冻融循环对五台山典型植被土壤微团聚体的影响

目的]研究气候变化背景下季节性冻融对土壤微团聚体的作用,为影响林线附近土壤地球生物化学过程的相关研究提供参考。方法]选择五台山林线附近3种典型植被:草甸、华北落叶松(Larix principis-rupprechtii)和云杉(Picea meyeri)覆盖下的土壤,通过土柱野外原位培养,测定不同时期土壤各粒径微团聚体含量以及土壤分形维数(D)。结果]在培养期内,3个样地的2～0.25mm和0.25～0.05mm团聚体含量变化趋势各不相同;0.05~0.02mm(先降后增再降),0.02～0.002mm(先降后增,华北落叶松样地除外),0.002mm(先增后降)团聚体含量变化趋势基本一致。在初冻期和融化期,季节性冻融导致3个样地土壤微团聚体含量发生显著变化(p0.05),深冻期无显著变化(p0.05)。生长季同样发生了土壤微团聚体含量的显著变化(p0.05)。不同样地植被组成的差别造成了土壤微团聚体含量差异显著(p0.05),体现在初冻期和融化期。季节性冻融期间,土壤微团聚体分形维数逐渐增加,而此时云杉样地土壤微团聚体分形维数最低;生长季期间,微团聚体分形维数逐渐降低,草甸样地土壤微团聚体分形维数最低,但在生长季末期,则是华北落叶松样地最低;但3个样地土壤微团聚体分形维数仅在生长季末期存在显著差异(p0.05),且培养期结束时的土壤分形维数与开始时无显著差异(p0.05)。结论]季节性冻融对3个样地土壤微团聚体含量都具有显著影响,且3种植被下土壤结构对季节性冻融的响应也明显不同,主要发生在初冻期和融化期;在培养期内,虽在冻融作用下土壤微团聚体分形维数增加,但进入生长季后都逐渐减少至培养前水平,3个样地土壤结构性和团聚能力均呈周期性变化,具有一定的自我恢复能力。

Effects of Freeze-thaw Cycles on Soil Micro-aggregates in Typical Vegetations of Wutai Mountain

Objective] The effect of seasonal freeze-thaw on soil micro-aggregates in the context of climate change was studied in order to provide references for the reserch of soil biochemical processes near the timberline.Methods] Soil samples from three typical vegetation types (meadow, Larix principis-rupprechtii and Picea meyeri) near the timberline of Wutai Mountain were collected for soil column in situ experiment. Soil micro-aggregates contents and fractal dimensions (D) were measured.Results] The variations of 2~0.25 mm and 0.25~0.05 mm aggregate contents were different among the three plots. The content of 0.05~0.02 mm aggregate reduced initially, then increased and finally reduced. The content of 0.02~0.002 mm aggregate reduced initially and then increased (except in Larix principis-rupprechtii plot), and the content of <0.002 mm micro-aggregates increased firstly and then reduced. The content of micro-aggregates changed significantly (p<0.05) due to seasonal freeze-thaw events in initial freezing and thawing periods, while there was no significant change in deep freezing period (p>0.05). Soil micro-aggregate contents also changed significantly (p<0.05) in the growing season. Different vegetation compositions caused significant differences (p<0.05) among micro-aggregate contents in three plots, especially, in initial freezing and thawing periods. During the freezing-thawing period, D values were increased, and that of Picea meyeri plots was the lowest. In growing season, D values were decreased, and that of meadou plots was the lowest. Significant differences (p<0.05) of D values among three researched plots were only observed in the late growing season, and the least D value is obtained in H. principis-rupprechtii.Conclusion] Freeze-thaw cycles have great impacts on soil micro-aggregate contents. The responses of soil structures to seasonal freeze-thaw events are significantly different, and mainly occur in initial freezing period and thawing period. The D values of all plots are increased by freeze-thaw cycles. Although the D value of soil microaggregates increased during the incubation period, it gradually decreased to the pre-incubation level after entering the growing season. Soil aggregations and structures of all three plots vary periodically and have certain self-recovery capabilities.