森林土壤是大气中甲烷重要的汇,降水变化是影响森林土壤甲烷吸收速率(VCH_4)的重要因子。以中亚热带地区不同降水减少程度的杉木林土壤为研究对象,采用静态箱-气相色谱法来测定不同模拟降水减少处理样地的土壤甲烷吸收速率。结果表明:模拟降水减少后显著改变了土壤中的含水量,降水减少60%、降水减少20%和对照样地的年均土壤含水量分别为18.87%、23.89%和28.33%。杉木人工林土壤甲烷吸收速率在月变化上存在较大幅度的波动,其中土壤甲烷吸收速率在8月份达到一年中的最大值(对照75 g m~(-2) h~(-1)),2月份达到一年中的最小值(对照10.93 g m~(-2) h~(-1))。3种处理样地的土壤全年均为甲烷汇,与对照样地的甲烷年通量(2.48 kg hm~(-2) a~(-1))相比,降水减少60%和20%样地的甲烷年通量分别增加44%和19%。在对照样地中,土壤甲烷吸收速率与土壤含水量呈现负相关(P=0.001),与温度相关性不显著(P>0.05);而模拟降水减少后,土壤甲烷吸收速率与土壤温度呈正相关关系(P=0.006和P=0.034),与土壤含水量相关性不显著(P>0.05)。总之,模拟降水减少后不仅提高了杉木人工林土壤甲烷吸收的能力,同时也可能改变影响土壤甲烷吸收的环境因子;在模拟降水减少前土壤甲烷吸收速率与土壤水分相关性更为密切,而模拟降水减少后土壤甲烷吸收速率可能主要受土壤温度的影响。
英文摘要:
Forest soil plays an important role in atmospheric methane uptake, the rate of which is affected by soil water content and precipitation change. In this study, we excluded precipitation by 20% and 60% in a Cunninghamia lanceolate plantation to analyze how precipitation reduction affects soil methane uptake in subtropical China. The results showed that soil water content changed significantly in precipitation exclusion treatments, with an annual mean value of 18. 87%, 23.89%, and 28.33% in 60% precipitation exclusion, 20% precipitation exclusion, and control treatments, respectively. We also found VCH_4 had strong and substantial fluctuations in the study year,with the highest rate hit in August ( control 75 g m~(-2) h~(-1)) and the minimum in February (control 10.93 g m~(-2) h~(-1)) . Annual flux of soil CH_4 uptake was 2.48 kg hm~(-2) a~(-1) in the control treatment, and increased by 44% and 19% in the 60% and 20% precipitation exclusion treatments, respectively. Precipitation exclusion may also alter the relationship of VCH_4 and environmental factors. We found a negative correlation between VCH_4 and soil water content (P = 0.001),and a weak relationship between VCH_4 and soil temperature in the control treatment. However, the relationship between VCH_4 and soil temperature became stronger after precipitation exclusion (P= 0.006 at 60% precipitation exclusion and P= 0.034 at 20% precipitation exclusion),and no significant correlation was found between VCH_4 and soil water content in both precipitation exclusion treatments. Our results suggest that precipitation decline may not only increase soil methane uptake in subtropical forests with global climate change in the future,but it may also change the main determining environmental factor of soil methane uptake rate from soil water content to soil temperature.