Abstract:

The degradation of forestland productivity of continuous cropping poplar plantations was closely related to accumulation of phenolic acids in rhizospheric soil. Knowledge of effects of phenolic acids on physiologic characteristics and morphologic developments of poplar roots was essential to reveal the degradation mechanism of poplar forestland productivity. Hydroponic cuttings of black poplar cultivar I-107 (Populus × euramericana ‘Neva’) were cultured in Hoagland nutrient solution added with phenolic acids of five levels(CK, 0.5X, 1.0X, 1.5X, 2.0X) according to actual content in the soil of continuous poplar plantation. Physiologic indexes were studied respectively at the 1^st d, 5^th d, 10^th d, 20^th d, 30^th d and 40^th d after treated with phenolic acids, and data of root morphologic characteristics were obtained at the 40^th d. The results showed that: Activity of superoxide dismutase(SOD) and peroxidase(POD) were both enhanced by low level phenolic acid(0.5X) and inhibited significantly by high level phenolic acids(1.0X, 1.5X, 2.0X)（Pa＜0.05）； and root activity reduced significantly while the level of phenolic acids rose（Pa＜0.05）； root malonaldehyde(MDA) content and root injury degree were both significantly enhanced by increased phenolic acids concentration (Pa＜0.05). Number of root tips, mean root length, mean root area, mean root forks, mean root fractal dimension were all significantly inhibited by phenolic acids while mean root diameter was significantly promoted by phenolic acids(Pa＜0.05). Lateral roots near the tip of the main root were obvious inhibited by phenolic acids. With phenolic acids level increased, the general shape of root system was changed from column aspect to inverted pyramid and to umbrella aspect . Root tips necrotized under high level phenolic acid treatments.

Key words: phenolic acids, poplar cuttings, allelopathy, root physiology, root morphology