Characteristics And Driving Factors Of Soil Reservoirs Of Different Types Color-leafed Forests In A Subalpine Of Western Sichuan

Water conservation is an important manifestation of forest ecological functions.Forest soil,as the main place for forest to conserve water,may make crucial impact on water circulation of forest ecosystem through precipitation redistribution.Therefore,exploring the forest soil reservoirs and the differences among different types of forests is important for understanding forest ecosystem functions.Subalpine forest in western Sichuan is located in the eastern Tibet Plateau and the upper Yangtze River of China.Due to the location in the alpine canyon area,frequent geological disasters,low temperature limitation and long-term human activities interfere the normal succession of forests,forming a large-scale color-leafed landscape.These forests occupied the dominant position in the area,thus becoming an important tourist landscape.However,whether the different types of color-leafed forest have great soil reservoir function while maintaining the landscape aesthetic value lacks the necessary attention still.Therefore,six different types of subalpine color-leafed forest located in the alpine gorge region（i.e.,Betula utilis-Abies faxoniana forest,Larix gmelinii forest,Betula platyphylla-Picea asperata-Acer caudatum var.prattii forest,Betula luminifera-Rhus potaninii forest,Quercus baronii forest and Quercus baronii-Sophora davidii-Cotinus coggygria forest）were taken as the research objects,and a bare land was used as the control.Soil water-holding and infiltration characteristics of different stands were measured in the growing season,before and after freezing-thawing from August 2018 to May 2019 to explore the soil reservoir characteristics of different color-leafed forests.The main results are as follows:（1）Soil water storage and water-holding characteristics of different types of color-leafed forest:In the growing season,before and after freeze-thaw,soil water storage of color-leafed forest was 25.13～287.55 mm,31.15～230.62 and 38.68～307.15 mm,respectively.The maximum water-holding capacity was 117.99 to 382.21 mm,102.07 to333.11 mm and 117.02～410.12 mm.Soil water storage and water-holding capacity were significantly different among stands.Soil water-holding capacities of bare land and L.gmelinii forest were higher than others,while B.platyphylla-P.asperata-A.caudatum var.prattii forest and B.luminifera-R.potaninii forest were lower than others.However,B.luminifera-R.potaninii forest had strong water holding capacity,and the soil water-holding rates of organic layer were significantly higher than others.The soil water storage and water-holding characteristics of mineral soil layers were significantly higher than those of soil organic layers,but the water-holding rates were significantly lower.（2）Soil infiltration characteristics of different color-leafed forest types:The soil infiltration rate and time fitted with Kostiakov model generally.The infiltration process appeared as infiltration rate dropped rapidly declined slowly reached to stability.In the growing season,before and after freeze-thaw,the stable infiltration rate of soil organic layer in the stands was 1.00～2.92 mm/min,1.51～4.72 mm/min and 1.34～4.07 mm/min,respectively.And that of mineral soil layer was 0.42～2.67 mm/min,0.81～2.61 mm/min and0.24～3.36 mm/min,respectively.Soil infiltration was significantly different among stands.The soil infiltration indexes of bare land were low and the infiltration capacity was the worst.Other stands soil infiltration patterns were not consistent among periods.Soil infiltration characteristics of soil organic layer were generally higher than those of mineral soil layer,but not significant.（3）The effect of soil physical structure on soil water conservation capacity:The soil physical structure was closely related to water conservation capacity.Correlation analysis showed that non-capillary water-holding capacity was positively related to soil depth and non-capillary porosity significantly,and was negatively related to capillary porosity significantly.Both soil depth and bulk density were positively correlated with water storage and other water-holding capacity significantly,and were negatively related to mass water content,water-holding rates and soil penetrability significantly,while total and non-capillary porosity showed opposite.Capillary porosity was significantly positively correlated with mass water content and water-holding rates.The formation of 1-2 mm size aggregate was conductive to soil penetrability,but 0.106-0.5 mm size had the opposite effect.Regression analysis showed that large aggregate content(R_0.25)and aggregate stability（MWD）were significantly negatively correlated with capillary water-holding capacity,maximum water-holding capacity,minimum water-holding capacity and minimum water-holding rate,and showed a significant positive correlation with mass water content and initial infiltration rate.Additionally,R_0.25 was significantly negatively correlated with capillary water-holding rate,and MWD was significantly positively correlated with accumulate infiltration and average infiltration rate.The total gravel volume content was significantly positively correlated with the non-capillary water-holding capacity,and was significantly negatively correlated with water storage,mass water content and water-holding rates.It had no significant correlation with soil penetrability.（4）The effect of seasonal freezing-thawing on soil water conservation capacity:the soil physical structure changed with season.Season significantly changed soil capillary porosity,total porosity,MWD and gravel volume content.After freezing-thawing,capillary and total porosity generally increased significantly,but the seasonal variation of MWD and gravel volume content among stands was inconsistent.Season had significantly changed the soil water storage and holding capacity.After freezing-thawing,the soil water storage and holding capacity increased significantly and water-holding rate increased at different levels.Season had a significant effect on the soil accumulate infiltration and average infiltration rate.After seasonal freezing and thawing,soil penetrability generally increased.In summary,there were significant differences in the soil water conservation capacity among different types of subalpine color-leafed forest in the western Sichuan,which was affected by the soil physical structure and season significantly.The color-broad-leaved mixed forest not only had high landscape aesthetic value,but also strong water conservation ability.However,the soil without vegetation covering had poor penetrability and was not conducive to precipitation infiltration and storage.It is suggested that more efforts could be made to plant color-broad-leaved mixed forests in the future afforestation and ecological restoration.These results can provide scientific basis for a profound understanding of the hydro-ecological benefits of subalpine color-leafed forest in the western of Sichuan and the development of region-ecological construction.