高山森林粗木质残体附生苔藓植物的重金属吸存特征

摘要

Coarse woody debris (logs,branches,snags,and stumps) constitutes a large component of forest biomass,and plays an essential role in many alpine forests.Coarse woody debris not only participates in material cycling and energy flow in the ecosystem,but also provides a suitable environment and abundant nutrients for the growth of epiphytic moss.Many studies have focused on the importance of moss as an absorber as well as indicator of heavy metal pollutants,especially pollutants from anthropogenic activities.Moss can absorb heavy metals from precipitation/wet deposition and directly from the substrate,and the concentrations of heavy metals in epiphytic moss are related to the local environmental conditions;total storage can be affected by the heavy metal content in the epiphytic moss and the biomass of the moss.However,the effect of the interaction between epiphytic moss and coarse woody debris on the sequestering of heavy metals in forest ecosystems remains unknown.In July 2015,the cadmium (Cd),lead (Pb),copper (Cu),and zinc (Zn) content and storage in epiphytic mosses on different types (logs,branches,snags,and stumps) and decay classes (Ⅰ-Ⅴ) of coarse woody debris were investigated in an alpine fir (Abies faxoniana) forest in western Sichuan.Results showed that an average of 4700 mg/hm2 of Cd,21236 mg/hm2 of Pb,6179 mg/hm2 of Cu,and 2622 mg/hm2 of Zn were sequestrated in the epiphytic mosses on the coarse woody debris in this region.The total storage of the four heavy metals in the epiphytic mosses was in the following order for coarse woody debris:logs ＞ branches ＞ snags ＞ stumps.Cd,Pb,Cu,and Zn storage in the epiphytic mosses on the logs accounted for 54.53％,66.08％,51.13％,and 66.30％ of total storage,respectively;Cd,Pb,Cu,and Zn storage in the epiphytic mosses on the roots accounted for less than 3％ of total storage.The characteristics of the heavy metal elements in the epiphytic moss was affected by the type and decay level of coarse woody debris.The content and storage of both Cd and Pb in the epiphytic mosses of the logs and large branches showed an "accumulation-release" pattern,and the highest values were observed in decay classes Ⅱ or decay classes Ⅲ.In contrast,the content and storage of Zn and Cu in the epiphytic mosses for all decay classes were insignificant.Overall,these results suggest that epiphytic moss on coarse woody debris greatly contributes to the sequestration of heavy metals in alpine forests;the results provide new insight into the cycling and transportation of heavy metals,as well as the role played by coarse woody debris in these alpine forest ecosystems.%粗木质残体及其附生苔藓植物是高山森林生态系统中两个相互联系的基本组成部分,二者的相互作用可能影响森林生态系统重金属循环,但有关不同类型和不同腐解等级粗木质残体对附生苔藓植物重金属吸存特征尚不清楚.因此,于2015年7月在川西高山森林调查了岷江冷杉(Abies faxoniana)原始林内不同类型和不同腐解等级的粗木质残体附生苔藓镉、铅、铜和锌浓度与吸存特征.结果表明:高山森林粗木质残体附生苔藓植物Cd、Pb、Cu和Zn的总吸存量依次为4700mg/hm2、21236mg/hm2 、6179mg/hm2和2622mg/hm2.粗木质残体附生苔藓的4种重会属吸存量都表现为倒木＞大枯枝＞枯立木＞根桩;倒木附生苔藓Cd、Pb、Cu和Zn吸存量分别占高山森林粗木质残体总吸存量的54.53％、66.08％、51.13％和66.30％,根桩附生苔藓重金属吸存量不足总吸存量的3％.粗木质残体的类型和腐解等级都会影响附生植物重金属吸存特征.随着腐解等级的增加,倒木和大枯枝附生苔藓中Cd和Pb呈现“积累-释放”的变化特征,其浓度和吸存量在第Ⅱ、Ⅲ腐解等级较高.附生苔藓Cu和Zn浓度和吸存量在不同腐解等级粗木质残体间的差异均不明显.这些结果表明,粗木质残体附生苔藓对重金属元素具有明显的吸存作用,为认识高山森林生态系统重金属元素循环及其迁移过程提供了新的思路,也为进一步了解粗木质残体在高山森林生态系统中的重要作用提供了新的角度.