Effects Of Freeze-thaw Cycles On Soil Aggregates Under Typical Vegetations Around Alpine Timberline In Wutai Mountain

Freeze-thaw cycles frequently occur in the soil from late autumn to early spring at high latitudes and middle and high altitudes,which will change the size,quantity and arrangement order of soil aggregates and lead to change of soil aggregate structure.To explore the effects of freeze-thaw cycles on soil aggregates,the soil of three typical vegetation plots(meadow(CD),Larix principisrupprechtii(HL)and Picea meyeri(YS))around the alpine timberline of Wutai Mountain were selected for soil column in situ experiment.The results were summarized as follows:(1)The content of soil macro-aggregates in three plots was significantly changed by seasonal freezing and thawing,and mainly occurred in the melting period.During the melting period and initial growing season,there were significant differences between the contents of the soil macro-aggregates in CD plots and those in HL and YS plots(p<0.05).(2)The content of soil micro-aggregates in three plots was significantly changed by seasonal freezing and thawing,and mainly occurred in the initial freezing period and melting period.During the melting period and growing season,there was a significant difference between the content of soil micro-aggregates in CD plots and those in HL and YS plots(p<0.05).(3)During the research period,except of the deep freezing period,the proportion of CD plot micro-aggregate was greater than that of HL and YS plots,and the proportion of macro-aggregate was smaller than that of HL and YS plots.In the deep freezing period,it was just the opposite.During the research period,except of the deep freezing period,the soil structure of CD plot was weaker than that of HL and YS plot.(4)During the incubation period,the fractal dimension of macro-aggregates in plots was between 2.472-2.619.And the fractal dimension of macro-aggregates in arbor communities was smaller than that in meadow communities and the structure of macro-aggregates is more stable than that of CD plot.The fractal dimension of soil macro-aggregates in three plots showed periodic changes.(5)The fractal dimension of soil micro-aggregates in three plots showed the same trend,which increased during the seasonal freeze-thaw period and decreased during the growing season,showing the regularity of periodic changes and the ability to restore the aggregate structure.Therefore,seasonal freeze-thaw cycles significantly affected soil aggregates in three plots.And the structure of soil aggregates were weaken in varying degrees.However,the three plots of soil aggregates recovered structurally during the growing season,and even optimized the structure of the soil aggregates.The structure of soil aggregates in three plots had certainly self-recovery capacity.