Chloroform Fumigation Extraction Research Articles

Seasonal Relationships of Alpine Plants and Microbes through a Stoichiometric and Enzymatic Lens

Alpine biomes experience harsh environmental conditions and short growing seasons, which necessitate interspecific and intraspecific interactions to ensure the stability of diversity and ecosystem multifunctionality. The relationship between plants and microbes in this environment is equally dynamic, with seasonal pulses of nutrients and the phenology of plants creating specific "hot moments" of biogeochemical activity. As a crucial zone of interaction between plant roots and microbial communities, the rhizosphere serves as a "hot spot" of biogeochemical cycling where the mineralization of nutrients, such as carbon, nitrogen, and phosphorus, allows for the transfer of nutrients between trophic levels. However, the nature of these interactions depends on edaphic and climatic conditions, potentially leading to cooperation or competition to meet the stoichiometric demands of organisms. Elevation gradients within alpine ecosystems provide dramatic shifts in temperature, precipitation, and soil development that allow for the study of these interactions over short geographical distances. In conjunction with seasonal sampling, this approach can provide a wide environmental context to observe the relationship between specific plants and microbial communities. By investigating the C/N ratios of plants, microbes, and soil, as well as microbial enzymatic potential, we can infer nutrient limitations, temporal niche partitioning, and biological responses to abiotic conditions. Within the Austrian Alps, we studied a selection of herbaceous plants and their associated microbial communities across an elevation gradient spanning 2200-2800 m (Fig. 1). The primary aims of the study were to assess the seasonal changes in C/N stoichiometry from both trophic levels, microbial enzymatic potential, and rhizosphere diversity of bacterial and fungal communities. To fulfill these aims, four locations were selected based on the two present biomes (alpine meadow and sub-nival zone) and the transition between them. Four to five plant species were collected during each season in 2023, including the often-neglected snow-covered winter season, along with rhizosphere and bulk soil for microbial biomass measurements and soil chemistry. Plant leaf tissue samples were analyzed using Isotope-ratio mass spectrometry for plant C/N ratios, while soil and microbial C/N ratios were calculated using chloroform fumigation extraction. Microbial enzymatic potential was assessed using hydrolase enzymatic assays for five fluorophore-labeled substrates. 16S-rRNA and 18S-rRNA genes were sequenced using an Illumina MiSeq platform from the fine roots of collected plant individuals to quantify the relative abundances of bacterial and fungal taxa. The findings of our study indicate that the higher microbial biomass (Cmic) in alpine meadow locations leads to increased enzymatic activity compared to sub-nival zones. However, specific plant species were found to enhance microbial biomass and enzymatic potential in different seasons, suggesting that plants promote microbial interaction and biogeochemical cycling during different seasons as a form of temporal niche partitioning. Most plant species demonstrated an increase in C/N ratios throughout the season, sometimes increasing by more than 200%. However, two Poa spp. showed the highest C/N ratios during the summer, which further correlated with higher microbial C/N ratios. By observing changes in stoichiometric ratios of organisms that interact and share nutrients, we propose that these relationships vary between host plants depending on their temporal niche and abiotic factors (soil and environmental conditions). Furthermore, the positive or negative correlation of plant and microbial C/N ratios may indicate the relative cooperation or competition between trophic levels.

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.

Soil Microbial Biomass, Microbial Population and Diversity in Maize-Banana Based Agroforestry System in Kisii County, Kenya

Soil microbes are involved in many important ecosystem processes including nutrient acquisition, biogeochemical cycling and soil aggregation. Soil microbial diversity affects the soil belowground dynamics and fate of carbon and nutrients. Soil microbes are important for agricultural and plant production systems, hence understanding the effects of agroforestry systems on the soil microbes, is necessary in order to improve on soil health and fertility. The objective of the study was to determine the soil microbial biomass, microbial populations and microbial diversity in maize-banana based agroforestry system. The study was conducted at Kenya Agricultural and Livestock Research Organization farm in Kisii County. The experiment was laid out in a randomized complete block design with maize and banana intercropped with agroforestry trees. The treatments were; Maize, banana (MMBB), Maize-banana, Calliandra (MBCC), Maize (MM), banana (BB), Maize-banana, Leucaena (MBLL), Maize-banana, Sesbania (MBSS) and Maize, fertilizer (MMF). Soil samples were collected from the agroforestry fields using a soil auger. Soil microbial biomass was measured using the chloroform fumigation extraction. Fungi and bacteria were enumerated by serial dilution plate method.Shannon diversity index (H’) and Simpson diversity index (1 - D) were used for the calculation of species diversity. SAS (version 9) statistical software was used for analysis. The treatments with agroforestry tree species had significantly higher soil microbial biomass (MBSS-86.33, MBCC-52.66 and MBLL- 47.0MgC/Kg) populations of bacteria (MBSS-197, MBCC-128.0 and MBLL-111.25x108cfu g-1soil) and fungi (MBSS-50.83, MBCC-29.167 and MBLL-14.0x105cfu g-1 soil) and diversity of bacteria (MBSS- (H' =1.61, D = 1), MBCC- (H' =1.04, D = 0.83), MBLL (H' = 0.52, D = 0.5) and fungi MBSS (H' =1.39, D = 1) MBCC (H' =1.04, D= 0.83), MBLL (H' =1.56, D = 0.93). MBSS increased microbial biomass, microbial populations and microbial diversity significantly an indication of improved soil health and hence recommended for adoption by farmers.

How do harvesting methods applied in continuous-cover forestry and rotation forest management impact soil carbon storage and degradability in boreal Scots pine forests?

Forest management affects soil carbon (C) storage through forest composition, microclimate and litter inputs. How two major forest management systems, continuous-cover forestry (CCF) and clear-cut-based rotation forest management (RFM), differ in their impact on soil C in boreal forests is still poorly understood, however. We compared their effects on soil organic carbon (SOC) storage and quality in boreal Scots pine (Pinus sylvestris L.) dominated forests in eastern Finland. We tested the hypotheses that (1) colder microclimates and continuous litter inputs will lead to higher SOC stocks in CCF plots than in clear-cuts and (2) the more labile litter in clear-cuts with varying ground vegetation will enhance SOC decomposition rates. We sampled uncut mature forests, clear-cuts, retention-cuts and gap-cuts, in which we analysed SOC concentrations and calculated the stocks. We measured stand characteristics such as diameter-at-breast height, basal area, dominant tree height, and understorey species coverage of the various treatments and modelled the above- and belowground litter inputs based on these parameters. We used laboratory incubation and sequential fractionation of SOC to assess its degradability under standardized conditions. To estimate the decomposition rate in the various environments we incubated cellulose bags in situ. We assessed the impact of microclimate on SOC decomposition, using data from soil-temperature and soil-moisture field measurements. We quantified the microbial biomass C pool, using chloroform fumigation extraction to gain insight on the impact of forest management practice on soil microbes. The SOC concentrations and SOC stocks did not differ significantly between the treatments, despite the presence of a warmer microclimate and lower litter inputs in the clear-cut plots. However, we found differences in the quality of the SOC. Soils in clear-cut sites showed lower proportions of labile SOC compounds than did the other treatments. As hypothesized, the decomposition rates were elevated in clear-cuts, but were equally as high within the canopy gaps on gap-cut stands. Our work highlights that forest management affects the quality, degradability, long-term accumulation and storage of SOC. We conclude that the accumulation of labile compounds in uncut forests and retention-cuts, combined with the decreased decomposition rates, indicate a higher potential for future C accumulation in the soil than in clear-cuts.

Chloroform‐labile trace elements in soil via fumigation‐extraction: Steps towards the soil microbial ionome beyond C:N:P

AbstractSecondary and trace elements may be limiting soil microbial functioning, albeit microbial demand and content remain largely unknown and methods for their in situ detection are limited. Thus, the objective of the present study was to take the first step towards the method development for the assessment of the soil microbial ionome, that is, the elemental composition of soil microbial communities. Chloroform (CHCl3) fumigation extraction was used for the detection of microbial CHCl3‐labile secondary and trace element concentrations in soils. The suitability of two extractants (NH4NO3, CaCl2) for the quantification of CHCl3‐labile concentrations of phosphorus, sulphur, potassium, sodium, and magnesium, as well as selenium, iron, zinc, manganese, copper, cobalt, nickel, molybdenum, vanadium, boron, silicon, barium, arsenic, and cadmium, were tested in six agricultural soils. Additionally, three soil to extractant ratios (1:5, 1:10, and 1:20) and two extraction durations, 1 or 2 h, were tested in a subset of two soils. Out of the two extractants tested, 0.01 M CaCl2was found to be the best‐suited extractant. For CaCl2, a soil‐to‐extractant ratio of 1:20 with an extraction time of 1 h was best for the majority of elements in the two soils tested. In a limited number of agricultural soils, we were able to show that CHCl3fumigation extraction can successfully be applied to the elements phosphorus, sulphur, potassium, sodium, magnesium, zinc, manganese, copper, nickel, vanadium, boron, silicon, and barium to yield a CHCl3‐labile element fraction. Conversion values to microbial biomass, accounting for elements contained in the cell envelope components, which are mostly not extractable, and to account for adsorption to soil colloids during extraction are yet to be determined in a larger variety of soils. To overcome some of the limitations of the fumigation extraction approach for secondary and trace elements, a pre‐extraction step may provide a suitable solution.

Long-term differences in fertilisation type change the bacteria:archaea:fungi ratios and reveal a heterogeneous response of the soil microbial ionome in a Haplic Luvisol

Organic farm management through farmyard manure application is associated with soil organic carbon sequestration facilitated by more balanced nutrient stoichiometry of macro- and micronutrients. Quantitative information on micronutrients within the soil microbial biomass is lacking. Using soils from a 40-year old long-term field trial (DOK), we investigated if fertilisation differences (farmyard manure equivalent to 0.7 or 1.4 livestock units per hectare and mineral fertilisation) and farm management (biodynamic, organic, conventional) changed the soil microbial ionome and stoichiometry and if this is related to microbial community shifts. Soil (15% sand, 70% silt and 15% clay) from the top 20 cm was analysed for microbial biomass carbon, nitrogen and phosphorus. Further elements were assessed via an adapted chloroform-fumigation extraction procedure. Abundances of bacteria, archaea, and fungi were determined (qPCR). Farmyard manure increased microbial biomass by approximately two-fold and the contribution of bacteria and archaea by up to approximately five-fold. Microbial biomass phosphorus and magnesium increased with mineral fertilisation (from 7 to 14 μg g−1 soil) and farmyard manure (from 0.5 to 2.7 μg g−1 soil), respectively. The microbial biomass carbon to potassium ratio remained similar, at around 47:1, revealing stoichiometric control. Microbial biomass manganese was reduced from 3.5 to 2.2 μg g−1 soil with lower availability due to raised pH in biodynamic management. The microbial stoichiometry and ionome were mainly affected by nutrient input and soil chemical properties; direct links between microbial (micronutrient-) stoichiometry and microbial community changes cannot be established with certainty due to potential confounding effects of pH changes.

Estimation of turnover time of microbial biomass potassium in paddy field soil

ABSTRACT Soil microbial biomass (microbial biomass) contains substantial amounts of potassium (K) as a reservoir of K in soils. However, information about K dynamics and K flux through the microbial biomass are lacking. In the present study, the turnover time of microbial biomass K was estimated for the first time using paddy field soils. The paddy field soils, either amended with substrates of carbon, nitrogen, and phosphorus, or not, were aerobically incubated for 60 days, during which the amounts of microbial biomass K were periodically determined by the chloroform fumigation-extraction procedure. Microbial biomass K increased to twice (51.4–72.3 mg K kg−1 soil) of that in the unamended control 5 days after addition of the substrates and gradually decreased to the values in the control (25.2–44.0 mg K kg−1 soil) until 60 days of the incubation. The turnover time of microbial biomass K was estimated from the declines in the substrate amended soils. The turnover time of microbial biomass K ranged from 80.4 to 98.5 days, which roughly corresponded to the cultivation period of rice (about 100 days). These results indicated that microbial biomass K plays important roles in the supply of K source as well as the reservoir of K in paddy field soil.

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 biomass carbon and nitrogen in historic convent gardens under long‐term horticultural cultivation in Krakow, Poland

AbstractThis paper evaluates the seasonal changes of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents as an indicator of urban soil health. Our research was conducted in six horticultural urban soils in Krakow that have been cultivated for centuries. We investigated the temporal dynamics of microbial biomass C and N in soil samples from 0 to 20 cm depth taken in spring, summer and autumn. The study plots were placed in suburban areas as well as in the centre of the city to distinguish whether the detected effect of altered soil properties is similar to suburban areas. Soil microbial biomass was determined by the chloroform fumigation–extraction (CFE) method. The concentrations of MBC and MBN were measured in the field‐moist soil samples. MBC in the soil ranged from 226.5 to 742.7 mg kg−1 and MBN from 62.7 to 359.6 mg kg−1 expressed in dry mass. Repeated‐measures analysis of variance (ANOVAR, match‐model) was performed to test the main effects and interactions of temporal changes for MBC and MBN. There were significant differences only between MBN concentration in summer and autumn (p < .05). Principle component analysis (PCA) gave insightful results for the whole soil profile. Detrended canonical correspondence analysis (DCCA) indicated that the most explanatory variables in the studied time period were concentration of silt, total nitrogen, MBN and MBC content in the surface layer. Molar ratios of total organic carbon and total nitrogen (TOC:TN) indicated that microbial activity for C and N is enhanced by stoichiometry demands and therefore may be important for vegetation.

会仙岩溶湿地4种覆被下土壤酶活性和微生物生物量

研究湿地系统中的稻田被撂荒以后土壤酶活性和微生物生物量的变化可以为湿地的保护提供参考依据。以桂林会仙岩溶湿地为研究样地，采集芦苇湿地、华科拉莎草湿地、稻田撂荒地（以双穗雀稗和莲子草为优势植被）和稻田的耕层土壤样品，采用比色法和氯仿熏蒸法分别检测土壤酶活性和微生物生物量。结果表明，稻田撂荒地的土壤微生物生物量碳（MBC）为（345.20±30.06） mg/kg，显著低于其它三种覆被下的土壤；微生物生物量氮（MBN）、微生物DNA、蔗糖酶活性和碱性磷酸酶活性分别为（48.03±18.48） mg/kg、（5.65±1.48）μg/kg、（19.16±1.43） mg g^-1（24h）^-1和（2.20±0.94） mg g^-1（24h）^-1，均显著低于稻田，而与两种天然湿地没有显著差异。主成分分析表明，稻田撂荒地能与稻田明显分开，而与其它两种覆被土壤有所交叉。统计分析表明，MBC和碱性磷酸酶活性均与pH呈显著正相关关系（P<0.05）；MBN、蔗糖酶活性和碱性磷酸酶活性均与土壤总有机碳（SOC）呈显著的正相关关系（P<0.05）；土壤微生物DNA与SOC、总氮（TN）和碱解氮（AN）均呈显著正相关关系（P<0.01），与Mg²⁺呈显著正相关关系（P<0.05）。以上研究结果表明，会仙湿地中的稻田在撂荒以后，土壤微生物生物量和两种土壤酶活性显著降低，影响微生物生物量和土壤酶活性变化的主要因素是pH、SOC、TN、AN和Mg²⁺。因此，建议在稻田撂荒地上重新种植水稻，以加快会仙岩溶湿地的恢复过程。;Study on the changes of soil enzyme activity and microbial biomass after paddy field was abandoned in wetland system can provide reference for protecting wetland. Top soils were collected from wetland with Phragmites communis (PW), wetland with Cyperus rotundus (CW), abandoned rice field (with dominant vegetation of Paspalum distichum and Alternanthera sessilis) (AF), and rice paddy field (with Oryza sativa) (RF) in Huixian karst wetland, Guilin, China. The soil enzyme activities and micro-biomass were detected using colorimetry and chloroform fumigation-extraction, respectively. The results showed that the micro-biomass carbon (MBC) in the RF was (345.20±30.06) mg/kg, which was significantly lower than that in PF and not significantly difference with that in PW and CW. The micro-biomass nitrogen (MBN), microbial DNA, invertase activity and alkaline phosphatase activity in RF were (48.03±18.48) mg/kg, (5.65±1.48) μg/kg, (19.16±1.43) mg g^-1 (24h)^-1, (2.20±0.94) mg g^-1 (2h)^-1, respectively, which were significantly lower than those in PF and no significant difference with those in PW and CW. Principal component analysis showed that the points of AF could be well separated from those of PF, but not separated from those of PW and CW. The statistical analysis showed that MBC and alkaline phosphatase activity were positively correlated with pH (P<0.05); MBN, invertase activity and alkaline phosphatase activity were all positively correlated with SOC (P<0.05); soil microbial DNA was positively correlated with SOC (P<0.01), TN (P<0.01), AN (P<0.01) and Mg²⁺ (P<0.05). The above results indicated that pH, SOC, TN, AN and Mg²⁺ decreased, resulting in significant decreases of soil microbial biomass and two enzyme activities after a paddy field was abandoned. Therefore, we suggest that Oryza sativa could be replanted in AF to accelerate the recovery process of Huixian karst wetland.

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.

MULTIVARIATE STATISTICS OF FERTILITY PARAMETER FLUXES IN CEMENT-DUST-POLLUTED SOILS IN MFAMOSING, NIGERIA: IMPACT ON AGRICULTURE

This study investigated the impact of cement-dust pollution on the fertility status of agricultural soils to ascertain their health and suitability for cropping. Relevant soil nutrients and enzyme activities were determined from 12 control soil, 12 NPK-treated polluted soil and 12 un-amended polluted soil samples, using standard soil analytical and biochemical procedures. Soil microbial biomass-carbon was quantified by chloroform-fumigation-extraction (CFE) method. Cultivable aerobic bacterial count was determined on Tryptic Soy Agar (TSA) while cultivable fungal quantitation was performed on Czapek-Dox agar. Corn (Zea mays) yield served to evaluate pollutant effect on tested parameters. Principal component analysis (PCA) extracted two components, PC1 and PC2, from nine studied dependent variables (DVs) which explained 68.33% variability about the data. Number and membership of extracted components were confirmed by two clusters obtained by agglomerative hierarchical cluster analysis (AHCA). Multivariate analysis of covariance revealed significant effect of soil type on the combined DVs when the effect of the covariate (planting period) was controlled. One-way analysis of covariance (one-way ANCOVA) revealed non-significant effect of planting period but a significant main effect of soil type on corn yield when controlling for the effect of the covariate. Relative to control soil, per cent loss in corn yield was 55.69% in cement dust-polluted soil but reduced to 36.07% in polluted soils treated with NPK. The research findings have shown that cement dust pollution significantly reduced corn yield and the stress may persist in agricultural soils amended with fertilizer.

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.