Nutrients and fungal identity affect the outcome of symbiotic germination in Bipinnula fimbriata (Orchidaceae)

Orchids produce small seeds with no energy reserves, relying entirely on orchid mycorrhizal fungi (OMF) for germination. This process, known as symbiotic germination, can lead to different outcomes depending on abiotic factors, such as nutrient availability. Previous studies have shown that nutrient addition has a negative effect on the outcome of symbiotic germination. However, if this effect varies across OMF species, and if it is related to a fungal response to nutrients, remains unknown. This paper examines the effect of fungal identity and nutrient addition (nitrogen and phosphorus) on the germination of the orchid Bipinnula fimbriata using seven OTUs of mycorrhizal fungi from the families Tulasnellaceae and Ceratobasidiaceae. We also evaluated the effect of nutrient addition on mycorrhizal fungi growth rates. Results showed that the nutrient effect on symbiotic germination varied depending on fungal identity. While there was a strong negative effect on symbiotic germination with all Tulasnella OTUs and two Ceratobasidium OTUs, less or no effectwas observed on the other two Ceratobasidium OTUs. Further studies are needed to understand the mechanism underlying this variation and how variable is the effect of nutrient addition on symbiotic germination in Orchidaceae and OMF species.
Bipinnula, Fungal identity, Symbiosis outcome, Nutrient addition, Orchidaceae, Orchid mycorrhiza, Symbiotic germination