高山森林林窗对苔藓及土壤微量元素含量的影响

苔藓植物和土壤在森林元素循环过程中具有重要作用,其元素含量特征可能受林窗和生长基质的影响,但有关不同林窗位置对苔藓和土壤微量元素含量影响的研究尚未见报道。为理解林窗更新对森林苔藓和土壤微量元素含量及分布特征的影响,于2016年10月,调查研究了在川西高山岷江冷杉(Abies faxoniana)原始林林下、林缘、林窗和旷地中地表苔藓和石生苔藓Na、Zn、Mg、Mn、Ca、Fe元素含量以及对应土壤有机层和矿质土壤层的元素含量。结果表明:川西高山森林地表苔藓与石生苔藓的Na、Zn、Mg、Fe、Ca含量差异不显著,地表苔藓的Mn元素含量显著高于石生苔藓;土壤有机层的Zn、Mg、Mn和Ca元素含量显著高于矿质土壤层,但Fe元素含量则相反,Na元素含量差异不显著。林窗位置对地表苔藓和石生苔藓Na、Zn、Ca和Fe元素含量具有相似的影响,均以林窗和旷地相对较高;石生苔藓与地表苔藓的Mn含量对林窗的响应存在差异,石生苔藓的Mn含量以林下最高,而地表苔藓则以林窗中心最高。但是,林窗对苔藓植物Mg元素含量的影响不显著。森林林窗位置对土壤有机层和矿质土壤层微量元素含量具有相似的影响。Na元素含量以旷地土壤最高,而Zn、Mn、Ca和Fe含量以林窗中心的土壤最高;除元素Na,所有微量元素均以林缘的土壤最低。此外,地表苔藓的Na、Zn、Mn和Ca含量显著高于土壤,而土壤中的Fe含量显著高于苔藓植物;苔藓中Ca和Mn元素含量与土壤的Ca和Mn元素含量呈显著正相关。可见,高山森林林窗更新过程在不同程度上影响了森林地表苔藓和土壤对微量元素的吸存特征,为进一步了解林窗和苔藓植物在高山森林生态系统物质循环中的作用提供了新的角度。

Effects of forest gaps on microelement concentrations of mosses and soil in an alpine forest

Moss is an essential component in most forest ecosystems, and plays critical roles in material cycling and water retention. It is also an indicator of environmental change. An increasing numbers of studies have demonstrated that the growth and reproduction of mosses can be determined by light regime, substrate, and hydro-thermal dynamics. Theoretically, a forest gap might improve the growth and element uptakes by mosses on different growth substrates by altering the light regimes and the temperature and moisture dynamics on the forest floor through the redistribution of light and precipitation. As yet, the effects of forest gap position on microelement uptakes by mosses on different growth substrates remain unclear. To understand the effect of gap regeneration on microelement uptakes by mosses, the concentrations of sodium (Na), zinc (Zn), magnesium (Mg), manganese (Mn), calcium (Ca), and iron (Fe) in epilithic and epigeic mosses, and in the soil organic and mineral soil layers were investigated in open areas, the gap center, the gap edge, and the closed canopy in an alpine fir (Abies faxoniana) forest in western Sichuan during October 2016. No significant differences for the concentrations Na, Zn, Mg, Fe, and Ca were recorded between epilithic mosses and epigeic mosses, while the Mn concentration in epigeic mosses were significantly higher than those in epilithic mosses. The Zn, Mg, Mn, and Ca concentrations in the soil organic layer were significantly higher than the mineral soil layer, but the Fe concentrations in the mineral soil layer were significantly higher than the soil organic layer. However, no significant difference was observed in Na concentrations between the soil organic layer and the mineral soil layer. Gap positions had similar effects on the concentrations of Na, Zn, Ca, and Fe in epilithic mosses and epigeic mosses, and the mosses in the gap center and open areas had higher Na, Zn, Ca, and Fe concentrations. In contrast, different responses to gap positions were found in Mn concentrations between epilithic and epigeic mosses. Higher Mn concentrations in epilithic moss were found in the microenvironment under the closed canopy, whereas higher Mn concentrations in epigeic moss were observed in the gap center microenvironment. However, gap positions had only slight effects on Mg concentrations in moss plants. Forest gap positions had similar effects on microelement concentrations in the soil organic layer and mineral soil layer. Higher Na concentrations in the soil organic and mineral soil layers were found in the open area, while higher Zn, Mn, Ca, and Fe concentrations in the soils were found at the gap center. The lowest concentrations of the measured microelements in the soil organic and the mineral soil layers were found at the gap edge. In addition, the Na, Zn, Mn, and Ca concentrations in epigeic mosses were significantly higher than those in the corresponding soils, while the Fe concentrations showed an opposite trend. Furthermore, the Ca and Mn concentrations in moss plants correlated positively and significantly with the Ca and Mn concentrations in the corresponding soils. In conclusion, gap regeneration affects microelement sequestration by mosses and soils in an alpine forest, which provides new insights into the roles of forest gap regeneration and mosses on bioelement cycles in the alpine forest ecosystem.