Irena Maček

Local Adaptation to Soil Hypoxia Determines the Structure of an Arbuscular Mycorrhizal Fungal Community in Roots from Natural CO2 Springs

ABSTRACT The processes responsible for producing and maintaining the diversity of natural arbuscular mycorrhizal (AM) fungal communities remain largely unknown. We used natural CO2 springs (mofettes), which create hypoxic soil environments, to determine whether a long-term, directional, abiotic selection pressure could change AM fungal community structure and drive the selection of particular AM fungal phylotypes. We explored whether those phylotypes that appear exclusively in hypoxic soils are local specialists or widespread generalists able to tolerate a range of soil conditions. AM fungal community composition was characterized by cloning, restriction fragment length polymorphism typing, and the sequencing of small subunit rRNA genes from roots of four plant species growing at high (hypoxic) and low (control) geological CO2 exposure. We found significant levels of AM fungal community turnover (β diversity) between soil types and the numerical dominance of two AM fungal phylotypes in hypoxic soils. Our results strongly suggest that direct environmental selection acting on AM fungi is a major factor regulating AM fungal communities and their phylogeographic patterns. Consequently, some AM fungi are more strongly associated with local variations in the soil environment than with their host plants distribution.

Effect of EDTA washing of metal polluted garden soils. Part II: Can remediated soil be used as a plant substrate?

In a field experiment on metal contaminated and EDTA-remediated soil we studied plant performance, mycorrhizal associations and prospects of potential re-use of remediated soil as a garden substrate. Two experimental plots of 4 × 1 × 0.3 m were filled, one with remediated and the other with original contaminated soil. Selected cultivars were rotated over the course of 16months. Pb, Zn, Cd and micronutrient plant uptake was measured and their phytoaccessibility was analyzed by the DTPA method. Plant fitness was assessed by chlorophyll fluorescence and gas exchange measurements and evaluation of root colonization were analyzed with mycorrhizal fungi. Remediation reduced Pb and Cd concentrations in roots, green parts and fruits in most of the plants. Phytoaccumulation of Zn was reduced in one half of the cultivars. Some plants suffered from Mn deficiency as total soil Mn was reduced 4-fold and phytoaccessibility of micronutrients Cu, Fe and Mn for 54, 26 and 79%, respectively. Plant biomass was reduced. Photosynthetic parameters of plants grown in original and remediated soil were similar, except for the reduction in Spinacia oleracea. The frequency of mycorrhizal colonization in the roots of Pisum sativum was reduced five-fold and no significant changes were found in Allium cepa roots. Remediation reduced plant uptake of Pb below the concentration stipulated by legislation. Measures to reduce plant accumulation of other toxic metals and to revitalize remediated soil are needed.

Photosynthesis of Cockspur [Echinochloa crus-galli (L.) Beauv.] at Sites of Naturally Elevated CO2 Concentration

High abundance of cockspur (Echinochloa crus-galli) at the geothermal carbon dioxide spring area in Stavešinci indicates that this species is able to grow under widely varying CO2 concentrations. Living cockspur plants can even be found very close to gas-releasing vents where growth is significantly reduced. Plant height correlated well with CO2 exposure. The δ13C value of the CO2 spring air was −3.9 ‰ and δ13C values of high-, medium-, and low-CO2 plants were −10.14, −10.44, and −11.95 ‰, respectively. Stomatal response directly followed the prevailing CO2 concentrations, with the highest reduction of stomatal conductance in high CO2 concentration grown plants. Analysis of the curves relating net photosynthetic rate to intercellular CO2 concentration (PN-Ci curves) revealed higher CO2 compensation concentration in plants growing at higher CO2 concentration. This indicates adjustment of respiration and photosynthetic carbon assimilation according to the prevailing CO2 concentrations during germination and growth. There was no difference in other photosynthetic parameters measured.

The Effects of Natural CO2 Enrichment on the Growth of Maize

SUMMARY Maize plants (Zea mays) were grown in a field influenced by a geothermal source of CO2 (CO2 spring Stavešinci, Slovenia). Yield parameters and the content of photosynthetic pigments, mineral nutrients, antioxidants and soluble sugars were measured and the photo-synthetic performance was followed in plants growing at different CO2 conditions. Growth parameters were negatively correlated with the soil CO2 concentration as measured at 20 cm depth. Analysis of A-Ci curves revealed lower maximum photosynthesis (CO2-saturated photosynthesis) and lower carboxylation efficiency in high CO2 plants when compared to low CO2 plants. Several biochemical parameters, as the decrease in chlorophyll content and the increase in antioxidants indicate stress in plants exposed to a high CO2 environment.

Occultifur mephitis f.a., sp. nov. and other yeast species from hypoxic and elevated CO 2 mofette environments

An inventory of culturable yeasts from the soil and water of natural CO2 springs (mofettes) in northeast Slovenia is presented. In mofettes, CO2 of geological origin reaches the soil surface causing temporarily and spatially stable hypoxic environments in soil and water. In total, 142 yeast strains were isolated and identified from high CO2 and control meadow soil, meadow ground-water, forest pond and stream water. All water locations showed below-ground CO2 release. They were assigned to six basidiomycetous yeast genera (six species) and 11 ascomycetous genera (18 species). All ascomycetous yeasts, with the exception of Debaryomyces hansenii, were able to grow under elevated CO2 and fermented glucose. Candida sophiae-reginae, Pichia fermentans and Candida vartiovaarae were the dominating species in meadow and forest high CO2 exposed water. Meyerozyma guilliermondii and Wickerhamomyces anomalus predominated in high CO2 exposed soils. Using high dilution plating of a mofette soil sample, four strains of an unknown basidiomycetous species were isolated and are here newly described as Occultifur mephitis based on molecular phylogenetic and phenotypic criteria. The type strain of Occultifur mephitis is EXF-6436T[CBS 14611=PYCC 7049, LT594852 (D1/D2), KX929055 (ITS)]. An additional three isolated strains are EXF-6437 (LT594853, KX929056), EXF-6473 (LT594863, KX929057) and EXF-6482 (LT594867, KX929054), as well as a strain reported from previous studies isolated from a leaf of Cistus albidus in Portugal (CBS 10223=PYCC 6067), EU002842 (D1/D2), KY308183 (ITS).

Arbuscular Mycorrhizal Fungal Communities Pushed Over the Edge – Lessons from Extreme Ecosystems

The diversity and structure of soil microbial communities are crucial elements in understanding the ecological impacts of rapidly changing environments. One important group of soil microbes is the ubiquitous plant symbiotic arbuscular mycorrhizal (AM) fungi. Their diverse communities are shaped by complex interactions of their abiotic and biotic environments. Locally extreme ecosystems have proven to be useful for natural long-term experiments in the ecology and evolution of AM fungi, giving an insight into much-needed processes of adaptation and acclimation of natural communities to abiotic stress. For example, data from natural CO2 springs (mofettes) show that when exposed to extreme long-term stress (soil hypoxia and elevated soil CO2 concentrations) specific and temporary stable AM fungal communities form with a high abundance of specialised, stress-tolerant taxa. Moreover, in both natural– and human-impacted ecosystems there are several such cases. This chapter covers a wide range of extremes (abiotic stresses) in the pedosphere, from high to low temperatures, drought and floods, hypoxia, salinity, and soil pollution. An overview of several specific stressed environments where AM fungal community ecology has been studied is presented. In some of these cases, locally extreme environments have already been used and could further serve as a powerful tool to study slow ecological and evolutionary processes that normally require long-term observations and experiments to study them.

Arbuscular Mycorrhizal Fungi in Hypoxic Environments

Hypoxia and even anoxia in plant rhizosphere are common phenomena that can be the consequence of flooding, submergence, soil compaction, or are a specific characteristic of some extreme ecosystems (e.g. due to geological CO2 release in natural CO2 springs or mofettes). The frequency and severity of flooding events will dramatically increase in the future, as projected by climate change models. Therefore, understanding the response of different organisms to soil hypoxia, including crop plants, and their interaction with symbiotic and ubiquitous arbuscular mycorrhizal (AM) fungi is becoming increasingly important in order to enhance plant yield and to promote sustainable agriculture in the future. Plants and soil fungi are known to be obligate aerobes and are sensitive to O2 deficiency since they need a sufficient amount of this gas to support their aerobic metabolism. However, some specific morphological and metabolic adaptations also enable plants to survive in habitats where O2 availability is severely limited. Moreover, recent reports show that diverse plant root endophytic fungal communities exist in these ecosystems with some specific (new) taxa being reported to even thrive there. This includes obligate biotrophic AM fungi that fully depend on the plant-derived carbon source. A new aspect in the biology of these organisms originating from the research into hypoxic environments is that in addition to carbon, they can also use a plant-derived O2 source delivered into the submerged organs via plant’s root aeration systems (e.g. aerenchyma). Moreover, in the field of community ecology, extreme hypoxic environments (e.g. mofettes) have been shown to represent a powerful tool for the study of slower ecological and evolutionary processes in still largely unexplored soil microbial communities. They can be used to gain insight into the adaptation of native communities to a specific permanent stress (e.g. soil hypoxia) as long-term natural experimental systems. In this chapter a review of the literature investigating AM fungi and their communities in hypoxic environments is presented. Considering this aspect will be essential for our capacity to adequately manage ecosystems and predict ecological and evolutionary responses to global change, with flooding and soil hypoxia being a consistent part of terrestrial ecosystems in the future.