 13C was mainly distributed in bacterial PLFA (up to 86% of total 13C-PLFA, including 59% in gram-positive and 27% in gram-negative bacteria) in paddy soil, and up to 75% of total 13C-PLFA distributed in fungal PLFAs was in upland soil. Thus, bacteria dominated the utilization of crop residue in paddy soil versus fungi in upland soil. Compared with that in upland soil, the microbial activity was suppressed in the anaerobic condition caused by flooding in paddy soil, with a stronger inhibition of fungi than bacteria. Considering the discrepancies of life strategies and necromass turnover between bacteria and fungi, the different dominant microbial groups in the utilization of crop residue in water-logged and well-drained conditions could lead to the distinct accumulation and stabilization of microbial-derived organic matter in paddy and upland soils.

Shift in soil microbial communities along ~160 years of natural vegetation restoration on the Loess Plateau of China

Natural restoration of vegetation has been widely implemented as an effective strategy for recovery of degraded ecosystems. However, how soil microbial communities vary with natural restoration of vegetation and associated drivers remains unclear. Here, we investigated the changes in soil microbial communities at 0–60 cm soil depths along ~160 years of natural restoration of vegetation from farmland to pioneer weeds, to herbs, to shrublands and early forests, and finally to climax forests on the Loess Plateau of China. Our phospholipid fatty acids (PLFA) analysis showed that natural restoration of vegetation largely enhanced the abundances of the total PLFA, the bacterial, fungal, Gram-positive (G+) bacterial, Gram-negative (G−) bacterial, arbuscular mycorrhizal fungal (AMF), actinomycete, monounsaturated, branched, and saturated straight-chain (SSC) PLFA in the surface soil layer (0–20 cm). However, its effect was negligible on the deep soil layer (20–60 cm). The biomass of these microbial communities declined sharply along with soil depth at each of the restoration stage. Natural restoration of vegetation significantly changed composition proportion of soil microbial communities. In particular, the ratio of G+: G−, proportions of G+ bacterial PLFA, and AMF PLFA in the total PLFA gradually decreased, while the proportions of bacterial PLFA and G− bacterial PLFA in the total PLFA gradually increased in the surface soil layer along vegetation restoration stages. Our finding suggested that natural restoration of vegetation altered the biomass and composition proportion of soil microbial communities, which was strongly driven by variations in soil nutrient substrates and physiochemical properties (e.g., soil moisture and pH), as well as litter and root biomass along the long gradient of vegetation. This study revealed that natural restoration of vegetation was an effective strategy for reestablishment of soil microbial communities. Additionally, the impacts of natural restoration of vegetation on soil microbial communities were primarily concentrated in the surface soil layer rather than deep soil layer, and soil microbial biomass reached maximum in the climax forests.

Progeny selection for enhanced forest growth alters soil communities and processes

AbstractGenetic enhancement of tree species is integral to global forest management practices with mass propagation of enhanced plant material being used to reforest whole landscapes. It is unclear, however, how genetic enhancement of basic traits such as tree growth may influence the function of life supporting soil ecosystems. We studied the potential cascading effects of genetic increases in growth of Norway spruce (Picea abies) on a range of soil chemical and biological properties. Because this species is a prime candidate for the genetic enhancement of boreal forest landscapes and it has been introduced around the world, its impacts on soil microbiomes are likely of importance both locally and globally. In a 40‐year common garden, we assessed how genetic increases in growth generated through controlled crossing of high‐quality “plus” trees from across the central boreal zone of Sweden influenced a range of soil properties beneath the canopies. Properties included pH, carbon, nitrogen, nitrate, ammonium, phosphate, respiration rate, and the composition of microbial communities assessed via phospholipid fatty acids (PLFAs). We found that Norway spruce family significantly affected each of the seven chemical properties assessed, with differences of up to 140% among families, and that three of the seven were significantly correlated with mean family growth rate. We also found that fungal PLFAs varied significantly across Norway spruce families, but these differences were not strongly related to mean family growth rate. This study, representing just one cycle of selective breeding, suggests that genetic increases in tree growth rates may also be inadvertently altering soil communities and ecosystem services. Such alterations across forest landscapes may have unexpected implications for the function of forest ecosystems (i.e., nutrient cycling) as well as processes of global significance (i.e., carbon sequestration).

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.

Effect of soil P status on barley growth, P uptake, and soil microbial properties after incorporation of cover crop shoot and root residues

AbstractBackgroundCover crops (CC) introduced to reduce leaching of nitrate may also improve soil microbial properties and phosphorus (P) uptake in crops that follow. These effects may depend on soil P status and the quality of the CC residues.AimOur aim was to quantify the more persistent effects of incorporation of residues of three different CC species on barley growth and P uptake and whether any response in growth and P uptake was related to soil P status and changes in soil microbial properties.MethodsWe examined the impact of soil P status, CC species, and residue fraction (shoots and/or roots) on the growth of winter barley (Hordeum vulgare) and soil microbial properties. Shoot and root residues from three contrasting CC (oats, Avena sativa; corncockle, Agrostemma githago; lupine, Lupinus angustifolius) were incubated for 2 months in soil with low and medium P status. Dry matter yield and P offtake characterized effects of CC residues on barley while phospholipid fatty acids (PLFAs), neutral lipid fatty acids (NLFAs), and enzyme activity characterized soil microbial properties after barley harvest.ResultsEffects of shoot residues on barley yield and P offtake appeared neutral or positive and not affected by soil P status, while the effect of root residues appeared negative for medium P soil and neutral for low P soil. With lupine shoot biomass, however, barley yield and P offtake increased in both soils. Neither CC treatments nor soil P status affected the microbial community composition (bacterial and fungal specific PLFAs). Lupine roots increased phosphomonoesterase, and lupine residues generally stimulated microbial abundance (total microbial PLFAs) compared to other CC treatments.ConclusionWe conclude that the effect of CC residues on the following crop and soil microorganisms depends on soil P status and that lupine had the largest positive impact on barley growth.

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.

Effects of understory removal and litter addition on leaf and twig decomposition in a subtropical Chinese fir plantation

AbstractSubtropical plantations have been undergoing understory removal and increased plant litter inputs due to global change and anthropogenic activities. However, how understory removal and increased litter inputs affect litter decomposition is still unclear in these plantations. Using a field manipulation experiment, we assessed the effects of understory removal and litter addition on decomposition rates of leaf litter, twig litter, and mixed leaf and twig litter over 16 months of incubation in a subtropical Chinese fir (Cunninghamia lanceolata) plantation in southern China. We also examined the changes in soil chemical properties and fungal and bacterial phospholipid fatty acids (PLFAs) after understory removal and litter addition. Litter decomposition rates were inhibited by understory removal due to the decreased fungal PLFAs and the associated declines in the ratio of fungal to bacterial biomass. Litter addition also retarded litter decomposition rates, despite the increases in soil NH4+‐N concentration and fungal PLFAs. However, both litter decomposition rates and soil microbial PLFAs remained unchanged in the presence of both understory removal and litter addition. In all treatments, mixed leaf and twig litter produced additive effects on litter decomposition rates. These results suggest that understory removal and litter addition interact to affect litter decomposition dynamics and highlight that litter mixture decomposition rates could be easily predicted from component litter in subtropical Chinese fir plantations of southern China.