Abstract: Understory removal was implemented in a Fraxinus mandschurica Rupr. plantation in order to investigate its effect on soil respiration, soil temperature and water content at 5 cm depth, fine root production, and soil microbial biomass carbon (MBC) and nitrogen (MBN) during the growing season in 2015. The results showed that average soil respiration rate increased by 11.87% after understory removal, particularly from the late August to the early September. The soil temperature and water content also increased. The temperature sensitivity of soil respiration (i.e., Q₁₀ value) showed an increment of 15.26% in understory removal treatment. Repeated measures ANOVA indicated that the effects of understory removal on soil variables were not significant, whereas sampling date did. Additionally, there were interaction effects between understory removal and sampling date on the soil respiration rate, temperature and water content. Fine root production of F. mandschurica increased (P>0.05), whereas that of other species (mainly shrubs) was markedly decreased after understory removal. Understory removal decreased MBC by 12.68% and 21.16%, and MBN 16.76% and 25.48% at the depth of 0-10 cm and 10-20 cm respectively, despite all of which were not statistically significant. In both the control and treatment plots, soil respiration rates was only exponentially correlated with soil temperature (P<0.01). Overall, the higher soil temperature and greater fine root production, as well as the alternation of fine root population may contribute to the seasonal increase in soil respiration rate following understory removal. Our findings yield some insights into the interrelationship between understory removal application and soil respiration in temperate forests.

Key words: germination percentage, antioxidant enzyme., seed pre-treatment, seed ageing, ultrasound