Phospholipid Fatty Acid Analysis Research Articles

The effects of struvite and sewage sludge on plant yield and the microbial community of a semiarid Mediterranean soil

Phosphorus (P) limitation will play a key role in the productivity of agriculture in the coming decades. Struvite is an ammonium magnesium phosphate mineral that can be recovered from wastewater-treatment plants and can be considered as an alternative source of P. However, the impact of struvite on the plant yield and, particularly, on the soil microbial community is barely known. Here, we tested the impacts of struvite, sewage sludge, and their combination on the barley yield, soil macro and micronutrients, and biochemical and microbiological soil properties. Amendment with struvite alone and its combination with sludge increased the availability of P in soil, the plant uptake of P and Mg, and the barley yield. The analysis of phospholipid fatty acids (PLFAs) and the utilization of metaproteomics approaches revealed significant effects of struvite on the biomass of Gram-positive bacteria and, particularly, on actinobacterial and verrucomicrobial populations in soil.

Ecotoxicity evaluation and human risk assessment of an agricultural polluted soil

The present study aims to evaluate the nature and level of chemical pollution as well as the potential toxicity and ecotoxicity of an agricultural soil irrigated by the water of Litani River. Our findings showed that the soil was mainly contaminated by alkanes (hentriacontane, octadecane, hexadecane) and metal trace elements (nickel, vanadium, chromium, and manganese). Soil organic extracts showed high cytotoxicity against human hepatic (HepG2) and bronchial epithelial cells (Beas-2B). Soil ecotoxicity was revealed by seed germination inhibition of several plant species (wheat, clover, alfalfa, tall fescue, and ryegrass) ranging from 7 to 30% on the polluted soil compared to non-polluted one. In addition, significant decreases in telluric microbial biomasses (bacterial and fungal biomasses), quantified by phospholipid fatty acids (PLFA) analysis were observed in polluted soil compared to non-contaminated soils. The density of the arbuscular mycorrhizal fungal (AMF) spores isolated from the polluted soil was about 316 spores/100g. Three main AMF species were identified as Funelliformis mosseae, Septoglomus constrictum, and Claroideoglomus lamellosum. Moreover, 16 indigenous plant species were inventoried with Silybum marianum L. as the dominant one. Plant biodiversity indices (Shannon, Simpson, Menhinick, and Margaleff) were lower than those found in other contaminated soils. Finally, it was found that all the present plant species on this polluted site were mycorrhized, suggesting a possible protection of these plants against encountered pollutants, and the possibility to use AMF-assisted phytoremediation to clean-up such a site.

Carbon and nitrogen availability in paddy soil affects rice photosynthate allocation, microbial community composition, and priming: combining continuous 13C labeling with PLFA analysis

Carbon (C) and nitrogen (N) availability in soil change microbial community composition and activity and so, might affect soil organic matter (SOM) decomposition as well as allocation of plant assimilates. The study was focused on interactions between C and N availability and consequences for rhizodeposition and microbial community structure in paddy soil. Rice continuously labeled in a 13CO2 atmosphere was fertilized with either carboxymethyl cellulose (CMC) (+C), ammonium sulfate (+N), or their combination (+CN), and unfertilized soil was used as a control. 13C was traced in aboveground and belowground plant biomass, soil organic matter, and microbial biomass. Microbial community composition was analyzed by phospholipid fatty acids (PLFAs). +CN application led to a higher yield and lower root C and N content: 13C assimilated in shoots increased by 1.39-fold and that in roots decreased by 0.75-fold. Correspondingly, after +CN addition, 13C from rhizodeposits incorporated into SOM and microorganisms decreased by 0.68-fold and 0.53-fold, respectively, as compared with that in the unfertilized soil. The application of +C or + N alone resulted in smaller changes. CMC led to a 3% of total N mobilized from SOM and resulted in a positive priming effect. Both fertilizations (+C, +N, or + CN) and plant growth stages affected soil microbial community composition. With decreasing microbial biomass C and N, and PLFA content under +CN amendment, +CN fertilization decreased Gram-positive (G+)/ Gram-negative (G-) ratios, and resulted in lower G+ bacteria and fungi abundance, whereas G- and actinomycetes were stimulated by N fertilization. Organic C fertilization led to a positive N priming effect. Organic C and mineral N application decreased C input by rhizodeposition associated with lower 13C recovery in SOM and microbial incorporation. C and N addition also altered microbial community composition, as +CN decreased content of microbial groups, such as G+ bacteria and fungi, but +N stimulated G- bacteria and actinomycetes.

Are secondary forests second-rate? Comparing peatland greenhouse gas emissions, chemical and microbial community properties between primary and secondary forests in Peninsular Malaysia

Tropical peatlands are globally important ecosystems with high C storage and are endangered by anthropogenic disturbances. Microbes in peatlands play an important role in sustaining the functions of peatlands as a C sink, yet their characteristics in these habitats are poorly understood. This research aimed to elucidate the responses of these complex ecosystems to disturbance by exploring greenhouse gas (GHG) emissions, nutrient contents, soil microbial communities and the functional interactions between these components in a primary and secondary peat swamp forest in Peninsular Malaysia. GHG measurements using closed chambers, and peat sampling were carried out in both wet and dry seasons. Microbial community phenotypes and nutrient content were determined using phospholipid fatty acid (PLFA) and inductively-coupled plasma mass spectrometry (ICP-MS) analyses respectively. CO2 emissions in the secondary peat swamp forest were > 50% higher than in the primary forest. CH4 emission rates were ca. 2 mg m−2 h−1 in the primary forest but the secondary forest was a CH4 sink, showing no seasonal variations in GHG emissions. Almost all the nutrient concentrations were significantly lower in the secondary forest, postulated to be due to nutrient leaching via drainage and higher rates of decomposition. Cu and Mo concentrations were negatively correlated with CO2 and CH4 emissions respectively. Microbial community structure was overwhelmingly dominated by bacteria in both forest types, however it was highly sensitive to land-use change and season. Gram-positive and Gram-negative relative abundance were positively correlated with CO2 and CH4 emissions respectively. Drainage related disturbances increased CO2 emissions, by reducing the nutrient content including some with known antimicrobial properties (Cu & Na) and by favouring Gram-positive bacteria over Gram-negative bacteria. These results suggest that the biogeochemistry of secondary peat swamp forest is fundamentally different from that of primary peat swamp forest, and these differences have significant functional impacts on their respective environments.

Effect of Growing Miscanthus x giganteus on Soil Microbial Communities in Post-Military Soil

Growing a second generation energetic plant Miscanthus x giganteus (Mxg) in former military sites appears to be a promising way to use such areas with synergic phytoremediation of contaminants (organic pollutants, potential toxic metals). Effect of Mxg growth on soil microbial communities during a two-year pot experiment with real post-military soil (Sliač, Slovakia) and the effect of potential toxic metal concentration was studied by analyses of microbial activities and phospholipid fatty acids (PLFA). Year-on-year positive changes in microbial community structure and state were detected (higher ratios of G+/G− bacteria and fungal/bacterial PLFA, and a decrease of stress indicators trans/cis and cy/pre PLFA). Portion of gram-positive bacteria correlated negatively with potential toxic metal concentrations; however, the concentration of potential toxic metals was not identified as the main stress factor—the access to bioavailable nutrients was more important. Overall, Mxg growth generally exhibited a positive effect on soil microorganisms.

Interactions of Mycorrhiza and Protists in the Rhizosphere Systemically Alter Microbial Community Composition, Plant Shoot-to-Root Ratio and Within-Root System Nitrogen Allocation

Arbuscular mycorrhizal fungi (AMF) are important symbionts for plant nutrient uptake, but their exact role in plant nitrogen (N) nutrition is unclear. Protists on the other hand play an acknowledged role in plant N acquisition, and there is increasing evidence for a close interaction with AMF. In a split root set up, we investigated the distinct roles of mycorrhiza (Rhizophagus irregularis), protists (Acanthamoeba castellanii), and their interaction on plant N uptake, within-root system allocation patterns, and shoot-to-root ratio of winter wheat. In addition, we applied a quantitative metabolomics approach to characterize associated changes in soil microbial communities by microbial phospholipid fatty acid (PLFA) analysis from rhizosphere soil. AMF markedly altered plant shoot-to-root allometry by reducing root biomass of wheat, and mycorrhiza partly took over root system functioning. Protists promoted shoot and root growth, and improved plant N uptake by the release of N from consumed bacterial biomass, a mechanism known as microbial loop. The shoot system however responded little to these alterations of the root system and of the rhizosphere community composition, indicating that the plants optimized shoot growth despite varying investment into roots. Mycorrhiza reduced root biomass and plant N, especially in the combined treatments with protists by changing within root system allocation of N and root biomass. These systemic effects on root allocation pattern suggest that mycorrhiza also gained control over N provided by protist grazers. Protists and mycorrhiza altered rhizosphere bacterial communities in contrasting but consistent ways as shown by quantitative shifts in microbial PLFA profiles. Remarkably, the changes in bacterial community composition were systemically conveyed within the root system to the split-root chamber where the symbionts were lacking. Accordingly the synergistic effects of protists and mycorrhiza indicated systemic effects on nutrient- and on root-allocation within root systems as an emergent property that could not be predicted from single treatments with mycorrhiza or protists alone. The tight plant and microbial feed backs uncovered in this study have far reaching implications for understanding the assembly of plant microbiomes, and testify central roles of both protists and mycorrhizas in the assembly process.

Effects of Soil-Applied Fungicides on Sugarcane Root and Shoot Growth, Rhizosphere Microbial Communities, and Nutrient Uptake

Sugarcane (Saccharum spp. hybrid) successive planting (also called monoculture) causes serious yield losses and its management is not well studied in Histosols. Based on very few studies in other sugarcane regions, root colonization by harmful soil fungi is considered as a major cause of this yield decline, but there is lack of knowledge on its management in Histosols. A two-year greenhouse study was conducted with soil-drench application of mancozeb, mefenoxam, and azoxystrobin fungicides to determine their effects on early root and shoot growth, soil microbial communities, and nutrient uptake by plants. The study indicated that mancozeb soil application improved sugarcane-shoot and -root dry matter by 3–4 times and shoot-root length, fine-root length, and root surface area by 2–3 times compared to untreated soil. Phospholipid fatty acid (PLFA) analyses of sugarcane rhizosphere soil showed significant reduction in fungal-biomarker abundance with mancozeb and azoxystrobin in comparison to the untreated check or mefenoxam treatments. Bacterial functional-group abundance was reduced by mancozeb and mefenoxam. All fungicides significantly reduced mycorrhizal colonization but not mycorrhizal spore counts. There was a functional relationship between fine-root systems and higher tissue concentration of nitrogen and silicon. The study indicated that application of fungicides to the soil may improve early root and shoot growth and plant-cane establishment that can potentially reduce the yield decline in successively planted sugarcane in histosols. Additional field research is needed in the future to determine the fungicide soil application method, sugarcane growth response in whole crop cycles, and any environmental effects.

Investigations of relationships among aggregate pore structure, microbial biomass, and soil organic carbon in a Mollisol using combined non-destructive measurements and phospholipid fatty acid analysis

Limitations of traditional measurement methods have impeded progress in understanding the role of soil aggregation in protecting soil organic carbon (SOC) from decomposition by soil microbes living in pore spaces. In this paper, we used the Scanning Electronic Microscope (SEM) and X-ray micro Computed Tomography (micro-CT) to study the relationships of the aggregate pore structure and microbial distribution in the interior and exterior of soil aggregates, and thereby gained an insight into protection of carbon within macroaggregates of an undisturbed Mollisol in northeastern China. There were close relationships between soil pore structure and distribution of soil microbes and soil organic carbon (SOC), but they were different on the exterior and interior of soil aggregate. On the exterior of macroaggregates, there were negative relationships between soil porosities, the number of pores and SOC, especially for soil pores in the 10–30 μm and 30–100 μm classes, indicating these two pore sizes are unlikely to help sequester C. In contrast, there was a positive correlation between soil pores > 100 μm and SOC. Furthermore, soil pore structure had no impact on soil microbial biomass and density or on SOC contents in the interior of soil aggregates. This study provides a new method by combining SEM with micro-CT technology for linking soil structure and soil microbial properties with C sequestration and SOC changes.

Microbial communities associated with barley growing in an oil sands reclamation area in Alberta, Canada.

Microbial communities that colonize the plant rhizosphere and the root interior can ameliorate plant stress and promote growth. These plant-microbe associations are being investigated to assist in reclamation soils in northern Alberta. This study assessed the diversity of bacterial species associated with barley plants growing at different cover managements and slope positions in an oil sands reclamation area. Phospholipid fatty acid analysis of the microbial communities indicated that both cover type and slope, in addition to soil total and organic carbon, NH4+, and organic matter, were significant determinants of microbial community composition. However, analysis of denaturing gel gradient electrophoresis (DGGE) banding patterns revealed that while most bulk and rhizosphere soils differentiated by cover management, no clustering was observed in endophytes. In addition, techniques to assess culture-dependent endophytic bacteria revealed a dominance of the class Gammaproteobacteria, in which Enterobacteriaceae (44%), Xanthomonaceae (30%), and Pseudomonaceae (26%) were the most abundant families in this class. Several endophytic isolates also matched those from DGGE profiles. The results of this study suggest that plants growing on oil sands reclamation covers host a wide range of bacterial endophytes, which should be assessed as to their potential to assist plant establishment and growth at such sites.

Analysis of Bacterial Communities in Partial Nitritation and Conventional Nitrification Systems for Nitrogen Removal

This work studied the microbial community in partial nitritation and complete nitrification processes, which were applied to treat the low Carbon Nitrogen ratio wastewater. The phospholipid fatty acid and quantitative PCR analysis showed that the sludge circulating ratio of 75% resulted in a good microbial growth and a higher abundance of ammonia oxidizing bacteria relative to the nitrite oxidizing bacteria. The Betaproteobacteria were observed to compose the most abundant sludge bacterial groups in the two processes, based on phylogenetic analysis. The phylogenetic analysis of both 16S rRNA and amoA gene indicated that the Nitrosomonas sp. were the dominant ammonia oxidizing bacteria in the partial nitritation process. The relative abundance of nitrite oxidizing bacteria, such as Nitrobacter sp. and Nitrospira sp., were significantly lower in the partial nitritation system over the complete nitrification system. The abundance of Planctomycetes was higher in the partial nitritation process, indicating the anammox reaction occurred in the partial nitritation system. These results suggested the nitrite accumulation rate of circulating ratios 75% was the highest, with an average of 92%,and a possibility to treat the low Carbon Nitrogen ratio wastewater using the partial nitritation/anammox process.

Plant drought resistance is mediated by soil microbial community structure and soil-plant feedbacks in a savanna tree species

Soil microbial communities have the potential to modify plant performance and condition plant species responses to environmental change, but the role of soil microorganisms for plant drought responses remains unclear. We used a novel experimental approach to examine the interactive effects of drought and presence of soil microbes on biomass production and plant traits in a savanna tree species. Seedlings of Bauhinia brachycarpa were grown in sterilized or ‘live’ soil, with or without drought, during a 24-week greenhouse experiment. Soil microbial community structure was assessed with phospholipid fatty acid analysis and soil-plant feedback effects were measured. Both drought and the presence of soil microbes decreased plant growth and biomass produced per gram nitrogen (a proxy for N use efficiency) but increased biomass allocation to roots. However, the presence of soil microbes increased plant drought resistance, driven by weakened soil-plant feedbacks under dry conditions. Experimental drought was associated with an increase in the Gram positive: Gram negative bacteria ratio, but did not affect the fungi: bacteria ratio or total microbial biomass. Our results suggest that soil microbes mediate plant responses to drought via soil-plant feedbacks and drought-induced changes in microbial community structure. These findings highlight the importance of plant-soil interactions for improved mechanistic understanding of savanna function, and confirm that characteristics of the soil microbial community could have significant implications for ecosystem stability in a changing environment.

Grass-Legume Mixtures for Improved Soil Health in Cultivated Agroecosystem

Planting grass-legume mixtures may be a good option to improve soil health in addition to increased forage productivity, improved forage nutritive value, and net farm profit in a hay production system. A field experiment was conducted from 2011 to 2014 at Lingle, Wyoming to evaluate soil microbial biomass under different seeding proportions of two forage grasses (meadow bromegrass, Bromus biebersteinii Roem. & Schult.; and orchardgrass, Dactylis glomerata L.) and one legume (alfalfa, Medicago sativa L.). Nine treatments included monoculture grass, monoculture legume, one grass and one legume mixture, two grasses and one legume mixture, and a control (not seeded with grass or legume). Monoculture grass received either no nitrogen (N) or N fertilizer (150 kg N ha−1 year−1 as urea) whereas monoculture legume, grass-legume mixtures, and control plots received no N fertilizer. The study was laid out as a randomized complete block design with three replications. The plots were harvested 3–4 times each year after the establishment year. Soil samples were collected and analyzed for microbial biomass using phospholipid fatty acid (PLFA) analysis at the end of May in 2013 and 2014. Soil samples were also analyzed for mineralizable carbon (C) and N in 2013 and 2014. The total above-ground plant biomass was higher in 50–50% mixture of grass and alfalfa than monoculture alfalfa and monoculture grass (with and without N fertilizer) during the entire study period. The application of N fertilizer to the grass hay production system had little effect on improving mineralizable soil C, N, and soil microbial biomass. However, grass-legume mixture without N fertilizer had great effect on improvement of mineralizable soil C and N, and total, bacterial, and actinomycetes microbial biomass in soil. The 50–50% mixture of grass and alfalfa performed consistently well and can be considered to use in Wyoming conditions for improving soil health and forage productivity.

Analysis of soil microbial dynamics at a cropland-grassland interface in an agro-pastoral zone in a temperate steppe in northern China

Grassland conversion is common around the world, and numerous studies have documented the effect of grassland conversion on biotic and abiotic soil conditions. Soil microbes are a key component of the underground ecosystem and are important in the circulation of materials and energy. In this study, we investigated the variations in the microbial community structures at a cropland-grassland interface. We used the transect line method and phospholipid fatty acid analysis in an agro-pastoral zone in northern China. The results show that significant differences occurred in the soil microbial community structures between grassland and cropland environments. These differences had significant seasonal variations. The variation pattern of soil microbial communities was very different from that of soil physical and chemical properties. Three main conclusions are presented: (1) Significant differences in soil properties, phospholipid fatty acid contents and microbial community structures occurred between the grassland and cropland environments after decades of reclamation. (2) At the grassland-cropland interface, we found a transition zone where the soil microbial community showed dramatic variations. (3) In the transition zone, soil microbial community structures were subjected to a stronger influence from farmland environments before sowing, but grassland played a major role after the crops were harvested.

Litter quality drives the differentiation of microbial communities in the litter horizon across an alpine treeline ecotone in the eastern Tibetan Plateau

Cellulose and lignin are the main polymeric components of the forest litter horizon. We monitored microbial community composition using phospholipid fatty acid (PLFA) analysis and investigated the ligninolytic and cellulolytic enzyme activities of the litter horizon across an alpine treeline ecotone in the eastern Tibetan Plateau. The activities of ligninolytic and cellulolytic enzymes and the biomass of microbial PLFAs were higher in the initial stage of litter decomposition than in the latter stage in the three vegetation types (coniferous forest, alpine shrubland and alpine meadow). Soil microbial community structure varied significantly over the course of litter decomposition in the three vegetation types. Furthermore, the BIOENV procedure revealed that the carbon to nitrogen (C:N) ratio, carbon to phosphorus (C:P) ratio and moisture content (MC) were the most important determinants of microbial community structure in the initial stage of litter decomposition, whereas pH and the lignin concentration were the major factors influencing the microbial community structure in the later stage of litter decomposition. These findings indicate that litter quality drives the differentiation of microbial communities in the litter horizon across an alpine treeline ecotone in the eastern Tibetan Plateau.

Influence of smallholder farm practices on the abundance of arbuscular mycorrhizal fungi in rural Zambia

While the effects of row crop agriculture on arbuscular mycorrhizal (AM) fungi have been studied in temperate climates, much less is known about the consequences of methods employed by smallholder farmers in Africa. We compared soils from 12 small farms in rural eastern Zambia with soil from nearby grasslands (control) to assess microbial abundances, including AM fungi, using phospholipid and neutral lipid fatty acid (PLFA/NLFA) analyses. We also measured soil pH, soil organic matter, and key nutrients, and categorized farms to link microbial abundances with agricultural practices including: low and high input cultivation, conservation farming, and agroforestry. Soil organic matter was significantly greater in grassland (control) soils, compared to any of the farms. Concentrations of N, P, and K were greater in farm soils compared to grassland soil. Extra-radical AM fungal biomass was significantly greater in grassland soils compared to farms, and grasslands contained more than double the total microbial biomass compared to any farm. Our results indicate agricultural practices in Zambia are negatively affecting AM fungi as well as other soil microbes. However, conservation farming shows promise in facilitating AM fungal recovery, with potential long-term benefits for soil stability via hyphal exudates and physical entanglement.

Natural forests maintain a greater soil microbial diversity than that in rubber plantations in Southwest China

The conversion of tropical forests to monoculture rubber plantations throughout Southeast Asia threatens to have widespread negative impacts on ecosystem services. The aim of this study was to identify the impacts of forest conversion to rubber plantations on soil microorganisms, using a space for time substitution design. Soil microbial communities from natural forests, young rubber and mature rubber plantations were investigated using phospholipid fatty acid (PLFA) analysis. Microbial PLFA biomass of all functional groups including actinomycete, arbuscular mycorrhiza, fungi, bacteria and protozoa was lower in rubber plantations as compared to natural forests. This was true for young rubber and mature rubber plantations tested in both dry and wet seasons. The composition of microbial communities differed between natural forests, young rubber and mature rubber plantations. Changes in microbial community composition were strongly correlated with pH, which was lower in mature rubber plantations than in natural forests and young rubber plantations. In addition, our results showed that the variation in soil microbial community composition was strongly affected by seasonality, with higher PLFA biomass recorded in the dry season than in the wet season. The low soil microbial biomass in rubber plantations has long term implications regarding the soil health of rubber plantations.

Rhizosphere microbial communities of canola and wheat at six paired field sites

Plant physical and chemical characteristics are known to alter rhizosphere microbial communities, but the effect of introducing canola (Brassica napus L.) into monoculture wheat (Triticum aestivum L.) rotations is not clear. Results from a field study in eastern Washington showed that winter canola (WC) influenced the bulk soil microbial community and differentiated it from the community associated with winter wheat (WW). Abundance of soil fungi, including mycorrhizae, was reduced with the introduction of WC. The objective of this research was to determine the differences and similarities in the rhizosphere microbial communities of WC and WW. Canola and wheat rhizosphere soil was collected from six dryland farms in Adams and Douglas Counties, WA. Each farm was a paired site with WC and WW grown in adjacent fields of the same soil type, landscape orientation, and crop history. Canola, or any non-cereal crop, had never been grown previously at the experimental sites. Rhizosphere microbial biomass and community composition, determined using phospholipid fatty acid analysis (PLFA), revealed differences associated with landscape position at the initial fall sampling when WC and WW were in the rosette and tiller development stages, respectively. However, data from spring samples, when WC and WW were in the early bolting and stem elongation growth stages, respectively, showed significant differences in microbial communities between WC and WW rhizosphere soils. Data suggest that initial (fall) microbial community composition were an artifact of previous histories of monocrop wheat production and varied with expected differences in landscape position. As the crops developed, microbial communities became more dissimilar and were differentiated by crop species. Our results show that WC can have significant effects on rhizosphere microbial biomass of specific microbial groups and community structure in wheat-based cropping systems, such as reductions in fungi and gram+ bacteria in some locations. Crop-related changes in the abundance of specific rhizosphere microbial groups may play a key role in the yield of subsequent crops, and overall soil health and nutrient turnover.

Effects of biochar and litter on carbon and nitrogen mineralization and soil microbial community structure in a China fir plantation

To investigate the effects of biochar addition (1 or 3%) to the soil of a China fir plantation with or without litter, we conducted a 90-day incubation experiment. We also studied the C and N dynamics and the microbial community structure of the soil. In soil without litter, the application of biochar at a rate of 3% significantly decreased CO2 emissions, while addition of 1% biochar had no effect. Biochar application did not affect the net N mineralization rate but significantly reduced the NH4+ concentration after 90 days. In litter-enriched soil, biochar application had no significant effect on total CO2 emissions; however, application of 3% biochar significantly reduced the net N mineralization rate. Biochar application to soil with or without litter immediately reduced the dissolved organic carbon (DOC) concentration independent of the application rate, which was primarily due to sorption of DOC by the biochar. Phospholipid fatty acid analysis demonstrated that both concentrations of added biochar to soil (with or without litter) altered the soil microbial community structure at the end of incubation, although the effect of biochar was not as strong as the effect of time or litter application. The effect of biochar addition alone on microbial community structure was inconsistent over time. Litter added to soil significantly increased fungi and reduced Gram-positive bacteria. In the presence of litter, biochar applied at both 1% and 3% significantly increased (p < 0.05) the proportion of actinomycete only at day 90. Our results indicate biochar as a potentially effective measure for C sequestration in the test soil of a China fir plantation, even in the presence of litter.

Effects of artificial warming on different soil organic carbon and nitrogen pools in a subtropical plantation

Uncertainty about the effects of climate warming on belowground processes of tropical and subtropical forests limits our ability to predict the response and feedback of such ecosystems to future climate change. Few field experiments in the tropics and subtropics have been conducted on the effects of manipulating warming on microbial community, enzyme activities and soil organic carbon (C) decomposition of forest ecosystems. Here, using buried cable techniques, we conducted a microcosm warming experiment to investigate extractable and acid resistant C and nitrogen (N) pools, microbial community composition, and enzyme activity after about 1.5 years of soil warming (+5 °C) in a subtropical plantation in southeastern China. The microbial community structure was quantified with phospholipid fatty acid (PLFA) analysis. Soil extractable and acid resistant C and N fractions were determined using a two-step sulfuric acid hydrolysis. We found that warming increased soil extractable C by 28% and acid resistant N decomposition by 20%. Soil warming decreased soil microbial N use efficiency by 31% but did not alter microbial C use efficiency. Warming differentially affected bacteria, fungi and enzymes activities. Our results suggest that climate warming can alter microbial community structure and enzyme activity and consequently lead to a serious imbalance between soil N and C decomposition in subtropical tree plantations.

Characteristics of soil microbial biomass and community composition in Pinus yunnanensis var. Tenuifolia secondary forests

ABSTRACTPinus yunnanensis var. Tenuifolia is an important species of timber and grease in southern China, but the characteristics of the soil microbial community in P. yunnanensis var. natural secondary forests are still poorly understood. Using a fumigation-extraction method and phospholipid fatty acid (PLFA) analysis, we study microbial biomass and community composition in the topsoil (0–10 cm) of three types of secondary forests (PYI, PYII, PYIII) dominated by P. yunnanensis var. to varing degrees. Microbial biomass carbon and nitrogen, total PLFA, and PLFA contents of bacterial, fungal, and arbuscular mycorrhizal fungi were significantly lower in PYI than PYII or PYIII, and there were significant differences in the monounsaturated/saturated fatty acid ratio among the tested forests. Principal component analysis indicated that the soil microbial community structure of the tested forests differed significantly. The changes in soil microbial biomass and community composition were positively correlated with soil water content, pH, organic matter (SOM), total nitrogen (TN), and total phosphorus. Season did not significantly affect the soil microbial community structure, but significantly affected soil microbial biomass, SOM, and TN, which were higher in the dry season than in the wet season.