Abstract:

A cycling collection device was used to collect root exudates of poplar I-107 (Populus×euramericana ‘Neva’) seedlings grown under N or P deficiency conditions. The ultrahigh performance liquid chromatography (UPLC) was used to assay the amount of phenolic acids in the root exudates, to study the secretion dynamics of several phenolic acids. The results showed that some phenolic acids, ie. p-hydrobenzoic, vanillin, benzoic acid and cinnamic acid, were able to be secreted from roots of the seedlings grown under normal and nutrient deficiency conditions. However, nutrient deficiency could significantly promote the secretion of phenolic acids from the roots. Under nitrogen-deficient conditions, the amount of p-hydrobenzoic acid was 125%-263%, vanillin 201%-316%, benzoic acid 230%-332%, cinnamic acid 138%-188% of that in normal conditions, respectively. The secretion amount of phenolic acids increased with the stress duration. But, there was no significant difference among three culturing periods (0-5 d, 6-10 d, 11-15 d). Under phosphorus-deficient conditions, the secretion amount of p-hydrobenzoic acid increased by 96%-124%, vanillin 58%-156%, benzoic acid 222%-734%, cinnamic acid 99%-328% in comparison with the normal conditions. Furthermore, the amount of benzoic acid and vanillin all increased with treatment duration under phosphorus deficiency conditions, while the amount of benzoic acid and cinnamic acid appeared increasing initially and then decreasing with treating time. Additionally, the average secretion rate of phenolic acids was significantly different between nitrogen and phosphorus deficiency conditions. The secretion rate of p-hydrobenzoic acid and vanillin under nitrogen-deficient conditions was faster than phosphorus-deficient conditions, while the secretion rate of benzoic acid and cinnamic acid was slower than phosphorus-deficient conditions. The secretion dynamics of phenolic acids reflected the effects of stress environments on the secretion of poplar roots, and shed light on the mechanism of their accumulation in the rhizosphere soil.

Key words: nutrition stress, poplar seedling, root exudates, phenolic acids