Study On Rainfall Redistribution Characteristics Of Typical Shrubs In The Eastern Section Of Qilian Mountains

The redistribution of rainfall by canopies is one of the important links in the water cycle process of Soil-Plant-Atmosphere continuum(SPAC),it plays an extremely important role in the hydrological cycle of forest ecosystem and has been the focus of research in hydrology,ecology and other related fields.Though the investigation of long-term observation sites in the eastern of Qilian Mountains,we choose the six typical vegetation of Salix oritrepha shrub community,Salix sclerophylla shrub community,Spiraea salicifolia shrub community,Rhododendron capitatum shrub community,Potentilla fruticose shrub community and Rhododendron thymifolium shrub community as the research objects.The characteristics of interception,throughfall and stemflow were studied by using the water balance method,and the effect of characteristic of rainfall and shrub on rainfall redistribution were discussed.The main conclusion of this study are as follows:(1)The characteristic of six alpine shrubs are significantly different,the plant height,crown width,basal diameter and leaf area of Salix oritrepha shrub and Salix sclerophylla shrub were significantly larger than others;the aboveground biomass was less than that of the underground of six specie shrubs;and the root shoot ratio was1.80-12.25,the root shoot ratio of Spiraea salicifolia shrub,Rhododendron capitatum shrub,Potentilla fruticose shrub and Rhododendron thymifolium shrub was significantly higher than that of the other two shrubs.(2)During the study period,there were 30 times of rainfall in the two rainy seasons(July to September 2017 and July to September 2018),with the total rainfall of 224.0 mm and 269.5 mm respectively.The maximum rainfall is 52.1 mm and the minimum rainfall is 1.8 mm.The results show that the main precipitation is the rainfall(J)≥ 5 mm,accounting for 97.11% of the total rainfall times;J ≥ 20 mm has the largest contribution to the total rainfall,and the cumulative rainfall accounts for61.52% of the total rainfall.(3)The interception of rainfall by canopies increased with the increase of rainfall with the linear function model,while the interception rate decreased with the increase of rainfall with the exponential function model.The maximum interception of Salix oritrepha shrub,Salix sclerophylla shrub,Spiraea salicifolia shrub,Rhododendron capitatum shrub,Potentilla fruticose shrub and Rhododendron thymifolium shrub were 8.57 mm,6.29 mm,24.76 mm,12.28 mm,17.91 mm and 8.27 mm respectively,and the theoretical minimum interception rates were 15.85%,14.10%,20.60%,14.79%,14.51% and 12.42% respectively.The changes of precipitation,species,basal diameter and aboveground biomass are the main factors regulating shrub interception and interception rate,which explained 61.9% of the variation of shrub interception of rainfall and interception rate.(4)The throughfall and throughfall rate increased with the increase of rainfall,and the throughfall is linear correlation to rainfall and the throughfall rate is exponential correlation to rainfall.The critical rainfall for throughfall of Salix oritrepha shrub,Salix sclerophylla shrub,Spiraea salicifolia shrub,Rhododendron capitatum shrub,Potentilla fruticose shrub and Rhododendron thymifolium shrub were 0.76 mm,0.92 mm,0.69 mm,0.61 mm,0.64 mm and 1.01 mm,respectively;and the theoretical maximum throughfall rates were 74.10%,78.61%,74.88%,78.51%,79.68% and 83.67%,respectively.Redundancy analysis showed that precipitation and species were the key factors regulating throughfall and throughfall rate,which explained 83.3% of the variation of throughfall and throughfall rate.(5)Stemflow and stemflow rate increased with the increase of rainfall,and showed linear and exponential functions correlation to rainfall,respectively.The critical rainfall for stemflow of Salix oritrepha shrub,Salix sclerophylla shrub,Spiraea salicifolia shrub,Rhododendron capitatum shrub,Potentilla fruticose shrub and Rhododendron thymifolium shrub were 2.50 mm,3.12 mm,2.27 mm,2.97 mm,5.35 mm and 3.21 mm,respectively,and the theoretical maximum stemflow rate was7.56%,7.29%,4.39%,6.56%,4.58% and 4.78%,respectively.Precipitation and leaf area were the key factors regulating stemflow and stemflow rate,which accounted for62.4% of the variation of stemflow and stemflow rate.(6)The funneling ratio of shrub increased exponentially with the increase of rainfall.Spiraea salicifolia shrubhad the highest funneling ratio and Salix oritrepha shrub had the lowest.There was a significant positive correlation between funneling ratio and precipitation,but a significant negative correlation between funneling ratio and plant height,crown width,leaf area and basal diameter.Redundancy analysis showed that precipitation,species and leaf area had the greatest influence on the redistribution process of the precipitation of rainfall by canopies,which could explain75.8% of the variation of redistribution process of the precipitation of rainfall by canopies.