Mechanism Analysis Of Soil Factors Influencing Regeneration Of Juglans Mandshurica And Phellodendron Armurense Seedling Stage

Forest regeneration is an important and complex ecological process which influenced by different ecological factors at different stages(i.e.seeds,seedlings and sapling stages).As important and precious broad-leaved trees in northern China,Juglans mandshurica and Phellodendron amurense have serious regeneration obstacles.In this study,we explored regeneration obstacles reason of the two kinds of species and to discover the soil factors that affected regeneration,and in order to provide theoretical basis and technical support for the sustainable development of both tree species from the aspects of plant-soil feedback(PSF),arbuscular mycorrhizal(AM)fungal communities,autotoxicity and pathogens by combining field and greenhouse experiments based on the seedling growth performance.Our research showed that:1.The survival rates of seedlings under the three kinds of plantations were all showed that J.mandshurica was highest.P.amurense was lowest.There was no significant correlation between survival rate of every kind of seedling and soil physicochemical properties.The first-order root diameter,vascular bundle diameter and cortex thickness of P.amurense seedlings were significantly positively correlated to MBC and MBN,and the first-order root diameter and cortex thickness were significantly negatively correlated with soil AP.The root length and root surfarea of J.mandshurica seedlings were significantly negatively correlated with the soil moisture content.and the first-order root vascular bundle diameter was significantly positively correlated with the soil moisture content.Only the PSF of P.amurense seedlings showed negative feedback,while the other two tree species showed neutral feedback.The PSF of the seedlings established a negative regression relationship with the special root length of seedlings and the soil water content.2.Glomus was the dominant genus of root infection of J.mandshurica and P.amurense seedlings.At the OTU level,roots had higher AM fungal diversity and richness than that in soil,while at the genus level,soil showed higher AM fungal diversity and richness than that in roots.J.mandshurica and P.amurense seedlings had lower AM fungi diversity and richness in each other's plantations.The composition of AM fungi community in roots was more affected by seedling species than plantation species,while the composition of AM fungi in soil showed no significant difference among seedlings or plantations.Soil total phosphorus(TP)had a significant negative effect on the abundance of AM fungi in roots,while soil pH had no significant effect on it.The content of W_phe in soil was positively correlated with the diversity of AM fungi.The survival rate.biomass and root traits of J.mandshurica seedlings were not affected by the diversity of AM fungi,but it was more benifited for Phellodendron amurense seedlings survived in lower AM fungi abundance and get more negtively feedback.The thicker the root cortex was.the more conducive to AM fungus infection.When P content in soil was low,P.amurense seedlings were more likely to obtain P supply through symbiosis with AM fungi3.The aboveground growth of the Juglans mandshurica seedlings was significantly inhibited with the addition of juglone,and Phellodendron amurense seedling growth was only inhibited when treated with berberine and jatrorrhizine treatments.The high concentration treatment of jatrorrhizine had stronger inhibition on seedling root growth.The absorption efficiency of firstorder rootof Junglans mandshurica and Phellodendron amurense seedlings stimulated with addition of autoxicity chemicals.Soil pH decreased significantly after the additon of juglone which led to the decrease of soil nitrification capacity,the decrease of NO3-content,the increase of NH4+content,and significant decrease of MBN content in soil.With the addition of autoxicity chemicals,pH was the most critical factor which affected the expansion of plant roots.4.With the addition of fungicide,the root biomass of J.mandshurica seedlings decreased.After adding the fungicide,the colonization of AM fungi in P.amurense increased by 45.8%,while the colonization of J.mandshurica decreased by 37.1%.The two kinds of seedlings had different dependences on AM fungi.Compared with J.mandshurica,P.amurens was better at using AM fungi to resist the negative effects of pathogens.Phenolic acids accumulated with the addition of fungicides which led to root absorption efficiency increase of both seedlings.It was benifit to AM fungi colonization with the increase of root diameter,cortex thikness and V/R ratio of P.amurens seedlings.Meanwhile,the addition of fungicide also increased the nitrogen availability in the soil.Overall,the effects of PSF,AM fungal communities,autotoxicity and pathogens on the regeneration of Juglans mandshurica and Phellodendron amurense plantations were commonalities,as well as process-specific differences.At the same time,different factors interacted with each other.AM fungi have proved to be a bridge that closely connected various factors.The results is not only of great theoretical value to understand the regeneration barriers of the two species at seedling stage,but also provides theoretical basis for revealing the ecological processes in which the underground part of the trees participates.