Autotoxicity of continuoulys cropped passion fruit (Passiflora edulis Sims) soil

We determined the soil autotoxicity in the rhizosphere soil of passion fruit continued cropping up to 3 years, and analyzed the changes in the enzyme activity, microbial quantity and diversity in rhizosphere soil. The results showed that the autotoxicity of passion fruit rhizosphere soil increases with the increase in continuous cropping years. The microbial biomass carbon, microbial respiration, and the activity of enzymes (protease, urease and catalase) in passion fruit rhizosphere soil decreased with increases in passion fruit continuous cropping years. Contrarily, the activity of polyphenol oxidase was opposite, showing an upward trend. The results of BIOLOG eco-plate showed that the differences in soil carbon sources between different continuous cropping years were mainly amino acids, carboxylic acids, phenolic acids and amine carbon sources. The ratio of bacteria, bacteria/fungus ratio, actinomycetes, protozoa and total marker PLFA in the rhizosphere soil decreased significantly with the increase of soil planting years, while the total PLFA of fungi increased. Thus, with the increase of continuous cropping years of passion fruit, the soil autotoxicity was intensified and the soil enzyme activity and soil microbial diversity decreased.

Evidence of rapid non-targeted effects of cycloheximide on soil bacteria using 13C-PLFA analysis

Stable isotope probing of phospholipid fatty acids (PLFA-SIP) is useful when studying bacterial contributions to soil processes, and it is an effective way to separate fungal and bacterial activity by linking 13C enrichment to specific PLFAs. Distinguishing bacterial contributions to soil processes often employs selective inhibitors; however, studies demonstrating their efficacy when using PLFA-SIP are less common. Here, we determined the effect of the fungal inhibitor cycloheximide (4.8 mg g−1 dry soil) and the bacterial inhibitor bronopol (0.48 mg g−1 dry soil) on microbial communities white spruce [Picea glauca (Moench) Voss] forest floor by measuring the uptake of 13C-enriched glucose (2 mg g−1 dry soil) in microbial PLFAs. We targeted [13C]glucose uptake by the bacterial community conditioned to a stable soil environment of 23 °C for over 2 wk rather than new bacteria generated from active colony growth caused by glucose addition. Nearly all bacterial PLFAs exhibited pronounced inhibition of 13C enrichment in the presence of bronopol. Limited inhibition of 13C enrichment in the presence of cycloheximide was observed as bacterial PLFA affected by cycloheximide had roughly one third less 13C enrichment than samples emended with [13C]glucose alone. Inhibitory effects only reduced 13C enrichment and did not affect total PLFA concentrations, implying that the inhibitors in the concentrations applied were impeding bacterial activity without causing cell death. Based on this work, we conclude that bronopol is an effective inhibitor for bacteria. Additionally, non-targeted effects of cycloheximide on soil bacteria must be accounted for when it is used in soil incubations.

Phospholipid biomarkers analysis as a tool for microbial community assessment on radionuclides contaminated territories

The presence of specific components in the environment can change the state of cenoses. The effect of ionizing radiation on plant communities, animals and humans have been well studied, while the effect on soil microflora has not been insufficiently studied. In this paper investigated the effect of radionuclide contamination on microflora of soil samples from the territory of PTLRW "Red Forest 1" (trench), "Red Forest 2" (outside the trench), " Cooling Pond " and " Zalissia ". Phospholipid fatty acid (PLFA) content was obtained by PLFA analysis. The highest level of total PLFA was observed in the territory of "Zalissia" which was 17.40 ± 10.59 μg / h. From the territory of PTLRW "Red Forest 1" (trench) and "Red Forest 2" (outside the trench) the level of total PLFA was 16.29 ± 3.43 μg / g and 16.40 ± 2.90 μg / h, respectively. The PLFA content of the "Cooling Pond" was significantly different from the "Red Forest" and " Zalissia ". The taxonomic groups assessment of the samples, a fungus, gram-positive and gram-negative bacteria content increased in PTLRW "Red Forest" relative to the point "Zalissia ".

Effects of Different Ages of Robinia pseudoacacia Plantations on Soil Physiochemical Properties and Microbial Communities

Robinia pseudoacacia is widely planted on the Loess Plateau as a strong drought-tolerant and salt-tolerant species for vegetation restoration. However, this mode of pure plantation has triggered great concern over the soil ecosystem. The aim of this study was to explore the effects of the plantation on soil physiochemical properties, soil microorganisms, and the relationship between them in Robinia pseudoacacia plantations of different ages. Four different ages of Robinia pseudoacacia stands, including 10-year-old, 15-year-old, 25-year-old, and 40-year-old (abbreviated as Y10, Y15, Y25, and Y40, respectively) were selected, and 20 soil physicochemical and biological indicators were determined. The variation in soil microbial biomass was influenced by sampling depth, and consistent with the variations in TN (soil total nitrogen) and SOC (soil organic carbon) during 25 years’ artificial forestation. Soil moisture increased significantly at Y15 and then decreased at Y40 but other soil properties remained relatively stable. The contents of phosphor lipid fatty acid (PLFA) of different microbial groups followed the order of B (Bacteria) > G− (Gram-negative) > G+ (Gram-positive) > A (Actinomycetes) > F (Fungi). The ratios of F/B (Fungi to Bacteria) and Sat/Mono (Saturated PLFAs to Monosaturated PLFAs) of different ages of plantations showed a similar trend, i.e., declined first, then rose, and declined again. The ratios of Cy/Pre (Cyclopropyl PLFAs to Precursor PLFAs) and G+/G− (Gram-positive to Gram-negative) of the soil of all ages of plantations showed a trend of slow growth and a trend of rapid growth, respectively. Redundancy analysis showed that the contents of individual PLFAs and total PLFA were positively correlated with SOC and TN, but variations of soil PLFA ratios mostly depended on other soil properties. After artificial forestation, the ratios of F/B and Sat/Mono were lower than before forestation, while the ratio of Cy/Pre varied with different soil layers. The ratio of G+/G− increased with the increase in afforestation time, peaking at the 25th year. The contents of individual PLFAs and total PLFA may be sensitive indicators of SOC and TN within 25 years’ plantation. Lower ratio of F/B and higher G+/G− suggest that the sustainability of the ecosystem is weaker and the fertility of the soil is lower after plantation of Robinia pseudoacacia.

Response of Soil Microbial Communities to Warming and Clipping in Alpine Meadows in Northern Tibet

In order to explore responses of soil microbial communities among different alpine meadows under warming and clipping, soil microorganisms of three alpine meadow sites (low altitude: 4313 m, alpine steppe meadow, 30°30′ N, 91°04′ E; mid-altitude: 4513 m, alpine steppe meadow, 30°31′ N, 91°04′ E; and high altitude: 4693, alpine Kobresia meadow, 30°32′ N, 91°03′ E) were measured using the phospholipid fatty acid (PLFA) method. Both warming and clipping significantly reduced PLFA content and changed the community composition of soil microbial taxa, which belong to bacterial and fungal communities in the alpine Kobresia meadow. Warming significantly reduced the soil total PLFA content by 36.1% and the content of soil fungi by 37.0%; the clipping significantly reduced the soil total PLFA content by 57.4%, the content of soil fungi by 49.9%, and the content of soil bacteria by 60.5% in the alpine Kobresia meadow. Only clipping changed the total fungal community composition at a low altitude. Neither clipping nor warming changed the microbial community composition at a moderate altitude. Soil temperature, soil moisture, and pH were the main factors affecting soil microbial communities. Therefore, the effects of warming and clipping on soil microbial communities in alpine meadows were related to grassland types and soil environmental conditions.

The effects of organic and inorganic phosphorus amendments on the biochemical attributes and active microbial population of agriculture podzols following silage corn cultivation in boreal climate

Phosphorus (P) is the second most important macronutrient that limits the plant growth, development and productivity. Inorganic P fertilization in podzol soils predominantly bound with aluminum and iron, thereby reducing its availability to crop plants. Dairy manure (DM) amendment to agricultural soils can improve physiochemical properties, nutrient cycling through enhanced enzyme and soil microbial activities leading to improved P bioavailability to crops. We hypothesized that DM amendment in podzol soil will improve biochemical attributes and microbial community and abundance in silage corn cropping system under boreal climate. We evaluated the effects of organic and inorganic P amendments on soil biochemical attributes and abundance in podzol soil under boreal climate. Additionally, biochemical attributes and microbial population and abundance under short-term silage corn monocropping system was also investigated. Experimental treatments were [P0 (control); P1: DM with high P2O5; P2: DM with low P2O5; P3: inorganic P and five silage-corn genotypes (Fusion RR, Yukon R, A4177G3RIB, DKC 23-17RIB and DKC 26-28RIB) were laid out in a randomized complete block design in factorial settings with three replications. Results showed that P1 treatment increased acid phosphatase (AP-ase) activity (29% and 44%), and soil available P (SAP) (60% and 39%) compared to control treatment, during 2016 and 2017, respectively. Additionally, P1 treatments significantly increased total bacterial phospholipids fatty acids (ΣB-PLFA), total phospholipids fatty acids (ΣPLFA), fungi, and eukaryotes compared to control and inorganic P. Yukon R and DKC 26-28RIB genotypes exhibited higher total bacterial PLFA, fungi, and total PLFA in their rhizospheres compared to the other genotypes. Redundancy analyses showed promising association between P1 and P2 amendment, biochemical attributes and active microbial population and Yukon R and DKC 26-28RIB genotypes. Pearson correlation also demonstrated significant and positive correlation between AP-ase, SAP and gram negative bacteria (G−), fungi, ΣB-PLFA, and total PLFA. Study results demonstrated that P1 treatment enhanced biochemical attributes, active microbial community composition and abundance and forage production of silage corn. Results further demonstrated higher active microbial population and abundance in rhizosphere of Yukon R and DKC 26-28RIB genotypes. Therefore, we argue that dairy manure amendment with high P2O5 in podzol soils could be a sustainable nutrient source to enhance soil quality, health and forage production of silage corn. Yukon R and DKC 26-28RIB genotypes showed superior agronomic performance, therefore, could be good fit under boreal climatic conditions.

Nitrogen Addition Affects Soil Respiration Primarily through Changes in Microbial Community Structure and Biomass in a Subtropical Natural Forest

Forest soil respiration plays an important role in global carbon (C) cycling. Owing to the high degree of C and nitrogen (N) cycle coupling, N deposition rates may greatly influence forest soil respiration, and possibly even global C cycling. Soil microbes play a crucial role in regulating the biosphere–atmosphere C exchange; however, how microbes respond to N addition remains uncertain. To better understand this process, the experiment was performed in the Castanopsis kawakamii Hayata Nature Reserve, in the subtropical zone of China. Treatments involved applying different levels of N (0, 40, and 80 kg ha−2 year−1) over a three-year period (January 2013–December 2015) to explore how soil physicochemical properties, respiration rate, phospholipid fatty acid (PLFA) concentration, and solid state 13C nuclear magnetic resonance responded to various N addition rate. Results showed that high levels of N addition significantly decreased soil respiration; however, low levels of N addition significantly increased soil respiration. High levels of N reduced soil pH and enhanced P and C co-limitation of microorganisms, leading to significant reductions in total PLFA and changes in the structure of microbial communities. Significant linear relationships were observed between annual cumulative respiration and the concentration of microbial biomass (total PLFA, gram-positive bacteria (G+), gram-negative bacteria (G−), total bacteria, and fungi) and the microbial community structure (G+: G− ratio). Taken together, increasing N deposition changed microbial community structure and suppressed microbial biomass, ultimately leading to recalcitrant C accumulation and soil C emissions decrease in subtropical forest.

Ammonium and nitrate additions differentially affect soil microbial biomass of different communities and enzyme activities in slash pine plantation in subtropical China

The ratios of nitrate to ammonium in wet atmosphere nitrogen (N) deposition compounds were increasing recently. However, the individual effects of nitrate and ammonium deposition on soil microbial communities biomass and enzyme activities are still unclear. We conducted a four-year N addition field experiment to evaluate the responses of soil microbial communities biomass and enzyme activities to ammonium (NH4Cl) and nitrate (NaNO3) additions. Our results showed that (1) the inhibitory effects of ammonium additions on total mass of phospholipid fatty acid (PLFA) were stronger than those of nitrate additions. Both decreased total PLFA mass about 24 % and 11 %, respectively. The inhibitory effects of ammonium additions on gram positive bacteria (G+) and bacteria, fungi, actinomycetes (A), and arbuscular mycorrhizal fungi (AMF) PLFA mass ranged from 14 %–40 %. (2) Both ammonium and nitrate additions inhibited absolute activities of C, N, and P hydrolyses and oxidases, and nitrate additions had stronger inhibition effects on the acid phosphatase (AP) than ammonium additions. Both ammonium and nitrate additions decreased N-acquisition specific enzyme activities (enzyme activities normalized by total PLFA mass) about 21 % or 43 %, respectively. However, ammonium additions increased P-acquisition specific enzyme activities about 19 % comparing to control. (3) Redundancy analysis (RDA) showed that the measured C, N, and P hydrolyses and polyphenol oxidase (PPO) activities were positively correlated with soil pH and ammonium contents, but negatively with nitrate contents; the mass of PLFA biomarkers were positively correlated with soil pH, soil organic carbon (SOC), and total N contents, but negatively with ammonium contents. (4) The soil enzyme activities varied seasonally in the order of March > June > October. On the contrary, microbial PLFA mass was higher in October than in March and June. Our results concluded that inhibition of mass of PLFA biomarkers and enzyme activities might be contributed to acidification caused by ammonium addition. Soil absolute enzyme activities were inhibited indirectly by acidification and nitrification, but specific enzyme activities normalized by PLFA were directly affected by N additions. It was meaningful to separate the effects of ammonium and nitrate additions on soil microbial communities and enzyme activities.

Arbuscular mycorrhiza enhance the rate of litter decomposition while inhibiting soil microbial community development

Although there is a growing amount of evidence that arbuscular mycorrhizal fungi (AMF) influence the decomposition process, the extent of their involvement remains unclear. Therefore, given this knowledge gap, our aim was to test how AMF influence the soil decomposer communities. Dual compartment microcosms, where AMF (Glomus mosseae) were either allowed access (AM+) to or excluded (AM−) from forest soil compartments containing litterbags (leaf litter from Calophyllum polyanthum) were used. The experiment ran for six months, with destructive harvests at 0, 90, 120, 150, and 180 days. For each harvest we measured AMF colonization, soil nutrients, litter mass loss, and microbial biomass (using phospholipid fatty acid analysis (PLFA)). AMF significantly enhanced litter decomposition in the first 5 months, whilst delaying the development of total microbial biomass (represented by total PLFA) from T150 to T180. A significant decline in soil available N was observed through the course of the experiment for both treatments. This study shows that AMF have the capacity to interact with soil microbial communities and inhibit the development of fungal and bacterial groups in the soil at the later stage of the litter decomposition (180 days), whilst enhancing the rates of decomposition.

Composition of microbial PLFAs and correlations with topsoil characteristics in the rare active travertine spring-fed fen

We studied soil PLFAs composition and specific soil properties among transect of small-scale fen in Stankovany, Slovakia. The aim of this study was to determine potential differences in the microbial community structure of the fen transect and reveal correlations among PLFAs and specific soil characteristics. PCA analyses of 43 PLFAs showed a separation of the samples along the axis largely influenced by i14:0, 16:1ω5, br17:0, 10Me16:0, cy17:0, cy17:1, br18:0 and 10Me17:0. We measured a high correlation of sample scores and distance from fen edge (Kendall’s test τ = 0.857, P < 0.01). Kendall’s test showed a negative correlation of PLFAs content (mol%) and distance from the fen border for Gram (+) bacteria, Actinomycetes, mid-chain branched saturated PLFAs and total PLFAs. The redundancy analysis of the PLFA data set for the eight samples using PLFAs as species and 21 environmental variables identified soil properties significantly associated with the PLFA variables, as tested by Monte Carlo permutation showing most significant environmental variables including dichlormethan extractables, water extractables, Klason lignin, acid-soluble lignin, holocellulose, total extractables, organic matter content, total PLFA amount, bacterial PLFA and total nitrogen negatively correlated to axis 1 and dry weight and carbonate carbon positively correlated to axis 1. The amounts of Klason lignin, acid-soluble lignin, holocellulose total extractables, total PLFA, bacterial PLFA and total nitrogen were significantly correlated positively to the distance from fen border while moisture and total carbonate carbon were correlated negatively.