小兴安岭天然林不同林分汞含量分布特征与生物质汞库估算

Distribution characteristics of mercury concentration and estimation biomass mercury pools in different natural forests of Xiaoxing′an Mountain

植被主要通过叶片气孔吸收大气气态单质汞,森林植被是大气汞重要的汇.量化森林生物质汞库对了解全球汞循环至关重要.为揭示森林乔木层(乔木层分为树干、树叶、树枝、树根和树皮)、灌木层、草本层和凋落物层(凋落物层分为未分解层(Oi)、半分解层(Oe)和已分解层(Oa))汞含量和汞库分配,本研究选取黑龙江省凉水自然保护区小兴安岭原始林阔叶红松林、次生原始林云冷杉林和次生原始林白桦林3种原始林开展植物和凋落物汞含量和汞库调查.结果表明,乔木层各组织中汞含量遵循树皮>树叶>树枝>树根>树干的规律,云冷杉林乔木层汞含量总体上高于阔叶红松林及白桦林乔木层汞含量.凋落物中汞含量排序为Oa>Oe>Oi,原始林阔叶红松林凋落物汞含量高于次生原始林白桦林凋落物汞含量,但低于次生原始林云冷杉林凋落物汞含量.进一步估算生物质总汞库发现云冷杉林、阔叶红松林和白桦林分别为212、192和163μg·m^(-2).乔木层地上部分是森林生物质汞库的主体,其树皮汞库占总汞库的37.4%~43.5%,灌木层和草本层仅占总汞库的1%左右.本研究可为进一步评估森林生态系统在大气汞循环中的作用及预测森林火灾发生时生物质燃烧汞释放潜势提供基础数据.

Forests are important atmospheric mercury sink for absorbing atmospheric gaseous elemental mercury through leaf stomata.Quantifying forest biomass mercury pools are critical to understanding the global mercury cycle.In order to reveal mercury concentration and distribution characteristics of mercury pools in natural forest,samples from tree layer(bole,leaves,branches,roots and bark),shrub layer,herb layer and litter layer(undecomposed surface litter(Oi),partially decomposed litter(Oe)and decomposed organic humus(Oa))were collected in mixed old-growth forest,secondary spruce⁃fir forest and secondary birch forest at the Xiaoxing′an Mountain located in the Liangshui National Nature Reserve in Heilongjiang Province,and mercury concentrations were analyzed using a direct mercury analyzer.The results showed that the concentration of mercury in tree layer was higher in spruce⁃fir forest than that of mixed forest and birch forest,where mercury concentrations in different tissues followed the order of bark>leaves>branches>roots>bole.In litter layer,the highest mercury concentration was found in Oa followed by Oe and Oi.Mercury concentration of litter layer in the mixed old⁃growth forest was higher than that of secondary birch forest,and lower than that of secondary spruce⁃fir forest.Furthermore,total biomass mercury pool was estimated to be 212μg·m^(-2) in spruce⁃fir forest,192μg·m^(-2) in mixed forest and 163μg·m^(-2) in birch forest,respectively.Mercury stores in the bark of tree layer accounted for 37.4%~43.5%of the total mercury pools,and yet those from the shrub layer and herb layer only accounted for about 1.00%.These obtained results are quite valuable for further assessing the role of forest ecosystems in the atmospheric mercury cycle and predicting the mercury release potential of biomass combustion during forest wildfires.