Effect Of Light Intensity On The Growth And Root AMF Community Structure Of Fraxinus Mandshurica And Phellodendron Amurense Seedlings

Arbuscular mycorrhizal fungi(AMF),as a class of symbiotic fungi,play an important role in promoting plant growth and enhancing plant resistance,and can form reciprocal symbiotic relationships with more than 80% of plants in terrestrial ecosystems,with a wide variety of species,forming communities as collections of several fungal taxa under natural conditions,and this symbiotic pattern strictly depends on the characteristics of the host plants themselves.It is well known that there is a wide variation in the characteristics of plants with changes in light intensity.It has not been fully revealed how the changes in host plant characteristics caused by light intensity changes affect the structure and formation of AMF communities on their roots.Therefore,in this experiment,1-year-old Fraxinus mandshurica and Phellodendron amurense seedlings were used as the study material,and different light intensity treatments(15%,45%,75%,and 100% full light,abbreviated as L15,L45,L75,and L100)were set up under nursery plot cultivation conditions to determine The growth indexes and root AMF community structure of seedlings of the two species were determined.The results of the study showed that:(1)Light intensity had a significant effect on the growth of Fraxinus mandshurica and Phellodendron amurense seedlings.Most of the growth indexes of Fraxinus mandshurica seedlings were highest under L45 light intensity,and some indexes were significantly different from L15 and L100 light intensity(p < 0.05);all growth indexes of Phellodendron amurense seedlings were highest under L100 light intensity,and significantly different from the other three light intensities(p < 0.05).1-year-old Fraxinus mandshurica seedlings had higher shade tolerance;1-year-old Phellodendron amurense seedlings were less shade tolerant.(2)Light intensity had a significant effect on the community structure of AMF in the root systems of seedlings of both tree species.The analysis of AMF taxonomic composition at the genus level showed that a total of 15 AM fungal genera were detected in all samples of Fraxinus mandshurica seedlings,of which Glomus and Paraglomus were the dominant genera,accounting for more than 80% of the total sequences.A total of 13 AM fungal genera were detected in all samples of Phellodendron amurense seedlings,among which Glomus,Paraglomus and Glomeromycota.unclassified were the dominant genera,close to 90% of the total sequences.In addition,α-diversity analysis showed that the patterns of diversity index(Shannon and Simpson)and abundance index(Sobs,Ace,Chao1)of AMF communities in the root systems of seedlings of the two species with increasing light intensity were L15>L100>L75>L45 and L100>L45>L75>L15.It showed that the root AMF community structure of Fraxinus mandshurica seedlings was the best at L15 light intensity and the worst at L45 light intensity;the root AMF community structure of Phellodendron amurense seedlings was the best at L100 light intensity and the worst at L15 light intensity.(3)There was a significant interaction between the growth characteristics of the seedlings of the two tree species themselves and their root AMF infestation rates under different light intensities.Pearson’s correlation analysis showed that H,Gs,Tr,SP,S-C/P of Fraxinus mandshurica seedlings were highly significantly correlated with AMF infestation rate(p <0.01),and LB,SC,RP were significantly correlated with AMF infestation rate(p < 0.05);H,D,TB,LB,RB,QI,RSR,LA,Pn,Gs,Ci,LUE,Chla,Chlb,Chl,LC,RC,TN,RP,and T-C/N of Phellodendron amurense seedlings were highly significantly correlated with AMF infestation rate(p < 0.01),and SN,RN,SP,and S-C/N were significantly correlated with AMF infestation rate(p < 0.05).(4)There was a clear interaction between the growth characteristics of the seedlings of the two species themselves and their root AMF community structure under different light intensities.The correlation heat map showed that,in the seedlings of Fraxinus mandshurica,Gs and R-SS with Glomus and Paraglomus,RSR and R-N/P with Glomeromycetes.unclassified,Gs with Glomeromycota.unclassified,Ci with Gigaspora,TP and T-C/P and L-C/P with Ambispora and L-C/P with Glomerales.unclassified,were all highly significantly correlated(p< 0.01).All AMF taxa in Phellodendron amurense seedlings were significantly influenced by plant characteristics except Glomeromycetes.unclassified and Glomeromycota.unclassified which were not significantly correlated with plant growth characteristics,where R-C/N was significantly correlated with Paraglomus,SB and SC and LP and TP and RV were significantly correlated with Claroideoglomus and Acaulospora and Diversispora at the 0.001 level.RDA analysis showed that RP,R-SS,LP,R-C/N,and RV had strong effects on the AMF community structure of the root system of Fraxinus mandshurica seedlings;S-S,R-C/P,and SC had strong effects on the AMF community structure of the root system of Phellodendron amurense seedlings.The Mantel Carlo test showed that: the diversity of root AMF of Fraxinus mandshurica seedlings was significantly correlated with RP(F=5.888,p=0.031);the diversity of root AMF community of Phellodendron amurense seedlings was significantly correlated with S-S(F= 12.704,p=0.009)was highly significantly correlated with R-C/P(F=7.648,p=0.015).Light intensity had different effects on AMF community structure in the root systems of seedlings of different shade tolerant tree species.Fraxinus mandshurica seedlings decreased AMF diversity and increased the abundance of dominant colonies under optimal growth light intensity;Phellodendron amurense seedlings increased both AMF diversity and the abundance of dominant AMF taxa under optimal growth light intensity.The effect of light intensity on AMF community structure in the root systems of Fraxinus mandshurica and Phellodendron amurense seedlings was closely related to the shade tolerance of the seedlings themselves.The structure of AMF community in the root system of Fraxinus mandshurica seedlings did not show significant changes with light intensity because they were less affected by changes in light intensity due to their smaller light requirement;the structure of AMF community in the root system of Phellodendron amurense seedlings showed significant differences with light intensity because they were more affected by changes in light intensity due to their larger light requirement.In this study,we found that the starch content in stems and root C and P content of seedlings of both species had the most significant effect on their root AMF community structure with increasing light intensity.