Camellia nitidissima, a rare and endangered shrub is narrowly distributed in South China and North Vietnam occurring in forest understory. Their light tolerance mechanism is unclear. We measured photosynthesis and related parameters on 2-years-old cuttings growing at 10, 30, 50 and 100% sunlight. Our research question was: At what light level are C. nitidissima cuttings responding most favorably, and what is the eco-physiological basis for their response to light? We hypothesized that as a forest understory growth of C. nitidissima would respond most favorably at low to intermediate light by optimizing photosynthetic activity, and high light will affect photosynthetic functions due to photoinhibition, damage of photosynthetic apparatus and concomitant enzyme activity. With increasing light, the maximum net photosynthetic rate (PNmax) and apparent quantum yield (AQY) decreased, while the light compensation point increased, and light saturation point first increased followed by a decrease. The PNmax and AQY under 50 and 100% sunlight were significantly lower than that under 10 and 30% sunlight. The chlorophyll fluorescence parameters Fm, Fv, Fv/Fm all decreased under high light (> 50%). The contents of chlorophyll a (Chla), chlorophyll b (Chlb), and carotenoid (Car) decreased with increasing light. Relative conductivity, malondialdehyde (MDA) and proline contents in leaves were significantly increased in high light but we found no significant difference in these indices at 10 and 30% sunlight. We conclude that C. nitidissima is a shade adapted plant with poor adaptability to high light (> 50%). The novelty of this research is the demonstration of the eco-physiological basis of its light tolerance (conversely, shade adaptation) mechanisms indicated by decreased photosynthetic activity, chlorophyll fluorescence, Chla, Chlb and Car contents and concomitant increase in relative conductivity, MDA and proline contents at high light causing photoinhibition. For artificial propagation of C. nitidissima we recommend growing cuttings below 30% sunlight. For in situ conservation of this valuable, rare and endangered shrub it is necessary to protect its natural habitats.

Mycorrhizal fungi plays important roles in the seed germination and subsequent growth of orchids. The research of fungi in orchid roots, especially dominant mycorrhizal fungi is critical for orchids protection. In this study, the fungal community and composition of mycorrhizal fungi in roots, rhizomes and rhizosphere soil of Bulbophyllum tianguii grown in three terrestrial environments were analyzed by the second generation sequencing technology. The results of OTU clustering and α and β diversity analysis showed that there were significant differences in fungal communities in roots, rhizomes and rhizosphere soil of B. tianguii. The total number of OTUs in rhizomes was much less than that in roots and rhizosphere soil. The number of OTUs in rhizosphere soil and the diversity of mycorrhizal fungi were the highest. Meanwhile, the species and abundance of mycorrhizal fungi in roots and rhizomes of B. tianguii were different from those in rhizosphere soil. For different elevations, compared with B. tianguii that grow in middle of Tiankeng and top of Tiankeng, the OTUs number of B. tianguii in orchid garden is richest, and the diversity of mycorrhizal fungi in orchid garden was significantly higher than other locations. Among the three different habitats of B. tianguii, the number of OTUs in humus soil and stone habitats was notably higher than tree habitats, and the diversity of mycorrhizal fungi in humus soil was the highest. The analysis of mycorrhizal fungi in different habitats and altitudes of B. tianguii showed that Sebacina and Exophiala were the dominant mycorrhizal fungi in B. tianguii. The results of species annotation, phylogenetic tree and co-occurrence network analysis showed the dominant mycorrhizal fungi of B. tianguii mainly included Sebacina, Cladosporium, Exophiala, Fusarium. This study reveals the symbiotic relationship between Sebacina, Exophiala, Cladosporium and the B. Tianguii. It will provide a theoretical basis for the protection and biological function study of B. Tianguii.

Shepherd's crook (Geodorum) is a genus of protected orchids that are valuable both medicinally and ornamentally. Geodorum eulophioides (GE) is an endangered and narrowly distributed species, and Geodorum densiflorum (GD) and Geodorum attenuatum (GA) are widespread species. The growth of orchids depend on microorganisms. However, there are few studies on the microbial structure in Geodorum, and little is known about the roles of microorganisms in the endangered mechanism of G. eulophioides. This study analyzed the structure and composition of bacterial and fungal communities in the roots and rhizosphere soil of GE, GD, and GA. The results showed that Delftia, Bordetella and norank_f_Xanthobacteraceae were the dominant bacteria in the roots of Geodorum, while norank_f_Xanthobacteraceae, Gaiella and norank_f_norank_o_Gaiellales were the dominant bacteria in the rhizosphere soil of Geodorum. In the roots, the proportion of Mycobacterium in GD_roadside was higher than that in GD_understory, on the contrary, the proportion of Fusarium, Delftia and Bordetella in GD_roadside was lower than that in GD_understory. Compared with the GD_understory, the roots of GD_roadside had lower microbial diversity. In the endangered species GE, Russula was the primary fungus in the roots and rhizosphere soil, with fungal diversity lower than in the more widespread species. Among the widespread species, the dominant fungal genera in the roots and rhizosphere soil were Neocosmospora, Fusarium and Coprinopsis. This study enhances our understanding of microbial composition and diversity, providing fundamental information for future research on microbial contributions to plant growth and ecosystem function in Geodorum.

Background: Understanding genetic diversity is a core issue in conservation genetics. However, previous genetic diversity evaluations of narrowly distributed species have rarely used closely related widespread species as a reference. Furthermore, identifying natural hybridization signals between narrowly and widely distributed sympatric species is of great importance for the development of species conservation programs.Methods: In this study, population genotyping by sequencing (GBS) was performed for a narrowly distributed species,Geodorum eulophioides(endemic and endangered in Southwest China), and a widespread species,G. densiflorum. A total of 18,490 high-quality single nucleotide polymorphisms (SNPs) were identified at the whole-genome level.Results: The results showed that the nucleotide diversity and heterozygosity ofG. eulophioideswere significantly higher than those ofG. densiflorum, confirming that narrowly distributed species can still preserve high genetic diversity. Consistent with taxonomic boundaries, all sampled individuals from the two species were divided into two genetic clusters and showed high genetic differentiation between species. However, in a sympatric population, a fewG. eulophioidesindividuals were detected with genetic components fromG. densiflorum, suggesting potential interspecific natural hybridization. This hypothesis was supported by Treemix analysis and hand-hybridization trials. Invasion of the habitat ofG. eulophioidesinvasion byG. densiflorumunder anthropogenic disturbance may be the main factor causing interspecific hybridization.Conclusions: Therefore, reducing or avoiding habitat disturbance is a key measure to protect theG. eulophioidespopulations. This study provides valuable information for future conservation programs for narrowly distributed species.

Many Dendrobium species, which hold a high status and value in traditional Chinese medicine, grow on barks and rocks in the wild, often encountering harsh environments and facing droughts. However, the molecular mechanisms underlying the shift in the photosynthetic pathway induced by drought remain unclear. To address this issue, three Dendrobium species with different photosynthetic pathways were selected for sequencing and transcriptome data analysis after drought treatment. The findings included 134.43 GB of sequencing data, with numerous Differentially Expressed Genes (DEGs) exhibiting different response mechanisms under drought stress. Gene Ontology (GO)–KEGG-based enrichment analysis of DEGs revealed that metabolic pathways contributed to drought tolerance and alterations in photosynthetic pathways. Phosphoenolpyruvate Carboxylase (PEPC) was subjected to phylogenetic tree construction, sequence alignment, and domain analysis. Under drought stress, variations were observed in the PEPC gene structure and expression among different Dendrobium species; the upregulation of Dc_gene2609 expression may be caused by dof-miR-384, which resulted in the shift from C₃ photosynthesis to CAM, thereby improving drought tolerance in Dendrobium. This study revealed the expression patterns and roles of PEPC genes in enhancing plant drought tolerance and will provide an important basis for in-depth research on Dendrobium’s adaptation mechanisms in arid environments.

Camellia pubipetala is an endemic and endangered species with small and isolated populations occurring only in karst regions in Guangxi of south China. To understand the reproductive biology of C. pubipetala and its possible influences upon its endangered status, its breeding system and pollination ecology were studied in the Longhushan (LHS) and Longzhao (LZ) populations of this species. The flowering duration of the C . pubipetala populations spanned from late January to early April and anthesis of a single flower usually lasted 5–7 days. This species is homogamous, and the pollen and stigma are viable throughout anthesis. Each bagged flower could secrete 141.5 μL of nectar at a sugar concentration of 25.0% during anthesis. The observed high pollen/ovule ratio, and the results of hand‐pollination experiments indicated that this species obligately outcrosses. Open pollination resulted in a significantly decreased fruit set (6.7%) and seed set (38.9%) compared to supplementary pollination treatment (23.3% and 64.7%, respectively), which is indicative of a pollen limitation in the process of pollination. The primary pollinator of C. pubipetala is the sunbird Aethopyga christinae and its visiting frequency is quite low, whereas the honeybee Apis cerana is only an occasional pollinator in wild populations. Low reproductive rates in C. pubipetala were found to be a consequence of few species of pollinators and their low visiting frequency. Pollen limitation may be a crucial factor that contributes to the endangered nature of this species. Artificial pollination and the release of pollinators are effective ways to increase the fruit and seed yield of this species.