影响关帝山华北落叶松天然更新与幼苗存活的微生境变量分析

采用野外典型样线调查法并结合室内实验对关帝山华北落叶松1年生幼苗更新和2～3年生幼苗存活的微生境变量进行分析。结果表明:微生境变量幼苗距大树距离、草本层盖度、土壤铵态氮两两间成极显著正相关,这3个变量与枯落物厚度和土壤硝态氮分别成极显著负相关,枯落物厚度与土壤硝态氮的正相关达到了极显著水平;通径分析表明,草本层盖度和土壤铵态氮对1年生幼苗的更新产生极显著直接负效应,幼苗距大树距离对幼苗的发生产生显著直接负效应,这3个变量的间接负效应使其对幼苗发生的阻碍作用进一步加强。枯落物厚度和土壤硝态氮对幼苗的发生产生极显著直接正效应,二者的间接效应促进了1年生幼苗的更新;枯落物厚度和幼苗距大树距离对2～3年生幼苗的存活产生极显著直接负效应,但其总间接正效应弱化了对幼苗存活的阻碍作用。草本层盖度对幼苗存活的直接负效应和间接负效应均不显著,但两效应叠加使其与2～3年生幼苗存活的负相关性增强,达极显著水平。     

喀斯特干热河谷植被类型和小生境对土壤活性有机碳和基础呼吸的影响

以贵州西南部典型喀斯特干热河谷地区荒草地(Ⅰ)、小灌丛(Ⅱ)、灌木疏林(Ⅲ)、灌木林(Ⅳ)和乔木林(Ⅴ)下一般土壤、石缝土壤和石沟土壤为研究对象,对比研究其土壤微生物生物量碳(MBC)、可溶性有机碳(DOC)、易氧化有机碳(EOC)和基础呼吸量(BR)的变化。结果表明:土壤MBC、DOC含量分别为123.2~616.8 mg kg-1和76.6~258.6 mg kg-1,EOC、BR含量分别为1.62~8.32 g kg-1和15.9~41.6 CO2μl g-1h-1。不同植被类型下,一般土壤、石缝土壤和石沟土壤MBC、DOC、EOC和BR含量均表现为:Ⅴ>Ⅳ>Ⅲ>Ⅱ>Ⅰ,差异显著,且土壤EOC与土壤总有机碳的比值总体也呈增加趋势。同一植被类型中,与一般土壤和石缝土壤相比,石沟土壤中EOC和DOC表现出了较高的含量水平。相关性分析表明,MBC、DOC和EOC可以作为喀斯特干热河谷地区土壤有机碳变化的敏感性指标。     

Does time or habitat make old-growth forests species rich? Bryophyte richness in boreal Picea mariana forests

The relative importance of time since disturbance and habitat variables in creating diversity in old-growth forests will influence conservation strategies. However, the independent roles of these factors are not well understood, as they are rarely examined independently. This study examines the respective roles of habitat variables and time (stand age) in determining bryophyte diversity in Picea mariana (Mill. (BSP)) forests. Bryophytes are frequently used as indicators of old-growth forest, but their true dependence on forest continuity is unknown. Bryophytes were classified into taxonomic-habitat guilds: true mosses (forest), forest liverworts, bog liverworts and sphagna (bog). Diversity increased with age and peaked at approximately 275 years since fire, driven by liverworts. Multiplicative habitat modeling indicated that time and habitat played different roles for the different taxonomic-habitat guilds. True mosses and forest liverworts were primarily influenced by habitat variables, while sphagna and bog liverworts were influenced by time and habitat variables. The models for sphagna were particularly strong, indicating that many important factors were included, while forest liverwort models were particularly weak. This unexplained variability may represent site specific random factors, such as secondary disturbances that create habitat in a fully occupied space. Overall, high richness was created by small species dependent on habitat variables and chance factors for establishment. Therefore, time since disturbance was not the primary factor limiting richness in these forests. These results suggest that in boreal North America, where forest fragmentation is limited and recent, conservation strategies that emphasize habitat variables rather than forest continuity may be effective for some bryophytes.