Local Adaptation to Soil Hypoxia Determines the Structure of an Arbuscular Mycorrhizal Fungal Community in Roots from Natural CO₂Springs

Abstract

The processes responsible for producing and maintaining the diversity of natural arbuscular mycorrhizal (AM) fungal communities remain largely unknown. We used natural CO 2 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 CO 2 exposure. We found significant levels of AM fungal community turnover (␤ 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 plant's distribution.

A decade of research in mofette areas has given us new insights into adaptation of soil microorganisms to abiotic stress / DESETLETJE RAZISKAV NA OBMOČJIH MOFET NAM JE OMOGOČILO NOVE VPOGLEDE V ADAPTACIJO MIKROORGANIZMOV NA ABIOTSKI STRES

“…The latter has been consistently shown as a major abiotic factor affecting soil microbes , Maček et al, 2011, Šibanc et al, 2012. Hypoxia is not only limited to mofette sites, but is a wider phenomenon and a common transient property of soils that often appears in waterlogged and flooded areas or due to soil compaction.…”

“…The nutrient exchange within plant root cells mainly takes place at the fungus-plant symbiotic interface formed around the finely branched fungal arbuscules (Parniske, 2008). Yet, despite its ecological importance, astonishingly little is known about their ecological and physiological responses to hypoxia (Maček et al, 2011).…”

“…FACE -Free Air Carbon dioxide Enrichment experiments), to measuring plant (Maček et al, 2005) and microbial responses (e.g. Maček et al, 2009, Krüger et al, 2011, Maček et al, 2011, Frerichs et al, 2013 to high soil CO 2 concentrations and CO 2 induced hypoxia. Only recently, the first reports on soil fauna responses to CO 2 induced soil hypoxia were also published, with a description of the new Collembola species, specific for mofette sites (Russell et al, 2011).…”

“…Thus, since the first rhizosphere study conducted within the Stavešinci mofette field, focusing on the research of high CO 2 concentrations and hypoxia on root respiration (Maček et al, 2005), hypoxia was chosen as the our stress of choice for further investigations: it is present in many natural ecosystems (Perata et al, 2011) and in addition, mofettes provide an unique example of plant and soil communities subject to well characterized (Vodnik et al 2006, localized, long-term selection pressure (Maček et al, 2011). This represents a relatively rare opportunity for research of the different aspects of soil ecology and the driving forces of soil diversity in natural ecosystems, and therefore sheds some light on an important research issue that needs immediate attention in order to better understand soil biodiversity and its ecological functions.…”

“…Kaligarič, 2001, Vodnik et al, 2002a, 2002b, Pfanz et al, 2004, Maček et al, 2005, Pfanz et al, 2007. An important but often neglected feature in practically all mofette sites is the CO 2 induced soil hypoxia (reduced O 2 concentration) that affects all the present biota in this ecosystem (Maček et al, 2005, Maček et al, 2011. Hypoxia is a common but usually transient abiotic stress factor that is also present in many other terrestrial ecosystems, e.g.…”