Chloroform Fumigation Extraction Method Research Articles

On the presence and detectability of polyphosphates in soil microbial biomass

Polyphosphates (PolyP), i.e. phosphate polymers, are commonly found in pure cultures of various microorganisms. Although they have been the subject of intensive microbiological research in the past, they have never been directly studied in species-rich soil microbial communities. So far, there are only few studies indirectly suggesting that soil microorganisms build up PolyP as a storage for phosphorus (P), and use them when soil P availability decreases. We attempted to provide direct evidence for PolyP presence in soil microorganisms, and test if the PolyP can be detected in the soil microbial biomass P pool applying the standard chloroform-fumigation extraction method. Twelve different soil samples were collected along the gradient of forest recovery after the bark beetle outbreak in the catchments of two adjacent glacier lakes (Plešné and Čertovo, Bohemian forest, Czech Republic). The presence of PolyP in the samples was assessed by staining in a manipulative experiment designed to deplete any PolyP present. Carbon (C), nitrogen (N), and P in the microbial biomass were estimated by the chloroform-fumigation extraction method and soil slurries of fresh samples stained by the Neisser method. The soils were then mixed with sterile sand and supplemented with growth medium without P. The rate of growth of microbial biomass was estimated from oxygen consumption during one week incubation at dark. After one week, the microbial biomass C, N, and the P were estimated again and samples stained. The combination of the incubation experiment and staining proved that the soil microorganisms in the collected samples contained PolyP and that PolyP were used to achieve maximum growth rate under P-limited conditions. The C to N to P ratio increased significantly over one week of incubation reflecting the changing PolyP content. To further confirm that the fumigation extraction method is sensitive to PolyP content, manufactured PolyP was added to all soils at different steps of the fumigation extraction method, and its recovery was estimated. Recovery ranged from 80 to 100%. Abiotic depolymerisation at acidic conditions required for the correct quantification of P-PO4 using molybdenum-blue method was very likely responsible for half of the recovery, the remaining being enzymatic depolymerisation. We conclude that PolyP are ubiquitous in soils and affect microbial biomass P estimation. The high recovery rate of PolyP around 90% implies that presence of PolyP can cause a significant overestimation of the microbial biomass P when typical correction factor 0.4 is used.

Enduring reduction of carbon and nitrogen emissions from landfills due to aeration?

The objective of the present work is to investigate to what extent emission reductions observed during landfill aeration are permanent. To do so, lab-scale degradation experiments using waste from an old landfill have been conducted under different conditions (anaerobic, (partly) aerobic returning to anaerobic, aerobic) and balances for carbon and nitrogen have been established. For the latter, all emissions of C and N (except N2) and their pools at the start and end of the experiment have been determined. In addition, the chloroform fumigation-extraction method (biocidal treatment) has been applied to determine microbially bound carbon and to estimate nitrogen in microbial biomass accordingly. The results reveal that 18g TOC·kg DM-1 of the waste material were mineralized during aerobic treatment for 699days, which is equivalent to about 14% of the initial TOC content. For the anaerobic treatment, only 10g TOC·kg DM-1 were released. For the aerobic-anaerobic reactors, a slight increase in methane emissions approximately 10months after termination of aeration was observed. With respect to leachate emissions, the results indicate significantly lower emission levels (factor 1.5 for TOC and factor 4 for TN) for the reactors, which were aerated at least sometimes. The biocidal treatment highlights that this emission reduction is rather based on an increased sorption capacity of aerated waste (higher ion exchange capacity) than a lower overall pollutant potential. It is shown that regardless of the operation mode, most nitrogen remained in solids (83.1-92.6%) and is subject to internal recycling during waste degradation.

Is microbial biomass measurement by the chloroform fumigation extraction method biased by experimental addition of N and P?

The chloroform fumigation extraction (CFE) method determines microbial biomass carbon (MBC) or nitrogen (MBN) by calculating the increase in extractable carbon (C) or nitrogen (N) due to microbial lysis during chloroform fumigation. In China, many studies have focused on the impacts of N and phosphorus (P) addition on soil MBC and MBN in forest ecosystems, where substantial atmospheric N deposition has strongly acidified soils. The addition of nutrients may alter the extraction process applied in the CFE method, potentially influencing the MBC and MBN determined by the CFE method independently of the actual microbial biomass. In this study, we tested whether the MBC and MBN determined by the CFE method were biased by the experimental addition of N and P in strongly acidified Chinese forest soils by adding N and P to the soils immediately before chloroform fumigation, which should not affect the actual microbial biomass. P addition significantly elevated the dissolved organic carbon (DOC) content, especially after fumigation, while N addition significantly reduced the dissolved nitrogen (DN) content. The added N was subtracted using blank samples without soil. However, the altered DOC and DN contents did not affect the MBC and MBN contents determined by the CFE method. In conclusion, our study suggests that the CFE is a relatively robust method to test the impacts of nutrient addition on microbial biomass in the strongly acidified soils of Chinese forests. We also suggested that: (i) even if a fertilization experiment results in an elevated DOC content following P addition, it does not necessarily indicate a stimulation of DOC production by microbes; and (ii) the soil adsorption capacity or the strength of microbial N uptake during the extraction procedure applied in the CFE method may affect the determination of MBN by influencing the DN extraction efficiency.

Soil microbial DNA concentration is a powerful indicator for estimating soil microbial biomass C and N across arid and semi-arid regions in northern China

Soil microbes exert critical control over ecosystem functions by regulating organic matter decomposition and nutrient cycling. Diverse methods have been adopted to estimate the soil microbial biomass carbon (Cmic) and nitrogen (Nmic), largely based on fumigation and respiration or biomarkers, such as phospholipids and ATP. Although soil microbial DNA is also an important biomarker, whether this biomarker can be used to estimate Cmic and Nmic at a large scale in arid and semi-arid regions that remains unclear. To explore this, the 124 soil samples collected from 28 different vegetation/microhabitat types in diverse ecosystems (i.e., desert, cropland, typical steppe, meadow steppe and forest) across arid and semi-arid regions in northern China; then, the strong linear relationships were developed among soil microbial DNA concentrations with the Cmic and Nmic contents estimated by the classic chloroform fumigation-extraction (CFE) method. The results showed that the soil microbial DNA concentrations were linearly related to the observed Cmic (r = 0.99) and Nmic (r = 0.97) across the diverse vegetation types, although soil microbial biomass presented an enormous fluctuation. Moreover, based on the above-mentioned coefficients of the linear relationship, it was further inferred that the mean proportions of carbon and nitrogen elements in DNA were 0.99% and 3.70% for Cmic and Nmic, respectively, when assuming the G-C base-pair proportion is 50% in double-stranded DNA. In conclusion, the study proved that soil microbial DNA as a powerful indicator may provide convenient and efficient estimates for Cmic and Nmic in arid and semi-arid systems. Although this method still needs to be further improved and examined at a larger scale, it provides a good addition to the already existing methods to determine microbial biomass.

Case Study upon Foliar Application of Biofertilizers Affecting Microbial Biomass and Enzyme Activity in Soil and Yield Related Properties of Maize and Wheat Grains.

Simple SummaryThe study evaluated the effects of the application of microbial inoculants (N-fixing Klebsiella planticola and Enterobacter spp.), two rates of composite mineral fertilizers, and their combination on microbial biomass carbon, dehydrogenase and proteinase activity in acid Lessivated Cambisol and yield-related properties of maize and wheat grains in a two-year trial. The results indicated that mineral fertilizers are not, in general, negative for soil microbiota when used in the context of sustainable agriculture without monoculture. It was found that the combined application of microbial inoculants and lower doses of mineral nitrogen, phosphorus, and potassium (NPK) fertilizers, increased the yield of maize and wheat compared to the use of only NPK fertilizers in our case study. The highest values of the examined parameters of soil fertility were determined in the period with better precipitation distribution during the vegetation period of the studied year due to the optimal values of soil moisture and air temperature. Concluding, the authors point out the task of science to offer the producer a solution for conducting intensive agricultural production, which must be economically and ecologically safer.This study evaluated the effects of the application of microbial inoculants (N-fixing Klebsiella planticola and Enterobacter spp.), two rates of composite mineral fertilizers, and their combination on microbial biomass carbon (MBC), dehydrogenase (DHA), and proteinase activity (PTA) in Lessivated Cambisol and yield-related properties of maize and wheat grains in a two-year trial. Unfertilized soil was used as a control variant. MBC was measured using the chloroform fumigation-extraction method, DHA was determined spectrophotometrically by measuring the intensity of the formed red-colored triphenyl formazan, while PTA was determined using a titration method by measuring the degree of gelatine decomposition. In grain samples, P was determined spectrophotometrically, K—by flame emission photometry, N—on an elemental carbon/nitrogen/sulfur (CNS) analyzer, and crude proteins—by calculation of N content. Measuring both crops’ yield was carried out at the end of the vegetation. The results indicated that mineral fertilizers are not, in general, negative for soil microbiota when used in the context of sustainable agriculture without monoculture. There is a significant increase in the values of soil MBC, DHA, and PTA in the variants with combined application of bacterial inoculants and lower rates of mineral fertilizers. The highest values of these parameters were determined in the period with a better distribution of precipitation during the vegetation period of the year. The mentioned combination also resulted in a higher grain yield of maize and wheat comparing to the application of lower rates of the NPK nutrients solely. The combined application of high rates of mineral fertilizers and bacterial inoculants resulted in significantly increased N, P, K, and protein content in the grains of crops, and the same applied to yield. Concluding, studied bacterial inoculants can be used to specify the replacement of nitrogen fertilizers, stimulating the microbial biomass and enzyme activity in the soil, helping to ensure that the supply of nutrients contributing to an optimized yield of crops is maintained.

Effect of land\xa0use, season, and soil depth on soil microbial biomass carbon of Eastern Himalayas

BackgroundSoil microbial biomass, an important nutrient pool for ecosystem nutrient cycling is affected by several factors including climate, edaphic, and land-use change. Himalayan soils are young and unstable and prone to erosion and degradation due to its topography, bioclimatic conditions and anthropogenic activities such as frequent land-use change. Through this study, we tried to assess how soil parameters and microbial biomass carbon (MBC) of Eastern Himalayan soils originated from gneissic rock change with land-use type, soil depth and season. Chloroform fumigation extraction method was employed to determine MBC from different land-use types.ResultsSoil physical and chemical properties varied significantly with season, land-use and soil depth (p < 0.001). The maximum values of soil properties were observed in the rainy season followed by summer and winter season in all the study sites. Annual mean microbial biomass carbon was highest in the forest (455.03 μg g− 1) followed by cardamom agroforestry (392.86 μg g− 1) and paddy cropland (317.47 μg g− 1). Microbial biomass carbon exhibited strong significant seasonal difference (p < 0.001) in all the land-use types with a peak value in the rainy season (forest-592.78 μg g− 1; agroforestry- 499.84 μg g− 1 and cropland- 365.21 μg g− 1) and lowest in the winter season (forest − 338.46 μg g− 1; agroforestry – 320.28 μg g− 1 and cropland − 265.70 μg g− 1). The value of microbial biomass carbon decreased significantly with soil depth (p < 0.001) but showed an insignificant increase in the second year which corresponds to a change in rainfall pattern. Besides, land-use type, season and soil depth, soil properties also strongly influenced microbial biomass carbon (p < 0.001). Microbial quotient was highest in the agroforestry system (2.16%) and least in the subtropical forest (1.91%).ConclusionsOur results indicate that land-use, soil depth and season significantly influenced soil properties and microbial biomass carbon. The physical and chemical properties of soil and MBC exhibit strong seasonality while the type of land-use influenced the microbial activity and biomass of different soil layers in the study sites. Higher soil organic carbon content in cardamom agroforestry and forest in the present study indicates that restoration of the litter layer through retrogressive land-use change accelerates microbial C immobilization which further helps in the maintenance of soil fertility and soil organic carbon sequestration.

Soil microbial biomass and composition from urban landscapes in a semiarid climate

Soil microbial communities have been used as indicators of changes in soil health agroecosystems. However, few studies have evaluated soil health under turfgrass systems especially in semiarid climates. Our study determined whether microbial biomass and composition in residential soils were controlled by home age along a turfgrass chronosequence and evaluated effects of turfgrass management in structuring soil microbial communities. Soil samples were obtained from nine locations within each home age category: oldest (1950–1970), middle (1971–1990), newer (1991–2010), and newest (2011–present) in summer 2018 and 2019. Soil microbial biomass and composition were assessed using chloroform fumigation extraction method (CFEM) and ester-linked fatty acid methyl ester (EL-FAME) analysis. Soil microbial biomass carbon (MBC) and nitrogen (MBN) were 46–52% and 65–75% higher in oldest homes when compared to newest homes, respectively. Neither total FAMEs nor fungal FAME abundance differed for home age categories, but bacterial FAME abundance increased with home age. Non-parametric analysis determined no microbial abundance differences with management practices or turfgrass species. Pearson correlations indicated soil organic matter and silt content most consistently altered the microbial community. Soil microbial communities within semiarid, urban environments shifted from high fungal to bacterial dominated as landscapes matured, potentially due to long-term effects of irrigation, fertilization, and pesticide use. Our results indicate time after establishment was more important to development of soil microbial communities in semiarid, perennial turfgrass systems than subtle differences in management, suggesting soil health and resource conservation goals in this setting may be achievable with relatively low levels of management over time.

Effects of broadleaved tree species on soil microbial stoichiometry in clear-cut patches of Cunninghamia lanceolata plantation

Investigating the response of soil microbial biomass and ecological stoichiometry to tree species transition is of great significance for understanding soil nutrient cycling and availability in forest ecosystems. We measured soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP) and their stoichiometry across 0-40 cm soil depth between Mytilaria laosensis and Cunninghamia lanceolata plantations by the chloroform fumigation extraction method, which were replanted after the harvest of C. lanceolata plantation. The results showed that soil MBC in the 0-10 cm layer and soil MBN and MBP in the 0-20 cm layer under the M. laosensis were significantly higher than those under the C. lanceolata. The MBC/MBP in the 0-20 cm layer and MBN/MBP in the 10-20 cm layer were significantly lower under the M. laosensis plantation. The MBC/MBN showed no significant differences between the two forests. Soil moisture, organic carbon, total nitrogen, total phosphorus, available phosphorus were positively correlated with MBC, MBN and MBP, but negatively correlated with MBC/MBP and MBN/MBP. Results of stepwise linear regression analysis showed that MBN and MBP were mainly affected by soil total nitrogen and available phosphorus, while MBC/MBP and MBN/MBP were mainly driven by available phosphorus and organic carbon, respectively. Our results indicated that tree species transition from C. lanceolata to M. laosensis could increase soil microbial biomass in the surface layers, accelerate soil nutrients turnover and enhance soil nutrient supply. The increases of MBP under M. laosensis indicate alleviation of soil phosphorus limitation for tree growth.

Land rehabilitation improves edaphic conditions and increases soil microbial biomass and abundance

Rehabilitation of farmland improves the local eco-environmental conditions. But to what extent this transformation influences soil microbial properties is less known. In our study we compared variations in soil microbial attributes following changes in land-use types to understand the influence of altered soil properties on microbial biomass and their community structure using chloroform fumigation extraction method and phospholipid fatty acid (PLFA) analysis. For this purpose, 3 agricultural (AL) (farmland, apple orchard and 2 years abandoned land) and 4 rehabilitated lands (RL) of various vegetations grassland, shrubland, mixed forest (Amorpha fruticosa and Pinus tabuliformis Carr.) and forest (Robinia pseudoacacia) were selected. Our results showed higher soil organic carbon (SOC) contents in RL soils (forest >mixed forest >grassland>shrub land) than that in AL soils. In RL soils, soil microbial biomass and abundance of group specific PLFA were significantly higher than those in AL soils. Under different land-use types, microbial community was bacteria dominated over fungi. The microbial physiological indices (G+/G–, cyc/prec and S/M) indicated decreased environmental stress in RL soils in comparison with AL soils. In loess soils, SOC and total N correlated positively (p < 0.05) with microbial biomass C, N and P and also with fungal and bacterial PLFA, indicating a positive microbial mediation in improving soil fertility. Taking together, our findings suggest that land rehabilitation, especially Robinia pseudoacacia planation, improves overall edaphic conditions and accelerates soil microbial biomass accumulation in local regions.

Spatial and temporal patterns in soil organic carbon, microbial biomass and activity under different land-use types in a long-term soil-monitoring network

Preservation of soil organic carbon (SOC) requires knowledge concerning the quantity and quality of both the SOC and the SOC-decomposing microbial community. In northern Germany, this information is assessed as part of Schleswig-Holstein’s long-term soil-monitoring programme, in which topsoils have been analysed since 1995. In this study, we evaluated long-term data from Schleswig-Holstein’s monitoring sites and compared the content of SOC and microbial biomass carbon (MBC) among croplands, grasslands and forests. We distinguished the microbial fractions as total MBC (chloroform fumigation extraction method) and glucose-responsive MBC, and we used the MBC/SOC ratio and soil basal respiration (SBR) to obtain a qualitative view of the SOC and its turnover potential. Additionally, we performed a temporal comparison for SOC and MBC between the periods 1995–2002 and 2005–2015. The results showed that median SOC content is the highest in forest soils (41 g kg−1), followed by grasslands (33 g kg−1), and croplands (12 g kg−1). Different ascending orders occurred for the total MBC (cropland < forest < grassland), however, and for the glucose-responsive MBC (forest < cropland < grassland), indicating differences in SOC quality and the microbial community structure. The different ratios between MBC and SOC showed that SOC in croplands and grasslands is characterised as easily degradable, but more stable in grasslands under no-till conditions. Forest SOC appears almost non-degradable, and thus is most stable in the long term. We concluded that land-use-specific carbon characteristics, including the functional microbial community structure, are beneficial for evaluation of SOC preservation potential. From the temporal perspective, a significant increase (45–114 %) was observable for the total MBC on cropland and grassland sites, whereas the changes in SOC were not significant. The remarkable growth of the total MBC in relation to the glucose-responsive MBC indicates shifts in the microbial community towards a K-strategy metabolism.

Microwave assisted biocidal extraction is an alternative method to measure microbial biomass of carbon from cultivated and non-cultivated soils.

Developing simple and cost-effective methods for soil microbial biomass carbon (MBC) measurement eases routine laboratory analysis and enables large numbers of soil samples to be measured in a relatively short period of time. Thus, the objective of this study was to develop a microwave-assisted biocidal-extraction (MWE) method which does not employ CHCl3 as biocide and K2SO4 as C-extractor, to estimate MBC. First, the microorganisms of soil samples are killed using microwave (MW) irradiation at energy level of 800 J g-1 soil as biocide followed by microwave irradiation extraction (MWE) at 562 W (120 J g-1 soil for 1 min), using deionized water as solvent. Microbial biomass of carbon from two contrasting soils microwaved with 80, 100, and 140 J g-1 soil did not differ from those obtained by using the chloroform fumigation-extraction (CFE) method with 0.5 mol L-1 K2SO4 as extractant. To evaluate the robustness of the MWE method, twenty-six soil samples, from cultivated and non-cultivated areas, with clay contents from 70-690 g kg-1, organic carbon from 5.52 to 50.82 g C kg-1 and pH values from 3.9 to 6.8 were analyzed for MBC using MWE and CFE methods. There was a linear regression (MW = - 17.87 + 0.92*K2SO4; R2 = 0.705; p < 0.001) between MWE and CFE. The biocidal microwave-assisted extraction method using 120 J g-1 soil for 1 min is a cleaner method for evaluating MBC, because it does not require chloroform, potassium sulfate salt and takes a shorter time to extract a set of soil samples.

Seasonal dynamics of soil microbial biomass C and N of Keteleeria fortunei var. cyclolepis forests with different ages

Soil microbial biomass is an important indicator to measure the dynamic changes of soil carbon pool. It is of great significance to understand the dynamics of soil microbial biomass in plantation for rational management and cultivation of plantation. In order to explore the temporal dynamics and influencing factors of soil microbial biomass of Keteleeria fortunei var. cyclolepis at different stand ages, the plantation of different ages (young forest, 5 years; middle-aged forest, 22 years; mature forest, 40 years) at the Guangxi Daguishan forest station of China were studied to examine the seasonal variation of their microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) by chloroform fumigation extraction method. It was found that among the forests of different age, MBC and MBN differed significantly in the 0–10 cm soil layer, and MBN differed significantly in the 10–20 cm soil layer, but there was no significant difference in MBC for the 10–20 cm soil layer or in either MBC or MBN for the 20–40 cm soil layer. With increasing maturity of the forest, MBC gradually decreased in the 0–10 cm soil layer and increased firstly and then decreased in the 10–20 cm and 20–40 cm soil layers, and MBN increased firstly and then decreased in all three soil layers. As the soil depth increased, both MBC and MBN gradually decreased for all three forests. The MBC and MBN basically had the same seasonal variation in all three soil layers of all three forests, i.e., high in the summer and low in the winter. Correlation analysis showed that MBC was significantly positively correlated with soil organic matter, total nitrogen, and soil moisture, whereas MBN was significantly positively correlated with soil total nitrogen. It showed that soil moisture content was the main factor determining the variation of soil microbial biomass by Redundancy analysis. The results showed that the soil properties changed continuously as the young forest grew into the middle-aged forest, which increased soil microbial biomass and enriched the soil nutrients. However, the soil microbial biomass declined as the middle-age forest continued to grow, and the soil nutrients were reduced in the mature forest.

Relationships between feeding and microbial faeces indices in dairy cows at different milk yield levels.

A study was carried out to gain quantitative information on the diet-dependent faecal microbial biomass of dairy cows, especially on the biomass fractions of fungi, Gram-positive (G+) and Gram-negative (G-) bacteria. Groups of high-yield, low-yield and non-lactating cows were investigated at four different farms. A mean faecal microbial biomass C (MBC) concentration of 33.5 mg g-1 DM was obtained by the chloroform fumigation extraction method. This is similar to a mean microbial C concentration of 31.8 mg g-1 DM, which is the sum of bacterial C and fungal C, estimated by cell-wall derived muramic acid (MurN) and fungal glucosamine (GlcN), respectively. However, the response of these two approaches to the feeding regime was contradictory, due to feeding effects on the conversion values. The higher neutral detergent fibre (NDF) and acid detergent fibre (ADF) concentrations in the non-lactating group led to higher (P < 0.05) concentrations of cellulose and lignin in their faeces in comparison with the lactating cows. This change in faecal chemical composition in the non-lactating group was accompanied by usually higher ratios of G+/G- phospholipid fatty acids (PLFA), ergosterol/MBC and fungal C/bacterial C. Although bacteria dominate the faecal microbial biomass, fungi contribute a considerable mean percentage of roughly 20% to the faecal microbiome, according to PLFA and amino sugar data, which requires more attention in the future. Near-infra red spectroscopic estimates of organic N and C fractions of cow faeces were able to model microbial biomarkers successfully, which might be useful in the future to predict its N2O emission potential and fertilizer value.

Microbial Biomass Soil Content and Activity Under Black Alder and Sessile Oak in the Western Black Sea Region of Turkey

Tree species have a remarkable impression on the physical, chemical and microbial properties of the soil. Some tree species like alders create a favorable environment for microbes in their soil–root interface in addition to carrying out soil reclamation. This study, conducted in the Western Black Sea Region of Turkey, compared the N-fixing in the roots of the black alder [Alnus glutinosa (L.) Gaertn.] and the non-N-fixing in those of the sessile oak [Quercus petraea (Matt.) Liebl.] species in terms of physical, chemical and microbiological soil characteristics. Samples of topsoil (0–6.5 cm) were collected randomly from under the black alder and the sessile oak trees, respectively, at seven different sites in the study area. Soil microbial biomass C and N were established by the chloroform fumigation extraction method. Basal respiration of soil was retained by the sodium hydroxide (NaOH) trap method. Contrary to expectations, the average organic C (2.59%), total N (0.22%), microbial biomass C (738.48 µg g−1) and N (99.56 µg g−1) were higher under the sessile oak trees, demonstrating the positive effect of sessile oak on soil microflora. The black alder and sessile oak tree soils exhibited significant differences in their content of organic C (Corg), total N, microbial biomass C (Cmic), and N. In addition, significant positive linear correlations were found between organic C and microbial biomass C, and also between organic C and basal respiration; however, the correlation between the metabolic quotient (qCO2) and Cmic/Corg percentages was negative for the black alder and sessile oak (r = − 0.589 and r = − 0.474, respectively), likely due to the fact that relatively more C was being utilized for growth than for respiration. These results indicated that, compared to the sessile oak, the relatively lower organic C and total N and subsequently, the microbial biomass C and N content under the black alder were most likely due to shallow and deep groundwater flow and thus, the loss of plant nutrients was probably brought about by weathering.

Effects of agronomic treatments on functional diversity of soil microbial community and microbial activity in a revegetated coal mine spoil

Successful restoration of coal mine spoil requires functional microbial community for soil development and biogeochemical cycling to ensure long term sustainability of established plants. The current study investigated functional diversity of the soil microbial community, microbial activities, and physico-chemical properties of a revegetated coal mine spoil that was exposed to different agronomic practices. Treatments included Control (conventional revegetation practice), selective herbicide (SH), mulching (M), succession planting (SP), and green manure (GM) crops. Fluorescein diacetate (FDA) hydrolysis revealed significantly (P < 0.05) higher microbial activity in the GM treatment compared to the Control and all other treatments. Patterns of microbial biomass C (MBC), determined by the chloroform fumigation extraction method, also showed significant (P < 0.05) differences between treatments, with the SH treatment showing the lowest MBC. Basal respiration (BR) and substrate induced respiration (SIR) did not differ amongst the treatments. Principal component analysis of community level physiological profiles data based on Biolog® Ecoplate data revealed differing bacterial functional (metabolic) diversity amongst the treatments. Overall, the study demonstrated significantly (P < 0.05) higher average well color development (AWCD), indicating high metabolic activity, and substrate richness (R) and Shannon's index (H) showed greater functional diversity of the bacterial community in the SP treatment, as compared to other treatments. These results demonstrate that the agronomic treatments such as SP will not only boost microbial activity, but they also play a constructive role in increasing functional diversity of soil microbial communities. Based on these results, we recommend that agronomic practices such as SP should be used as an important component in mine site revegetation programs.

Effect of vegetation type and season on microbial biomass carbon in Central Himalayan forest soils, India

Soil microbial biomass is an important component of soil organic matter constituting from 2 to 5% of the soil organic carbon and play a significant role in the cycling of nutrients and overall organic matter dynamics. The present study assessed the effects of three forest types (Banj-oak forest, Chir-pine forest and Mixed oak-pine forest) on the soil physico-chemical properties and microbial biomass Carbon in Central Himalaya, India. The soil microbial biomass carbon was determined by chloroform fumigation extraction method. In the 2 year of study period, the soil microbial biomass carbon (Cmic) was significantly higher in Mixed oak-pine forest (681 ± 1.81–763 ± 1.82 μg g−1) than in the Banj-oak (518 ± 1.50–576 ± 1.73 μg g−1) and Chir-pine forest (418 ± 1.42–507 ± 2.05 μg g−1). Though insignificant, all the forest types showed distinct seasonal variations in microbial biomass carbon with a minimum value in winter season and maximum value in rainy season. The soil microbial quotients (Cmic to Corg) were higher in Chir-pine (2.52–4.18) and Banj-oak forest (2.26–4.02) than those reported in Mixed oak-pine forest (1.44–2.24). These results indicate that Mixed oak-pine forest is better in sustaining the soil microbial biomass and soil nutrients than Banj-oak and Chir-pine forest. It recommends that nutrients rich Mixed oak-pine forest should be preferred as a forest management practice to promote microbial diversity, their activities and soil quality enhancement in Central Himalayan forests.

Conversion factor (k factor) for estimation of soil microbial biomass potassium by the chloroform-fumigation extraction method

ABSTRACTThe conversion factor, kK, for estimation of microbial biomass potassium (K) by the chloroform-fumigation extraction method was determined for some arable soils: upland field soils under different fertilization conditions, an upland field soil under a greenhouse condition, and a paddy field soil under a flooded condition. The kK value varied with land utilization (paddy or upland) or fertilization (chemical or organic fertilizer). Value of kK was different between paddy field soil (0.28–0.38) and upland field soil (0.41–0.73). This study indicates that the value could be useful for the estimation of microbial biomass K in soil by the chloroform-fumigation extraction method and further investigation of the amounts of biomass K in different types of soils under conditions with varied field managements will be necessary.

Effects of straw mulching and plastic film mulching on improving soil organic carbon and nitrogen fractions, crop yield and water use efficiency in the Loess Plateau, China

A field experiment was conducted in the Loess Plateau of Northwest China to study the effects of plastic film mulching and straw mulching on soil water, soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN), dissolved organic carbon (DOC) and nitrogen (DON), crop yield and water use efficiency under winter wheat (Tricicum aestivum L.)—summer maize (Zea mays L.) double-cropping system conditions using the following three cultural practices: (i) traditional plough with no mulching (CK), (ii) traditional plough with plastic film mulching (PM), and (iii) traditional plough with straw mulching (SM). Soil water contents were measured by the gravimetric method. SOC was determined using the dichromate oxidation method. TN was analyzed by the Kjeldahl method. MBC and MBN were determined using the chloroform fumigation extraction method. DOC and TDN were determined following Jones’ procedures proposed by Jones and Willett (2006). The results showed that soil water was higher under the PM treatment than under the SM treatment and mainly changed in the upper 60 cm soil layer. Compared with the CK treatment, the concentrations of SOC and TN under the SM treatment were increased by 16.9% and 7.7% at the 0–10 cm soil depth, respectively, and the PM treatment had the similar SOC and TN concentrations. Compared with the CK treatment, soil C:N ratio was increased under the SM treatment by 6.2% (P < 0.05), and that under the PM treatment was decreased by 5.2% (P < 0.05) after three years. The concentrations of MBC under the PM and SM treatments were significantly increased by 42.0% and 24.1%, respectively, and MBN under the PM treatment was significantly increased by 5.6% at 0–10 cm soil depth after the maize season. Compared with the CK treatment, DOC was significantly increased by 21.0% under the SM treatment and decreased by 13.1% under the PM treatment, and DON was significantly increased by 10.5% under the SM treatment and decreased by 4.3% under the PM treatment at the 0–10 cm soil depth after the maize season. Relative changes of labile soil organic carbon and nitrogen fractions were more sensitive than that of SOC and TN. The relative decline or increase of labile soil organic carbon and nitrogen fractions was on average almost 13.6% for the mulching practices. Compared with the CK treatment, the average maize yields under the PM and SM treatments were increased by 26.4% and 9.8%, and the average wheat yields under the PM and SM treatments were increased by 21.3% and 7.4%, respectively. The average water use efficiencies under the PM and SM treatments were 24.5%, 8.8% in winter wheat and 22.9%, 6.3% in summer maize higher than that under the CK treatment, respectively. Our results suggested that plastic film mulching could be used as an effective practice to improve low soil quality with adequate nitrogen and increase crop yield and water use efficiency in the Loess Plateau, China.

Chloroform fumigation extraction for measuring soil microbial biomass: The validity of using samples approaching water saturation

The chloroform fumigation-extraction method for determining soil microbial biomass is commonly applied at soil moisture (SM) levels of 40–50% water-holding capacity (WHC). Below that moisture range, restricted enzymatic autolysis might limit the fumigation flush of extractable cellular material, thus underestimating microbial biomass. Likewise, the upper range of SM (i.e., >50% WHC) is considered problematic due to an alleged reduced fumigation efficiency when vapor diffusivity through soil is reduced. The current investigation demonstrated relatively constant fumigation flushes along a 40–90% WHC moisture gradient alongside unchanging carbon-to-nitrogen flush ratios corresponding to characteristic cellular values. This clearly refuted the proposed reduced fumigation efficiency under elevated moisture conditions, and thus validated the applicability of the method to samples collected moist.

Effect of Leaf Litter Treatment on Soil Microbial Biomass

Soil microbial biomass is an active fraction of soil organic matter. It shows quicker response than soil organic matter to any change in the soil environment. Being an index of soil fertility, it plays a key role in the decomposition of litters and fast release of available nutrients. Leaf litters of leguminous and non-leguminous species in alone and mixed form were applied as treatments in the soil to observe the changes in the magnitude of soil microbial biomass. Soil microbial biomass C and N were determined by chloroform fumigation extraction method. Increment in the concentration of microbial biomass C and N was higher in the treatments with leguminous leaf litter (497 - 571 μgCg−1, 48 - 55 μgNg−1) than the non-leguminous one (256 - 414 μgCg−1; 22 - 36 μgNg−1). However, when non-leguminous litters were mixed with leguminous litters then the values increased distinctly (350 - 465 μgCg−1, 28 - 48 μgNg−1). On the basis of increment in soil microbial biomass, leaf litters of the species considered potential to improve soil nutrients are—Cassia siamea and Dalbergia sissoo from leguminous trees, Anthocephalus + Cassia and Shorea + Dalbergia from mixed form of non-leguminous and leguminous one and Eichhornia crassipes, an alien aquatic macrophyte. The leaf litters of these species can be used as source of organic matter to improve the crop yield.