Relationships Between Juglone And Microorganisms And Influence Of Juglone On Understory Vegetation Under Manchurian Walnut(Juglans Mandshurica Maxim.) Plantations

Root exudates have impacts on soil microbial community, the resistance to insects. They also support the beneficial symbiotic relationships and improve soil physical and chemical properties and inhibit the growth of competing plants. Their amount varied with different plant species, variety, age and limiting factors. It has great importance for the contribution to chemical ecology to further understanding the distribution of the specific root exudate and the relationships between plants and microbes. In this study, we detected juglone and PLFAs using high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) in different stand ages of manchurian walnut (Juglans mandshurica) plantation. Controlled experiment was carried out to test the hypothesis regarding the relationship between juglone and PLFAs. And we attempt to find out contacts between juglone and vegetation diversity by investigating shrub and grass diversity. Our results showed that:Juglone concentration was obviously impacted by stand age and season.15a (0.05-0.63μg/g)<50a (0.02-17.76μg/g)<25a (0.05-39μg/g). It had a sustainable growth from spring to summer to fall.Total PLFAs was significant varied seasonally (P<0.05), they decreased from spring to summer to fall. There was no obvious law of the effects of stand age on total PLFAs and microbial community structure in different season. Obvious effects of season on soil microbial community structure was observed. Principle component analysis showed that the microbial community structure in spring was obviously differed from it in summer and fall. In spring, the rhizosphere soil has the highest ratio of fungi and G-(gram negative bacteria) and the lowest ratio of G+(gram positive bacteria), the bulk soil has the highest ratio of actinomycetes. There was no obvious difference of microbial community structure between summer and fall. Principle component analysis between juglone concentration and microbial community structure showed that juglone concentrations as the PCI explained77.1%variance of the microbial community structure. So we hypothesized that juglone concentrations played a key role to control microbial community structure. Hypothesis was accepted through controlled experiments which showed that some of the G-accelerated the degradation of juglone in soil, and juglone with high concentration inhibited the growth of soil microbes. Diferent soil microbial community was inhibited at different concentration of juglone. G+needs the highest juglone concentration to be inhibited, next is actinomycetes and last is fungi. The grass diversity decreased and the shrub diversity increased as the manchurian walnut stand age increased. Correlation analysis showed that all the habitat factors restricted the vegetation diversity together. Juglone concentration had a small effect on vegetation diversity. We obtained dynamics of juglone concentration and soil microbes in manchurian walnut plantations. The relationship between juglone and micorbes is more clear. These will help us to provide reasonable suggestions to manage the manchurian walnut plantations. In addition, it help us better to know the relationships between allelochemicals and microorganisms.