Why is there a tripartite symbiosis in banana crops?

Dark septate endophytes (DSE) and arbuscular mycorrhizal fungi (AMF) can simultaneously colonize the roots of different plants; their function and association can range from symbiotic to parasitic. The type of interaction is believed to be dependent on environmental and soil nutritional conditions. We quantified banana root colonization by arbuscular mycorrhizal fungi and by dark septate endophyte, to evaluate the relationship between these and certain edaphic factors. Since banana is cultivated under high P it is unlikely the fungal symbionts help with P nutrition. Organic carbon had a positive and K+ content a negative relation with colonization by DSE and AMF, while the clay content had a negative correlation with the DSE/AMF relationship with values between 0.4 and 0.7 in banana crops in Colombia. Under these circumstances, organic carbon and K+ are nutritional influencers on the colonization by DSE and AMF but the ratio DSE/AMF colonisation did not indicate a significant influence of soil nutritional factors. Both the ecological function and benefit to the plant of both organisms in this three way symbiosis remain unknown.