Canopy Hydrological Process of Caragana Intermedia in Desert Steppe
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【Author in Chinese】 古君龙；
【Author's Information】 宁夏大学， 恢复生态学， 2018， 硕士
【Abstract in Chinese】 冠层降水再分配,特别是茎流富集效应是旱生灌木适应干旱生境的一种生态水文过程机制。研究荒漠草原退化人工柠条林(中间锦鸡儿)冠层降水再分配的过程与格局,对阐明土壤旱化背景下带状人工柠条林植被格局维持的生态水文机理,具有重要的理论意义。形态因子是决定冠层降水再分配与富集效率的关键要素。从实践的角度,形态退化也是人工林退化的一种外在表现形式,与土壤旱化相伴相生。形态退化是否以及如何影响灌木的生态水文特性,对于深入剖析旱化成龄人工林的稳定性维持机制具有重要的现实意义。本研究选取荒漠草原带状人工柠条林的典型退化灌丛为对象(退化组),以临近的自然散生中间锦鸡儿群落的天然灌丛为对照(健康组),在灌丛形态结构对比分析基础上,分别开展了冠层降水再分配格局,穿透雨及其空间分布,茎流及其与形态因子的关系,茎流水文统计模型构建等方面的研究工作。主要研究结果与结论如下:(1)中间锦鸡儿形态结构特征相对于散生的中间锦鸡儿,行生的中间锦鸡儿形态退化明显。统计分析表明,退化组中间锦鸡儿的冠幅、基径、分枝角度、枝长、叶面积、冠幅面积均显著低于健康组,但是在灌丛尺度上,其地径、分枝数却大于健康组中间锦鸡儿。分枝尺度形态结构指标因子聚类分析表明,健康组33个形态结构因子指标总体上可以分为三类,即整体分枝属性指标组,分级分枝属性指标组和叶构件指标组。倒梯形结构参数与各类指标都有关联,且相对分散,具有较高的综合指示价值,可以看做整个分枝的微缩。退化组也可大体聚为三类,包括以分枝总体内在格局指标组、叶面积指标组和分枝数量指标组。相对而言,形态退化对分枝形态结构的影响还是比较明显的:首先,枝构件与叶构件的联系弱化。其次,倒梯形结构因子的综合指示价值弱化。第三,分枝构件属性指标间内在关联性弱化,分枝发生与枝叶构件协调建成的正常过程被打破。(2)冠层降水再分配格局实验期间共监测降水事件26次,单次降雨最小值为0.2 mm,最大值为40.2 mm。茎流、穿透雨、截留水占总降雨量的百分比均值分别为8.4%(CV=56%)、73.4%(CV=19%)和18.2%(CV=22%)。随着降雨量的增加,截留水的变化不大,穿透雨呈现出类指数性增加趋势。当降雨量小于4.4 mm时,茎流可忽略不计;降雨量在6.0～14.8 mm时,茎流随降水增加而明显增加(0.4～2.0 mm);当降雨量大于24.4 mm时,茎流量趋于稳定(3.8～4.6 mm),平均值为4.2 mm。小降水条件下,形态变化对降水的再分配格局影响不大;当降水大于5 mm时,健康组截留损失比例相对更高,茎流比例明显降低。穿透和截留差值对降雨强度变化不敏感;但是当降雨强度大于0.90 mm/h时,退化组的茎流比例明显提高。就均值而言,健康组茎流、穿透雨、截留占总降雨量比值分别为8.5%、66.7%和24.8%。退化组分别为8.7%、75.4%和15.9%。在灌丛尺度上,形态退化显著降低了冠层降水的截留损失,同时显著增大了穿透雨比例,但是对茎流无显著影响。(3)穿透雨水文过程健康组穿透雨百分比7.9%～87.4%,退化组为25.4%～88.9%,变异系数分别为29%和17%。穿透雨量均值分别为7.13 mm和7.38 mm。降雨量、降雨历时、降雨强度与穿透雨量都具有极显著的线性关系(P<0.01)。但穿透雨百分比与降水特征参数的关系较为复杂,以对数函数关系为主,穿透雨变异系数与降雨量、降雨历时、降雨强度的关系,以幂函数拟合效果较好,且健康组拟合显著性均强于退化组。形态因子对灌丛尺度的穿透雨影响作用不明显,只有退化组分枝数、基径和灌木投影面积与穿透雨百分比之间存在显著的相关性。但是形态退化对穿透雨的空间分布影响显著,健康组穿透雨百分比普遍随距基部距离的增大而线性增大,但是退化组灌丛变化趋势不明显。穿透雨百分比在不同径向方向上也存在显著差异,西向普遍高于东向,南北间差距相对较小,退化组南北向穿透雨百分比明显高于健康组。穿透雨“旱区”集中出现在健康组灌木的基部,向外百分比逐步提高;退化组分布更为复杂,甚至出现多个“旱区”和“雨极”镶嵌分布的情况,规律性不明显。(4)茎流水文过程健康组茎流百分比为0%～18.1%,退化组为0%～18.9%,变异系数分别为52%和69%。茎流量均值分别为1.00 mm和1.14 mm,退化组比健康组大0.14 mm;均无显著区别。降雨量、降雨历时、降雨强度和茎流都具有显著的线性关系(P<0.01),但茎流百分比与降水特征参数的关系较为复杂,以对数函数关系为主,退化组拟合的显著性高于健康组。茎流百分比在不同径向方向上存在显著差异,健康组西向高于东向,南北间差距相对较小;退化组北向高于南向,东西间差距相对较小。退化组东向茎流百分比明显高于健康组,南向茎流明显低于健康组。灌丛尺度形态因子与茎流的相关性整体好于穿透雨。健康组茎流率(mL/mm)与基径、灌木高度、枝长、叶面积、灌木投影面积呈线性正相关,与分枝角度呈线性负相关。退化组只有灌木基径与茎流率(mL/mm)之间存在显著线性正相关。(5)茎流水文统计模型在单枝尺度上,降水量和汇流率关系符合二次多项式(R2=0.6202,P<0.01),20 mm降雨量是两者关系变化的临界点。基径与汇流率关系符合负幂函数关系(R2=0.3101,P<0.01)。在降水分级基础上,我们系统比较分析了结构因子与茎流率的回归拟合关系。降水经验分级条件下,枝填塞度、单枝冠幅、枝鲜重、叶鲜重是决定茎流率的四个重要因子。微量降水条件下,亚分枝尺度的精细结构因子起关键作用,小降水条件下叶构件作用凸显且集中,但是随降水的逐渐增强,格局性结构因子的作用逐渐显现,而精细结构因子的作用逐步弱化。降水量经验分组下结构因子与茎流率的回归关系模型,0～2 mm:y=-42.438+0.760x5+32.444x16+0.045x0-5.532x1+0.658x25+0.019x7(R2=0.830,P=0.000);2～6 mm:y=-10.680+0.272x14+0.624x5(R2=0.916,P=0.001);6～20 mm:y-77.178+162.833x13+44.680x17+0.635x5+11.082x24(R2=0.992,P=0.000);20～40 mm:y-51.131+196.317x13+31.217x24+0.211x2(R2=0.971,P=0.000)。多元回归树分析中,相对经验分组结果,首先,整体上除0～2mm区间外,各个降水区间的解释因子数量更少。其次,由于区间分割的变化,各个区间的因子构成也有所改变。基于多元回归树的结构因子与茎流率的回归关系模型,0～2.4 mm:y=42.438+0.760x5+32.444x16+0.045x 10-5.532x1+0.658x25+0.019x7(R2=0.933,P=0.000);2.4～4.0 mm:y-24.803+1.427x9+133.155 x13(R2=0.942,P=0.000);4.0～6.8: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)。
【Abstract】 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).