Pedobiologia最新文献

The extraradical mycelium of mycorrhizal fungi is among the major carbon pools in soil that is hard to quantitatively assess in-situ. Established method of in-growth mesh bags in temperate ecosystems is difficult to apply in the tropics, where mesh bags are often damaged by termites. Here we introduce a modification of the in-growth mesh bag technique, in which mesh bags are enforced by stainless steel mesh. Its performance was tested in the Đồng Nai (Cát Tiên) National Park in Vietnam across two monsoon tropical forests, dominated by tree species associated with either ectomycorrhizal (ECM) or arbuscular mycorrhizal (AM) fungi. Armored in-growth mesh bags remained intact, while about 60 % of non-armored mesh bags were damaged by termites after 180 days of exposure. The biomass of extraradical mycelium of ectomycorrhizal fungi estimated by PLFA analysis was similar in the armored and non-armored mesh bags and did not differ between studied forests. However, fungal community composition slightly differed between armored and non-armored mesh bags in the ECM- but not in the AM-dominated forest. Fungal mycelium gathered in the AM-dominated forest was depleted in ¹⁵N compared to that collected in the ECM-dominated forest. Overall, our results argue for using armored mesh bags as a robust tool for harvesting the biomass of extraradical mycelium of mycorrhizal fungi in tropical ecosystems.

Plant litter decomposition is driven by soil biota and biophysiochemical conditions as well as substrate quality. Prescribed burns can affect the abundance and diversity of soil arthropods and the biophysiochemical conditions in terrestrial ecosystems. In this study, we examined the effects of a prescribed burn on soil arthropods and litter chemistry in decomposing litter during a total of 469-days field incubation using litter from two grasses, Dichanthium annulatum and Megathyrsus maximus, in a subtropical moist pastureland of Puerto Rico. We found the prescribed burn substantially elevated ultraviolet (UV) radiation and soil temperature; and significantly decreased the diversity of litter total arthropods, especially predators and Mesostigmata mites, during the initial 5 months after the burn. However, the prescribed burn had no effect on either the biophysical environment nor on arthropod abundance and diversity during the subsequent incubation period of >5 months after the burn. Furthermore, the prescribed burn substantially increased the immobilization of iron (Fe) and manganese (Mn), and decreased sulfur (S) concentration in the decomposing litter. Prescribed burn had no interactions with substrate quality for percent mass remaining (PMR) and elemental release or accumulation. Low substrate quality D. annulatum litter with a carbon to phosphorus (C/P) ratio of 614 was associated with higher microbivore diversity and higher predator density than higher substrate quality M. maximus litter with a C/P ratio of 266 during the entire incubation period. Lower initial concentration of litter P, magnesium (Mg) and calcium (Ca) in D. annulatum resulted in higher immobilization of these elements in decomposing litter than in M. maximus. Our study suggest that prescribed burn can impose short-term changes in biophysiochemical conditions and the diversity of arthropods in litter decomposition during the initial recovery period of about 5 months after a burn, thus highlighting a high resilience of the grassland ecosystem to fire disturbance, and that it can bring lasting changes in the cycling of Fe, Mn, and S in subtropical moist pastureland that can alter ecosystem productivity.

Red wood ants are keystone species in forest ecosystems. Because ants are active polyphagous predators, they control the abundance of other arthropods. In addition to direct effects on other species, there are a number of indirect effects caused by ants. In our study, we investigated the influence of ants on springtails, which they rarely come into contact with. Springtails have been set as a model group to assess the state of soil animals, since they are one of the most numerous and widespread groups of soil microarthropods. They are characterized by high sensitivity to environmental changes. The basic characteristics (abundance, species richness, and species diversity) of the springtail community and the response of certain species to the presence of ant trails have been studied. The total abundance and species richness of springtails decreased along ant trails. Among occurred species Parisotoma ParIsotoma notabilis, Lepidacyrtus lignorum, Isotomiella minor, Desoria tigrina, and Pseudasinella alba are the most numerous species both along ant trails and in control samples. There are no significant changes in species diversity (assessed by the Shannon-Weaver index). Species structure of springtail communities along ant trails and in control is different. Two groups of common Collembola species are identified: (1) increasing their numbers in the presence of ants, (2) on the contrary, decreasing. The presence of ants in a forest ecosystem influences the soil springtail community, although ant-Collembola interactions are indirect.

Establishing soil biological crusts will result in the long-term restoration of ecosystems. Nonetheless, little research has been conducted to demonstrate the influence of soil endemic microorganisms on suppressing the adverse effects of freezing-thawing on soil properties. This current study evaluated the formation of biological crusts, the enhancement of physical and chemical characteristics of soil, and surface soil stability by inoculating native bacteria and cyanobacteria into the soil during a freezing-thawing cycle. The soil was collected from the Badranlou Region in North Khorasan Province, Northern Iran, and native bacteria and cyanobacteria were isolated, identified, chosen, and cultured. The native treatments of bacteria and cyanobacteria were then inoculated in individual bacteria, cyanobacteria, and combined inoculation of cyanobacteria and bacteria onto an experimental soil in six replications. After 60 days, they were subjected to freezing-thawing conditions to have maximum effect on the soil environment, and finally, the soil surface properties were statistically compared. The results of the significant effect (p<0.001) of inoculation treatments on the physical and chemical properties of the study soil revealed that the carbon, nitrogen, organic matter, phosphorus, potassium, and surface soil stability in bacterial treatment compared to the control treatment increased by 68, 39, 68, 17, 25, 99 %, respectively. While under cyanobacterial treatment, they rose by 83, 61, 83, 18, 73, and 172 %, respectively. The combination inoculation treatment of bacteria and cyanobacteria enhanced the study variables by 73, 66, 73, 25, 58, and 189 %, respectively. Compared to control plots, the soil bulk density in bacterial, cyanobacterial, and compound inoculation treatments was substantially reduced (p<0.001) by 9, 15, and 12 %, respectively. The soil stability, carbon, and organic matter were among the most essential properties of the soil, and they best showed the difference between the various treatments applied. It confirmed the region's potential restoration by inoculating native soil microorganisms.

Cover cropping is a well-established strategy to improve soil health, especially in arid and semi-arid agricultural systems. Benefits to soil health are often mediated via effects of cover crops on soil microbial community structure, function and diversity, crucial for regulating soil biogeochemical cycles, eventually promoting agricultural sustainability. However, limited water availability is a major constraint for both cover crop growth and soil microbial activity. This study sought to characterize and elucidate the shifts in soil microbial community structure in response to different cover crops and differential irrigation treatments using phospholipid fatty acid (PLFA) profiling in southern New Mexico. We tested five cover crop treatments: Pisum sativum (Australian winter pea), Hordeum vulgare cv. Stockford (barley), Brassica juncea cv. Caliente 199 (brown mustard), a three-way mix, and a fallow control — in combination with irrigation treatments of one, two, or three irrigation applications — in a split-plot design over two years. Zea mays (sweet corn) was grown as the summer cash crop. We collected soil samples just after cover crop planting in the fall of 2018, following second year cover crop termination but during Z. mays growth in June 2020, and after the second season of Z. mays growth in October 2020. Differential irrigation treatments did not lead to consistent patterns of change under any cover crop or irrigation treatment. However, PLFA parameters in cover cropped compared to winter fallow plots tended to decrease under one and three irrigations but increased with two irrigations. Changes were more common for bacterial than for fungal PLFA biomarkers, and more common in B. juncea and H. vulgare cover crops than in P. sativa or the mix. It is important to note that, while cover crop effects were inconsistent, cover cropping did lead to some shifts in PLFA biomarkers, even in the short two-year period of cover cropping.

Soil organic matter (SOM) is the main pathway of carbon (C) input to the soil with the decomposition of shoot residues, roots and their exudates. The objective was to evaluate the contribution of different vegetal composition and plant parts of Caatinga species and the effects of introducing a grass in the soil microbial community structure and biochemical composition of SOM. A trial was conducted under controlled conditions (120 days) using, separately, the shoot and roots residues of native species from the herbaceous (HERB) and shrub-arboreal (ARB) strata and a grass (GRASS). Megathyrsus maximum, which is native from Africa, but well adapted to the semi-arid conditions of Brazil, was used. Combinations of these species in different proportions were also evaluated: (i) 55 % shrub and trees + 45 % grass (MIX1) and (ii) 75 % shrub and trees + 25 % grass (MIX2). At the end of incubation, soil samples were collected to evaluate the microbial community structure through the phospholipid fatty acids (PLFA). Physical fractioning of SOM into particulate organic matter (POM) and mineral-associated organic matter (MAOM) was also performed, followed by biochemical characterization of these fractions by thermochemolysis analysis. The ARB shoot residue resulted in a 181.5 % increase (p < 0.05) in total PLFA biomass in the soil. A significant increase (p < 0.05) in the abundance of fungi and bacteria was observed with the incorporation of shoot residues. MAOM was characterized by a higher abundance of aliphatic (31.6 ± 5.0 %) and nitrogen-bearing compounds (21.0 ± 2.0 %), while higher lignin derivatives were observed in POM (18.0 ± 0.6 %). The ground cover provided a diversity of compounds in the SOM, thus regulating the structure of the microbial community. These results highlight the importance of conserving biodiversity, both in natural ecosystems and in agroecosystems in the semi-arid environment.

Soil organic matter is the dominant pool of carbon (C) in terrestrial ecosystems. Recent advances in understanding of the mechanisms of C stabilization in the soil emphasize microbes as the main drivers. Special attention is placed on the accumulation of bacterial and fungal necromasses. This calls for development of fast and reliable methods to estimate microbial necromass in a various type of soils, including peat soils. Here we provide precise method to measure fungal and bacterial necromasses with high-pressure liquid chromatography-fluorescence detector (HPLC-FLD) and its comparison with gas chromatography method. Purity of the chromatographic peaks was confirmed with mass spectrometry. The HPLC-FLD method provides reliable results for mineral, organic and highly organic peat soils.

The Mediterranean forest has an important ecological and economic role, being holm oak (Quercus ilex), Pyrenean oak (Quercus pyrenaica), umbrella pine (Pinus pinea) and Scot pine (Pinus sylvestris) some of its main tree species. The fungal damping-off disease caused by Fusarium seriously threatens the establishment of these forest species in nurseries and reforestation, requiring the search for environmentally friendly alternatives to control the disease. We have used different species of ectomycorrhizal fungi (EMF) as potential biological control agents (BCAs) effective against the disease: Lactarius sanguifluus, Tricholoma portentosum, Suillus luteus and Agaricus silvicola from Pinus-species, and Leccinum lepidum, Amanita rubescens and Xerocomus ferrugineus from Quercus-species. A direct in vitro confrontation was performed and conidial germination of Fusarium in contact with cell-free filtrates produced by EMF was studied. Le. lepidum was the most effective Quercus-fungus in vitro against F. oxysporum, reducing its growth up to 32 % and its conidial germination up to 87 %. S. luteus was the most effective Pinus-fungus in vitro against F. oxysporum and F. verticillioides, reducing in direct confrontation, reducing its growth up to 30 %. However, La. sanguifluus was the Pinus-fungus that inhibited conidial germination of both pathogens, up to 55 %. In planta trials were carried out with seeds of the four forest species growing on substrate colonized by Le. lepidum (in Q. ilex and Q. pyrenaica seeds, infected by F. oxysporum) or by La. sanguifluus (P. pinea and P. sylvestris seeds, infected by F. oxysporum or F. verticillioides). Only La. sanguifluus was effective in reducing disease caused by F. oxysporum (strain Fo4) on P. sylvestris seeds. Therefore, EMF may be a potential tool in the control of damping-off in forest species, requiring further research.

Larger soil organisms have often been reported as the most sensitive to disturbances caused by cropping practices. However, soil macrofauna comprises groups with a wide diversity of morphological and ecological features, which may respond differently to applied practices. In order to further assess the effect of cropping systems on soil macrofauna, macrofauna organisms were extracted from soil blocks over 21 fields (each comprising three plots) located in the Paris basin, in autumns 2020 and 2021. Fields belonged to conventional, conservation or organic systems, either long-established (≥ 7 years) or in transition (≤ 3 years). Tillage, pesticide treatment and organic matter input intensity were assessed in each field using composite indexes of practice intensity. Macrofauna density and diversity, earthworm ecological categories, species richness and functional traits were investigated. Our results showed that the density and diversity of macrofauna demonstrated few differences regarding different cropping systems, with highly variable effects across groups and years. Specific macroarthropod groups responded differently to tillage, pesticide treatment and organic input intensity, but not over the two years of the study. Regarding earthworms, high tillage intensity had a negative effect on the density and biomass of epi-anecic juveniles and on species with a small body size. Higher organic matter inputs had a negative effect on the density and biomass of endogeic earthworms, and could be related to several earthworm functional traits (body length, mass/length ratio, carbon preferences). Effects of pesticide treatments were less clear, although they could have impacted some earthworm species. More generally, taxonomic and functional trait approaches of earthworm community led to similar conclusions. Overall, our results support the need to account for (i) the actual intensity of practices in cropping systems and (ii) the different taxonomic, trophic and ecological groups of macrofauna, in order to assess the effects of cropping systems on soil biodiversity.

Amongst climate change’s impacts a major concern is salinization of soils, for example due to saltwater intrusion. The aim of the present study was to investigate in a standard field soil the impacts of soil salinity increase. The purpose was to study this in two soil invertebrates that are key model ecotoxicology test-species, Enchytraeus crypticus and Folsomia candida as surrogate representatives of the soil ecosystem. The exposure followed the standard ecotoxicity OECD (Organization for Economic Cooperation and Development) test guidelines, and the assessed endpoints were survival, reproduction and size. Exposure done in LUFA 2.2 soil, spiked with 0,0.6,1,2,3,4,5,6,8 g NaCl/kg soil dry weight (DW) for E. crypticus (21 days) and 0,0.06,0.6,1,2,3,4,5,6 g NaCl/kg soil DW for F. candida (28 days). There was a similar impact for both species in terms of survival (LC₅₀=4.2 g NaCl/kg soil DW), whereas at the reproductive output level of F. candida (EC₅₀=2.1 g NaCl/kg soil DW) was more sensitive than E. crypticus (EC₅₀=2.4 g NaCl/kg soil DW). Further, size was impacted for F. candida in a monotonic dose-response curve for both adults (EC₅₀=3.5 g NaCl/kg soil DW) and juveniles (EC₅₀=2 g NaCl/kg soil DW), whereas for E. crypticus there was an increase in reproductive output at lower concentrations (0.6–1 g NaCl/kg soil DW). This increased reproduction was associated with a larger size of adults within the same concentration range. Considering the prediction from the climate models, the soil invertebrate community will be affected. As upper soils are likely to have the highest salinity increase due to evaporation, soil surface species, such as the collembolan tested here, are at higher risk. Negative population effects were occurring within salinity levels predicted by climate change models.