CO2浓度倍增、高氮沉降和高降雨对南亚热带人工模拟森林生态系统土壤呼吸的影响

 土壤呼吸响应全球气候变化对全球C循环具有重要作用。应用大型开顶箱(Open-top chamber, OTC)人工控制手段, 研究了大气CO₂浓度倍增、高氮沉降和高降雨处理对南亚热带人工森林生态系统土壤呼吸的影响。结果表明: 对照箱、CO₂浓度倍增处理以及高氮沉降处理下土壤呼吸速率都具有明显的季节变化, 雨季(4~9月)的土壤呼吸速率显著高于旱季(10月至次年3月) (p<0.001); 但高降雨处理下无明显的季节差异(p>0.05)。CO₂浓度倍增能显著提高土壤呼吸速率(p<0.05), 其他处理则变化不大。大气CO₂浓度倍增、高氮沉降、高降雨处理和对照箱的土壤呼吸年通量分别为4 241.7、3 400.8、3 432.0和3 308.4 g CO₂·m^–2·a^–1。但在不同季节, 各种处理对土壤呼吸的影响是不同的。在雨季, 大气CO₂浓度倍增和高氮沉降的土壤呼吸速率显著提高(p<0.05), 其他处理无显著变化; 而在旱季, 高降雨的土壤呼吸速率显著高于对照箱(p<0.05), 氮沉降处理则抑制土壤呼吸作用(p<0.05)。各处理的土壤呼吸速率与地下5 cm土壤温度之间具有显著的指数关系(p<0.001); 当土壤湿度低于15%时, 各处理的土壤呼吸速率与地下5 cm土壤湿度具有显著的线性关系(p<0.001)。

EFFECTS OF CO_2 ENRICHMENT, HIGH NITROGEN DEPOSITION AND HIGH PRECIPITATION ON A MODEL FOREST ECOSYSTEM IN SOUTHERN CHINA

Aims Responses of soil respiration to global change play an important role in global carbon cycling, but the effects of increasing atmospheric carbon dioxide concentration ([CO_2]), nitrogen (N) deposition and precipitation on soil respiration in subtropical China are unclear. Our objective was to test the effects of increased [CO_2], N deposition and precipitation on soil respiration and to determine how they influence soil respiration in subtropical China.Methods A model forest ecosystem was constructed of six tree species native to South China. The species were exposed to four experimental treatments in open-top chambers beginning March 2005. Three chambers were used for elevated [CO_2] (CC), two for high N treatment (NN) and the control (CO) and one for elevated precipitation (HR). The CC treatment was achieved by supplying additional CO_2 from a tank until the chambers had a concentration of (700 ± 20) μmol CO_2·mol~(-1). The NN treatment was achieved by spraying seedlings once a week for a total amount of NH_4NO_3 of 100 kg N·hm~(-2)·a~(-1). The HR treatment was achieved by weekly irrigation with 100 L water. Important findings For two years, soil respiration displayed strong seasonal patterns with higher values observed in the wet season (April to September) and lower values in the dry season (October to March) in the control chambers (CO) and the CC and NN treatments (p<0.001). There was no seasonal difference in the HR treatment (p>0.05). The CC enrichment affected soil respiration significantly(p<0.05), and there were no significant differences in annual CO_2 effluxes between CO and the other two treatments. The annual CO_2 effluxes reached 4 241.7, 3 400.8, 3 432.0 and 3 308.4 g CO_2·m~(-2)·a~(-1) in the CC, NN, HR and CO treatments, respectively. Soil respiration showed diverse responses between dry and wet seasons under different treatments. Higher soil respiration in the CC and NN treatments occurred in the wet season (p<0.05). In the dry season, soil respiration increased in the HR treatment (p<0.05) and decreased in the NN treatment (p<0.05). We found significant exponential relationships between soil respiration rates and soil temperature and significant linear relationships between soil respiration rates and soil moisture (below 15%).