Temporal Variation in Community Composition of Root Associated Endophytic Fungi and Carbon and Nitrogen Stable Isotope Abundance in Two Bletilla Species (Orchidaceae)

Abstract

Mycorrhizae are an important energy source for orchids that may replace or supplement photosynthesis. Most mature orchids rely on mycorrhizae throughout their life cycles. However, little is known about temporal variation in root endophytic fungal diversity and their trophic functions throughout whole growth periods of the orchids. In this study, the community composition of root endophytic fungi and trophic relationships between root endophytic fungi and orchids were investigated in Bletilla striata and B. ochracea at different phenological stages using stable isotope natural abundance analysis combined with molecular identification analysis. We identified 467 OTUs assigned to root-associated fungal endophytes, which belonged to 25 orders in 10 phyla. Most of these OTUs were assigned to saprotroph (143 OTUs), pathotroph-saprotroph (63 OTUs) and pathotroph-saprotroph-symbiotroph (18 OTUs) using FunGuild database. Among these OTUs, about 54 OTUs could be considered as putative species of orchid mycorrhizal fungi (OMF). For both Bletilla species, significant temporal variation was observed in the diversity of root endophytic fungi. The florescence and emergence periods had higher fungal community richness of total species and endemic species than did other periods. Both Bletilla species were dominated by Agaricomycetes and Basidiomycota fungi throughout the whole year; however, their abundances varied between two Bletilla species and among phenological stages. Meanwhile, the ranges of 13C and 15N natural abundance were also highly dynamic across all growth stages of Bletilla species. Compared with the surrounding autotrophic plants, significant 13C enrichments (ε13C) were found across all phenological stages, while significant 15N enrichment in the florescence period and strong 15N depletion during the fruiting period were found for both Bletilla species. We can deduce that both Bletilla species obtained carbon from root endophytic fungi during the whole year. Additionally, the temporal varying tendency of root endophytic fungal diversity was consistent with 13C enrichments, which was also accord with the nutritional requirement of plant.

Progress and Prospects of Mycorrhizal Fungal Diversity in Orchids

“…At a finer time scale, Oja et al (2015) confirmed the turnover of OMF colonizing the roots of N. ovata to be 1 month and that their richness increases at the beginning of the flowering period. Interestingly, the diversity and richness of the detected total fungi tended to show a similar trend, and the flowering period was often accompanied by a significant enrichment of 15 N (Herrera-Rus et al, 2020;Zeng et al, 2021). One of the explanations for the high diversity of fungal partners at flowering period could be host orchids recruit a large number of fungal assemblages that can supplement the nutrients consumed by blooming by releasing specific signals, and that they may even be crucial to the successful completion of the pollination process.…”

Mycorrhizal Fungal Partners Remain Constant during a Root Lifecycle of Pleione bulbocodioides (Orchidaceae)

“…This indicates that the endophytes have occupied more ecological niches in the aging roots when mycorrhizal activities decreased. One recent study also found that species of Bletilla have higher fungal richness from March to May, when the plants have high physiological activity [51]. In some root-persistent perennial orchids (such as Neottia ovata), the fungal richness is not significantly affected by time and aboveground phenological variations [25].…”

“…The fungal community of N. ovata and Bletilla spp. change significantly over time, but those of Corallorhiza maculata, Paphiopedilum spicerianum, and Cypripedium calceolus are not sensitive to seasonal changes [23,25,51,55]. Since fungal migrations across old and young tissues are more difficult in orchids with annual roots, they are inclined to recruit fungi from the soil species pool and thus have more frequent fungal changes [8,24,25,56,57].…”

Spatiotemporal dynamics and functional characteristics of the composition of the main fungal taxa in the root microhabitat of Calanthe sieboldii (Orchidaceae)

“…It is worth noting that the composition of orchid microhabitat fungal communities, including endophytic fungi, is unstable and can change seasonally or interannually [20,21]. Only a few studies have considered the seasonal dynamics of fungal colonization and community composition in adult orchid roots [22,23]. For example, Tulasnella were found more frequently as orchid mycorrhizal fungi in the summer, and Leohumicola sp.…”