Canopy Hydrological Process Of Caragana Intermedia In Desert Steppe

The canopy precipitation redistribution,especially the stemflow enrichment effect,is an eco-hydrological process mechanism in which drought-bearing shrubs adapt to arid habitats.The study of the process and pattern of canopy precipitation redistribution by artificial desert Caragana trees in degraded desert grassland has important theoretical significance for elucidating the ecological and hydrological mechanism of maintaining the vegetation pattern of strip-like artificial Caragana intermediaunder the background of soil aridity.Morphological factors are usually the key factors that determine the redistribution and enrichment efficiency of canopy precipitation.From a practical point of view,morphological degradation is an external manifestation of degraded plantation associated with soil aridity;whether and how this degradation affects the ecological and hydrological characteristics of the shrub,which has important research significance for the in-depth analysis of the stability maintenance mechanism of age plantation.In this study,the typical degraded shrubs of the strip-shaped artificial Caragana intermedia in desert steppe were selected as the object(degenerate group),and the natural shrubs of the adjacent natural scattered Caragana korshinskii community were used as the control(healthy group).Based on the comparative analysis of shrub morphological structure,the research work of the canopy precipitation and redistribution patterns,penetration rain and its spatial distribution,sap flow and its relationship with morphological factors,and stemflow hydrological statistical model construction were carried out respectively.The main findings and conclusions are as follows:(1)Morphological characteristics of Caragana intermediaCompared with the scattered middle caragana,the morphological degradation of Caragana intermedia is obvious.Statistical analysis showed that the crown width,base diameter,branching angle,branch length,leaf area,and crown area of Caragana intermedia in the degraded group were significantly lower than those in the healthy group,However,on the shrub scale,the diameter and number of branches were larger than that of the healthy group.The cluster analysis of the branch-scale morphological structure index factors showed that the 33 morphological and structural factor indicators of the healthy group can be generally divided into three categories,namely the overall branch attribute index,the graded branch attribute and the leaf component index group.The inverted trapezoidal structure parameters are related to various types of indicators,and are relatively decentralized,and have a high integrated indication value,which can be seen as a miniature of the entire branch.The degraded group can also be generally grouped into three categories,including the indicator of the internal structure of the branch,the leaf area group and the branch quantity index group.Relatively speaking,the effect of morphological degradation on the morphological structure of branches is still quite obvious:First,the connection between the twig members and leaf members is weakened.Second,the integrated indication value of the inverted trapezoidal structural factor is weakened.Third,the intrinsic correlation between the indicators of branch component attributes is weakened,and the normal processes of branch occurrence and the coordination of branches and components are broken.(2)Canopy precipitation redistribution patternA total of 26 precipitation events were monitored during the experiment,with a minimum of 0.2 mm and a maximum of 40.2 mm for a single rainfall.The mean percentages of total rainfall about stemflow,through rain,and retained water were 8.4%(CV=56%),73.4%(CV=19%),and 18.2%(CV=22%),respectively.With the increase of rainfall,the change of intercepted water did not fluctuate obviously,and the penetrating rain showed an exponential increase.When the rainfall is less than 4.4 mm,the sap flow is negligible;when the rainfall is in 6.0?14.8 mm,the sap flow increases with the increase of precipitation(0.4?2.0 mm);when the rainfall is greater than 24.4 mm,the stemflow with an average of 4.2 mm tends to be stable(3.8?4.6 mm).On small precipitation conditions,morphological changes have little effect on the redistribution pattern of precipitation;when the precipitation is greater than 5 mm,the proportion of retained losses in the healthy group is relatively higher,and the proportion of stemflow is significantly reduced.In small precipitation conditions,morphological changes have little effect on the redistribution pattern of precipitation;when the precipitation is greater than 5 mm,the proportion of retained losses in the healthy group is relatively higher,and the proportion of stemflow is significantly reduced.Penetration and rejection differences are insensitive to changes in precipitation intensity;however,when the intensity is greater than 0.90 mm/h,the proportion of stemflow in the degraded group is significantly increased.In terms of mean value,the ratios of stemflow,through rain,and total rainfall interception in healthy groups were 8.5%,66.7%,and 24.8%,respectively.Degenerative groups were 8.7%,75.4%,and 15.9%,respectively.At the shrub scale,morphological degradation significantly reduced the interception loss of canopy precipitation,and at the same time significantly increased the rate of penetrating rain,but had no significant effect on stemflow.(3)Throughfall hydrological processThe percentage of rain penetration in healthy groups was 7.9%?87.4%,in the degenerative group was 25.4%?88.9%,and the coefficient of variation was 29%and 17%,respectively.The average values of throughfall were 7.13 mm and 7.38 mm.Rainfall,rainfall duration,rainfall intensity and rain penetration have a highly significant linear relationship(P<0.01);however,the relationship between the percentage of penetrating rain and precipitation parameters is more complex and mainly depends on the logarithmic function.The relationship between the coefficient of variation and rainfall,rainfall duration,and rainfall intensity was well fitted with the power function,and the significance of the fit was stronger in the healthy group than in the degenerative group.The effect of morphological factors on the penetration rain of shrub scales was not obvious.Only the branch number,base diameter and shrub projection area of degraded components were significantly correlated with the percentage of rain penetration.However,the morphological degradation had a significant impact on the spatial distribution of penetrating rain.The percentage of penetrating rain in the healthy group generally increased linearly with distance from the base,but the change trend of shrubs in the degraded group was not obvious.(4)Stemflow hydrological processThe percent of stemflow in the healthy group was 0%to 18.1%,in the degenerative group was 0%to 18.9%,and the coefficient of variation was 52%and 69%,respectively.The average stem stalk flow rate was 1.00 mm and 1.14 mm,respectively.The degraded group was 0.14 mm larger than the healthy group;there was no significant difference.There was a highly significant linear relationship between rainfall,rainfall duration,rainfall intensity,and sap flow(P<0.01),However,the relationship between the percentage of stemflow and the characteristic parameters of precipitation was more complicated,mainly with the logarithmic function,and the significance of the regression was better in the degenerative group than in the healthy group.The percentage of stemflow differed significantly in different radial directions.The western part of the healthy group was higher than the eastern part,and the gap between the north and the south was relatively small;the northern part of the degenerative group was higher than the south,and the gap between east and west was relatively small.The percentage of stemflow in the east of the degraded group was significantly higher than that of the healthy group,and stemflow in the southern part of the trunk was significantly lower than that in the healthy group.The correlation between the morphological factors of the shrub scale and the sap flow is better than that of the penetrating rain.There was a linear positive correlation with base diameter,shrub height,branch length,leaf area,shrub projection area,and a linear negative correlation with branching angle.In the degraded group,there was only a significant linear positive correlation between the base diameter of the shrub and the stemflow rate(mL/mm).(5)Stemflow hydrological modelOn the branching scale,there is a significant quadratic polynomial relationship between pre cipitation and confluence rates(R2=0.6202),and 20 mm is the critical point for the relationship between the two changes.There is a negative power function relationship between the baseline and the convergence rate(R'=0.3101).Based on the classification of precipitation,we systemat ically analyzed the regression and fitting relationship between structural factors and stemflow rat es.Under the condition of precipitation experience grading,the degree of branching,branch cro wn,fresh branch weight and leaf fresh weight are the four important factors that determine the stemflow rate.Under the condition of micro-precipitation,the fine-structure factor of the sub-br anch scale plays a key role.Under the condition of small precipitation,the effect of the leaf m ember is prominent and concentrated.However,with the gradual increase of precipitation,the r ole of structural structural factors gradually emerged,and the role of fine structural factors grad ually weakened.mult-variation regression based on experience grouping,0?2 mm:yj-42.438+0.760x5+32.444x16+0.045x10-5.532x1+0.658x25+0.019x7(R3=0.830,P=0.000);2?6 mm:y=10.680+0.272x14+0.624x5(R3=0.916,P=0.001);6?20 mm:y=77.178+162.833x13+44.680x17+0.635x5+11.082x24(P=0.992,P=0.000);20?40 mm:y=-51.131+196.317x13+31.217x24+0.211x 2(R2=0.971,P=0.000).Based on the statistics and grading conditions of multivariate regression trees,first of all,i n addition to the 0?2mm interval,there are fewer explanatory factors for each precipitation int erval.Second,due to the change in the interval division,the factor composition of each interva 1 also changed.mult-variation regression based on multivariate regression trees,0-2.4 mm:y=-42.438+0.760x5+32.444x16+0.045x10-5.532x1+0.658x25+0.019x7(R2=0.933,P=0.000);2.4?4.0 mm:y-24.803+1.427x9+133.155x13(R2=942,p=0.000);4.0?6.8 mm:y=-28.078+0.125x10+16.912x17(R2=0.940,P-0.000);6.8?10.6 mm:y=-143.184+109.382x17+22.619x1(R2=0.944,P=0.000);10.6?40 mm:y=3.593+203.790x13(R2=0.825,P=0.000).