Effects of arbuscular mycorrhizal fungi on metabolism and chemical defense of Populus alba × P. berolinensis leaves

  Objective   This study aims to investigate the effects of two arbuscular mycorrhizal fungi, Glomus mosseae (GM) and Glomus intraradices (GI) on the metabolism and chemical defense of Populus alba × P. berolinensis leaves.

  Method   In this study, each poplar seedling cut was planted into a pot filled with 1.3 kg sterilized soil mixed with 20 g fungal substrate containing 15 spore/g of either GM or GI. The contents of N, P elements, nutrients and secondary metabolites, as well as the activity of defense proteins in leaves of the poplar seedlings were analyzed on the 90th day after the planting when the fungal infection rate reached the peak.

  Result   The contents of N, P elements and soluble proteins in the poplar leaves from the GM or GI treatment group were significantly higher than those from the control group (P < 0.05), whereas the soluble sugar content was significantly lower (P < 0.05). There were no significant differences in starch contents between the GM or GI treatment group and the control group (P > 0.05). The contents of secondary metabolites, lignin, flavonoids, total phenols and tannins were significantly higher in the GM or GI treatment group than those in the control group (P < 0.05). The activities of defense proteins, phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), trypsin inhibitor (TI) and chymotrypsin inhibitor (CI) were all significantly higher in the treatment groups than those in the control group (P < 0.05).

  Conclusion   The above results indicate that GM and GI might promote the metabolism of Populus alba × P. berolinensis leaves, including increase in the contents of N, P elements and soluble proteins and decrease in the content of soluble sugars, resulting in potential changes in leaf quality, and improvement of leaf tolerance. GM or GI infestation seems to increase the chemical defense ability of the poplar leaves, such as the increase of secondary metabolite contents and activity of defense proteins, thus might affect the resistance of Populus alba × P. berolinensis leaves to pests. However, further research is surely needed to determine whether these two arbuscular mycorrhizal fungi can significantly enhance the resistance of Populus alba × P. berolinensis to pest insects.