The abundance of arbuscular mycorrhizal fungal species in symbiosis with okra plants is affected by induced drought conditions in a calcareous substrate

Here we examined the effect of soil drought conditions on the community and abundance of arbuscular mycorrhizal fungi (AMF) in symbiosis with okra (Abelmoschus esculentus), where the inoculated AMF community was originally obtained from the rhizosphere of an okra crop grown in the Sudan. Okra seedlings were cultivated in a calcareous pot substrate, where the water content was either maintained at 20% for the well-watered (W) or reduced to 10% for the drought treatment (D). At harvest, in both irrigation treatments the root length was highly AMF colonised and compared with treatment W, the drought condition (D) significantly limited the uptake of phosphorus but not that of nitrogen, potassium, iron or zinc. The AMF DNA sequences recovered from the initial field soil, substrate and root samples identified twelve AMF taxa in total belonging to the two Glomeromycotina families Glomeraceae (91%) and Claroideoglomeraceae (9%). The number of operational taxonomic units (OTUs) in root tissue and pot substrate samples was unaffected by the stress treatment D. However, while certain AMF taxa (notably Glomus hoi) were likewise present in samples recovered from both the water treatments, there was a shift of abundance for other taxa. The abundance of Rhizophagus aff. arabicus was significantly higher in D than in W, mainly at the expense of Dominikia sp. The results suggested that, within a few weeks of root colonisation, soil drought together with low P availability imposes a major shift in the relative abundance of some AMF taxa. Moreover, under the given dry substrate conditions, R. aff. arabicus appeared to comprise a high competitiveness within the Glomeraceae - dominated AMF community.