Diversity of orchid mycorrhizal fungi is influenced by P availability in chilean orchids

Background/Question/Methods

The seeds of Orchidaceae are very small and lacking of energetic reserves, so they need to associate with mycorrhizal fungi for germination and early development. The requirement of find a compatible fungus to germinate can limit the distribution and abundance of orchids. In this way it is expected that orchids with specialist association will present more restricted distribution than generalist orchids. There has been largely studied how the distributional range of orchids is related with mycorrhizal diversity, but little is known about how physical conditions as soil parameters can determinate the diversity of orchid mycorrhizal fungi.  

Results/Conclusions

In this study we evaluated the relation between soil parameters as P, N, K, organic matter and pH, and the diversity of orchid mycorrhizal fungi on four species of Bipinnula (Orchidaceae) in Chile. We collected roots from 10 individuals in seven populations of Bipinnula fimbriata, six of B. plumosa, two of B. apinnula and one of B. volckamnii representing the distributional range of each species.  We extracted DNA directly from roots pieces and from isolated fungi, amplified with ITS1/ITS4 and the more specific primers ITS1/ITS4tul, ITS1/ITS4B, sequenced and identified by BLAST search. We found 58 different haplotypes representing two fungal families, Ceratobasidiaceae and Tulasnellaceae. We found that P available is significantly related with mycorrhizal diversity, in sites with low availability of P this relation is positive while in sites of high P availability the relation is negative. Our results suggest that the specificity in orchid mycorrhizal interaction can be influenced by physical conditions as soil nutrients, something that has been poorly studied and appears to be fundamental to understand the ecology of this association.