Arbuscular Mycorrhizal Fungi in Hypoxic Environments

Abstract

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.