Morphological and physiological responses of the external mycelium of Rhizophagus intraradices to water stress
Most studies dealing with mycorrhizal associations and drought have focused on the plants, not on the fungi, and tolerance and adaptations of arbuscular mycorrhizal (AM) fungi to cope with water stress are virtually unknown. This study was conducted to assess how water stress directly affects an AM fungus isolate, particularly through morphological and physiological changes in the external mycelium. We used two-compartment pots separated by mesh and an air gap that allowed us to apply water stress treatments only to the external mycelium. Clover (Trifolium subterraneum L.) plants inoculated with Rhizophagus intraradices grew at high humidity until external mycorrhizal mycelium developed in the mycelium compartment. Then, we started three watering treatments: high (H, 70% of soil water holding capacity), low (L, 10%), and mixed watering (HLHL, 70–10–70-10%) only in the hyphal compartment. The HLHL treatment was rewetted once to 70% after 42 days. We measured total mycelium length, hyphal length in diameter categories, respiration activity, and protoplasm fragmentation 42 and 76 days after starting the treatments. Rhizophagus intraradices mycelium responded to water stress by reducing its length, maintaining larger diameter hyphae, and concentrating protoplasm activity in fragments in the HLHL and L treatments. In both water stress treatments, changes suggested a trade-off between avoiding desiccation and storing resources, and maintaining soil exploration and water uptake capacity.
KeywordsDrought Hyphae Hyphal diameter Respiratory activity
We thank Horacio Paz, Fernando Pineda, John Larsen and Miguel Nájera for sharing their experience and lab facilities. This research was supported by Dirección General de Asuntos del Personal Académico (DGAPA) from Universidad Nacional Autónoma de México (UNAM) through project PAPIIT-IN224010. MEG thanks DGAPA-PASPA for a sabbatical scholarship at the University of Copenhagen.
Conceived research: MEG, SMCS, RLM
Performed research: RLM, SMCS
Analyzed data: RLM, MEG
Wrote the manuscript: RLM, MEG
This research was funded by Dirección General de Asuntos del Personal Académico (DGAPA) from Universidad Nacional Autónoma de México (UNAM) through project PAPIIT-IN224010 and a sabbatical fellowship from PASPA at the University of Copenhagen, Denmark, to MEG.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Brundrett MC (2009) Mycorrhizal associations and other means of nutrition of vascular plants: understanding the global diversity of host plants by resolving conflicting information and developing reliable means of diagnosis. Plant Soil 320(1-2):37–77Google Scholar
- Decagon (2010) Generating a soil moisture characteristic using the WP4C. Decagon application note 13380–01Google Scholar
- Gavito ME (2007) Mycorrhizas and crop production in a world with rapidly changing climate: a warning call. In: Hamel C, Plenchette C (eds) Arbuscular mycorrhizae in crop production. Haworth Press, New York, pp 293–310Google Scholar
- Gavito ME, Olsson PA (2008) Foraging for resources in arbuscular mycorrhizal fungi: what is an obligate symbiont searching for and how is it done? In: Varma A (ed) Mycorrhiza: genetics and molecular biology, eco-function, biotechnology, eco-physiology, structure and systematics. Springer Verlag, Berlin Heidelberg, pp 73–88CrossRefGoogle Scholar
- Öpik M, Vanatoa A, Vanatoa E, Moora M, Davison J, Kalwij JM, Reier Ü, Zobel M (2010) The online database MaarjAM reveals global and ecosystemic distribution patterns in arbuscular mycorrhizal fungi (Glomeromycota). New Phytol 188(1):223–241Google Scholar
- Querejeta JI (2017) Soil water retention and availability as influenced by mycorrhizal symbiosis: consequences for individual plants, communities and ecosystem. In: Collins-Johnson N, Gehring C, Jansa J (eds) Mycorrhiza mediation of soil fertility, structure and carbon storage. Elsevier, Amsterdam, pp 299–317CrossRefGoogle Scholar
- Smith SE, Read JD (2008) Mycorrhizal Symbiosis, third edn. Elsevier Ltd, AmsterdamGoogle Scholar
- Staddon P, Thompson K, Jakobsen I, Grime JP, Askew AP, Fitter AH (2003) Mycorrhizal fungal abundance is affected by long-term climatic manipulations in the field. New Phytol 9:186–194Google Scholar
- Staddon P, Gregersen R, Jakobsen I (2004) The response of two Glomus mycorrhizal fungi and a fine endophyte to elevated atmospheric CO2, soil warming and drought. New Phytol 10:1909–1921Google Scholar