Abstract:

 Phenolic acids in rhizosphere soils are mainly derived from root exudates, litter, and the decomposition of soil humus. They play an important role in the formation and stability of organic and organicinorganic composite colloids, the activation and transformation of heavy metals in soils, and the growth and metabolism of microorganisms. Here, we investigated the effects of elevated CO₂ \[(750±31)umol·L^-1\] on the accumulation of phenolic acids in the rhizosphere soil of Robinia pseudoacacia L. seedlings exposed to different Cd levels (0, 0.45, and 4.5 mg·kg^-1 dry weight soil). Elevated CO₂, Cd level, seedling growth time, and their interaction had significant effects on the accumulation of phenolic acids in the rhizosphere soil. Elevated CO₂ enhanced the contents of hydroxybenzoic acid, caffeic acid and pcoumaric acid in the rhizosphere soil of R.pseudoacacia seedlings exposed to Cd (P<0.05). The responses of gallic acid to the combined treatments were different from that of the three phenolic acids. Under the combined treatment relative to Cd exposure alone, the content of gallic acid increased at day 45 (P<0.05), decreased at day 90 (P<0.05), and was not detected at day 135. The content of total phenolic acids increased under the combined treatment relative to Cd exposure alone at day 90 (P<0.05). The results of Pearson correlation analysis and redundancy analysis showed that root biomass, root C content, root Cd accumulation, and soil Cd content affected the content of phenolic acids in rhizosphere soils.

Key words:  total phenolic acids, phenolic acid monomer, elevated atmospheric CO₂, Cdcontaminated soil, rhizosphere.