Veronika Řezáčová

Organic and mineral fertilization, respectively, increase and decrease the development of external mycelium of arbuscular mycorrhizal fungi in a long-term field experiment

Effects of long-term mineral fertilization and manuring on the biomass of arbuscular mycorrhizal fungi (AMF) were studied in a field experiment. Mineral fertilization reduced the growth of AMF, as estimated using both measurements of hyphal length and the signature fatty acid 16:1ω5, whereas manuring alone increased the growth of AMF. The results of AMF root colonization followed the same pattern as AMF hyphal length in soil samples, but not AMF spore densities, which increased with increasing mineral and organic fertilization. AMF spore counts and concentration of 16:1ω5 in soil did not correlate positively, suggesting that a significant portion of spores found in soil samples was dead. AMF hyphal length was not correlated with whole cell fatty acid (WCFA) 18:2ω6,9 levels, a biomarker of saprotrophic fungi, indicating that visual measurements of the AMF mycelium were not distorted by erroneous involvement of hyphae of saprotrophs. Our observations indicate that the measurement of WCFAs in soil is a useful research tool for providing information in the characterization of soil microflora.

Hyphal growth and mycorrhiza formation by the arbuscular mycorrhizal fungus Glomus claroideum BEG 23 is stimulated by humic substances

Effects of humic substances (humic acid or fulvic soil extract) or saprophytic microorganisms (Paecilomyces lilacinus and an unidentified actinomycete) on growth of mycelium and mycorrhiza formation by Glomus claroideum BEG23 were studied in a hydroponic system. Humic substances stimulated root colonization and production of extraradical mycelium by the mycorrhizal fungus. Both humic and fulvic acids tended to decrease populations of culturable bacteria and fungi in the cultivation system, indicating a moderately antibiotic activity. The addition of saprophytic microorganisms able to use humic substances to the cultivation system further stimulated the development of the mycorrhizal fungus. However, stimulation of G. claroideum was also observed when the saprophytic microorganisms were heat-killed, suggesting that their effect was not linked to a specific action on humic substances. The results indicate that humic substances may represent a stimulatory component of the soil environment with respect to arbuscular mycorrhizal fungi.

Influence of Mineral and Organic Fertilization on Soil Fungi, Enzyme Activities and Humic Substances in a Long-Term Field Experiment

Changes in microfungal communities, fungal activities and humic substances (HS) in agricultural soils kept under different fertilization regimes were observed and their causal relationships were investigated in a long-term field experiment. Fertilization did not change the abundance of HS-utilizing microfungi and, except for organic amendment alone, total culturable microfungi were also unaffected by this factor. Organic fertilization increased activities of manganese peroxidase (MnP) and proteinase, but decreased endo-1,4-β-glucanase activity compared to the corresponding control without organic fertilization. In soils treated with mineral fertilizers, the activities of MnP, endo-1,4-β-glucanase and proteinase were higher than in control without any mineral treatment. Both the aromaticity of fulvic acid and the molar mass of humic acid was lower in soil with organic fertilization, which may be a result of oxidative degradation mediated by higher MnP activity observed in treatments with organic fertilization.

Carbon flow from plant to arbuscular mycorrhizal fungi is reduced under phosphorus fertilization

Background and aimsArbuscular mycorrhizal fungi (AMF) are plant root symbionts highly specialized upon phosphorus (P) supply to their hosts. We investigated plants’ ability to regulate carbon (C) flow to AMF depending on the soil P supply.MethodsLeek (Allium porrum), medic (Medicago truncatula), and ryegrass (Lolium perenne) were subjected to AMF inoculation and/or P fertilization in a glasshouse experiment. The C flows were traced using 13C pulse labelling.ResultsMycorrhizal P uptake responses were lowered by P fertilization in all tested plant species. Independently from the C flow to the roots, the C flow to AMF-signature fatty acid 16:1ω5 were reduced by P fertilization in leek and ryegrass (but not in medic). Calculated mycorrhizal C costs ranged between 0.9% and 10.5% of the plant C budget.ConclusionsSuppression of the C flow from the plants to AMF resulted from both reduced abundance of AMF in the roots and lowered relative C income per unit of AMF biomass in P-fertilized pots. Although inconsistencies amongst different plant species demand caution in making generalizations, these results suggest an active role of host plants in regulating the C flow to AMF.

Utilization of organic nitrogen by arbuscular mycorrhizal fungi—is there a specific role for protists and ammonia oxidizers?

Arbuscular mycorrhizal (AM) fungi can significantly contribute to plant nitrogen (N) uptake from complex organic sources, most likely in concert with activity of soil saprotrophs and other microbes releasing and transforming the N bound in organic forms. Here, we tested whether AM fungus (Rhizophagus irregularis) extraradical hyphal networks showed any preferences towards certain forms of organic N (chitin of fungal or crustacean origin, DNA, clover biomass, or albumin) administered in spatially discrete patches, and how the presence of AM fungal hyphae affected other microbes. By direct 15N labeling, we also quantified the flux of N to the plants (Andropogon gerardii) through the AM fungal hyphae from fungal chitin and from clover biomass. The AM fungal hyphae colonized patches supplemented with organic N sources significantly more than those receiving only mineral nutrients, organic carbon in form of cellulose, or nothing. Mycorrhizal plants grew 6.4-fold larger and accumulated, on average, 20.3-fold more 15N originating from the labeled organic sources than their nonmycorrhizal counterparts. Whereas the abundance of microbes (bacteria, fungi, or Acanthamoeba sp.) in the different patches was primarily driven by patch quality, we noted a consistent suppression of the microbial abundances by the presence of AM fungal hyphae. This suppression was particularly strong for ammonia oxidizing bacteria. Our results indicate that AM fungi successfully competed with the other microbes for free ammonium ions and suggest an important role for the notoriously understudied soil protists to play in recycling organic N from soil to plants via AM fungal hyphae.

Carbon Fluxes in Mycorrhizal Plants

Although declared as a research priority more than 40 years ago, the knowledge about the magnitude and mechanisms of carbon (C) fluxes between plants and their mycorrhizal fungal symbionts remains fragmentary. In spite of a number of experiments with isotopically labeled C documented rapid and directed C transfer from the host plant to its mycobionts, the molecular mechanisms and their regulation involved in such a transport remain largely unknown. It seems that in many arbuscular mycorrhizal (AM) symbioses, the C costs remains well below 10% of the C fixed photosynthetically by the host plants. Higher values were detected in the past only under specific situations such as in young plants, under low light intensities, and/or for particular partner combinations, involving very costly (in terms of C demand) and little nutritionally beneficial AM fungi such as Gigaspora sp. Ecological context of the common mycorrhizal networks in terms of redistribution of symbiotic C costs and nutritional benefits on one hand and C movement through soil food webs beyond mycorrhizal hyphae on the other are briefly discussed in this chapter, and further research challenges and open knowledge gaps with respect to C fluxes in mycorrhizal plants are outlined.

Mycorrhizal symbiosis induces plant carbon reallocation differently in C 3 and C 4 Panicum grasses

AimsAlthough arbuscular mycorrhizal symbiosis is common in many plants with either C3 or C4 photosynthesis, it remains poorly understood whether photosynthesis type has any significant impact on carbon (C) fluxes in mycorrhizal plants. Thus, we compared mycorrhizal and non-mycorrhizal (NM) plants belonging to Panicum bisulcatum (C3) to its congeneric P. maximum (C4).MethodsPlants were or were not exposed to arbuscular mycorrhiza (AM) fungal inoculation and/or phosphorus (P) fertilization. Plants’ C budgets were assembled based on 13CO2 pulse-chase labelling and sequential harvesting.ResultsMycorrhizal plants allocated on average 3.9% more recently fixed C belowground than did their NM counterparts. At low P, mycorrhizal C3-Panicum plants allocated less C to aboveground respiration as compared to their respective NM controls. In contrast, mycorrhizal C4-Panicum increased the rates of photosynthesis and allocated more C to aboveground respiration than the respective NM controls. At high P, the differences were less prominent.ConclusionsWe demonstrated consistent differences in aboveground C allocation due to AM symbiosis formation in congeneric C3 and C4 grasses. Both grasses benefited from AM symbiosis in terms of improved P uptake (at least at low P). These results advocate a holistic (whole-plant) perspective in studying C fluxes in mycorrhizal plants.

Enoplognatha bryjai new species, a bizzare cobweb spider of the Pannonian swamps (Araneae, Theridiidae)

During faunistic research of reed beds associated with lakes in the Pannonian region of Czechia we found an Enoplognatha species with spectacular morphology of the male chelicerae. Despite this species being found in an arachnologically well researched area, and that the European species of the genus Enoplognatha have been recently revised (Bosmans & Van Keer 1999), it appears to be a new species.

European species of the Gnaphosa alpica complex (Araneae, Gnaphosidae)

Members of the genus Gnaphosa belong to the largest gnaphosid spiders. They are particularly interesting in nature conservation as their distribution is mainly restricted to disappearing natural non-forest habitats. In Europe, several Gnaphosa species groups occur. The exclusively Palaearctic group G. bicolor is characterised by a retrolaterally-shifted embolus, which occupies at least part of the middle one-third of the palpal bulb; females have laterally expanded epigyne and often have very elongated median epigynal ducts (Ovtsharenko et al. 1992). So far four species of this group have been identified in Europe, with a fifth species found in Central Asia (G. tarabaevi Ovtsharenko, Platnick Song, 1992). Two of the European species, G. bicolor (Hahn, 1831) and G. badia (L. Koch, 1866), are well known and their taxonomy and nomenclature is stable, but the same does not hold true for the other two.

Taxonomic revision and insights into the speciation mode of the spider Dysdera erythrina species-complex (Araneae : Dysderidae): sibling species with sympatric distributions

Abstract. The genus Dysdera Latreille, 1804, a species-rich group of spiders that includes specialised predators of woodlice, contains several complexes of morphologically similar sibling species. Here we investigate species limits in the D. erythrina (Walckenaer, 1802) complex by integrating phenotypic, cytogenetic and molecular data, and use this information to gain further knowledge on its origin and evolution. We describe 16 new species and redescribe four poorly known species belonging to this clade. The distribution of most of the species in the complex is limited to southern France and the north-eastern Iberian Peninsula. The species studied do not show any obvious differences in habitat preference, and some of them even occur sympatrically at certain sites. They probably feed on the same type of prey as they readily capture woodlice. On the other hand, they differ in body size, mouthparts shape, sculpturing of carapace, morphology of the copulatory organs, karyotype and DNA sequences. Experimental interspecific mating showed a partial precopulatory behavioural barrier between D. erythrina and D. cechica, sp. nov. Our data suggest that karyotype evolution of the complex included chromosome fusions and fissions as well as translocations (between autosomes as well as autosomes and sex chromosomes). We hypothesise that chromosome rearrangements generating reproductive incompatibility played a primary role in speciation within Dysdera complexes. Dysdera spiders are poor dispersers, and their original distribution areas (forested areas in the Mediterranean) were repeatedly fragmented during Quarternary climatic oscillations, facilitating integration of chromosome rearrangements into karyotypes by genetic drift. Sympatric occurrence of closely related species may have been promoted by prey segregation as suggested by differentiation in body size in co-occurring species. The following new species are described: D. catalonica, sp. nov., D. cechica, D. dolanskyi, sp. nov., D. fabrorum, sp. nov., D. garrafensis, sp. nov., D. graia, sp. nov., D. kropfi, sp. nov., D. minairo, sp. nov., D. portsensis, sp. nov., D. pradesensis, sp. nov., D. pyrenaica, sp. nov., D. quindecima, sp. nov., D. septima, sp. nov., D. stahlavskyi, sp. nov., D. tredecima, sp. nov. and D. undecima, sp. nov.