Ozone (O3) 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 O3 fumigation (charcoal-filtered air or O3 at 1.0 or 1.5 times ambient concentration) in combination with three levels of nutrient supplies (non-, lowor 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 O3 on soil respiration rate was not observed in all measurements. There was a significant interaction between O3 and nutrient supply for whole-root dry mass. The dry mass in non-fertilised and low-fertilised treatments was reduced by O3, whereas O3 did not affect dry mass in the high-fertilised treatment. On the other hand, neither significant effects of O3, nor a significant interaction between O3 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 O3 on soil respiration was mainly attributable to no response of fine root dry mass to elevated O3. 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 O3. To clarify the response of soil respiration to elevated O3, future researches on the effect of O3 on fine root dynamics including turnover and indirect effect on soil microbial respiration are needed.

中文翻译：

---

臭氧对不同土壤养分条件下西博尔德山毛榉幼苗土壤呼吸速率的影响

臭氧 (O3) 是一种空气污染物，会对木本植物的碳收支产生负面影响。在本研究中，我们旨在阐明臭氧对不同土壤养分条件下生长的 Siebold 山毛榉幼苗 (Fagus crenata) 土壤呼吸率的影响。幼苗在三个级别的 O3 熏蒸（木炭过滤空气或 1.0 或 1.5 倍环境浓度的 O3）结合三个级别的营养供应（非、低或高施肥）下生长两个生长季节。我们确定了第二个生长季节的 7 月、8 月、9 月和 10 月的土壤呼吸速率。在 10 月份收获幼苗以确定干重。在所有测量中均未观察到 O3 对土壤呼吸速率的显着影响。O3 与全根干重的养分供应之间存在显着的相互作用。O3 减少了不施肥和低施肥处理的干质量，而 O3 不影响高施肥处理的干质量。另一方面，对于生物量分配，既没有观察到 O3 的显着影响，也没有观察到 O3 与养分供应之间的显着相互作用。各处理土壤呼吸速率与细根干质量的正相关系数均高于土壤呼吸速率与粗根和全根干质量关系的正相关系数。这些结果表明 O3 对土壤呼吸没有显着影响主要是由于细根干质量对 O3 升高没有反应。8 月份土壤养分供应降低了土壤呼吸速率。我们的结果强调了细根在土壤呼吸对 O3 升高的响应中的重要性。