模拟酸雨对杉木幼苗-土壤复合体系土壤呼吸的短期效应

A short-term effect of simulated acid rain on the soil respiration of the compound system of Chinese fir seedling-soil

为了解酸雨对土壤碳释放的作用,选取对酸沉降敏感的杉木(Cunninghamia lanceolata)幼苗-土壤复合系统,分成重度酸雨(pH值2.5)、中度酸雨(pH值4.0)和对照(pH值5.6)3个处理区组,进行了2a模拟酸雨胁迫盆栽实验。通过分析酸雨短期作用下土壤酸化的状况以及土壤呼吸的变动,发现:(1)对照组土壤pH值虽有下降,但土壤缓冲体系无显著变化。重度酸雨组土壤pH值持续下降至3.71,土壤残留交换性Ca2+和Mg2+含量明显降低,土壤缓冲体系转成铝缓冲体系,土壤明显酸化。中度酸雨组土壤pH值略低于对照,土壤残留交换性Ca2+含量维持在40.15-42.76μg·g-1(烘干土),而交换性Mg2+含量下降,土壤缓冲体系无显著变化。(2)非模拟酸雨胁迫状况下(对照组),2007年和2008年年均土壤呼吸速率分别为1.41μmol·m-2·s-1和1.42μmol·m-2·s-1,土壤呼吸作用稳定。模拟酸雨短期内以抑制土壤呼吸为主。重度酸雨使土壤呼吸作用持续减弱,2007年和2008年年均土壤呼吸速率分别下降了14%和28%;中度酸雨虽未造成土壤的显著酸化,但该处理组年均土壤呼吸速率2007年增加了8%,2008年则降低了15%。模拟酸雨对土壤呼吸的影响随着酸雨的持续而加强。

Chinese subtropical forest zones have been damaged by long term acid rains.The acid rain usually increases the decomposition rates of soil organic carbon and impacts the release of soil carbon by accelerating the soil acidification.Consequently,an uncertainty of the variation of soil carbon is leaded by the effect.Meanwhile,the effluxes of carbon dioxide CO2 released from soil into the air contribute to a potential climate change.In order to figure out the effect of acid rain on the release of soil carbon,an acid rain menace control experiment was carried out on a compound system of Cunninghamia lanceolata seedling-soil.The system is sensitive to the acid rain stress in Zhejiang Province and is located in the middle Chinese subtropical areas,which is suffered from the severe acid rain pollution in a long term.The Cunninghamia lanceolata seedling-soils constructed in plots were divided into three groups,which represented the severe acid rain treatment ST（pH 2.5）,the moderate acid rain treatment MT（pH 4.0） and the check experiment CK（pH 5.6）.Then the samples were sprayed by artificial acid rains with different pH values in a greenhouse for 2 years.The artificial acid rain was consisted of H2SO4（98%） and HNO3（75%） at the volume ratio of 8：1,and was diluted by pure water into spay solutions,of which pH values were 2.5,4.0 and 5.6 respectively.The trend of soil acidification and the variation of soil respiration in the seedling-soil system were experimentally analyzed with a response model of soil carbon release developed to simulated acid rain stress.The results showed that（1） the pH-value of soil treated with CK decreased,but the soil-buffer system had not been strongly changed.The mass of hydrogen ion H ＋ rushing into soil due to a severe acid rain（pH 2.5） made the pH-value decrease to 3.71.Meanwhile the residual of Ca2 ＋ and Mg2 ＋ decreased sharply.After which the soil-buffer system changed into aluminum buffer system and the soil was apparently acidified.Moderate acid rain（pH 4.0） did not significantly acidify soil,although the pH-values of soil and the residual of Mg2 ＋ in soil slightly dropped.On the other hand,the residual of Ca2 ＋ remained 40.15-42.76 μg·g-1（oven-dried soil）.（2） The mean annual effluxes of soil carbon of control group did not strongly vary,which were 1.41 μmol·m^-2·s^-1n 2007 and 1.42 μmol·m^-2·s^-1in 2008.The acid rain inhibited the soil respiration of Cunninghamia lanceolata seedling-soil mainly in the first 2 years.Compared to CK,the inter-annual effluxes of soil respiration of the conifer seedling-soil sprayed by a severe acid rain（pH 2.5） dropped by 14% and 28% respectively in the two years.Even though the moderate acid rain（pH 4.0） could not make a severe soil acidification,it enhanced the release of soil carbon by 8% in 2007 and reduced the effluxes of soil respiration by 15% in 2008.Moreover,the effect of acid rain on the release of soil carbon became more significant with the prolongation of simulated acid rain.