Allocation Of Phenolic Compounds In Populus Euphratica In Ejina Oasis And Their Variation With Environmental Factors

Phenolic compounds are the important secondary metabolites. This paper summarized their chemical components and biological activities, and reviewed the research advances in ecological significance and quantification methods. With colorimetric methods, the contents of total phenolics, flavonoids and condensed tannins were measured in nine categories of different organs within Populus euphratica in Ejina Nature Reserve, including lanccolate leaves, ovate leaves, green branches, junior branches (D <5 mm in diameter), mature branches (5-10 mm), barks, roots (D<2 mm in diameter), roots (2-5 mm) and roots (5-10mm). The variation of phenolic compounds in different Populus euphratica communities was also analyzed to discuss their relationship with environmental factors. The results showed so as following:1) Phenolic compounds were present throughout the collected organs in P. euphratica, and the order of concentrations of total phenolics was showed as follow: barks>leaves>roots>branches; flavonoids: barks>roots>leaves>branches; condensed tannins: roots>barks>branches>leaves. The relatively higher concentration in barks and leaves indicated that plants synthesized and accumulated phenolics in epidermics.2) There was no significant difference between the phenolic compounds of lanccolate leaves and ovate leaves (P>0.05). Phenolic compounds in branches decreased with the branches maturation and resulted in the orders as follow: green branches > branches (D<5 mm) > branches (5-10 mm) and concentrations of total phenolics and flavonoids showed significantly different between green branches and branches (5-10 mm) (for total phenolics, P=0.022; flavonoids, P=0.023).3) Roots contained high phenolic compounds with the highest condensed tannins in all collected organs, which meant the potential ecological significance of phenolic compounds in soil nutrientcycling. Condensed tannins in roots decreased with the root diameter, and the highest condensed tannins contents were found in small root (D<2mm), indicating the higher pressure of herbivory and pathogen on small root.4) Phenolic compounds in ovate leaves had negative relation with soil water contents (P<0.05), and the r values for total phenolics, flavonoids and condensed tannins were - 0.949, -0.923 and -0.944 respectively. This result confirmed the intensive effects of soil water contents on synthesis of phenolic compounds.5) Ten soil factors which influenced the phenolics of different communities in the soils were analyzed through principal component analysis to find the integrated effect. The results showed the first principal component was an integrated factor mainly determined by the water contents in the soil, Organics, total P, and total N. The soil salinity was another important factor influencing the phenolics in P. euphratica communities, because the second principal component (PC2) was determined by the soil salinity.6) In this study, resource availability hypothesis failed to explain the variation of phenolics compounds in different P. euphratica communities. In terms of the different plants and complicated environmental factors, it was unreasonable to explain such variation with a simple hypothesis.