Effects of pests on non-structural substance contents and enzyme activities in leaves of Machilus pauhoi and Phoebe bournei

Objective  Damages in subtropical regions of China caused by forest pests have been intensified due to environmental changes such as global warming. It is of great importance to study the relationship between leaf physiological traits and pest infestation grade.

Method  The relationships of main physiological traits, including non-structural substance contents and enzyme activities, and pest infestation grade on healthy leaves of Machilus pauhoi and Phoebe bournei artificial mixed forest were studied by typical plot survey.

Result  Pest damage caused significant increase in the relative water contents of healthy leaves of affected individuals, while did not have significant effect on leaf dry matter content. The soluble sugar contents of healthy leaves of M. pauhoi and P. bournei were the lowest in trees with moderate pest damage. The soluble protein content decreased in M. pauhoi healthy leaves with the increase of pest infestation grade. The soluble protein content of healthy leaves of P. bournei was the highest with slight pest damage. Total amino acid contents of healthy leaves of P. bournei and M. pauhoi were the highest with moderate pest damage and slight pest damage respectively. The ratios of soluble protein conents to soluble sugar contents reached the maximum in trees with moderate pest damage for both species, but the lowest values appeared in different pest levels for two species. The ratio of soluble protein content to soluble sugar content in leaves of P. bournei was significantly different between slight pest and moderate pest infestation grade. The peroxidase (POD) activities of healthy leaves of two species generally decreased first and then increased with the increase of pest infestation grade. The superoxide dismutase (SOD) activities were the highest under moderate pest infestation grade and the lowest under severe pest infestation grade, yet the differences among different pest infestation grade were not significant.

Conclusion  Two tree species have different response in non-structural substance contents to the same infestation grade of pest, while they have the same response in enzyme activities to the same infestation grade of pest. The damaged leaves and healthy leaves of two species have mutual compensation and self-regulation, and both species have self-healing ability and defense mechanism. The research results can provide a theoretical basis for further exploring the response mechanism of plant leaves to pests under future environmental changes and carrying out research on pest control techniques for artificial forest.