Microbial Respiratory Activity Research Articles

Mixed Chinese Fir Plantations Alter the C, N, and P Resource Limitations Influencing Microbial Metabolism in Soil Aggregates

Assessing the limitations of microbial metabolic resources is crucial for understanding plantation soil quality and enhancing fertility management. However, the variation of microbial resource limitations at the aggregate level in response to changes in stands remains unclear. This research explores carbon (C), nitrogen (N), and phosphorus (P) limitations affecting microbial metabolism in bulk soils and aggregates in two mixed and one pure Chinese fir stands in subtropical China, analyzing resource limitations concerning soil carbon, nutrients, and microbial indicators. The results revealed that microbes in all aggregates of the pure stands and in the micro aggregates (<0.25 mm) of the three stands were relatively limited by C and P. In contrast, microbial metabolism was more N-limited in macroaggregates (>2 mm) and small aggregates (2–0.25 mm) in the mixed stands. Additionally, in the mixed stands the proportion of soil macroaggregates increased, and that of micro aggregates decreased, resulting in a shift from C and P limitation to N limitation for bulk soil microbial metabolism. Redundancy analysis identified soil aggregate organic carbon and nutrient content as the main factors affecting microbial resource limitation, rather than their stoichiometric ratios. Pathway analysis further confirmed that soil nutrients and their stoichiometric ratios indirectly influenced soil microbe resource limitation by regulating microbial biomass, microbial respiration, and extracellular enzyme activities. Thus, the impact of mixed plantations on soil nutrients and microbial activity at the aggregate level may be crucial for maintaining land fertility and achieving sustainability.

Prediction of microbial activity and abundance using interpretable machine learning models in the hyporheic zone of effluent-dominated receiving rivers

Serving as a vital linkage between surface water and groundwater, the hyporheic zone (HZ) plays a fundamental role in improving water quality and maintaining ecological security. In arid or semi-arid areas, effluent discharge from wastewater treatment facilities could occupy a predominant proportion of the total base flow of receiving rivers. Nonetheless the relationship between microbial activity, abundance and environmental factors in the HZ of effluent-receiving rivers appear to be rarely addressed. In this study, a spatiotemporal field study was performed in two representative effluent-dominated receiving rivers in Xi'an, China. Land use data, physical and chemical water quality parameters of surface and subsurface water were used as predictive variables, while the microbial respiratory electron transport system activity (ETSA), the Chao1 and Shannon index of total microbial community, as well as the Chao1 and Shannon index of denitrifying bacteria community were used as response variables, while ETSA was used as response variables indicating ecological processes and Shannon and Chao1 were utilized as parameters indicating microbial diversity. Two machine learning models were utilized to provide evidence-based information on how environmental factors interact and drive microbial activity and abundance in the HZ at variable depths. The models with Chao1 and Shannon as response variables exhibited excellent predictive performances (R2: 0.754–0.81 and 0.783–0.839). Dissolved organic nitrogen (DON) was the most important factor affecting the microbial functions, and an obvious threshold value of ∼2 mg/L was observed. Credible predictions of models with Chao1 and Shannon index of denitrifying bacteria community as response variables were detected (R2: 0.484–0.624 and 0.567–0.638), with soluble reactive phosphorus (SRP) being the key influencing factor. Fe (Ⅱ) was favorable in predicting denitrifying bacteria community. The ESTA model highlighted the importance of total nitrogen in the ecological health monitoring in HZ. These findings provide novel insights in predicting microbial activity and abundance in highly-impacted areas such as the HZ of effluent-dominated receiving rivers.

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.

Soil Health in an Integrated Production System in a Brazilian Semiarid Region

Soil health is directly related to sustainable development goals (SDGs) and can be affected by inadequate management practices. In this work, soil edaphic respiration and changes in microbial biomass promoted by cover crops in an integrated crop–livestock system (ICLS) were evaluated using soil health indicators with the respirometry method. The design was completely randomized in a 3 × 6 factorial arrangement, and multivariate principal components analysis (PCA) was performed according to MANOVA. Edaphic respiration was determined based on the respirometry technique. The results showed that edaphic soil respiration was significant in the nine evaluation periods, demonstrating the importance of grass cover in edaphic respiration arising from the biological activity of microorganisms, which is directly related to the amount of soil organic carbon. The cover crops increased soil organic matter and consequently microbial respiratory activity.

Plant species and soil depth differentially affect microbial diversity and function in grasslands

AbstractIntroductionGrassland ecosystems are a major store of terrestrial carbon (C), yet little is known about their capacity to cycle and store C in deeper soil horizons. Further, it is unclear how plant community composition within agricultural grasslands mediates this capacity and influences microbial community composition. We investigated whether the aboveground community composition in intensively managed agricultural grasslands influenced belowground microbial community composition, abundance, respiration and enzyme activities with depth.Materials and MethodsSoil was sampled in four soil layers: A (0–15 cm), B (15–30 cm), C (30–60 cm) and D (60–90 cm) in monocultures of six grassland species and a mixture of all six. Functional capacity was measured through enzymatic and substrate‐induced respiration assays, and microbial abundance and diversity were assessed via quantitative polymerase chain reaction and sequencing (16S, Internal transcribed spacer), respectively.ResultsMicrobial abundance and C cycling enzyme activity decreased and community composition changed, along the soil depth gradient, regardless of the plant community. Microbial abundance was not significantly influenced by plant community type across the entire soil depth profile. However, prokaryotic community composition was significantly influenced by plant community in the top 15 cm of soil, and fungal community composition was significantly influenced between 15 and 30 cm in depth. Plant community types mediated the rate at which C cycling enzyme activity decreased along the soil depth gradient, and selected C cycling enzymes were significantly more active at 15–60 cm depth when Cichorium intybus (a deep rooting species) was present.ConclusionThis study provides an improved understanding of how agricultural grassland communities affect the soil microbiome with depth; this has potential implications for the management of these systems for enhanced soil health. Our work indicates the potential for multispecies mixtures with deep rooting species to be a practical strategy to increase C cycling capacity in deeper soil layers within grasslands, which may have implications for policy goals related to C storage.

Exploring the Influence of Diverse Viticultural Systems on Soil Health Metrics in the Northern Black Sea Region

The present study investigates the functionalecological status of typical light clay soils in vineyards in the southern region of Crimea, using both traditional (including fallow soils) and organic land-use systems. This analysis was carried out by examining agrochemical indicators, microbial respiratory activity, microbial biomass, and the ecological status of the microbial community. In organic vineyard soils, the mean substrate-induced respiration, microbial biomass carbon and the ratio of microbial biomass to organic carbon were found to be 2.8, 4.0, and 4.1 times higher, respectively, compared to conventional farm soils. On the contrary, the microbial metabolic coefficient was 1.4 times lower, signifying more favorable conditions for the functioning of the soil microbiota. The increased mobile sulfur content in organic vineyard soils (18.3 mg kg−1 vs. 8.0 mg kg−1 in traditional farms) and inadequate mobile phosphorus supply in some farms present potential risks. The suboptimal functional state of the microbiome in fallow soils previously under traditional plant protection necessitates comprehensive ecotoxicological analyses before development. Assessing the soil functional ecological status through an ecophysiological evaluation of the microbiome is vital for understanding ampelocenosis soils and making informed decisions on vineyard management practices.

Short-term legacy effects of long-term nitrogen and water addition on soil chemical properties and micro-bial characteristics in a temperate grassland.

Nitrogen deposition and summer precipitation in eastern Inner Mongolia are predicted to increase in recent decades. However, such increases in nitrogen inputs and precipitation may not be continuous under the future new patterns of global change, with the direction and magnitude of which may change or weaken. The legacy effects of nitrogen and water addition after cessation on ecosystems are still unclear. Based on a 13-year nitrogen and water addition experiment in temperate grassland of northern China, we examined the short-term (2 years) legacy effects of historical nitrogen and water addition on soil physicochemical properties and microbial properties after the cessation of nitrogen and water addition in the 14th year. The results showed that the positive effects of historical nitrogen addition on most of soil nutrient variables diminished after two years of cessation, including ammonium nitrogen, nitrate nitrogen, dissolved organic carbon and nitrogen, and Olsen-P concentrations. In contrast, there were legacy effects on soil microbial characteristics. For example, the historical nitrogen input of 15 g N·m-2·a-1 reduced microbial biomass carbon, respiration, and alkaline phosphomonoesterase activity by 73.3%, 81.9%, and 70.3% respectively. It implied that microbial parameters restored slowly in comparison with soil nutrients, showing a hysteresis effect. Results of Pearson's correlation and redundancy analysis showed that the legacy effects of historical nitrogen addition on microbial parameters could be attributed to the negative effects of nitrogen addition on soil pH. Historical water addition showed significant legacy effects on soil pH, ammonium nitrogen, dissolved organic carbon and nitrogen, respiration, and soil enzyme activities, which significantly interacted with historical nitrogen addition. These results are of great significance to predict the changes in grassland ecosystem functions and services under the local environmental improvement conditions, and to reveal the restoration mechanism of degraded grassland.

Reconstruction of Original Content of the Kurgan Funeral Vessels Based on Microbial and Enzymatic Parameters

The original content of ritual vessels from the burials of the two kurgan cemeteries was reconstructed using the multisubstrate testing system of microbial respiration and enzymatic activity of the soil from the pots. For this purpose, a laboratory model experiment was conducted and the decomposition of protein, lipid and polysaccharide organic materials was studied. Basing on the results of the model experiment, most indicative enzymes produced by soil microbial community under decomposition of each type of organic materials were found. They were nonanoate esterase, alkaline phosphatase, acid phosphatase, and leucine-aminopeptidase. The results of the assessment of enzymatic activity made it possible to reconstruct the original contents of burial vessels from two burial mounds “Beysuzhek-35” (Bronze Age) and “Spokoynyy” (Bronze Age and Early Iron Age). We found that most of the pots contained plant food. Animal proteins and fats were in three out of nine pots. One pot was empty or had water in it. In the male burials of the Yamnaya culture, ritual food in pots was more nutritious and included animal fats and proteins, while in the female burial in pots there was a plant starch and protein food. Multisubstrate testing of the respiratory responses of the soil microbial community and determination of the activities of the enzymes nonanoate esterase, alkaline phosphatase, acid phosphatase, and leucine-aminopeptidase are promising approaches to study the type of ritual food in the pots from ancient burials.

Early spring snowmelt and summer droughts strongly impair the resilience of bacterial community and N cycling functions in a subalpine grassland ecosystem

Subalpine grasslands support biodiversity, agriculture, and tourism but their resilience to extreme climatic events is challenged accelerating their vulnerability to tipping points. Microbial communities, central in ecosystem functioning, are usually considered more resistant and highly resilient to extreme events albeit their functional redundancy and strong selection by local harsh climatic conditions. This study explored the soil microbial responses upon recurrent spring‐summer droughts associated with early snowmelt in subalpine grasslands mesocosms set‐up at the Lautaret Pass (French Alps). Potential soil microbial respiration, nitrification and denitrification activities were monitored over a period of two growing seasons along with quantification of related gene abundances. Impacts of simulated spring‐summer drought and early snowmelt were quantified to assess their resistance and recovery. Results revealed that droughts had a low and short‐term adverse impact on bacterial total respiration supporting their hypothesized high resilience, i.e. resistance and ability to recover. Nitrification and abundances of the corresponding functional guilds showed relatively strong resistance to summer droughts but declined in response to early snowmelt. This resistance of nitrification was paralleled by the recovery of denitrification and abundances of denitrifying communities from all climatic extremes, except from the summer droughts where nitrifiers were collapsed. Denitrification and respective functional groups faced high impact of applied stresses with strong reduction in abundance and activity. Although, consequently lower denitrifiers' competition for nitrate may be positive for plant biomass production, warnings exist when considering the potential nitrate leaching as well as risks of greenhouses gases emission such as N2O from these ecosystems.

Effect of application of lime with vermicompost on the activities of microorganisms of some acidic soils of West Bengal

Aim: To evaluate the efficacy of integrated application of lime at partial doses of lime requirement (LR) with vermicompost in acid soils to minimize the soil acidity, improve the population of beneficial microorganisms and their microbial activities in comparison to sole treatment of lime as per Lime Requirement dose. Methodology: Two highly acidic soils collected from the farmer’s field of South 24 Parganas district, West Bengal having no history of acidity management were used. The soils were treated with different rates of lime requirement (LR, ⅔LR & ½LR) and lime (½LR) + vermicompost (5 tha-1) treatments and incubated for 60 days. Soil pH, soil organic carbon content, different microbial populations, microbial respiration and enzymatic activities (FDHA and DHA) were assessed at different days. Results: The study indicated that the lime treatments showed rapid increase in soil pH towards the slightly alkaline condition whereas lime +vermicompost treatment (T5) successfully maintained the neutralized condition. Integrated treatment of lower doses of lime and vermicompost (T5) was found to efficiently promote the microbial population (rhizobium, phosphate and potassium solubilizing bacteria) and microbial respiration (basal and substrate induced respiration) activity, which might be attributed to the improvement soil microbial status. FDHA and DHA increased significantly with ‘lime’ as well as the ‘lime with vermicompost’ treatments in comparison to control. Interpretation: The incorporation of lower amount of lime and organic matter efficiently neutralizes the acidity and boosted up the microbial activities simultaneously that in turn might improve the soil health. The high cost to purchase the huge quantity of lime as recommended LR (9.25 tha-1) for studied soils turns the farmers uninterested to follow lime practice and interrupted the mitigation of soil acidity. Thus, the study might conclude that the integrated approach of lime application@½LR with vermicompost might successfully ameliorate the acid soils in terms of acidity as well as the soil microbial activities. Key words: Acid soil, BSR, Dehydrogenase, Fluorescein diacetate, SIR, Lime, Vermicompost

Stenotrophomonas pavanii DJL-M3 inoculated biochar stabilizes the rhizosphere soil homeostasis of carbendazim-stressed rice

Plant–microbe interactions have been effectively used in phytoremediation to reduce agrochemical contamination of crops and soils, but little information is available regarding the general effect of such association on rhizosphere soil homeostasis. In this study, we immobilized Stenotrophomonas pavanii DJL-M3, a carbendazim (CBZ)-degrading endophyte, in rice husk-derived biochar to control fungicide residue in the rice microenvironment. The influence of biochar inoculated with strain DJL-M3 on rhizobacterial communities was also investigated, including activity and fundamental function predictions. An adsorption kinetics test showed that strain DJL-M3 slowed the adsorption rate slightly without sacrificing the adsorption capacity of rice-husk biochar on CBZ. Immobilization in biochar helped S. pavanii DJL-M3 to establish an ecological niche in rhizosphere soils. This process significantly reduced CBZ levels in rice and rhizosphere soil while maintaining stable heterotrophic microbial respiration and carbon (C) metabolic activity. Soil amendment with the strain DJL-M3–biochar composite resulted in relatively little disturbance of fundamental soil functions, such as nitrogen (N) and sulfur (S) cycling, which explained the better plant growth and higher soil fertility observed with CBZ contamination. Overall, the combination of biochar and S. pavanii DJL-M3 demonstrated the potential to safeguard the microbiological environment of rice.

Microplastics in agricultural soil: Polystyrene fragments inhibit soil microbial and enzymatic activities but promote nutrient concentration of Cowpea (Vigna unguiculata)

The disintegration and fragmentation of plastics into microplastics (MPs) and their transport from aquatic and terrestrial ecosystems into agricultural soils have been reported to be hazardous to soil health and crop growth. However, it is unknown how biological soil quality indicators and agronomic indices of a C3 plant respond to MPs' ecotoxicity after short-term exposure. Here, we conducted two experiments to define the eco-toxicity impact of polystyrene-MPs (PS-MPs) exposure at concentrations of (i) non-amended control, (ii) 0.5% PS-MP (w/w), (iii) 1% PS-MP (w/w), (iv) 2% PS-MP (w/w), and (v) 4% PS-MP (w/w) on the soil microbial biomass, respiration, and enzymatic activity—indicators of soil quality, and cowpea (model C3 plant) growth and nutrient concentrations. Our results demonstrate that PS-MPs, generally considered nontoxic, negatively inhibit microbial biomass and extracellular enzymatic activities after 30 days of soil incubation. On the other hand, increasing concentrations of PS-MPs increased soil basal respiration and the microbial metabolic quotient (qCO2), indicating microbial stress. Cowpea growth, irrespective of PS-MPs concentration and exposure time, showed neutral or non-inhibitory responses after 60 days. However, PS-MPs at low concentration (0.5% w/w) promoted an increase in cowpea leghemoglobin content, total chlorophyll pigment, and shoot and root nutrient concentrations (N, P, Zn, and Fe) over the control. Overall, our findings affirm the short-term ecotoxicity effect of PS-MPs on soil biological indicators of soil quality but also indicate that PS-MP exposure may not always have negative impacts on the agronomic performance of certain C3 plant species, such as cowpea.

Trade-off between microbial carbon use efficiency and specific nutrient-acquiring extracellular enzyme activities under reduced oxygen

• Reduced oxygen increased microbial metabolic quotient (qCO2).• Reduced oxygen enhanced microbial specific C-, N- and P-acquiring enzyme activity.• Reduced oxygen increased microbial C relative to N and P limitation. • Reduced oxygen increased microbial N relative to P limitation. • Specific enzyme activity was positively related to qCO2 under reduced oxygen.Mangroves are one of the most ecologically sensitive ecosystems to global climate change, which have cascading impacts on soil carbon (C), nitrogen (N) and phosphorus (P) cycling. Moreover, mangroves are experiencing increasing N and P loadings and reduced oxygen availability due to intensified climate change and human activities. However, both direct and interactive effects of these perturbations on microbially mediated soil C, N and P cycling are poorly understood. Here, we simultaneously investigated the effects of N and P loadings and reduced oxygen on microbial biomass, microbial respiration, and extracellular enzyme activities (EEAs) in mangrove soils. We calculated the microbial metabolic quotient (qCO2), which is regarded as a useful inverse metric of microbial C use efficiency (CUE). Our results show that reduced oxygen significantly increases both qCO2 and microbial specific EEAs (enzyme activity per unit of microbial biomass) for C-, N- and P-acquisition regardless of N or P loadings. Furthermore, we found that qCO2 positively correlated with microbial specific EEAs under reduced oxygen, whereas no clear relationship was detected under ambient oxygen. These results suggest that reduced oxygen increases microbial specific EEAs at the expense of increasing microbial respiration per unit biomass, indicating higher energy cost per unit enzyme production.

Temporal Stability of Soil Microbial Properties in Responses to Long-Term Application of Compost Obtained from Tannery Sludge

Successive applications of compost obtained from tannery sludge affected the soil microbial biomass and activity. However, the effect of this practice on the temporal stability of soil microbial properties is not known. This study evaluated the temporal stability of microbial biomass, respiration, and enzymes activities in soil with successive applications of compost obtained from tannery sludge. Soil samples (0–10 cm depth) were collected from sites with successive application of compost at the lowest (2.5 ton/ha) and highest (20 ton/ha) rates, including the control (0 ton/ha). Soil microbial biomass carbon (MBC) and nitrogen (MBN), respiration, dehydrogenase, and urease activities were evaluated at 0, 30-, 60-, 90-, and 150-days post-application. The soil microbial properties varied as per treatments and sampling time. The principal response curve showed higher variation of soil microbial properties in the treatment having highest rate of compost. This analysis showed dehydrogenase, urease, and MBC as the most responsive parameters. The temporal stability of soil microbial parameters showed highest values at the lowest rate of compost. This study showed that the successive application of compost contributed to a decrease in variation and increase in temporal stability of soil microbial properties at the lowest rate.

Biological quality and organic matter dynamics in minesoil at 18 years reclamation with perennial grasses

Mining is one of the most destructive economic activities on natural ecosystems. There are around 750 ha impacted by open-pit coal mining in Candiota Mine, the largest in Brazil, with 1.2 billion tons subject to mining. In soils impacted by mining, litter decomposition, always linked to a more extended period of restoration and maintenance of the vegetation, presents positive correlations with the diversity of the edaphic fauna and the enzymatic activity of these areas, promoting improvements in the ecological functions of the new ecosystem. The objective of the present study was to analyze the impact of revegetation with different summer perennial grasses subjected to different mowing managements on the biological and chemical quality of soils after coal mining in an experimental area at the Candiota Mine. Analyzes were performed to identify edaphic organisms using modified Berlese-Tüllgren funnels and microbiological analyzes to quantify Microbial Biomass Carbon (MBC), Microbial Respiration (MR), and urease enzymatic activity. The different fractions of Soil Organic Matter (fulvic, humic acids, and humin) were also quantified to understand the degree of humification in the area. All results were compared in mean tests by Tuckey's test (p < 0.05) and by Principal Component Analysis. After 18 years of revegetation and 11.6 years of mowing management in the area, there was an improvement in MBC and MR compared to the Control, evidencing the positive effect of the perennial grasses used in the experimental area. However, mowing management cannot yet be considered the most promising management for improving edaphic conditions.

Batch-mode stimulation of hydrocarbons biodegradation in freshwater sediments from historically contaminated Alūksne lake

Historical contamination of freshwater lakes with hydrocarbons (HC) due to anthropogenic activities represents a serious problem worldwide. This study was focused on hydrocarbons-contaminated sediments sampled in Lake Alūksne of glacial origin in Northeast Latvia. The batch experiments were aimed at evaluating the effect of bio-stimulation and bioaugmentation on the biodegradation of hydrocarbons in lake sediments (LS), as well as changes in microbial community structure and metabolic activity. The sediments were sampled from two points of the lake, 4–5 m and 8 m depth, respectively. These samples slightly differed by colour, count of diatoms, microbial respiration intensity and colour intensity of 2,6- dichlorophenolindophenol. Nevertheless, the trend in biodegradation activity was similar for both LS samples. The concentration of HC in LS during the 32-day incubation decreased in average from 465 mg/kg to 165 mg/kg and 117.5 mg/kg in the LS amended with nutrients and nutrients+microbial community, respectively. Different treatment types of LS resulted in differences in microbial respiration and HC-degrading activity. The Shotgun sequencing has revealed the main phyla present in the intact LS being Proteobacteria (48.8%), Actinobacteria (24.4%), Firmicutes (10.4%) and Bacteroidetes (5.0%). Incubation of LS for 32 days resulted in increasing abundance of Proteobacteria from 48.8% in the raw LS to 58–62%, mainly due to the increase of Betaproteobacteria. The functional annotation of gene families revealed that the most abundant gene families were associated with ATP binding, metal ion, magnesium ion, sulfur cluster, zinc ion binding, DNA binding and other essential components for cell functioning. The Shannon biodiversity index of culturable microorganisms in EcoPlates™ ranged from 2.28 to 2.85. The data obtained in this study indicated that the suggested approach is a potent remediation technology for further ex situ scaling up.

Distinct Changes in Abundance of Culturable Microbial Community and Respiration Activities in Response to Mineral–Organic Mixture Application in Contaminated Soil

The availability and affordability of fertilizers are the main risks currently faced by the fertilizer market. Therefore, there is a need to look for other sources of nutrient supply for plants, while taking care of soil properties. The application of fertilizers with the addition of functionalized materials could help in the efficient use of nutrients. The aim of the study was to assess the impact of the application of mixtures with the addition of zeolite–vermiculite composites (NaX–Ver) on the culturable microorganisms and selected soil properties. A two-year pot experiment was conducted on soil with elevated contents of cadmium, zinc, and lead. The test treatments included soil mixed with NPK and additives in two doses of NaX–Ver combined with leonardite (Leo) or lignite (L). The test plant used in the experiment was maize. The soil material was analyzed for the number of bacteria, mold fungi, actinomycetes, and ammonifiers. Furthermore, soil pH, EC, N total, and SOC contents, as well as soil respiration activity, were tested. The applied fertilizer mixtures had a great effect on changes in the N total and SOC contents. The N total increase was 45.5% in NaX–Ver3%L3% and 51% in NaX–Ver9%Leo6%, and the largest SOC increase (24.3%) was recorded in the NaX–Ver3%Leo3% treatment. The highest respiration activity was determined in NaX–Ver3%Leo3% and NaX–Ver9%Leo6%: 2.12 µg C-CO2 g−1 DM h−1 and 2.14 µg C-CO2 g−1 DM h−1, respectively. A significant correlation between pH values and the number of culturable microorganisms was found. The number of soil microorganisms depended on the type of fertilization used. The best stimulation of the number of culturable soil microorganisms was found in treatments with the addition of 3% of L or Leo in combination with NaX–Ver. The percentage increases in the number of the analyzed culturable microorganisms after the application of leonardite-based fertilization in combination with the zeolite–vermiculite composite were, on average: bacteria, 1096%; mold fungi, 1529%; actinomycetes, 1477%; ammonifiers, 910%.

Small-Scale Variability of Soil Quality in Permafrost Peatland of the Great Hing’an Mountains, Northeast China

Permafrost peatland is a unique ecosystem that represents a huge carbon terrestrial pool. Soil quality has a relatively high level of variation at small scale in this ecosystem and is closely related to the carbon cycle. To quantify this variability, we analyzed total organic carbon, total nitrogen, total phosphorus, nutrient, and element (sodium, magnesium, potassium, and calcium), and microbial respiration activities (microbial biomass carbon, soil basal respiration, metabolic, and microbial quotients) in the humus layer to deeper soil layer of 6 plots at small scale (meters). For all samples, the coefficients of variation (CV) values of total carbon concentrations were lowest and these values of sodium, magnesium, potassium, and calcium concentrations were higher than those of total carbon, nitrogen, and phosphorus concentrations. The largest variations of total phosphorus, ash, and Na were in the 10–20 cm layer with soil depths. The litter decomposition and water table may cause this variation at small-scale. The CV values of microbial respiration activities were largest compared with soil properties. There were different correlations between basal respiration and soil properties among the plots. Our results showed that soil properties and microbial respiration activities in permafrost peatland exhibits considerable variability at small scale. This variability indicates that sampling location and number are very important in peatland studies if we want to accurately estimate the biogeochemistry in a peatland.

Automatic system for monitoring gaseous concentration in a packed-bed solid-state cultivation bioreactor

In this work, the respiration gases were sampled from a packed-bed bioreactor used for solid-state cultivation (SSC) using different gas-sampling procedures. As a case study, Myceliophthora thermophila I-1D3b was cultivated at 45 °C in a mixture of sugarcane bagasse/wheat bran (7:3 w/w). Respiration gases were sampled at the top of the column (end-do-end mode) and in three other alternatives of sampling gases. Axial temperature profiles were obtained during the experiments and axial moisture contents and endoglucanase activities were determined after cultivation. The results showed that sampling gases at low flow rate produced similar results to the end-to-end operation. On the other hand, when part of the bed was subjected to inefficient aeration, the process was strongly affected in terms of accumulated gas concentrations and temperature. From the results, it was possible to infer some aspects of the microbial respiratory activity, which will be of help to SSC packed-bed bioreactor developers.

Biostimulant Effects of Micro Carbon Technology (MCT®)-Based Fertilizers on Soil and Capsicum annuum Culture in Growth Chamber and Field

Due to the environmental issues that conventional fertilization is causing, biostimulants are proposed as environmentally friendly alternative for crop nutrition in agriculture. The aim of this study was to determine the effects of new Micro Carbon Technology (MCT®) fertilizers with biostimulant activity based on humic acids biologically digested from leonardite on pepper plant growth in three different soils with different textures. The assays were performed under controlled conditions in a growth chamber and in commercial greenhouses in Spain. The effects on soil were analyzed after the addition of the fertilizers by microbial respiration and enzymatic activities (hydrolase, dehydrogenase and urease). For the plant assays, biometric parameters (fresh weight and fruit hardness) and foliar analysis (chlorophyll indices and nutrients) were evaluated. Under controlled conditions, the use of these biostimulants resulted in a greater soil microbial activity in a 24 h interval with increased soil enzymatic activity. In plants, a positive correlation was found between fertilizers with biostimulant activity and Dualex indices of leaves and content of macronutrients Ca and Mg. In commercial greenhouses, the fertilizers with biostimulant activity strongly depended on the soil texture. In conclusion, these products have real potential to replace conventional fertilizers in commercial production fields.