ObjectiveThis study aims to investigate the effects of Zn stress on growth development of Populus alba 'berolinensis' (PAB) seedlings and their chemical defense patterns in response to the Zn stress.

MethodWe analyzed the growth development status, nutrient content and secondary metabolites, as well as the protease inhibitor activities in the leaves of PAB seedlings growing in either non-contaminated soil (CK/control) or Zn-contaminated soil (300, 500 and 700 mg/kg).

ResultOur results showed that the growth parameters (plant height, root length and ground diameter) and biomass parameters (the fresh and dry mass of root, stem and leaf) of the PAB seedlings in all the Zn-treated groups were significantly lower than those in the control (P < 0.05) in a concentration/dose-dependent fashion. On the 30th, 40th and 50th days after Zn stress, the contents of proteins and soluble sugars in PAB leaves in all the Zn-treated groups were significantly lower than those in control (P < 0.05). There were no significant differences in protein contents between the Zn treatment groups (P>0.05), while soluble sugar contents increased with the increase of Zn concentration. Zn stress, regardless of its concentration level, significantly increased the contents of flavonoids and lignin in the leaves on all three sampling dates compared with the control, whereas the trypsin inhibitor (TI) and the chymotrypsin inhibitor (CI) activities were significantly decreased (P < 0.05).

ConclusionThe above results illustrate that excessive Zn in the growing environment may inhibit the growth of PAB seedlings and affect their chemical defense. The response patterns of nutrient substances, secondary metabolites related to the plant resistance to insects as well as the protease inhibitors in the PAB leaves to Zn stress are inconsistent, as was evidenced by the reduced nutrient contents, the increased secondary metabolite contents and the weakened protease inhibitor activities.