Symbiotic seed germination and seedling growth of mycorrhizal fungi in Paphiopedilum hirsutissimun (Lindl.Ex Hook.) Stein from China.

Similar to other orchid species, Paphiopedilum hirsutissimum (Lindl.ex Hook.) Stein, relies on nutrients provided by mycorrhizal fungus for seed germination and seedling development in the wild owing to a lack of endosperm in its seeds. Therefore, obtaining suitable and specialized fungi to enhance seed germination, seedling formation, and further development is considered a powerful tool for orchid seedling propagation, reintroduction, and species conservation. In this study, we investigated the diversity, abundance, and frequency of endophytic fungal strains in the root organs of P. hirsutissimum. One family and five genera of the fungi were isolated and identified through rDNA-ITS sequencing. The ability of isolated fungi to germinate in vitro from the seeds of this species was evaluated, and the development of P. hirsutissimum protocorm has been described. The findings showed that the treatments inoculated with endophytic fungal DYXY033 may successfully support the advanced developmental stage of seedlings up to stage 5. In addition, scanning electron microscopy (SEM) revealed that the mycelium of this strain began to invade from either end of the seeds up to the embryo, extending rapidly from the inside to the outside. Its lengthening resulted in the bursting of the seed coat to form protocorms, which developed into seedlings. The results showed that DYXY033 has a high degree of mycobiont specificity under in vitro symbiotic seed germination conditions and is a representative mycorrhizal fungus with ecological value for the species. In summary, this strain may particularly be significant for the protection of P. hirsutissimum species that are endangered in China. In the long run, it may also contribute to global efforts in reintroducing orchid species and in realizing in situ restorations of threatened orchid populations.

Performance of a sulfidogenic bioreactor and bacterial community shifts under different alkalinity levels.

The performance of a sulfidogenic bioreactor and the response of bacterial populations to influent alkalinity changes were investigated. The bioreactor reached 40% of sulfate removal efficiency (SRE) with 0 mg l(-1) of alkalinity, and single-stranded conformation polymorphism profiles showed that some members of Bacteroides, Dysgonomonas, Sporobacter, Quinella, and Citrobacter became dominant populations. 16S rRNA gene library analysis indicated that the Actinobacteria group increased from 0% in seed to 23% in sludge. An increase in alkalinity to 1300 mg l(-1) led to a rapid increase of SRE to 65% and changes in the bacterial community. Sequences representing Dysgonomonas, Raoultella, Kluyvera, and Phascolarctobacterium were now found. When alkalinity was deceased to 0 mg l(-1), SRE dropped and the bands representing Raoultella, Kluyvera, and Phascolarctobacterium disappeared, while bands representing Clostridium appeared. A second cycle of low/high alkalinity did not result in obvious changes to the bacterial community. These results indicate that the sulfidogenic bioreactor favored higher influent alkalinity and that the different functional microbial populations responded well to the alkalinity changes.