Soil Dilution Research Articles

Effects of different parameters on cellulase production by Trichoderma harzianum TF2 using solid‐state fermentation (SSF)

Solid‐state fermentation is one of the easiest and cheapest methods for producing microbial bioactive com‐ pounds. Trichoderma harzianum has long been recognised as one of the potential fungi for this purpose. Trichoderma sp. were isolated from banana rhizosphere using the soil dilution method and later screened for their ability to produce cellulases using filter paper activity (FPase) and the carboxylmethyl cellulase (CMCase) test. Trichoderma sp. were also subjected to one factor change at a time to determine the effects of different parameters on cellulase production. It was observed that T. harzianum TF2 showed the ability to produce higher cellulase activity when wheat bran was used as the substrate. The results showed that 38.5 U/g of cellulase was produced with the use of wheat bran coupled with an incubation temperature of 28 °C and moisture content of 60%. T. harzianum TF2 showed good potential for use as a culture for cellulase production in this study due to its higher cellulase production under solid‐state fermentation, with the possibility of its application to industry.

Microclimatic, climatic, and anthropogenic factors strongly affect cultivable soil microfungal communities at a canyon in the Mediterranean region

In this study, we focused on the effects of microclimatic, climatic, and anthropogenic factors on culturable microfungal communities in the soil of the north-facing slope (NFS) and the south-facing slope (SFS) at the Metzar “Evolution Canyon” in the Golan Heights, Israel. Using the soil dilution plate method, 94 species from 47 genera were isolated. The communities’ composition was subjected to pronounced interslope variations in both summer and winter. Whereas xerotolerant melanin-containing species and thermotolerant Aspergillus spp. predominated in the SFS soil, peaking in the summer, mesophilic Penicillium spp. were especially abundant in the NFS soil. The quantitative parameter—density of microfungal isolates—exhibited the strongest seasonal variations, showing that it was the most sensitive to the fluctuation in soil temperature and moisture. Comparison of microfungal communities in the currently recovered and previously disturbed SFS soil showed that intensive pasturage followed by soil degradation led to the simplification of communities, decreased their diversity level, and resulted in the prevalence of species with different ecological preferences. Comparison of the native NFS communities isolated in the summers of 2002 and 2019 revealed changes in the community structure, which could be related to global warming. These changes were associated with stress-tolerant fungal traits, which may be useful under increasing soil temperature and desiccation.

Isolation and Screening from Soil Biodiversity for Fungi Involved in the Degradation of Recalcitrant Materials.

Environmental pollution is an increasing problem, and identifying fungi involved in the bioremediation process is an essential task. Soil hosts an incredible diversity of microbial life and can be a good source of these bioremediative fungi. This work aims to search for soil fungi with bioremediation potential by using different screening tests. Mineral culture media supplemented with recalcitrant substances as the sole carbon source were used as growth tests. First, soil dilutions were plated on Petri dishes with mineral medium amended with humic acids or lignocellulose. The growing fungal colonies were isolated and tested on different substrates, such as complex mixtures of hydrocarbons (petrolatum and used motor oil) and powders of different plastic polymers (PET, PP, PS, PUR, PVC). Qualitative enzymatic tests were associated with the growth tests to investigate the production of esterases, laccases, peroxidases, and proteases. These enzymes are involved in the main degradation processes of recalcitrant material, and their constitutive secretion by the examined fungal strains could have the potential to be exploited for bioremediation. More than 100 strains were isolated and tested, and several isolates with good bioremediation potential were found. In conclusion, the described screening tests are an easy and low-cost method to identify fungal strains with bioremediation potential from the soil. In addition, it is possible to tailor the screening tests for different pollutants, according to requirements, by adding other recalcitrant substances to minimal culture media.

Aftershocks of the Samarco disaster: diminished growth and increased metal content of Raphanus sativus cultivated in soil with mining tailings

The collapse of the Fundão tailings dam of the Samarco mining complex in Mariana, Brazil, was the largest mining disaster in the world to date with many socio-economic and environmental impacts. Soil affected by mining tailings was severely altered with negative impacts for agriculture. We tested whether diluting mining tailings with organic soil would eliminate or at least attenuate the ecotoxic effects on plant development and performance. We cultivated radish, Raphanus sativus, in substrates containing different proportions of mining tailings and organic soil: pure tailings (T100%); 2) tailings75% + soil25% (T75%); 3) tailings50% + soil50% (T50%); 4) tailings25% + soil75% (T25%), and 5) pure organic soil (Soil100%, control). There were large differences in soil quality parameters between the 100% tailings treatment (T100%) and the control (Soil100%), as well as for some parameters in the most diluted treatment - T25% (Ca2+, Fe, Mn) in relation to the control treatment. Although dilution of the tailings soil improved radish development, there was lower radish productivity (leaf area, total biomass, and root/tuber biomass) than for pure soil (control). There were also significantly higher amounts of bioaccumulated metals in radish tubers grown with tailings, even when grown in T25% for Fe content and in T75% for Mn content. These results present a worrisome scenario for human communities in the region of the Doce river, as human consumption of crops produced in soil contaminated with tailings is not recommended due to potential toxicological effects from high metal concentrations.

Structure of rhizosphere mycocomplexes and phyloplanes of cultural peanuts

Relevance . Peanut seeds are rich in oils, protein, carbohydrates, vitamins and flavonoids, therefore they are widely used in the production of food, feed, biodiesel, as well as in medicine. When cultivating peanuts, the problem of reducing the yield and sometimes the quality of seeds necessarily arises due to the impact of phytopathogenic microscopic fungi, and the main factors in the transmission of the infectious principle are soil and plant residues. The plant protection system should be based on knowledge of the structure of mycocomplexes of the rhizosphere and phylloplane. Methods . On a typical black soil on a natural infectious background in Belgorod (Russia), a sample of cultural peanuts V-2012 (Vietnam) from the collection of the Department of Biotechnology and Microbiology of the Institute of Pharmacy, Chemistry and Biology of the National Research University "BelSU" was studied. The species composition of microscopic fungi in the peanut rhizosphere was analyzed in comparison with fallow soil (control), which was found by seeding soil dilutions and leaf samples on dense nutrient media, followed by identification to species. Results . Compared with the control soil, the mycocomplex of the peanut rhizosphere (the Shannon index value at the level of 2.5 and 2.7 in the rhizosphere and control, respectively) was characterized by a lower degree of diversity and the degree of similarity of soil samples was high (the Jaccard coefficient was 50%), which means that that the cultivation of peanuts has lit- tle effect on the composition and structure of a typical black soil. In the peanut rhizosphere, a decrease in the frequency of occurrence of the phytopathogenic species F. oxysporum was observed, which may be associated with an increase in the rank in the mycocomplex of the mycophilic species T. lignorum. Aspergillus ochraceus, A. terreus, A. ustus, Candida albicans, Curvularia lunata, Fusarium oxysporum, Trichothecium roseum species were found to be sen- sitive to peanut cultivation. Peanut leaf spot was caused annually by the species Alternaria alternate , which can lead to a decrease in seed productivity up to 80%.

Preservation and Recovery of Metal-Tolerant Fungi from Industrial Soil and Their Application to Improve Germination and Growth of Wheat

Heavy metals contaminate soil and adversely affect plant growth. These soils contain different fungi and bacteria which exhibit metal tolerance and work as bioremediation agents to detoxify polluted soils. In the present study, polluted soil samples were collected to estimate the contamination of copper (Cu) and cadmium (Cd). From this contaminated soil, metal tolerant fungi were isolated and characterized. Copper and cadmium were found in a range of 190.2–300.4 mg/kg and 46.8–56.1 mg/kg, respectively. For the isolation of metal tolerant fungi, soil dilutions were made in water and inoculated on potato dextrose agar (PDA) media. Fungal growth was observed on PDA and successive screening resulted in the isolation of four multi-metal tolerant fungal species, including Penicillim oxalicum, Fusarium solani, Aspergillus niger and Trichoderma harzianum. Sequencing of 18S rRNA genes of isolated fungi also efficiently identified them. To reveal minimum inhibitory concentrations (MIC), these fungi were exposed to increasing concentrations of cadmium and copper chlorides (100 to 1000 ppm) and a variable MIC range of 400 ppm to 1000 ppm was estimated. Based on tolerance index analysis, F. solani was found to be resistant at 1 mM copper, while P. oxalicum was the most tolerant species under cadmium stress. F. solani and P. oxalicum demonstrated the highest biosorption capacity of Cu and Cd, respectively. Both metals negatively affected wheat seedlings in a pot experiment, while the treatment of both F. solani and P. oxalicum positively influenced the germination and growth of wheat. Based on these observations, it could be inferred that F. solani and P. oxalicum can be used for the myco-remediation of Cu and Cd, respectively.

The Isolation and Characterization of Antagonist Trichoderma spp. from the Soil of Abha, Saudi Arabia.

Background: The genus Trichoderma is widely spread in the environment, mainly in soils. Trichoderma are filamentous fungi and are used in a wide range of fields to manage plant patho-genic fungi. They have proven to be effective biocontrol agents due to their high reproducibility, adaptability, efficient nutrient mobilization, ability to colonize the rhizosphere, significant inhibitory effects against phytopathogenic fungi, and efficacy in promoting plant growth. In the present study, the antagonist Trichoderma isolates were characterized from the soil of Abha region, Saudi Arabia. Methodology: Soil samples were collected from six locations of Abha, Saudi Arabia to isolate Trichoderma having the antagonistic potential against plant pathogenic fungi. The soil dilution plate method was used to isolate Trichoderma (Trichoderma Specific Medium (TSM)). Isolated Trichoderma were evaluated for their antagonistic potential against Fusarium oxysporum, Alternaria alternata and Helminthosporium rostratum. The antagonist activity was assessed by dual culture assay, and the effect of volatile metabolites and culture filtrate of Trichoderma. In addition, the effect of different temperature and salt concentrations on the growth of Trichoderma isolates were also evaluated. Results: The most potent Trichoderma species were identified by using ITS4 and ITS 5 primers. Total 48 Trichoderma isolates were isolated on (TSM) from the soil samples out of those six isolates were found to have antagonist potential against the tested plant pathogenic fungi. In general, Trichoderma strains A (1) 2.1 T, A (3) 3.1 T and A (6) 2.2 T were found to be highly effective in reducing the growth of tested plant pathogenic fungi. Trichoderma A (1) 2.1 T was highly effective against F. oxysporum (82%), whereas Trichoderma A (6) 2.2 T prevented the maximal growth of H. rostratum (77%) according to the dual culture data. Furthermore, Trichoderma A (1) 2.1 T volatile metabolites hindered F. oxysporum growth. The volatile metabolite of Trichoderma A (6) 2.2 T, on the other hand, had the strongest activity against A. alternata (45%). The Trichoderma A (1) 2.1 T culture filtrate was proven to be effective in suppressing the growth of H. rostratum (47%). The temperature range of 26 °C to 30 °C was observed to be optimum for Trichoderma growth. Trichoderma isolates grew well at salt concentrations (NaCl) of 2%, and with the increasing salt concentration the growth of isolates decreased. The molecular analysis of potent fungi by ITS4 and ITS5 primers confirmed that the Trichoderma isolates A (1) 2.1 T, A (3) 3.1 and A (6) 2.2 T were T. harzianum, T. brevicompactum, and T. velutinum, respectively. Conclusions: The study concludes that the soil of the Abha region contains a large population of diverse fungi including Trichoderma, which can be explored further to be used as biocontrol agents.

STUDY OF RHIZOSPHERIC MYCOFLORA OF TURMERIC (CURCUMA LONGA L.) GROWING AREAS FROM JHANSI VICINITY

Turmeric (Curcuma longa L.) is an ancient and sacred spice of India. It is used in diversified forms as a condiment, flavouring, colouring agents, as curry powder and as a medicine. It is grown by its finger rhizome. Turmeric grows on diversified soil types, but it thrives best in sandy loam well drained soil. Soil is the habitat of a complex microbial community where interaction and the struggle for existence in this microbial world are equally complex. Rhizosphere is a region around roots; it is complex environment inhabiting microorganisms where roots interact with physical, chemical and biological properties of soil. To explore the soil mycoflora from turmeric growing areas of Jhansi vicinity, experiment were conducted during 2018-2019 in Department of Botany, Bundelkhand University Jhansi. The most promising genera/specie abundantently present in the soil mycoflora was also estimated. For this experiment. Soil samples were collected from 15 different turmeric growing areas of Jhansi vicinity. The soil mycoflora was obtained by soil dilution technique. About 25 different fungal species belonging to 18 genera were isolated. These species were member of Phycomycetes, Ascomycetes and Deuteromycetes.

Cultivation and Detection of Unculturable Fungi in Soil Using Soil Infusion Agar(SIA)

Unculturable and non sporulating fungi represent a great challenge in studying biotrophic ,endotrophic and mycorrhizal fungal groups. In this study a novel culture dependent technique complemented with PCR was used to detect and identify of unculturable fungi in soil . To develop techniques for cultivation of unculturable fungi for the purpose of expanding studies on fungal biodiversity in soil , Soil Infusion Agar (SIA) was developed . By this technique, from higher dilutions of soil five tiny colonies (less than 1mm in diameter) had grown on SIA after incubation for 1-3 months at 280C , but had not shown growth when replicated on traditional mycological media ,were selected , purified studied culturally and microscopically and identified by molecular methods . Growth of the five clones on PDA, but not Sabouraud Dextrose Agar and Czpak Dox Agar of incubation when a loopful of a colony grown after several successive subculturing on SIA was transferred to PDA. The growth on PDA has been empirically proven due to the inoculums size effect and the period of incubation at 280C. Two fungal specific primer sets (EF4F/ITS4r and EF60F/ITS4r) were used to amplify partial sequences of fungal r RNA gene included ITS sequences .The five partial sequences of the five clones were aligned through the BLASTN phylogenetic analysis against NCBI database which revealed higher identities. The blast tree showed that all clones are neighbor joined to Aspergillus ssp and Pichia sp. These results led us to consider the clones as viable but non culturable fungi (VBNC fungi) like the common phenomenon found in some bacterial species.

Harnessing the Phytase Production Potential of Soil-Borne Fungi from Wastewater Irrigated Fields Based on Eco-Cultural Optimization under Shake Flask Method

Indigenous fungi present in agricultural soils could have synchronized their inherent potentials to the local climatic conditions. Therefore, the fungi resident in the untreated wastewater irrigated agricultural field might develop their potential for producing various enzymes to handle the induced full organic load from domestic wastewater and toxic chemicals from the textile industry. Around 53 various fungal isolates were grown and separated from the soil samples from these sites through soil dilution, soil-culture plate, and soil-culture plate methods. All the purified fungi were subjected to a phosphatase production test, and only 13 fungal strains were selected as phosphatase producers. Among them, only five fungi identified as Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, Penicillium purourogenum, and Mucor rouxii based on morphological similarities, showing higher phosphate solubilizing indices, were utilized for eco-cultural fine-tuning to harness their full production potential under shake flask (SF) method. Among various media, orchestral tuning, 200 µM sodium phytate as substrate with 1.5 mL of inoculum size of the fungi, pH 7, temperature 30 °C, glucose, and ammonium nitrate as carbon and nitrogen additive with seven days of incubation were found to be the most appropriate cultural conditions to harness the phytase production potential of the selected fungi. Aspergillus niger and Aspergillus flavus showed initial phytase activity (5.2 Units/mL, 4.8 Units/mL) and phytase specific activity (2.85, 2.65 Units/mL per mg protein) during screening to be enhanced up to 17 ± 0.033 (Units/mL), 16 ± 0.033 (Units/mL) and (13 ± 0.012), 10 ± 0.066 (Units/mL per mg protein), respectively, with the above-mentioned conditions. The phytase enzyme produced from these fungi were found to be almost stable for a wide range of pH (4–8); temperature (20–60 °C); insensitive to Ca2+ and Mg2+ ions, and EDTA, Ni2+, and Ba2+ inhibitors but highly sensitive to Mn2+, Cu2+, and Zn2+ ions, and Co2+, Cr3+, Al3+, Fe2+ and Ag1+ inhibitors. It was suggested that both phytase-producing strains of A. niger and A. flavus or their crude phytase enzymes might be good candidates for application in soils to release phosphates from phytate and a possible valuable substitute of phosphate fertilizers.

New soil-inhabiting Chaetosphaeriaceous records from Thailand

Soil fungi represent the most abundant and diverse taxonomic group on Earth. Tropical forest soil-based habitats contain both edaphic and climatic factors that boost fungal activities in soil. Despite having vital functions in terrestrial ecosystems, information on diversity, taxonomy, and ecological preferences of soil fungi on a global scale is lacking. This study focuses on fungal species inhabiting tropical forest soils in Krabi, Thailand. Fungal isolation was performed using the soil dilution plate method, and species delimitation was conducted via morphological characterization and phylogenetic analyses. Chloridium gonytrichii and Kionochaeta microspora are introduced herein as the soil-inhabiting records from Thailand. For each species, comprehensive descriptions and micrographs are provided.

Exploring Citrus Nematodes and its Antagonists in Citrus Growing Areas of Punjab, Pakistan

Citrus nematode (Tylenchulus semipenetrans) is a major threat to the citrus industry in Pakistan. During 2019-20, a survey was carried out for citrus nematode and its antagonists in citrus orchards (Both healthy and declining trees were samples) of Punjab, Pakistan. Bhalwal, Shahpur, Sillanwali, Kotmomin, Sargodha, Quaidabad, Jhang, and Rahim Yar Khan were surveyed for disease incidence, prevalence, and association of T. semipenetrans. Maximum disease prevalence (100%) was recorded in Rahim Yar Khan while minimum (20%) in Bhalwal and Kotmomin. Maximum slow decline with 80% field incidence was observed in Rahim Yar Khan while a minimum of 20% in Quaidabad. Soil and root samples were used for nematode extraction using Baerman's funnel method and the Whitehead Hemming tray method. A maximum number of J2s/100ml of soil were observed in soil samples taken from Rahim Yar Khan (1674) followed by Shahpur (1534), Qaidabad (1432), Sargodha (1347), and Bhalwal (1172). The highest number of nematode females per gram of root were recorded in Rahim Yar Khan (652) followed by Quaidabad (611), Bhalwal (490), Kotmomin (421), Sillanwali (387). Isolation of different fungal and bacterial antagonist isolates was also done by soil dilution plate technique using nutrient agar media and potato dextrose agar media. Identification of fungal antagonists was made on colony growth, color, and spore structure. Bacterial identification was also done on morphological characters and gram tests. Trichoderma harzianum, Trichoderma viride, Trichoderma koningii Trichoderma atroviride, Pseudomonas fluorescens, Pseudomonas putida, Bacillus cereus and Bacillus subtilis were found associated.

FUNGAL AND BACTERIAL RHIZOSPHERE MICROBIOME ASSOCIATED WITH SELECTED MELON AND SNAKE MELON GENOTYPES

The composition of rhizospheric microbial community may be shaped by plant genotype. Forty five melon (Cucumis melo L.) and seven snake melon (Cucumis melo var. flexuosus) genotypes were tested for their growth and yield parameters compared to a commercial melon cultivar “Star plus”. To estimate the microbial community in the rhizospheric soil of these genotypes, soil dilution plating technique on specific agar medium was used and compared to control. The majority of melon genotypes showed significantly comparable height, fruit weight and fruit yield per plant as “Star plus”. The fruit yield per plant varied significantly depending on tested genotypes. The total bacterial population in the rhizosphere of ten melon and two snake melon genotypes was significantly 59 to 68% higher than control soil. For most tested genotypes, a significant increase in the culturable rhizospheric actinomycetes, about 28.5 to 92.6%, was recorded comparatively to control soil. Fungal population counts in the rhizosphere of tested genotypes were significantly comparable to control. The genotypic difference in melon and snake melon reflects the quantum and diversity of their microbiomes that melon breeders could benefit when seeking at the holobiont concept to include associated microbiomes in breeding programs.

Mechanisms of Anaerobic Soil Disinfestation: Volatile Fatty Acids Reduce Viability of Athelia (Sclerotium) rolfsii Sclerotia in Acidic Soil Conditions and Have Limited Effects on Endemic Trichoderma spp.

Volatile fatty acids (VFAs), such as acetic and n-butyric acid, released during anaerobic decomposition of organic soil amendments during anaerobic soil disinfestation (ASD) likely play a role in soilborne plant pathogen inoculum suppression. However, research is limited on the direct effects of soil VFA exposure on fungal plant pathogen inoculum, effects on pathogen antagonists such as Trichoderma spp., and the role of soil microbial VFA metabolism on reducing exposure effects. The present study addresses these limitations through a series of studies evaluating the effects of VFA (acetic or n-butyric acid), VFA concentration (4, 8, or 16 mmol/kg soil), soil sterilization by autoclaving, and soil amendment on the viability of Athelia rolfsii (Sclerotium rolfsii) sclerotia post VFA exposure, and soil populations of Trichoderma spp. HCl and water-only controls were included. After 4-days exposure in an acidic, anaerobic environment, sclerotial viability, and colonization by culturable fungi or bacteria were assessed with standard procedures. Greenhouse experiments were similarly conducted to evaluate endemic soil populations of Trichoderma spp. following soil exposure to VFAs and Trichoderma spp. populations assessed with standard soil dilution plating onto semi-selective medium. Sclerotial germination was generally reduced by soil exposure to acetic (35.1% germination) or n-butyric (21.9% germination) acids compared to water (74.3% germination) and HCl (62.7% germination). Germination was reduced as VFA concentration increased from 4 to 8 and 16 mmol/kg (39.5, 29.1, and 16.9%, respectively). In amended soils, there was no difference in sclerotial germination compared to non-amended soils, but in the greenhouse experiment there was a Trichoderma spp. population increase of over 300% in amended soil [3.4 × 106 colony forming units (CFU)/g soil] compared to the non-amended soil (9.6 × 105 CFU/g soil). Soil autoclaving had no effect on sclerotial germination at low VFA concentrations, but sclerotial germination was reduced at higher VFA concentrations compared to non-autoclaved soil. Our results suggest that VFAs contribute to sclerotial mortality in strongly acidic soil environments, and mortality is influenced by VFA components and environment. Antifungal activity is less for acetic acid than for n-butyric, and less in non-sterile soil environments more typical of field conditions than in sterile laboratory conditions.

English

Cotton is an important cash crop of Pakistan and is severely affected with wilt in cotton-growing areas of Punjab province. Research was carried out on two major pathogens of cotton Fusarium oxysporum f. sp. vasinfectum and Meloidogyne incognita and their possible role in wilt disease complex. During 2017-19, a survey of cotton growing areas of Punjab (Jhang, Multan, Vehari, Mianwali, Rahim Yar Khan, Bahawalpur, Kabir Wala, Dakota, Basti Dharik, Tibba Sultan Pur, Rajan Pur, Chak 27 (Layyah), Chak 99B (Layyah), Lodhran, Fateh Pur and Dagar Rohtass) was conducted to collect a sample on symptomology basis of yellowing of leaves, discoloured bark of lower part of the stem, blackened xylem vessel and wilting. Data were recorded on wilt disease incidence, prevalence, associated pathogens and root-knot nematodes. Prevalence of cotton wilt was recorded the maximum 85% in areas of Vehari, Kabir Wala and Rajan Pur while the maximum incidence in both Multan and Tibba Sultan Pur was 15%. Percentage association of wilting fungi was recorded from the soil, roots, stem and leaves on placing them in artificial media and soil dilution techniques were used to determine fungi in rhizosphere such as Fusarium oxysporum, Verticillium spp., Penicillium spp., Aspergillus spp., Rhizoctonia spp., Colletotrichum spp., Rhizopus spp., Mucor and Pythium. Root associated fungi were isolated by Hyphal tip method and isolated F. oxysporum, Rhizoctonia spp. and Pythium spp. From stem and leaf sample, F. oxysporum, Verticillium spp., Colletotrichum spp., Alternaria spp. and Botryodiplodia spp. were recorded. Relative density nematode was recorded from different locations and highest occurrence was observed in Bahawalpur (85%) by using different extraction methods. Eggs masses of root knot nematodes were staining by using Phloxin B and nematodes inside root system was done by using acid fuchsin. Nematode reproduction parameters like No. of J2/roots system, J2 in 100ml of soils, eggs masses/root system, females/ roots system, galls/ root system were recorded. Cotton wilt caused by the interaction of Fusarium and Root knot nematode is threat to cotton industry in Pakistan and it should be treated to avoid economic losses.

Microclimatic Gradient as a Source of Variations in Cultivable soil Microfungal Communities at the Negev Desert, Israel

We studied the effect of microclimatic gradient on the spatial (8 habitats) and seasonal (autumn, winter, and summer) variations of culturable soil microfungal communities at the north-facing slope (NFS) and the south-facing slope (SFS) of Nahal Boker, the Central Negev Desert, Israel. Using the soil dilution plate method, a total of 122 species from 56 genera was isolated. The communities' composition was subjected to pronounced interslope variations in each season. While xerotolerant melanin-containing species (mainly with the protective multicellular spore morphology) predominated in the soil of NFS, peaking up in the summer, thermotolerant and thermophilic Aspergillus spp. were especially abundant at the SFS. Aspergilli also dominated the thermotolerant communities isolated at 37 °C from both slopes. The more severe microclimatic regime at the SFS resulted in the least pronounced spatial and seasonal intraslope variability of the community composition as compared to the more benign and heterogeneous NFS. The quantitative parameter—the density of microfungal isolates, exhibited significant and positive relationship with organic matter and moisture content. In seasonal dynamics, the severe summer conditions significantly reduced the differences in isolate density at the NFS, which were markedly expressed in the autumn and winter between habitats receiving additional water by runoff and the adjacent habitats that did not benefit from runoff water.

Quantifying nitrogen uptake and translocation for mature trees: an in situ whole-tree paired 15N labeling method.

Nitrogen (N) is one of the major nutrients limiting plant growth in terrestrial ecosystems. To avoid plant-microbe competition, previous studies on plant N uptake preference often used hydroponic experiments on fine roots of seedlings and demonstrated ammonium preference for conifer species; however, we lack information about N uptake and translocation in the field. In this paper, we described a method of in situ paired 15N labeling and reported the rates and time course of N uptake and translocation by mature trees in situ. We added 15N-enriched ammonium or nitrate, together with the nitrification inhibitor dicyandiamide, to paired Larix kaempferi (Lamb.) Carr (larch) trees from 30-, 40- and 50-year-old plantations. Fine roots, coarse roots, leaves and small branches were collected 2, 4, 7, 14 and 30days after labeling. Nitrate uptake and translocation averaged 1.59±0.16μg 15N g-1 day-1, which is slightly higher than ammonium (1.08±0.10μg 15N g-1 day-1), in all tree organs. Nitrate contributed 50-78% to N uptake and translocation, indicating efficient nitrate use by larch in situ. We observed no age effect. We suggest that sampling leaves after 4days of 15N labeling is sufficient to detect mature tree N uptake preference in situ. Whole-tree 15N-ammonium recovery equaled that of 15N-nitrate 30days after 15N addition, implying the importance of both ammonium and nitrate to mature larch N use in the long run. We conclude that our method is promising for studying mature tree N uptake preference in situ and can be applied to other conifer and broadleaf species. We suggest using highly enriched 15N tracer to overcome soil dilution and a nitrification inhibitor to minimize ammonium transformation to nitrate. Our study revealed mature tree N preference in situ and demonstrated the strong contribution of nitrate toward mature larch growth on soils rich in nitrate.

Increased Likelihood of High Nitrous Oxide (N2O) Exchange in Soils at Reduced Microbial Diversity

Rare soil organisms are normally considered of less importance for ecosystem functioning. We present results that oppose this view. In otherwise well-aerated soils, anaerobic/microaerophilic production or consumption of the trace gas N2O occurs in small soil volumes, when intense decomposition activity at the site leads to local oxygen depletion. At such patch scales, the control of microbial growth and oxygen consumption may depend on the specific organisms present. We assessed N2O turnover in an experiment, where soil dilution from 10−2 over 10−4 to 10−6 followed by microbial regrowth resulted in similar microbial biomass and respiration but reduced diversity. We found an increasing number of very high N2O turnover rates when soil dilution increased from 10−2 over 10−4 to 10−6, as revealed from a significantly increased skewness of the frequency distribution of N2O turnover levels. N2O turnover also tended to increase (p = 0.08) by 20–30% when soil was diluted from 10−2 to 10−6. This suggests that rare soil organisms regulate the local activity of fast-growing microorganisms and thus reduce the probability that anoxic/microaerophilic soil volumes develop. Future studies may reveal which less abundant organisms prevent development of anoxic/microaerophilic conditions in well-aerated soils.

Weak effect of plant canopy but strong impact of depth on variation of cultivable microfungal communities through soil profiles in semiarid Spain

We studied the effect of plant canopy on the distribution of microfungi through 0−30-cm soil profiles under canopies of three plant species and in their adjacent interspace at sun-exposed plain and north-facing slope in the Tabernas Desert, Spain. Using the soil dilution plate method, 142 species from 68 genera were isolated. Melanin-containing fungi dominated in the topsoil layers because of high temperatures and dryness. By contrast, light-colored fungi generating a high amount of small thin-walled conidia substantially increased their abundance in the deeper soil layers – thermotolerant Aspergillus spp. in the 1−5-cm layers and mesophilic Penicillium spp. in the 10−20-cm layers. The significant increase in density of microfungal isolates at 1−10 cm-depth could be associated with the deposition of conidia of aspergilli and penicillii caused by shallow water infiltration in the fine-grained soil and their survival at these depths due to more appropriate edaphic conditions (mainly higher water availability and root concentration). Generally, the effect of plant canopy on microfungal communities was only weakly expressed in higher variations of isolate densities and species richness through the profiles, and in reduced abundance of melanized species with protective multicellular spore morphology in the topsoil layers; at the same time, soil depth strongly influenced all community characteristics. The study highlights the remarkable role of edaphic factors (temperature, water regime, and soil texture) in the distribution of microfungi through soil depth in semi-arid areas.

Conditions of soils dilution of dams under seismic impacts

This report presents the results of the author's research on the dilution of water-saturated cohesive soils in the conditions of concussions. The nature of the weakening of the soil connectivity during vibration and the dynamic pressure that occurs in the thickness during the compaction of the disturbed soil structures, which contribute to the liquefaction and spreading of the soil from the body of the structure, is described. The criterion of the possibility of violation of the soil structure in the conditions of concussions is given. A theoretical method for determining this important indicator of the seismic strength of the soil is given.