The Responses Of Soil Water-stable Macroaggregates To Seasonal Freeze-thaw In Typical Timberline Vegetation Of Wutai Mountain

Freezing and thawing is a common climate phenomenon in high altitude areas of northern China.In the process of freeze-thaw cycle,there are many phenomena,such as temperature difference,phase change of water and low-temperature metabolism of microorganism,which will make the soil go through complex physical,chemical and biological changes.These processes will change the stability of soil aggregates,which will affect the soil structure,and ultimately affect the soil erodibility.Soil samples from three typical vegetation(subalpine meadow CD?Larix Principis-rupprechtii HL and Picea meyeri×Larix Principis-rupprechtii mixed forest YH)near the timberline of Wutai Mountain were collected for soil column in situ experiment.This paper analyzed its amounts of water-stable aggregates in different soil fractions?amounts of soil water-stable macroaggregates(>0.25 mm WSA)?mean weight diameter(MWD)and geometric mean diameter(GMD)during the incubation period,aimed to study the effects of seasonal freeze-thaw cycle on the soil water-stable macroaggregates.Furthermore,the principal component analysis were used to comprehensively evaluate the corrosion resistance of the water-stability of soil macro-aggregates in the three vegetations.The main results are as follows:(1)Soil water-stable macroaggregates in the three vegetation changed obviously during the incubation period.During the late growing period?the deep freezing period and the thawing period,the water-stable macroaggregates composition?>0.25 mm WSA?MWD and GMD changed significantly(p<0.05).In the late growing period,the amounts of 5?10mm and 2?5mm soil water-stable aggregates?>0.25 mm WSA in the three vegetations decreased significantly(p<0.05);MWD and GMD decreased significantly in HL and YH(p<0.05).During the deep-freezing period,the amounts of 5 ? 10 mm soil water-stable aggregates and MWD decreased significantly in CD(p<0.05);the amounts of 2?5mm soil water-stable aggregates and GMD increased significantly in YH(p<0.05).During the thawing period,the amounts of 2?5mm soil water-stable aggregates and >0.25 mm WSA decreased significantly in CD(p<0.05);the amounts of 2?5mm and 1?2mm soil water-stable aggregates?MWD?GMD increased significantly in HL(p<0.05).(2)The responses of soil water-stable macroaggregates to seasonal freeze-thaw were significantly different.During the initial and deep freezing periods,the water-stable macroaggregates composition?>0.25 mm WSA?MWD and GMD were significantly different from HL and YH(p<0.05),which the amounts of 2?5mm and 1?2mm soil water-stable aggregates?>0.25 mm WSA?MWD and GMD in CD were significantly higher than HL and YH.During the growing season,the water-stable macroaggregates composition?>0.25 mm WSA?MWD and GMD in the three vegetations were significantly different(p<0.05).The amounts of 5?10mm and 2?5mm soil water-stable aggregates?>0.25 mm WSA MWD and GMD in the three vegetations showed the increasing trend in the early and middle growing season;the amounts of 2?5mm soil water-stable aggregates?MWD and GMD in HL and YH were significantly lower than CD.The results showed that the water-stability of soil aggregates of the three vegetations was restored in the early and middle growing season,and the water-stability of soil aggregates in HL and YH decreased obviously at the end of the growing season.(3)There was a significant correlation between several indexes of water-stability of soil aggregates.In HL and YH,there was a significant negative correlation between soil moisture and >0.25 mm WSA?MWD?GMD(p<0.05),while >0.25 mm WSA was positively correlated with MWD?GMD(p<0.05).(4)The water-stability of soil aggregates was evaluated comprehensively by principal component analysis,and the water-stability of soil aggregates from three vegetation in the area was as follows: CD>YH>HL.