Comprehensive Evaluation Of Photosynthetic Characteristics,Genetic Diversity And Ornamental Value Of Three Geodorum

Geodorum G.Jacks.belongs to the Eulophiinae group of the Eulophiinae subfamily of orchids（Trib.Epidendreae）in the Orchidaceae subfamily（Subfam.Orchidoideae）.and Pacific islands.There are five species in China,with distribution records in Guangdong,Hainan,Guangxi,Guizhou,Taiwan,Sichuan and Yunnan.In this paper,we studied the Geodorum densiflorum,Geodorum eulophioides and Geodorum attenuatum for their photosynthetic characteristics,genetic diversity and ornamental evaluation,with a view to providing a rational basis for the selection,exploitation and conservation of their excellent germplasm resources.The main findings of the study are as follows:1、To investigate the differences of photosynthetic characteristics of G.densiflorum,G.attenuatum and G.eulophioides,daily photosynthetic changes,light response curves,CO₂response curves,chlorophyll content,leaf anatomical structure and other indexes were measured.The results showed that（1）Compared with G.densiflorum and G.eulophioides,G.attenuatum has larger leaf thickness and smaller stomatal density.（2）the daily variation of net photosynthetic rate（P_n）of the three species of Geodorum showed a"bimodal"curve,and the photosynthetic"siesta"was mainly caused by non-stomatal limitation.The average daily values of P_nand water use efficiency（WUE）were all in the range of G.attenuatum>G.densiflorum>G.eulophioides,indicating that G.eulophioides has a weaker ability to accumulate photosynthetic products and is less adaptable to drought conditions.（3）The three species of Geodorum are shade plants,and G.densiflorum has the smallest LCP and the largest LSP,which have a wider range of adaptation to light intensity.G.attenuatum has a higher maximum net photosynthetic rate(P_max)and apparent quantum efficiency（AQY）,and its photosynthetic capacity is stronger.G.eulophioides has the smallest potential maximum net photosynthetic rate（Amax）,and its utilization capacity of CO₂is weaker.（4）The chlorophyll a（Chl a）,chlorophyll b（Chl b）and total chlorophyll（Chl a+b）contents were significantly（P<0.05）higher in G.densiflorum and G.attenuatum than in G.eulophioides.（5）There was a significant correlation between the leaf thickness,chlorophyll content and photosynthetic capacity parameters of the three species of Geodorum.The above results indicate that proper shade and increased CO₂concentration are beneficial to photosynthesis of the three species of Geodorum.The photosynthetic capacity and adaptability of G.eulophioides are poor compared with those of G.densiflorum and G.attenuatum,which may have a strong relationship with their endangerment.2、The photosynthetic characteristics of G.eulophioides were measured under different light intensities（8%,20%,45%and 100%natural light intensity）by setting up different light intensity treatments by artificial shading methods.The results showed that:（1）under 20%,45%and 100%light intensity,the P_nof G.eulophioides showed a"double peak"curve,with an obvious"siesta"phenomenon,while under 8%light intensity,the Pn showed a"single peak"curve,the average daily P_nwas the highest under 20%light intensity(1.922±0.453μmol·m^-2·s^-1).（2）The maximum net photosynthetic rate(P_max),light saturation point（LSP）and apparent quantum efficiency（AQY）of Geodorum eulophioides leaves were the highest under 20%light intensity,and the photosynthetic capacity was the strongest under this light intensity.（3）Chlorophyll fluorescence parameters F_m,F_v,F_v/F_mand F_v/F₀in 100%light intensity treatment were significantly lower than those in the other three treatments,which indicated G.eulophioides was severely photoinhibited under 100%light intensity.（4）Chlorophyll a（Chla）,chlorophyll b（Chl b）,carotenoid（Car）contents and total chlorophyll（Chl）decreased with increasing light intensity,while Car/Chl showed the opposite trend.（5）Under 20%light intensity,plant height,base diameter,maximum leaf length and maximum leaf width were the highest,followed by 8%light intensity,and the lowest under 100%light intensity.G.eulophioides has a certain degree of adaptability to different light environments,and it is most suitable to grow under 20%light intensity.In ex situ protection,it can choose a relatively open environment with certain shading effect for seedling planting.In the process of population restoration,trees and shrubs in the upper layer can be thinned properly to increase the light transmittance under the forest,improve the growth rate of G.eulophioides and promote its natural regeneration.1、The genotyping-by-sequencing（GBS）technique was used to mine single-nucleotide-polymorphism（SNP）loci and analyse the genetic diversity of 109individuals from 14 populations of three species of namely G.densiflorum,G.eulophioides and G.attenuatum.The results showed that（1）the genetic diversity of G.densiflorum（H_o=0.0071,H_e=0.1020,π=0.0110）,G.eulophioides（H_o=0.1136,H_e=0.0863,π=0.0962）and G.attenuatum（H_o=0.1546,H_e=0.1472,π=0.1714）was obtained from the analysis of 29,649 high-quality SNP loci.0.1714),G.attenuatum showing the highest genetic diversity,and the genetic diversity of the widespread species G.densiflorum being higher than that of the narrow range species G.eulophioides.（2）There is a high degree of genetic differentiation among the 14populations(F_ST=0.6080),but there is also a degree of genetic exchange.（3）Population phylogenetic analysis,cluster analysis,and principal component analysis indicated that there was geographical clustering of the three species of Geodorum.The analysis of genetic diversity and genetic structure of the three species of Geodorum.provides a theoretical basis for the formulation of scientific and effective conservation strategies.2、A comprehensive evaluation of the ornamental and ecological adaptability of Geodorum.was carried out using hierarchical analysis（AHP）.The results showed that:（1）Photosynthetic ability,light adaptation ability,number of flowers,plant shape and number of leaves were the main indicators for the evaluation of the comprehensive ornamental value of Geodorum,and the best plants for plant shape,flowers and leaves in each part were G.recurvum,G.eulophioides and G.attenuatum respectively.（2）The ornamental rating of G.eulophioides has the highest score,followed by G.recurvum,followed by G.densiflorum,with the lowest ornamental score for G.attenuatum.（3）Except for the uncertainty of the ecological adaptability of G.recurvum,G.attenuatum had the strongest ecological adaptability,followed by G.densiflorum,and G.eulophioides had the weakest ecological adaptability.the results of the AHP model evaluation of Geodorum will provide a theoretical basis for their future development and use.