Fungal PLFA Research Articles

Foliar Roundup application has minor effects on the compositional and functional diversity of soil microorganisms in a short-term greenhouse experiment

The herbicide Roundup (and glyphosate, its active ingredient) is extensively used for weed control on a worldwide scale. It is absorbed after foliar application and quickly translocated inside the plant. In this study, we investigated the effects of Roundup speed, a commercial glyphosate formulation, on the structural composition (dominance of microbial groups, phospholipid fatty acid analysis - PLFA) and functional diversity (use of carbon sources, Multiple Substrate Induced Respiration - MSIR) of soil microorganisms. We specifically aimed at understanding the potential impact of biotic interactions on herbicide effects and included plants, earthworms, and endomycorrhizal fungi in the experimental setup. For this, we grew clover (Trifolium repens) in the greenhouse and added mycorrhizal inoculum (Glomus mosseae) and earthworms (Lumbricus terrestris) to the pots. Two weeks after foliar Roundup application and subsequent plant death, the pots were destructively sampled. The application resulted in a significant increase of microbial respiration (SIR) by approximately 30%. A multivariate analysis of the MSIR data exhibited small but significant differences between the microbial communities of treated and untreated pots, while no significant difference was apparent for the PLFA data. Bacterial PLFAs generally decreased following herbicide application, while mycorrhizal and fungal PLFAs were not affected. We did not find a consistent difference between the fatty acid markers of gram negative and gram positive bacteria. For all investigated parameters, there were highly significant differences between the upper (0–5 cm depth) and lower (5–10 cm) soil layers. The fact that rooting density differed by a factor of 3.5 between the two layers indicated that herbicide effects were especially pronounced in the clover rhizosphere and were likely due to changes in root exudate composition. We found significant, though very small, interactions between Roundup and other experimental factors (especially mycorrhizal inoculum).

Dynamics of soil respiration and microbial communities: Interactive controls of temperature and substrate quality

Soil microbial communities mediate soil feedbacks to climate; a thorough understanding of their response to increasing temperatures is therefore central to predict climate-induced changes in carbon (C) fluxes. However, it is unclear how microbial communities will change in structure and function in response to temperature change and to the availability of organic C which varies in complexity. Here we present results from a laboratory incubation study in which soil microbial communities were exposed to different temperatures and organic C complexity. Soil samples were collected from two land-use types differing in climatic and edaphic conditions and located in two regions in southwest Germany. Soils amended with cellobiose (CB), xylan, or coniferyl alcohol (CA, lignin precursor) were incubated at 5, 15 or 25 °C. We found that temperature predominantly controlled microbial respiration rates. Increasing temperature stimulated cumulative respiration rates but decreased total microbial biomass (total phospholipid fatty acids, PLFAs) in all substrate amendments. Temperature increase affected fungal biomass more adversely than bacterial biomass and the temperature response of fungal biomass (fungal PLFAs, ergosterol and ITS fragment) depended upon substrate quality. With the addition of CB, temperature response of fungal biomass did not differ from un-amended control soils, whereas addition of xylan and CA shifted the fungal temperature optima from 5 °C to 15 °C. These results provide first evidence that fungi which decompose complex C substrates (CA and xylan) may have different life strategies and temperature optima than fungal communities which decompose labile C substrate (CB). Gram-positive and gram-negative bacteria differed strongly in their capacity to decompose CB under different temperature regimes: gram-positive bacteria had highest PLFA abundance at 5 °C, while gram-negative bacteria were most abundant at 25 °C. Bacterial community composition, as measured by 16S rRNA gene abundance, and PLFAs showed opposite temperature and substrate decomposition trends. Using multivariate statistics, we found a general association of microbial life strategies and key members of the microbial community: oligotrophic Alphaproteobacteria and Acidobacteria were associated with complex substrates and copiotrophic Actinobacteria with labile substrates. Our study provides evidence that the response of C cycling to warming will be mediated by shifts in the structure and function of soil microbial communities.

Understory vegetation plays the key role in sustaining soil microbial biomass and extracellular enzyme activities

Abstract. While we know that understory vegetation affects the soil microbial biomass and extracellular enzyme activities in subtropical Chinese fir (Cunninghamia lanceolata) forests, we are less certain about the degree of its influence. We determined the degree to which the soil abiotic and biotic properties, such as PLFAs and extracellular enzyme activities, were controlled by understory vegetation. We established a paired treatment in a subtropical Chinese fir plantation, which comprised one plot from which the understory vegetation and litter were removed (None) and another from which the litter was removed but the understory vegetation was left intact (Understory). We evaluated how the understory vegetation influenced the soil abiotic properties, the bacterial, fungal, and actinobacterial PLFAs, and the activities of five hydrolases and two oxidative enzymes. The dissolved organic carbon (DOC), particulate organic carbon, soil organic carbon, ammonia nitrogen (NH4+–N), and total nitrogen contents and soil moisture were 18 %, 25 %, 12 %, 34 %, 8 %, and 4 % lower in the None treatments than in the Understory treatments, respectively (P<0.05). Soil bacterial, fungal, and total PLFAs, and the potential activities of β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase, phenol oxidase, and peroxidase, were as much as 24 % lower in None treatments than in Understory treatments (P<0.05). The specific activities of C-acquiring enzymes were as much as 41 % higher (P<0.05), and the ratio of C- to N-acquiring enzymes was also higher in the None treatments than in the Understory treatments. This suggests that in the absence of understory vegetation microbes invested more in C acquisition than N acquisition because the carbon (C) inputs were less labile. The negative relationship between DOC and AP shows that DOC is consumed when P-acquiring enzymes are produced. The positive correlation between NH4+–N and βG suggested the increased availability of N promoted the decomposition of C. More extracellular enzymes that degrade soil organic matter are produced when there is understory vegetation, which leads to losses of soil C. On the other hand, the soil C sink is maintained by increased inputs of C. We can therefore conclude that understory vegetation contributes to C sequestration in Chinese fir forests and suggest that understory should be maintained to sustain soil quality in subtropical Chinese fir plantations.

Spatial heterogeneity of microbial community and enzyme activities in a broad-leaved Korean pine mixed forest

Soil microbial communities support a great belowground biodiversity, but our knowledge regarding their spatial patterns and underlying driving mechanisms in small scale is very limited, especially for forest ecosystems. The spatial distributions of microbial community and enzyme activities depending on soil environmental factors were studied using geostatistical tools. 55 soil samples were collected across a 30 m × 40 m plot in a broad-leaved Korean pine mixed forest in the Changbai Mountains. Abundances of total and bacterial PLFAs had stronger spatial dependence than fungal PLFAs. Gram-positive bacteria had stronger spatial dependence than Gram-negative bacteria, suggesting that Gram-negative bacteria are more susceptible to stochastic factors. The proportions of structural variance for the activities of β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase (NAG) and acid phosphatase (AP) were 0.997, 0.519 and 0.966, respectively, suggesting that βG and AP had high spatial dependence. Cross-variogram analysis showed that root biomass played a critical role in structuring the spatial distributions of total and bacterial PLFAs. Fungi had close spatial connection with total nitrogen (TN), particulate organic carbon and root biomass within the ranges of 8.2–13 m. The βG, NAG and AP activities were closely spatially connected to the soil organic carbon and TN and were all spatially correlated with fungal abundance. Overall, microbial community and enzyme activities were patchily distributed at small spatial scales. Close spatial connections between microbial communities, enzyme activities, and root biomass and soil variables help to understand the main drivers of belowground soil biodiversity in the forest.

Nutrient optimization of tree growth alters structure and function of boreal soil food webs

Nutrient optimization has been proposed as a way to increase boreal forest production, and involves chronic additions of liquid fertilizer with amounts of micro- and macro-nutrients adjusted annually to match tree nutritional requirements. We used a short-term (maintained since 2007) and a long-term (maintained since 1987) fertilization experiment in northern Sweden, in order to understand nutrient optimization effects on soil microbiota and mesofauna, and to explore the relationships between plant litter and microbial elemental stoichiometry. Soil microbes, soil fauna, and aboveground litter were collected from the control plots, and short- and long-term nutrient optimization plots. Correlation analyses revealed no relationships between microbial biomass and litter nutrient ratios. Litter C:N, C:P and N:P ratios declined in response to both optimization treatments; while only microbial C:P ratios declined in response to long-term nutrient optimization. Further, we found that both short- and long-term optimization treatments decreased total microbial, fungal, and bacterial PLFA biomass and shifted the microbial community structure towards a lower fungi:bacterial ratio. In contrast, abundances of most fungal- and bacterial-feeding soil biota were little affected by the nutrient optimization treatments. However, abundance of hemi-edaphic Collembola declined in response to the long-term nutrient optimization treatment. The relative abundances (%) of fungal-feeding and plant-feeding nematodes, respectively, declined and increased in response to both short-term and long-term treatments; bacterial-feeding nematodes increased relative to fungal feeders. Overall, our results demonstrate that long-term nutrient optimization aiming to increase forest production decreases litter C:N, C:P and N:P ratios, microbial C:P ratios and fungal biomass, whereas higher trophic levels are less affected.

Seasonal dynamics of soil microbial community and enzyme activities in Hippophae rhamnoides plantation

We investigated the effects of forest age and season on soil microbial community structure and enzyme activities in Hippophae rhamnoides plantation. The results showed that the amounts of total PLFAs, bacterial PLFAs, and fungal PLFAs increased with the increases of forest age. The highest values presented in mature plantation (CL). Soil enzyme activities showed the same trend as soil microbial communities. The total PLFAs, bacteria PLFAs, and fungal PLFAs exhibited significantly positive correlations with soil pH, total nitrogen, and available phosphorus. In conclusion, forest age and season has significant impacts on soil microbial community structure and enzyme activities. H. rhamnoides plantation is a suitable afforestation model, which would help improve soil fertility.

Soil microbial communities and enzyme activities in sea-buckthorn (Hippophae rhamnoides) plantation at different ages.

The aim of this study was to assess the impact of forest age and season on the soil microbial community and enzyme activities in sea-buckthorn plantation system and to determine the relative contributions to soil microbial properties. Soil sampling was carried out in the dry season (April) and wet season (September) in four areas, including: abandoned farmland (NH), an 8-year- old plantation (young plantation, 8Y), a 13-year-old plantation (middle-aged plantation, 13Y), and an 18-year-old plantation (mature plantation, 18Y). The results showed that forest age and season have a significant effect on soil microbial community structure and enzyme activities. The total, bacterial, fungal, Gram-negative (G+), and Gram-positive (G-) PLFAs increased gradually with forest age, with the highest values detected in 18Y. All the detected enzyme activities showed the trend as a consequence of forest age. The microbial PLFAs and soil enzyme activities were higher in the wet season than the dry season. However, there were no significant interactions between forest age and season. A Correlation analysis suggested that soil microbial communities and enzyme activities were significantly and positively correlated with pH, total nitrogen (TN) and available phosphorus (AP). Season had a stronger influence on soil microbial communities than forest age. In general, sea-buckthorn plantations establishment might be a potential tool for maintaining and increasing soil fertility in arid and semi-arid regions.

Biomass, activity and structure of rhizosphere soil microbial community under different metallophytes in a mining site

Microbial properties are often used to assess the recovery of soil health during phytoremediation. A field survey was conducted to test the effects of different plant metallophytes (excluder and hyperaccumulator) on soil microbial characteristics. Microbial properties in the rhizosphere of four metallophytes (Sedum alfredii, Rubus hunanensis, Lysimachia christinae and Clinopodium gracile) growing naturally on highly Cd-, Zn- and Pb-contaminated soils were investigated. Microbial biomass carbon, basal respiration, enzyme activities and phospholipid fatty acids were analyzed to study microbial community function and composition. The total microbial biomass, bacterial, actinomycete, fungal, and protozoan PLFAs, basal respiration and enzyme activities in the rhizosphere of metallophytes were significantly higher than in bulk soil. Moreover, the largest increases were found in the rhizosphere of the hyperaccumulator S. alfredii. The microbial community composition in the rhizosphere of S. alfredii was significantly different from the other 3 plants. Redundancy analysis showed that soil physico-chemical properties such as metal concentrations, labile carbon and pH explained most of the variation in microbial community biomass, activity and structure. Metallophytes using different strategies to adapt to metal-rich soils induced different effects on soil microbial properties, which were also influenced by physico-chemical characteristics.

Functional differences in the microbial processing of recent assimilates under two contrasting perennial bioenergy plantations

Land use change driven alteration of microbial communities can have implications on belowground C cycling and storage, although our understanding of the interactions between plant C inputs and soil microbes is limited. Using phospholipid fatty acids (PLFA's) we profiled the microbial communities under two contrasting UK perennial bioenergy crops, Short Rotation Coppice (SRC) willow and Miscanthus Giganteus (miscanthus), and used 13C – pulse labelling to investigate how recent carbon (C) assimilates were transferred through plant tissues to soil microbes. Total PLFA's and fungal to bacterial (F:B) ratios were higher under SRC willow (Total PLFA = 47.70 ± 1.66 SE μg PLFA g−1 dry weight soil, F:B = 0.27 ± 0.01 SE) relative to miscanthus (Total PLFA = 30.89 ± 0.73 SE μg PLFA g−1 dry weight soil, F:B = 0.17 ± 0.00 SE). Functional differences in microbial communities were highlighted by contrasting processing of labelled C. SRC willow allocated 44% of total 13C detected into fungal PLFA relative to 9% under miscanthus and 380% more 13C was returned to the atmosphere in soil respiration from SRC willow soil compared to miscanthus. Our findings elucidate the roles that bacteria and fungi play in the turnover of recent plant derived C under these two perennial bioenergy crops, and provide important evidence on the impacts of land use change to bioenergy on microbial community composition.

Agro-forestry management of Paulownia plantations and their impact on soil biological quality: The effects of fertilization and irrigation treatments

Short-rotation plantations for biomass production are wood systems in which fast growing tree species are grown under intensive agricultural practices to achieve high biomass yields. Paulownia sp. is an extremely fast-growing tree species which is commonly used to produce biomass for energetic purposes. This tree species has a great nutrient and water demand, and the establishment of its plantations may affect soil fertility and quality. For this fact, this study is focused on the evaluation of the responses of the soil microbial community – in terms of biomass, community structure, and activity – in a Paulownia plantation submitted to a semiarid climate. Particular attention was paid to the impact of the soil fertilization (mineral fertilizer or an organic-mineral amendment, BAN, obtained from the forestry industry) and level of irrigation on the soil microbial community. For both irrigation regimes, a significant increase in TOC was observed with the addition of the BAN to the soil. The content of water soluble C in the soil was affected by both factors (fertilization and irrigation) and their interaction. Both enzyme activities related with the C and P cycles in soil and dehydrogenase activity were significantly affected by the fertilization, irrigation, and their interaction. Regardless of the irrigation level, the microbial respiration rate was highest with the BAN treatment. The content of total PLFAs and PLFA biomarkers of microbial groups showed no significant differences between the fertilization treatments. However, the total PLFAs and the Gram-positive, fungal, and saturated PLFA concentrations differed significantly between the irrigation levels. In general, the use of residues generated in the forest biomass industry (pine bark and biomass ash) as a soil amendment had a positive effect on the soil microbial activity without altering the structure of the soil microbial community. Considering the water deficit of semiarid areas, such as SE Spain, the low level of irrigation tested in this study would be enough to maintain both the soil microbial activity and suitable production of biomass by Paulownia trees.

Soil Biology Changes as a Consequence of Organic Amendments Subjected to a Severe Drought

AbstractEffect of severe drought events in combination with organic amendments (municipal solid waste, MSW, sheep manure, SM, and cow manure, CM) on soil dehydrogenase, urease, β‐glucosidase and phosphatase activities and microbial community by analyzing phospholipid fatty acids was studied under controlled laboratory conditions for one year. Two levels of irrigation were used: (1) watered soils, where the soils were maintained at 60% of their water holding capacity through the experiment, and (2) non‐watered soils, without irrigation through the experiment. The severe drought conditions negatively affected the soil enzymatic activities and total bacterial and fungal PLFA concentrations. The application of organic amendments to the soil subjected to severe drought increased soil water retention and encouraged the growth and activity of soil microbial populations. However, the chemical composition of the organic matter applied to the soil also strongly influenced soil moisture. In non‐watered soils and compared with the unamended soil, the dehydrogenase activity was 71 · 3%, 60 · 9% and 38 · 6% higher in the soil with SM, CM and MSW, respectively. Urease activity was 60 · 6%, 51 · 5% and 37% higher in the soil with SM, CM and MSW, respectively. β‐glucosidase and phosphatase activities had a similar trend. Water retention was higher when the organic wastes applied to the soils had a higher content of humic acids than fulvic acid contents. Copyright © 2016 John Wiley & Sons, Ltd.

Endophytic fungus Phomopsis liquidambari and different doses of N-fertilizer alter microbial community structure and function in rhizosphere of rice.

Microbial community structure and functions of rhizosphere soil of rice were investigated after applying low and high doses of nitrogenous fertilizer and Phomopsis liquidambari. Average well color development, substrate richness, catabolic diversity and soil enzymes activities varied after applying N-fertilizer and P. liquidambari and were greater in P. liquidambari treated soil than only N-fertilization. Multivariate analysis distinctly separated the catabolic and enzymes activity profile which statistically proved alteration of microbial functional diversity. Nitrogen fertilizer altered microbial community structure revealed by the increased content of total PLFAs, specific subgroup marker PLFAs except fungal PLFAs and by the decreased ratio of G+/G−, sat/monunsat, iso/anteiso, F/B except trans/cis while P. liquidambari inoculation enhanced N-fertilization effect except increased fungal PLFA and decreased trans/cis. PCA using identified marker PLFAs revealed definite discrimination among the treatments which further statistically confirmed structural changed of microbial community. Nitrogenase activity representative of N-fixing community decreased in N-fertilizer treatment while P. liquidambari inoculation increased. In short, application of P. liquidambari with low doses of N-fertilizer improved rice growth and reduced N-fertilizer requirement by increasing enzymes activities involved in C, N and P cycling, structural and functional diversity of microbes, nitrogenase activity involved in N2 fixation and accumulation of total-N.

Litter input decreased the response of soil organic matter decomposition to warming in two subtropical forest soils.

Interaction effect of temperature and litter input on SOM decomposition is poor understood, restricting accurate prediction of the dynamics and stocks of soil organic carbon under global warming. To address this knowledge gap, we conducted an incubation experiment by adding 13C labeled leaf-litter into a coniferous forest (CF) soil and a broadleaved forest (BF) soil. In this experiment, response of the temperature sensitivity (Q10) of SOM decomposition to the increase in litter input was investigated. The temperature dependences of priming effect (PE) and soil microbial community were analyzed. The Q10 for CF soil significantly decreased from 2.41 in no-litter treatment to 2.05 in litter-added treatment and for BF soil from 2.14 to 1.82, suggesting that litter addition decreases the Q10. PE in the CF soil was 24.9% at 20 °C and 6.2% at 30 °C, and in the BF soil the PE was 8.8% at 20 °C and −7.0% at 30 °C, suggesting that PE decreases with increasing temperature. Relative PE was positively related to the concentrations of Gram-negative bacterial and fungal PLFAs. This study moves a step forward in understanding warming effect on forest carbon cycling by highlighting interaction effect of litter input and warming on soil carbon cycling.

Impacts of nitrogen‐fixing and non‐nitrogen‐fixing tree species on soil respiration and microbial community composition during forest management in subtropical China

AbstractForest management with N‐fixing trees can improve soil fertility and tree productivity, but have little information regarding belowground carbon processes and microbial properties. We aimed to evaluate the effects of three forest management regimes, which were Erythrophleum fordii (N‐fixing tree), Pinus massoniana (non‐N‐fixing tree), and their mixed forest, on soil respiration and microbial community composition in subtropical China, using Barometric Process Separation and phospholipid fatty acid profiles, respectively. We found that the inclusions of N‐fixing species in forests significantly increased the soil respiration, but have no effects on SOC and ecosystem total C stock. In addition, soil microbial communities were obviously different among the three forest management regimes. For instance, total and bacterial PLFAs were higher in the E. fordii and mixed forest than in the P. massoniana forest. Conversely, fungal PLFAs in the P. massoniana forest were elevated versus the other two forests. Soil total N, nitrate‐N and pH were the key determinants shaping the microbial community composition. Our study suggests that variations in soil respiration in the studied forests could be primarily explained by the differences of root biomass and soil microbial biomass, but not soil organic carbon. Although soil fertility and microbial biomass were promoted, N‐fixing plantings also brought on increased CO2 emissions in laboratory assays. The future decision of tree species selection for forest management in subtropical China therefore needs to consider the potential influences of tree species on CO2 emissions.

Species-specific effects of plant invasions on activity, biomass, and composition of soil microbial communities

This study assessed the effects of Reynoutria japonica, Rudbeckia laciniata, and Solidago gigantea invading sites within and outside river valleys on activity, biomass, and composition of soil microbial communities. Microbial properties such as soil respiration, urease and arylsulfatase activities, microbial biomass (based on substrate-induced respiration, or SIR, and phospholipid fatty acids, or PLFA), and community composition (based on PLFA) were determined. R. japonica encroached on sites characterized by the lowest values of microbiological properties and R. laciniata on sites with the highest microbiological quality. The effect of invasion on soil microbial properties depended on the invasive plant species. R. japonica significantly decreased microbial biomass, determined by both SIR and total PLFA, urease activity, fungal PLFA, fungal:bacterial PLFA ratio, gram-negative bacterial PLFA, and soil respiration in comparison to soil under adjacent native plant communities. Microbial community composition also differed between soils under R. japonica and those under native plants. In contrast, R. laciniata and S. gigantea did not influence most microbial properties, though S. gigantea significantly increased fungal PLFA and R. laciniata and S. gigantea increased fungal:bacterial PLFA ratio. The effects of plant invasion on microbial properties were basically similar in soils located within and outside river valleys, probably because initially (i.e., before invasion) soils from the two locations were largely similar in terms of basic properties such as texture, moisture, pH, C:N ratio, and most microbial properties.

Response of soil nematode community composition and diversity to different crop rotations and tillage in the tropics

Soil nematode community composition and diversity response to banana-pineapple (BA), banana-papaya (BP), banana-rice (BR) rotations and banana monoculture (CK) (12-year annual crops) under no-tillage (NT) and conventional tillage (CT) were assessed in the Wanzhong Farm in Hainan Island, China. Soil samples were taken at depth of 0–40cm in 2014–2015. A total of 47 nematode genera with relative abundance over 0.1% were identified. Acrobeloides in BANT and BRCT, Aphelenchus in BANT, BACT, BRNT and BRCT, Helicotylenchus, Rotylenchulus and Meloidogyne in CKNT and CKCT were the dominant genera. In comparison with CK, BA, BP and BR increased the number of bacterivores, fungivores and omnivore–carnivores, and the concentration of bacterial PLFA and fungal PLFA. The no-tillage soils favored bacterivores, fungivores and high colonizer-persister (c-p) value omnivores and carnivores, but reduced plant parasites. Soil food web in the rotation combined with no-tillage systems was highly structured, mature and moderately enriched as indicated by Structure (SI), Maturity (MI) and Enrichment (EI) index values, respectively. Higher number of bacterivores and lower values of Channel index (CI) suggested bacterial-dominated decomposition in no-tillage soil. Soil nematode diversity and functional metabolic footprint were much greater after 12 years of crop rotation. The descriptive indicators were useful to provide insight into the effect of rotation and tillage, and the evaluative indicators were more comprehensive for interpreting the structure and function of the soil food web under different crop rotations and tillage.

Riparian reforestation: are there changes in soil carbon and soil microbial communities?

Reforestation of pastures in riparian zones has the potential to decrease nutrient runoff into waterways, provide both terrestrial and aquatic habitat, and help mitigate climate change by sequestering carbon (C). Soil microbes can play an important role in the soil C cycle, but are rarely investigated in studies on C sequestration. We surveyed a chronosequence (0–23years) of mixed-species plantings in riparian zones to investigate belowground (chemical and biological) responses to reforestation. For each planting, an adjacent pasture was surveyed to account for differences in soil type and land-use history among plantings. Two remnant woodlands were included in the survey as indicators of future potential of plantings. Both remnant woodlands had significantly higher soil organic C (SOC) content compared with their adjacent pastures. However, there was no clear trend in SOC content among plantings with time since reforestation. The substantial variability in SOC sequestration among plantings was possibly driven by differences in soil moisture among plantings and the inherent variability of SOC content among reference pastures adjacent to plantings. Soil microbial phospholipid fatty acids (PLFA, an indicator of microbial biomass) and activities of decomposition enzymes (β-glucosidase and polyphenol oxidase) did not show a clear trend with increasing planting age. Despite this, there were positive correlations between total SOC concentration and microbial indicators (total PLFA, fungal PLFA, bacterial PLFA and activities of decomposition enzymes) across all sites. The soil microbial community compositions (explored using PLFA markers) of older plantings were similar to those of remnant woodlands. There was a positive correlation between the soil carbon:nitrogen (C:N) and fungal:bacterial (F:B) ratios. These data indicate that in order to maximise SOC sequestration, we need to take into account not only C inputs, but the microbial processes that regulate SOC cycling as well.

Differential effects of conifer and broadleaf litter inputs on soil organic carbon chemical composition through altered soil microbial community composition

A strategic selection of tree species will shift the type and quality of litter input, and subsequently magnitude and composition of the soil organic carbon (SOC) through soil microbial community. We conducted a manipulative experiment in randomized block design with leaf litter inputs of four native subtropical tree species in a Pinus massoniana plantation in southern China and found that the chemical composition of SOC did not differ significantly among treatments until after 28 months of the experiment. Contrasting leaf litter inputs had significant impacts on the amounts of total microbial, Gram-positive bacterial, and actinomycic PLFAs, but not on the amounts of total bacterial, Gram-negative bacterial, and fungal PLFAs. There were significant differences in alkyl/O-alkyl C in soils among the leaf litter input treatments, but no apparent differences in the proportions of chemical compositions (alkyl, O-alkyl, aromatic, and carbonyl C) in SOC. Soil alkyl/O-alkyl C was significantly related to the amounts of total microbial, and Gram-positive bacterial PLFAs, but not to the chemical compositions of leaf litter. Our findings suggest that changes in forest leaf litter inputs could result in changes in chemical stability of SOC through the altered microbial community composition.

No synergistic effects of water and nitrogen addition on soil microbial communities and soil respiration in a temperate desert

Soil microbial communities play an important role in regulating land–atmosphere CO2 exchange in terrestrial ecosystems. However, their responses to climate change are unclear. We explored the effects of water and nitrogen addition and their interaction on soil microbes and the resulting impacts on soil carbon emissions in the Gurbantunggut Desert, northwestern China. A manipulative 30% increase in precipitation and 5gNm−2year−1 deposition alone and in combination was applied across three years from 2011 to 2013. Water addition significantly increased microbial biomass and respiration, metabolic quotient, and the utilization of carbohydrates, carboxylic acids and amino acids. Water addition did not change the microbial community composition. Nitrogen addition only significantly increased soil bacterial PLFAs, while exerting no significant impacts on soil fungal PLFAs, microbial respiration and soil respiration. Moreover, nitrogen addition had no significant impacts on microbial community composition. Water and nitrogen addition in combination did not generate synergistic effects on microbial communities and soil respiration. Across treatments in three years, soil respiration and microbial respiration were positively correlated with microbial total PLFAs, microbial carbon utilization profiles, while being independent of microbial community structure. This study suggests water addition can increase soil carbon emission through increasing microbial utilization of labile carbon, and water plus nitrogen addition had no synergistic effects on soil microbial communities and soil respiration, demonstrating nitrogen is not a limiting factor for soil microbial communities in the scenario of increasing precipitation in this desert ecosystem.

Effect of rice straw application on microbial community and activity in paddy soil under different water status.

Rice straw application and flooding are common practices in rice production, both of which can induce changes in the microbial community. This study used soil microcosms to investigate the impact of water status (saturated and nonsaturated) and straw application (10 g kg(-1) soil) on soil microbial composition (phospholipid fatty acid analysis) and activity (MicroResp(™) method). Straw application significantly increased total PLFA amount and individual PLFA components independent of soil moisture level. The amount of soil fungal PLFA was less than Gram-negative, Gram-positive, and actinomycete PLFA, except the drained treatment with rice straw application, which had higher fungal PLFA than actinomycete PLFA at the initial incubation stage. Straw amendment and waterlogging had different effects on microbial community structure and substrate-induced pattern. PLFA profiles were primarily influenced by straw application, whereas soil water status had the greater influence on microbial respiration. Of the variation in PLFA and respiration data, straw accounted for 30.1 and 16.7 %, while soil water status explained 7.5 and 29.1 %, respectively. Our results suggest that (1) the size of microbial communities in paddy soil is more limited by carbon substrate availability rather than by the anaerobic conditions due to waterlogging and (2) that soil water status is more important as a control of fungal growth and microbial community activity.