Fumigation-extraction Method Research Articles

Shift in microbial biomass, soil and microbial stoichiometry in different land uses of Northeast India

The change in soil microbial biomass and stoichiometry in different land uses of Northeast India were assessed by using the fumigation extraction method. The pattern of microbial biomass C, N, and P followed the sequence of forest (650.36, 62.86 and 254.54μgg−1) > grassland (62.86, 39.30 and 31.76 μgg−1> cropland (31.84,18.62 and 15.54 μgg−1), and exhibits seasonality with the lowest concentrations during the winter season across all land uses. The maximum concentrations were recorded during the rainy season in the forest and the summer season in both grassland and cropland. Microbial ratios (C: N, C: P and N: P) and proportions of microbial biomass to total soil nutrients vary with a variance in land use types. Soil microbial biomass exhibited a positive significant relation with soil nutrients but negatively related with soil temperature and moisture in all the study sites. Two-way ANOVA of soil microbial biomass exhibits significant differences due to seasons and land use types (p< 0.01). The microbial stoichiometry of the present study indicates N limitations in the study sites, while the proportion of microbial nutrients to total soil nutrients reveals nutrient mineralization in the forest and immobilization and competition in grassland and cropland. Furthermore, this study indicates that landuse and soil management practices interfere with microbial stoichiometry and nutrient release and immobilization patterns. Improving the retention of organic matter in ecosystems may enhance microbial activity and soil health.

Influence of Planting Techniques and Integrated Nutrient Management on Soil Health in Rice (Oryza sativa L.)

The study investigated the impact of different planting techniques and nitrogen management at Sardar Vallabhbhai Patel University of Agriculture &amp; Technology, Meerut (UP) during the rainy (kharif) season of 2019-20 on soil health in rice. Soil samples were collected at two depths, air-dried, and analyzed for aggregate size distribution using wet sieving. Particulate organic carbon (POC) was determined through aggregate slaking, while total organic carbon (TOC) content was assessed using rapid titration. Microbial biomass carbon (MBC) was calculated by incubating soil samples, followed by fumigation-extraction methods. Results revealed that soil pH and electrical conductivity remained unaffected by planting techniques and fertility levels. Aggregate size distribution analysis revealed that the Furrow Irrigated Raised Bed (FIRB) treatment promoted larger macro-aggregates (&gt;2mm) at varying soil depths, while Conventional Tillage (CT) encouraged smaller micro-aggregates. Reduced Tillage (RT) combined with Farmyard Manure (FYM) and chemical fertilizer increased POC and TOC content, emphasizing the importance of reduced soil disturbance and organic matter addition. Conversely, CT exhibited lower POC and TOC levels due to intensive soil disturbance. RT with FYM and chemical fertilizer significantly enhanced soil MBC, highlighting their role in improving soil health and fertility.

Biological Activities in Artificially Heavy-Metal-Contaminated Growing Substrates

The ingestion of vegetables grown in soils or in cultivation substrate contaminated with heavy metals (HMs) and irrigated with wastewater is a potential problem for human health and food quality. The increasing disappearance of fertile soils has led to an increase in the practice of soil-less cultivation and the use of growing substrates, but the choice of the right substrate and its sustainable management is essential to ensure the production of quality and safe vegetables for all while minimizing the impact on the environment and human health. The present study measures the combined effects of different HMs (V, Ni, Cd, Pb, Cu, Cr) on microbial biomass, respiration, and enzyme activities (EAs) in an artificially contaminated commercial growing substrate. The concentrations of HMs were estimated by Atomic Absorption Spectroscopy; enzyme activities via spectrophotometric assays; respiration via CO2 evolution; and microbial biomass C via the fumigation extraction method. The results showed a reduction in both respiration and all enzyme activities. The reduction in EAs highlighted a notable influence on microorganism-mediated C, N, S, and P cycles, strongly reducing substrate health. Microbial biomass did not show significant differences, but the increase in the metabolic quotient highlighted how the toxicity of HMs reduces the energy use efficiency of microbial metabolic processes.

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.

Effects of p-Hydroxyphenylacetic Acid and p-Hydroxybenzoic Acid on Soil Bacterial and Fungal Communities

Soil phenolic acids mainly come from crop residue and root exudates, which are often reported as allelochemicals affecting crop growth and soil microbial community. Here, two phenolic acid compounds, p-hydroxyphenylacetic acid (HPA) and p-hydroxybenzoic acid (HBA) were amended to the soils and were incubated under room conditions, and the soil samples were collected from soybean and corn fields separately. The soil microbial community was determined by PCR-DGGE (polymerase chain reaction-denatured gradient gel electrophoresis) and clone methods. Microbial biomass carbon (MBC) was measured based on the fumigation–extraction method. The result revealed that HPA/HBA amendment significantly affected soil bacterial and fungal community structures. HPA/HBA enriched some distinct bacteria and fungi. The induced bacteria were mainly Gemmatimonas, Bacillus, and Acidobacteria, while the induced fungi were mainly Penicillium and Aspergillus. HPA amendment enhanced the more bacterial quantities of corn and soybean soils than HBA. The fungal diversity in corn and soybean soils treated with HBA was higher than that treated with HPA. It was speculated that the diversity of degrading HBA fungi was higher than that of degrading HPA. This study comprehensively analyzed the effects of phenolic acids on soil microbial community and increased the understanding of the monoculture barrier to agricultural production.

Lysis of soil microbial cells by CO2 or N2 high pressurization compared with chloroform fumigation

The classical chloroform fumigation-incubation (CFI) and fumigation-extraction (CFE) methods are nowadays among the most used for determining soil microbial biomass, although the chloroform lysing of microbial cells is not always complete. Here, we have tested a physical method, used for sterilizing foods but never in soil, based on N2 or CO2 high pressurization (N2HP or CO2HP, respectively) to cause microbial cell lysis. The N2HP and CO2HP were tested on two soils differing for their organic matter content, one agricultural (AGR) and one forest (FOR), and firstly were compared with the CFI. The CO2 extra-flush from both soils during 10-d incubation by N2HP was lower than that by CFI method, whereas that by CO2HP was greater. Then, the lysis by CO2HP was compared with that by the CFE method by varying CO2 pressure and duration. The CO2HP, at proper conditions, was more efficient than CFE method to cause the lysis of soil microbial cells. Moreover, both CO2 pressure value and duration were important in increasing the extractable organic C compared to the CFE. The most successful combination of high CO2 pressure and duration was 4.13 MPa and 32 h. However, we cannot exclude that CO2HP might have caused the release of soil organic C not ascribable to living organic matter. Further studies using 13C and/or 15N-labeled microbial cells should assess the release of abiotic organic C.

INDICATOR ATTRIBUTES OF SOIL QUALITY IN AREAS UNDER DIFFERENT LAND USE SYSTEMS, IN THE WESTERN AMAZON

The anthropization of natural environments, when performed inadequately, promotes the disruption of the ecological balance and can influence the fauna, flora and biodiversity in general, including the edaphic environment and its components. The objective was to evaluate the soil attributes in areas with different types of vegetation cover and different forms of soil management. The study was carried out in native forest area (Subperennial Equatorial Forest) and cultivated area (annual species), in Porto Velho, Rondônia, Brazil. Samples were collected in two layers (0-10 and 10-20cm), on a Latossolo Vermelho-Amarelo, to evaluate microbial biomass by the fumigation-extraction (FE) method, as well as the chemical and physical soil attributes. It was possible to verify a significant increase in soil density and reduction of moisture and improvement of chemical attributes resulting from the use of the area. The organic matter content decreased sharply in the managed area (25%), compared to the forest, in the superficial layer (0-10cm). Microbial C-biomass under the native forest showed 54% higher mean value (883 mgC g-1) compared to the managed area (410 mgC g-1) in the superficial layer. The microbial N-biomass ranged from 21.3 to 19.5 mgN.g-1 in the native forest area, and from 9.3 to 11.5 mgN g-1 in the managed area, respectively in the 0-10 and 10-20cm layers. In the native forest area, the addition of organic matter to the soil by the vegetation litter was an important conditioning factor for the microbial community, demonstrating the use of this attribute as an indicator of soil quality.

Seasonal Dynamics of Soil Microbial Biomass C, N and P along an Altitudinal Gradient in Central Himalaya, India

This study was conducted in a temperate mixed oak–pine forest of Central Himalaya, India to (i) evaluate altitudinal and seasonal variations in the microbial biomass carbon (C), nitrogen (N) and phosphorus (P) and (ii) analyse the relationships between soil microbial biomass C, N and P and physico-chemical properties of soil. Three permanent plots were established in natural forest stands along an altitudinal gradient, three replicates were collected seasonally from each site, and microbial biomass (C, N and P) were determined by a fumigation extraction method. Microbial biomass C, N and P decreased significantly (p &lt; 0.01, correlation coefficient 0.985, 0.963, 0.948, respectively) with increasing altitude having maximum values during rainy season and minimum values during winter season. Microbial biomass C, N and P showed positive correlations with silt particles, water holding capacity, bulk density, soil moisture, organic C, total N and P and negative correlations with sand particles, porosity and soil pH. Microbial biomass C was strongly associated with soil microbial N (r = 0.80, p &lt; 0.01) and P (r = 0.89, p &lt; 0.01) content and soil microbial biomass N and P also showed a strong linear relationship (r = 0.92, p &lt; 0.01). Soil microbial biomass exhibited weak seasonality and was highly influenced by altitude and abiotic variables. The significantly high microbial C, N and P during the rainy season (p &lt; 0.01) and low microbial biomass during the winter season may be due to higher immobilization of nutrients from decomposing litter by microbes as the decomposition rate of litter and microbial activity are at their peak during the rainy period. The microbial C:N ratio indicated that soil fertility is influenced by species composition. Our findings suggested that high microbial biomass and low C:N ratios during the rainy season could be considered a nutrient conservation strategy of temperate mixed oak–pine forest ecosystems.

Improvement of degraded agricultural soil in an arid zone following short- and long-term treated municipal wastewater application: A case study of Gabes perimeter, Tunisia

This work aimed to study the short, medium, and long-term influences of treated wastewater (WWTP) as a soil irrigation technique on physical, chemical, and microbiological properties. Sampled soil plots were irrigated with WWTP for 1, 7, and 15 years. Rain-fed regime soil has been used as a control. This study was conducted in El Hamma of Gabes (southeast of Tunisia), an arid zone, during the dry season. Three soil profiles at 0–20, 20–40, and 40–60 cm were sampled. Physical and chemical analyzes, including pH, electrical conductivity, total organic carbon, total nitrogen, cation exchange capacity, and active and total CaCO3 were evaluated. Soil microbial biomass C and N were performed according to the fumigation extraction method. Soil microbial contamination was assessed by enumerating total, Fecal Coliforms, E. coli, and Fecal Streptococci with the most probable number (MPN) method and plate medium count. Bacterial and fungal enumeration were evaluated by the plate count agar method. In addition, the DGGE molecular analysis was also assessed in the different soil samples. The obtained physical and chemical evaluation proved that the WWTP irrigation practice improves soil fertility. Microbial biomass C and N increased by increasing the time of WWTP irrigation. In addition, the sanitary quality of the soil is affected by the increase of pathogens. We have observed an increase in microbial biomass as demonstrated by an increase in heterotrophic bacteria and filamentous fungi in the soil irrigated with WWTP compared to the control. Long-term WWTP irrigation has increased the activities of the soil microorganisms and then soil fertility. Meanwhile, the same pathogens and bacteria could pose a serious threat to sanitary soil quality and a limiting factor for the use of WWTP in agriculture areas without tertiary treatment.

Changes in microbial biomass and activity of tropical soil submitted to successive Eucalyptus rotations in the semi-arid region of Brazil

Soil microbial biomass (SMB) is considered an important indicator of changes in the soil organic carbon dynamics. Although there are several studies on SMB in Eucalyptus plantations in Brazil, there are still no records of investigations which have evaluated the effect of successive crop rotations on soil microbial biomass. Therefore, the aim of this study was to evaluate changes in the biomass and microbial activity of tropical soil submitted to successive Eucalyptus cultivation rotations. The study was carried out in commercial plantations of Eucalyptus urophylla in the first, second and third rotations (area cultivated 4, 9 and 15 years ago, respectively) using a fragment of native forest as a reference. Soil collections were performed at a depth of 0–10 cm. The carbon and nitrogen contents of the soil microbial biomass were determined by the fumigation-extraction method and the soil microbial activity was based on the amount of CO2 evolved. The increase in Eucalyptus cultivation time caused increases in litter accumulation and soil organic carbon, which represented an increase of 50% in rotation 1 compared to rotations 2 and 3. This was reflected in increases in C immobilization in microbial biomass (MB-C) and in the efficiency of converting organic carbon to MB-C and reducing soil carbon losses. Following a similar pattern, the microbial biomass carbon (MB-C) levels showed increases of 52 and 47% in rotation 3 in relation to rotation 1 and 2, respectively. Only the metabolic quotient among the microbiological indices was sensitive to the Eucalyptus cultivation time, with a significant reduction in rotation 3 (131.0 mg g−1 day) compared to rotations 1 and 2 (average of 269.1 mg g−1 day). The change imposed by the progressive increase in the Eucalyptus cultivation time positively influenced the activity and C transformation of SMB.

Impacts of rice-husk biochar on soil microbial biomass and agronomic performances of tomato (Solanum lycopersicum L.)

Tomato is beneficial to human health because it contains valuable vitamins such as vitamins A, C and several minerals. However, to meet up with the demands of the ever increasing population, there is need to improve tomato production. This research, thus, investigated the impact of rice-husk biochar on the agronomic performances of tomato plant and microbial biomass of carbon, nitrogen and phosphorus in different tomato growth stages. The rice husk biochar pyrolyzed at 350 °C was amended with soil at four different application rates: 0, 2.5, 5.0 and 7.5 t/ha. Physicochemical property of soil was conducted using Mid Infrared Reflectance Spectroscopy method. Impact of biochar on Microbial Biomass Carbon, Microbial Biomass Nitrogen and Microbial Biomass Phosphorous was conducted using fumigation extraction method and monitored at three functional stages. Biochar application appreciably increase the soil physicochemical properties such as pH, Ca, Na, H+, S, P, B, C, Zn and cation exchangeable capacity in comparison with the control. Biochar amended soil significantly enhanced tomato height, stem girth, leaf area, flowers, fruit yields and weight. Although, B3 recorded the lowest leaf area, it possessed the highest number of fruits and fruit weight of 3 and 40%, respectively. The ratio of Microbial biomass C:N:P for biochar amended soil at 7.5 t/ha (B3) was 302.30:18.81:11.75 µg/g, compared to control, which was 242.12:18.30:11.49 µg/g. This study revealed that biochar amendments significantly (p < 0.05) increased the yields and microbial biomass of tomato plants. Conclusively, the application of rice-husk biochar (7.5 t/ha) to soil is considered as a suitable approach to improve tomato growth and yield.

Paddy soils have a much higher microbial biomass content than upland soils: A review of the origin, mechanisms, and drivers

Many studies have shown that the microbial biomass content in paddy soils is much higher than that in upland soils, but a comprehensive review of the underlying mechanisms and processes is lacking. We conducted a meta-analysis of published literature on the microbial biomass content in continuous paddy soils (>1700 data pairs) and paddy-upland rotation soils (>1100 data pairs) as compared to that in adjacent upland soils (>360 data pairs), measured by the fumigation extraction or fumigation incubation method. The microbial biomass carbon (MBC) content in paddy soils was double that in upland soils. This MBC surplus in paddy soils compared to upland soils was explained by (1) higher input of root C and rhizodeposits by rice plants compared with upland crops; (2) lower oxygen availability and consequently slower microbial turnover; (3) higher microbial C assimilation efficiency in paddy soils; and (4) additional C stabilization on iron (oxyhydr)oxides in paddy soils. The proportion of MBC in total soil organic C in paddy-upland rotation, paddy, and upland soils was 3.5%, 2.5%, and 2.1%, respectively. The higher microbial biomass C/N ratio in paddy soils (12.4 ± 0.11) compared to upland soils (9.9 ± 0.21) reflects greater N losses (through nitrate leaching and denitrification) in relation to slower C losses under anoxic conditions. Despite higher temperature and better water availability, microbial biomass turnover was 1.1–1.6 times slower in paddy soils than in upland soils because of oxygen limitation. Multiple stepwise regression and redundancy analyses showed that microbial biomass in continuous paddy and paddy-upland rotation soils was affected by similar soil factors (such as total N and organic C), whereas microbial biomass in upland soils was mainly affected by pH and the organic C content. Paddy-upland rotation soils undergo oxic–anoxic cycles and consequently can absorb and coprecipitate organic compounds with iron (oxyhydr)oxides as an additional advantage for C stabilization. We conclude that the reduced microbial activity and slower microbial turnover under oxygen-limited conditions lead to nearly two times higher microbial biomass content in paddy than in upland soils.

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.

Effects of stocking rate on the interannual patterns of ecosystem biomass and soil nitrogen mineralization in a meadow steppe of northeast China

Understanding the effects of livestock grazing on the ecosystem biomass and soil nitrogen processes of grassland ecosystems is critical to improving knowledge on the mechanisms underlying grassland degradation and accurately assessing the influence of grazing management on grassland functions. We examined the interannual patterns of ecosystem biomass and soil nitrogen mineralization in response to cattle grazing in a Chinese meadow steppe. The soil core incubation method was employed for soil N transfer estimation, whilst the fumigation extraction method, a modified Baermann funnel method and harvest method were used for various measurements of ecosystem biomass parameters. We found that cattle grazing caused consistent significant increases in soil temperature, irrespective of the stocking rate and year, whereas significant effects on soil moisture and edaphic properties were observed only in individual years and/or at specific stocking rates. Consistent positive effects at moderate stocking rates were observed for aboveground net primary production and soil nematode biomass in all study years. The across stocking rate pattern of N mineralization in response to cattle stocking appeared to be year-specific, although negative effects were found in most cases. In contrast, the interannual pattern of N mineralization was determined principally by the interannual patterns in precipitation and soil moisture and was much less affected by cattle grazing. Soil N mineralization in this meadow steppe was affected by cattle grazing via two major mechanisms, i.e., its effects on the aboveground net primary production (ANPP) and thus the quantity of plant litter input into the soil and its effects on soil temperature and moisture. Overall, our study spanned the longest consecutive years with the broadest range of stocking rates thus far of its kind, which revealed for the first time that the soil nitrogen mineralization pattern with respect to stocking rate was year-specific. Our findings have important implications for adaptive management and sustainable utilization of Chinese grasslands.

Phosphorus mineralization in response to organic and inorganic amendment in a semi-arid pasture soil

Phosphorus deficient soil was amended with compost (C) (organic source of phosphorus) and inorganic P (KH2PO4 as inorganic phosphorus) at different rates and incubated for 28 days. Six treatments were used including i) Control ii) Inorganic P (0.79 mg per 30 g of soil sample) iii) 100 % C (0.13 g) iv) 75% C (0.1 g) + 25% P (0.2 mg) v) 50% C (0.065 g) + 50% P (0.4 mg) vi) 25% C (0.03 g) + 75% P (0.6 mg). Soil respiration was recorded using Infra-red CO2 gas analyzer. MBC was determined by using fumigation extraction method. Resin P and MBP extraction was carried out by anion exchange membranes and was determined colorimetrically. P pools were determined by using DeLuca method. Cumulative respiration microbial biomass significantly increased in organic amended soil with higher increase in soil emended with 75% C +25% P rate followed by 50% C and 50% P rate. It was concluded that compost amended with high inorganic P stimulated the formation of P labile pools which supply long term slow release of P for plants and microbes.

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.

Biomasa y respiración microbiana: Respuesta ante cambios en la humedad del suelo en la Estepa Magallánica Seca de Santa Cruz, Argentina

El carbono y el nitrógeno de la biomasa microbiana (CBM y NBM) del suelo son bioindicadores que tienen el potencial de mostrar cambios en el suelo de los ecosistemas, y están condicionados por la humedad disponible en el suelo. Se evaluó como varían CBM, NBM y la respiración heterotrófica (RH) en función de la cantidad de humedad en suelos de la Estepa Magallánica Seca de Santa Cruz, Argentina. El ensayo consistió en 3 tratamientos: a) Control, conteniendo la precipitación normal caída, como testigo, b) Riego, equivalente a un aumento del 54% en las precipitaciones respecto a la media anual, y c) Sequía, con una disminución del 54% en las precipitaciones respecto a la media anual. Se estimó el CBM mediante el método de fumigación-extracción. Se encontraron diferencias significativas en el CBM entre los tratamientos, el riego obtuvo la mayor cantidad de CBM. Los valores fueron: 505,3 (±81,4), 406,7(±39,2) y 380,4 (±98,4) µg de C g-1 para riego, sequía y control, respectivamente. No se encontraron diferencias en el NBM entre los tratamientos, siendo los valores 93,3 (±13,5), 82,8 (±68,9) y 80,7 (±31,1) µg de N g-1 de suelo seco para sequía, control y riego, respectivamente. La RH diaria por su parte, presentó valores de 13,04 (±3,32), 11,17 (±1,47) y 10,60 (±1,29) mg C-CO2Kg-1 de suelo seco día-1 para el tratamiento control, riego y sequía, respectivamente. Solo el CBM evidenció un cambio relevante frente a la sequía, las demás variables no presentaron diferencias significativas. Los resultados denotan que la humedad es un factor importante para el C en BM, por lo que es importante seguir monitoreando y establecer como cambios en la precipitación alterar la biomasa microbiana en estos ambientes australes.

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.

Short-term effects of forest management on soil microbial biomass and activity in caatinga dry forest, Brazil

The Caatinga is among the most threatened and least studied tropical dry forests in the world. Sustainable forest management is a rational exploitation practice adopted in the biome, but it can impact a variety of ecosystem attributes. We still have a limited understanding of forest management impacts on the soil, especially on microbial biomass. Thus, we developed this work by asking how do soil microbial biomass and activity respond in the short-term to Caatinga forest management and how do these responses differ between forest management practices? Three types of forest management were evaluated (clear cutting - CC, selective cutting by diameter - SCD, and selective cutting by species - SCS), using unmanaged Caatinga (UC) as a reference. Litter and soil (depth of 0–10 cm) collections were carried out. Soil microbial activity was determined based on the amount of evolved CO2, and the microbial biomass C and N were estimated by the fumigation-extraction method. The management provided a reduction in leaf litter (CC = 16%; SCD = 25%; SCS = 38%; UC = 55%) and an increase in branch litter (CC = 73%; SCD = 66%; SCS = 46%; UC = 35%). It also caused a 42% reduction in MB-C. The metabolic quotient had an increase in CC and SCD management (average of 690.6 mg g−1 day) compared to UC (365.9 mg g−1 day). SCD and CC influenced the activity and C transformation of soil microbial biomass in the short-term, while SCS less intensely affected these variables, approaching the unmanaged forest condition.