施氮对湿地松(Pinus elliottii)林土壤呼吸和相关因子的影响

The effect of nitrogen addition on soil respiration and associated factors in Pinus elliottii forest

人类活动引起陆地生态系统氮输入水平持续升高,对全球碳循环产生影响。为探究氮素对土壤呼吸的影响,2010年6月至2012年1月,采用氮添加试验对亚热带湿地松林的土壤呼吸进行了研究。试验共设置4种氮添加水平:对照CK,0 g m^(-2)a^(-1);低氮LN,5g m^(-2)a^(-1);中氮MN,15 g m^(-2)a^(-1);高氮HN,30 g m^(-2)a^(-1);每月上、下旬采用Li-cor 8100测定土壤呼吸速率。结果表明:(1)氮添加对土壤呼吸有着显著的抑制作用,LN、MN和HN处理的土壤呼吸年累积量较CK处理分别降低了26.6%、23.7%和29.5%,而施氮处理间的土壤呼吸无显著差异;(2)林分生长期间(6-9月),施氮第1年的土壤呼吸所受抑制作用显著高于第2年同期的水平,显示施氮对土壤呼吸的影响随时间的推移而降低;(3)湿地松林土壤呼吸存在明显的季节动态,最大值出现在8月(356.32 mgCO_2 m^(-2)h^(-1)),最小值出现在1月(99.12 mg CO_2 m^(-2)h^(-1)),施氮处理并不改变土壤呼吸的季节性变化规律;(4)CK处理林分中,土壤呼吸与土壤温度间存在极显著的指数关系,而与土壤湿度无显著相关。施氮处理没有改变土壤呼吸与土壤温度之间的相互关系,但抑制了土壤呼吸的温度敏感性(Q_(10));(5)施氮处理显著减少了林分凋落物量、土壤微生物碳、氮量,并轻微抑制了细根生物量,这些改变导致了土壤呼吸的下降。上述结果表明施氮会显著抑制亚热带湿地松林的土壤呼吸速率,而这种抑制作用将随着时间的推移而降低。

Human activities have raised nitrogen input to terrestrial ecosystems and influenced the global carbon cycle. To determine how soil respiration responds to nitrogen addition, a simulated nitrogen deposition experiment was conducted in Pinus elliottii forest in a subtropical zone in China from June 2010 to January 2012. Four-levels of N treatment-control check （CK,0 g m-2 a-1） ,low nitrogen（ LN, 5 g m-2 a-1） ,medium nitrogen（ MN, 15 g m-2 a-1） and high nitrogen（ HN, 30 g m-2 a-1 ） -were applied and infrared gas analyzer techniques were used to quantify the soil respiration twice a month. The results showed that （1） soil respiration exhibited a clearly seasonal pattern, with the highest rates found in the August （356.32 mg CO2 m-2 h-l） and the lowest rates in January （99.12 mg CO2 m-2 h-1）, and that nitrogen addition significantly depressed soil respiration. The soil annual accumulative soil respiration in the LN, MN, and HN treatments was 26.56%, 23.72%, and 29.54% lower, respectively, than CK treatment, but there is no significant difference between the nitrogen addition treatments. Furthermore, the inhibitory action weakened over time. Analysis of the soil respiration rate from June to September showed that （ 1 ） the inhibitory effect of nitrogen addition in the first year was weaker than that in the second year; （2） there was no strong diurnal soil respiration pattern; during daytime, nitrogen addition did not repress of soil respiration; and （3） soil respiration rates showed a significant positive exponential relationship with soil temperature at 5 cm depth. Soil temperature was the dominant driving factor and nitrogen addition reduced the Q10 values. Our results suggest that soil respiration declined in response to N addition in subtropical Pinus elliottii forest.