【作者】 刘晓丽；

【导师】 汪有科；

【作者基本信息】 西北农林科技大学 ， 农业水土工程， 2013， 博士

【摘要】 干旱半干旱地区，深层细根吸收土壤中的水分对于旱季林地耗水、维持林木蒸发蒸腾及其生长具有重要的意义。针对黄土丘陵区人工经济林普遍出现的土壤干层问题，本论文以黄土丘陵区人工经济林——矮化密植滴灌枣林（Ziziphusjujube Mill.）为研究对象，以稀植无灌溉枣林为对照，开展深层细根分布及土壤水分特征方面的研究，对该区人工经济林的水分管理及可持续发展具有重要意义。本论文采用根钻法，利用洛阳铲分层获取了从地表至细根分布最大深度范围内的土壤样品，经过室内处理、数据分析，重点研究了密植枣林细根的空间分布特征、基于根系分布的深层土壤水分分层特征、林龄及滴灌对枣林细根分布及土壤水分的影响，得到以下主要结论：（1）密植枣林细根（直径＜2mm）干重密度随土层深度的增加而骤减、随林龄的增长而增加。水平方向上，同林龄枣林各水平位置细根干重密度间无显著差异。但是2年生和4年生枣林在离树干最近位置的细根干重密度较大，离树干最远位置较小；而9年生和12年生枣林在离树干最近及最远（四株树中间）这2个位置的细根干重密度较大，其它位置较小。垂直方向上，枣林（9年生）细根干重密度符合幂函数分布规律，0-0.6m土层细根干重密度总和占整个土层的63%。有序聚类分层凸显了枣林细根垂直分布的特征，枣林细根可划分为细根密集层（0-0.6m）、细根扩散层（0.6-1.6m）及细根稀疏层（1.6-5m）三层。2、4、9和12年生枣林细根干重密度总和分别为619.1，1109.84，1360.14和2319.41g.m^-3，不同林龄枣林细根干重密度总和间有显著差异。（2）枣林细根分布最大深度随林龄的增长而增加，一定林龄后（9年）趋于稳定。2年生枣林细根分布最大深度为2m，4年生枣林细根分布最大深度为4m，9年生和12年生枣林细根分布最大深度均为5m。细根分布最大深度在枣树生长的前4年增加得较快，而在其后5年增加得缓慢，9年以后细根分布最大深度维持稳定，不再增加。不同林龄枣林细根干重密度累计百分比D50均位于0-0.8m土层，但D95随着林龄的增长不断向土层深处延伸。（3）结合根系分布特征进行土壤水分垂直分层的结果更符合林地实际水分消耗状况。将枣林深层土壤水分（2m以下）划分为强耗水层（2.0-4.4m）、弱耗水层（4.4-5.0m）及微弱耗水层（5.0-7.0m）三层。随着林龄增长，根系不断地向深层土壤吸水，导致土壤水分不断被消耗直至接近凋萎湿度，形成一段土壤水分低值区，该低值区位于降水入渗最大深度和细根分布最大深度之间。4年生枣林地土壤含水率在2^-3.6m土层逐渐下降，但其值高于凋萎湿度；9年生和12年生枣林均在1.8^-3.6m土层出现土壤含水率低值区，土壤含水率接近凋萎湿度。这说明，4年生枣林已经开始少量吸收深层土壤水分，9年之后的枣林细根已经大量吸收深层土壤水分，土壤出现了严重的干化现象。细根干重密度和土壤含水率呈负相关关系。（4）灌溉措施对枣林细根干重密度、细根分布最大深度、土壤含水率均有显著影响。密植滴灌枣林的细根干重密度较稀植无灌溉枣林的高，前者（0-5m）细根干重密度为2319.38g.m^-3，后者（0-10m）为1969.06g.m^-3。密植滴灌枣林细根分布最大深度仅为稀植无灌溉枣林的一半，前者细根分布最大深度为5m，后者为10m。密植滴灌枣林土壤含水率均值高于稀植无灌溉枣林，前者土壤含水率为8.52%（0-10m），后者为6.6%。密植滴灌枣林土壤水分低值区的范围较稀植无灌溉枣林上移，前者土壤水分低值区分布于1.8^-3.6m，后者分布于1.8-4.6m。相当于当地年平均降雨量（451.6mm）7.4%的滴灌水量（33.3mm）显著影响了细根分布最大深度和土壤含水率。枣林能够根据上层土壤水分供应状况调整扎根深度。虽然现有枣林出现了土壤干层，但理论上滴灌可以减短细根分布最大深度、减缓深层土壤水分的消耗，甚至抑制黄土丘陵半干旱区人工经济林利用性土壤干层的形成，一定量的滴灌可以维持林地的可持续发展。研究结论对黄土丘陵区枣林水分科学管理有重要的理论指导意义，能为进一步揭示黄土丘陵区人工经济林深层土壤水分的消耗过程、阐明土壤干层形成的机理、抑制土壤干化的形成提供一定的理论基础。更多还原

【Abstract】 Soil water absorbed by deep fine root play an important role in forest land waterconsumption, maintaining forest evapotranspiration, and growing in arid and semiarid region.Oriented at commonly occurred soil dry layer problem in artificial economic forest in loesshilly region, this paper aimed at dwarfed drip irrigated densely jujube plantation primarily,widely jujube plantation without irrigation as control, stuied deep root distribution and soilwater profile dynamics. It would have important significance in artificial economic forestwater management and sustainable development. A soil coring method with a LuoYangshovel was used to obtain root sampling from surface to maximum fine root depth until nomore roots in consecutive two soil layers. Through indoor processing and data analysis, fineroot spatial distribution, deep soil water stratifying characteristic based on root distribution,the effect of stand age and drip irrigation on jujube plantation fine root distribution and soilwater were investigated. The main conclusions of this study were as follows:（1） Fine root dry weight density （diameter<2mm） decreased with soil depth andincreased with stand age. Horizontally, fine root dry weight density was larger in the nearestof the trunk than other position in2and4-yr-old jujube plantation, while it was higher in thenearest of the trunk and the centre of the four trees in9and12-yr-old jujube plantation, and ithad no significant difference among different horizontal position in the same year old jujubeplantation. Vertically, the relation between fine root dry weight density and soil depthconformed to power function,63%of fine roots concentrated in0-0.6m soil layer. Sequentialcluster stratifying results highlighted the fine root vertical distribution characteristic. Fineroots were divided into three layers, i.e. dense root layer （0-0.6m）, diffusion root layer（0.6-1.6m） and sparse root layer （1.6-5m）. The fine root dry weight density was619.1,1109.84，1360.14，2319.41g.m^-3in2,4,9and12-yr-old jujube plantations respectively. Thetotal fine root dry weight had significant difference among different jujube stands.（2） It showed that the maximum fine rooting depth increased with stand age andmaintained stable after9years. The maximum fine rooting depth reached2m in2-yr-old jujube plantation, it extended4m in4-yr-old jujube plantation, it reached5m in a9-year-oldjujube plantation, but it stabilized and did not increase thereafter. And it was5m in9-yr-oldand12-yr-old jujube plantation respectively. The maximum fine root depth extended deepinto the soil rapidly during the first four years, but more slowly in the subsequent five years.The cumulative percent of fine root dry weight density D50was always located in0-0.8m soillayer, but D95extended deeper into soil with stand age.（3） Combined with root distribution characteristic, the stratification result of soil watercould well reflect jujube plantation soil water depletion status. Deep soil water （below2m）was divided into three layers, i.e. strong depletion layer （2-4.4m）, less strong layer （4.4-5m）and weak depletion layer （5-7m）. Root extended deep to absorb soil water gradually withstand age, thus soil water was depleted until wilting point, formed a low soil water zone, andthe low soil water zone was located in the maximum precipitation infiltration depth and themaximum fine root depth. Soil water content decreased gradually between2^-3.6m, and itwas higher than wilting point in4-yr-old jujube plantation. The low soil water zone wasoccurred in1.8^-3.6m both in9-yr-old and12-yr-old jujube plantation, and the soil water wasclose to wilting point. It showed that4-yr-old jujube plantation has depleted deep soil waterslightly, fine root has depleted deep soil water completely after9years, and thus there wasserious dried layer in this soil layer. The relationship between fine root dry density and deepsoil water content was negative.（4） Irrigation has significant effect on fine root dry weight density, the maximum fineroot depth and soil water content. Fine root dry weight density was higher in densely jujubeplantation than widely plantation, and the total fine root dry weight density was2319.38g.m^-3in densely jujube plantation, while it was1969.06g.m^-3in widely jujube plantationrespectively. The maximum fine root depth in densely jujube plantation was only half of thewidely jujube plantation, it extended5m and10m respectively. The profile soil watercontent was higher in densely jujube plantation than widely jujube plantation in0-10m soildepth. It was8.52%and6.6%respectively. The low soil water content zone moved up indensely jujube plantation, it located in1.8^-3.6m in densely jujube plantation and1.8-4.6m inwidely jujube plantation. Irrigation water equivalent to7.4%average rainfall had animportant effect on the maximum rooting depth. Jujube could reasonably adjust root depthaccording to the surface soil water supply status. Although dried layer has occurred in jujubeplantation, drip irrigation could reduce the maximum fine root depth, alleviate deep soil waterconsumption, and inhibit the dried soil layer formation, a certain amount of irrigation couldmaintain the forest land sustainable development.This conclusion has important significance in jujube water management and vegetation restoration. It can provide theoretical basis for revealing the process of deep soil waterconsumption in artificial economic forest.更多还原