鼎湖山南亚热带天然针阔叶混交林臭氧吸收特征

Ozone uptake by the dominant canopy tree species in a natural mixed coniferbroadleaf forest in Dinghushan,Guangdong Province,south China

针阔叶混交林是我国南亚热带针叶林向地带性常绿阔叶林演替的中间林分类型,为我国南亚地区主要森林类型,发挥着重要的生态系统服务功能。基于树干液流技术和对臭氧浓度的连续监测,评价该森林类型的臭氧吸收特征和能力有着重要的环境生态学意义。对鼎湖山天然针阔叶混交林优势种马尾松(Pinus manssoniana)、锥栗(Castanopsis chinensis)、木荷(Schima superba)和华润楠(Machilus chinensis)在自然环境条件下的臭氧吸收能力进行了分析研究。结果表明:在日尺度上,4个优势树种的冠层气孔对臭氧导度(GO_3)和臭氧吸收通量(FO_3)均呈单峰型曲线,其最大值的时间在干季(10月至竖年3月)比湿季(4月至9月)滞后;季节尺度上,臭氧浓度在湿季达到最大值48.94 n L/L,湿季GO_3、FO_3和年臭氧吸收累积量(accumulative stomatal O_3flux,AFst)均显著高于干季(P <0.01),华润楠的臭氧吸收能力最强,在干季和湿季可分别达1.11 nmol m^(-2)s^(-1)和1.71nmol m^(-2)s^(-1)。随着水汽压亏缺(VPD)增大,优势种GO_3降低。光合有效辐射(PAR)超过1500 umol m^(-2)s^(-1)时,优势树种GO_3和FO_3呈下降趋势。针阔叶混交林的年臭氧吸收累积量超过了保护森林树木所采用的临界阈值,可认为鼎湖山针阔叶混交林受臭氧危害的潜在风险较高。

We determined ozone （O3） uptake rates of the dominant tree species （Pinus manssoniana, Castanopsis chinensis, Schima superba, and Machilus chinensis） in a natural mixed conifer-broadleaf forest based on sap flow measurements and environmental monitoring. On a diurnal scale, the ozone uptake flux （FO3） by the dominant tree species had a unimodal pattern, and that the maximum flux appeared earlier in the wet season （April-September） than in the dry season （October-March）. Compared to the wet season, the time of the maximum flux in the dry season was delayed. Seasonally, the maximum O3 concentration occurred in the wet season （48.94 nL/L）. Canopy stomatal conductance for O3 （GO3）, FO3, and annual accumulative stomatal O3 uptake （AFst） in the wet season were significantly higher than in the dry season （P 〈 0.01）. Machilus chinensis had the highest O3 uptake capacity among the four species considered. The maximum FO3 was 1.11 nmol m-2 s-1 in the dry season and 1.71 nmol m-2 s-1 in the wet season. GO3 decreased with increasing vapour pressure deficit （VPD） in all the studied species. At photosynthetically active radiation （PAR） 〉 1500 umol m-2 s-1, GO3 and FO3 for all species declined at higher PAR. Annual AFst exceeded the threshold that could be tolerated by forest trees, suggesting a potential O3 risk for mixed conifer-broadleaf forest in Dinghushan.