Effects of ozone on soil respiration rate of siebold’s beech seedlings grown under different soil nutrient conditions

Abstract

Ozone (O 3 ) is an air pollutant that negatively affect carbon budget in woody plants. In the present study, we aimed to clarify the effects of ozone on soil respiration rate of Siebold’s beech seedlings (Fagus crenata) grown under different soil-nutrient conditions. Seedlings were grown under three levels of O 3 fumigation (charcoal-filtered air or O 3 at 1.0 or 1.5 times ambient concentration) in combination with three levels of nutrient supplies (non-, low-or high-fertilised) for two growing seasons. We determined soil respiration rate in July, August, September, and October of the second growing season. The seedlings were harvested to determine the dry mass in October. Significant effect of O 3 on soil respiration rate was not observed in all measurements. There was a significant interaction between O 3 and nutrient supply for whole-root dry mass. The dry mass in non-fertilised and low-fertilised treatments was reduced by O 3 , whereas O 3 did not affect dry mass in the high-fertilised treatment. On the other hand, neither significant effects of O 3 , nor a significant interaction between O 3 and nutrient supply for the biomass allocations were observed. Coefficient of positive correlation in the relation of soil respiration rate with dry mass of fine-root across the all treatments was higher than that in the relation of soil respiration rate with coarse-root and whole-root dry mass. These results indicate that no significant effect of O 3 on soil respiration was mainly attributable to no response of fine root dry mass to elevated O 3 . Soil nutrient supply decreased soil respiration rate in August. Our results emphasize the importance of fine root in the response of soil respiration to elevated O 3 . To clarify the response of soil respiration to elevated O 3 , future researches on the effect of O 3 on fine root dynamics including turnover and indirect effect on soil microbial respiration are needed.