Effects Of Shading And Fertilization On The Growth And Physiological Characteristics Of Abies Beshanzuensis M.H.Wu Seedlings And Transcriptome Analysis Under Shading Treatment

Abies beshanzuensis M.H.Wu is a species of the genus Abies in the Pinaceae family.With only three adult plants remaining in the wild,natural growth conditions for seedlings are poor,resulting in a high mortality rate.In this study,different shading treatments(full light,15%,30%,45%,60%,75% shading)and fourteen fertilization formulas(“3414” formula)were applied to 2-year-old A.beshanzuensis seedlings to explore their growth pattern,stress resistance,and relationship with environmental conditions,respectively.Growth indicators and physiological indicators were measured to identify the optimal shading treatment and fertilization ratio,respectively.The findings provide a scientific basis for the cultivation and protection of A.beshanzuensis seedlings.Additionally,the transcriptome of A.beshanzuensis seedlings responding to shading treatment was preliminarily analyzed,offering a theoretical basis for the in-depth study of the molecular mechanism underlying A.beshanzuensis seedlings’ response to different light conditions.The main results are as follows:(1)Different shading treatments have significant effects on the growth status,photosynthetic physiology,osmoregulation substance content,and antioxidant enzyme activity of A.beshanzuensis seedlings.As shading degree increased,plant height,crown width,total root volume,total root length,root average diameter,total root surface area,chlorophyll a,chlorophyll b,total chlorophyll,SOD,POD and CAT enzyme activities initially increased and then decreased,reaching their maximum value at 45% shading treatment.Conversely,as shading increases,MDA,proline,and soluble protein contents initially decrease and then increase.Furthermore,chlorophyll a and chlorophyll b contents gradually increase with increasing shading,reaching maximum values in the45% shading group,followed by a decline in the 60% and 75% shading groups.The chlorophyll a/b values of the 15% shading,45% shading,and 75% shading treatments were lower.Under high light intensity,the Yield value of leaves in the full light treatment group significantly decreased.The Yield value and ETR value of leaves in the75% shading treatment group were the lowest.The NPQ was higher in the full light and15% shading treatment groups.Compared to full light group,the q P values of each shading treatment group were higher.Therefore,it can be concluded that A.beshanzuensis is a shade-tolerant plant and moderate shading is beneficial to the growth of A.beshanzuensis seedlings,with the 45% shading treatment being the most effective.(2)The experiment examined the effects of different ratios of N,P,and K fertilization on the growth status,chlorophyll content,osmoregulation substance content,and antioxidant enzyme activity of A.beshanzuensis.The results showed that the N2P2K2 fertilization treatment had the highest seedling height,crown width,leaf number,aboveground biomass,underground biomass,total biomass,chlorophyll a,chlorophyll b,total chlorophyll,and soluble sugar content.The proline content in the N2P1K2,N2P2K2,N3P2K2,and N1P2K1 groups is relatively low.In the N2P2K2 and N2P2K0 fertilization treatment groups,the POD and SOD activities were significantly higher than other treatment groups.Under the N2P0K2,N2P2K2,and N1P1K2 fertilization treatment,the CAT activity of the leaves of A.beshanzuensis seedlings was significantly higher than other treatment groups.The MDA content was lower in the N1P2K2,N2P2K2,N2P2K3,and N3P2K2 groups.Based on the fuzzy evaluation of membership functions for multiple indicators,it can be concluded that moderate fertilization is beneficial for the growth of A.beshanzuensis seedlings,with the N2P2K2 fertilization treatment being the most effective.(3)Transcriptome sequencing was performed on the leaves of A.beshanzuensis seedlings under different shading levels.All 44,096 assembled Unigenes were annotated with the databases of GO,KEGG,Pfam,Swiss Prot,egg NOG,and NR,respectively.Among them,the maximum number of annotations to the NR database was 26,254.The minimum number of annotations to the KEGG database was 18,038.Compared to the control group(full light),746,1,871,and 2,946 differentially expressed genes(DEGs)were identified in the leaves of A.beshanzuensis seedlings under 15%,45%,and 75% shading,respectively.In the KEGG metabolic pathway analysis,compared to the control group,18,23,and 37 DEGs were annotated in the photosynthesis-related,photosynthesis-antenna protein,carbon fixation,and carotenoid metabolism pathways under 15%,45%,and 75% shading,respectively.In the photosynthesis and photosynthesis antenna protein pathway,7 DEGs were downregulated in the 75% shading treatment group,while in the carbon assimilation pathway,3 DEGs were upregulated in the 15% shading group,7 were upregulated in the 45% shading treatment group,and 11 were downregulated in the 75% shading treatment group.Compared with the control group,DEGs in the 45% shading and 75%shading treatment groups were enriched and significantly downregulated in the carotenoid metabolism pathway.Therefore,after receiving shading treatment,the photooxidation of seedlings decreased.Under 45% shading treatment,the seedlings of A.beshanzuensis may have accumulated more biomass,but excessive shading has a negative impact on the photosynthesis of A.beshanzuensis seedlings.