【作者】 单立山；

【导师】 李毅；

【作者基本信息】 甘肃农业大学 ， 水土保持与荒漠化防治， 2013， 博士

【摘要】 根系是植物吸收水分和养分的器官，提供地上部分光合作用的物质基础。不同生境条件下根系在形态特征、空间分布和构型上有较大的差异，研究不同生境条件下根系形态结构、养分特征及其抗旱生理特性，对揭示根系结构和功能对环境因子变异的响应机制以及对环境的生理适应策略具有重要意义。在我国西北干旱半干旱区，以典型荒漠植物红砂和白刺为研究对象，按自然降水梯度在一个较大的自然地域上，采用壕沟法和根系跟踪相结合的方法对红砂和白刺根系进行了整株挖掘。测定了2种荒漠植物根系形态指标和构型参数，并绘制根系分布图；同时采集不同生境条件下2种荒漠植物完整的细根根系，并采用Pregitzer细根分级法对其进行了分级，用细根分析软件（Win-RHIZO2008a）测定了各序级细根形态特征参数，并对各序级细根的养分特征（C、N含量）进行了测定，比较了不同生境条件下2种荒漠植物根系形态特征和构型以及细根的序级结构和功能差异，揭示了2种荒漠植物根系形态特征和构型对环境变化的响应与适应机制，阐明了细根形态结构和功能随序级的变化规律。同时结合控制条件下人工模拟水分梯度实验，测定了不同土壤水分条件下红砂根系的生理参数，比较了典型荒漠植物红砂根系形态结构和功能对水分变化的响应差异，进一步探明了红砂根系形态特征和功能对水分变化的适应机制及抗旱生理机制。结果表明：1.自然条件下2种荒漠植物随降水的减少干旱胁迫程度的增加其主根生长均受到了抑制，但物种不同又有所差异，其中红砂主根生长抑制明显。在西北干旱半干旱区，2种荒漠植物主要通过侧根的形态改变来适应胁迫环境，其中在半干旱区的黄土丘陵沟壑区2种荒漠植物主要是通过侧根的分支增多、侧根数目和总侧根长的增加来适应胁迫环境，而在干旱的河西走廊风沙区2种荒漠植物主要是通过延长侧根的平均连接长度来适应逆境环境，表明2种荒漠植物具有明显的形态可塑性。2.自然条件下2种荒漠植物根系的拓扑指数均较小，根系分支模式均近似为叉状分支结构。红砂和白刺根系具有较好的分形特征，其分形维数分别为(1.18±0.04)和(1.36±0.06)；分形维数、分形丰度与根系平均连接长度均呈显著正相关。2种荒漠植物根系的平均连接长度均较大，以扩大植物的有效营养空间，从而适应干旱贫瘠的土壤环境。2种荒漠植物根系分支前的横截面积等于根系分支后的横截面积之和，验证了Leonardoda Vinci法则。其中根系拓扑指数、根系连接数量、逐步分支率和根系直径等4个根系构型参数能很好地表征2种荒漠植物根系构型特征。3.不同生境条件下红砂根系的拓扑指数均较小，根系分支模式接近叉状分支模式，但在干旱的河西走廊风沙区和戈壁区红砂根系拓扑指数均逐渐增加，表明干旱有使红砂根系分支由叉状分支模式向鱼尾分支模式变化的趋势。干旱的河西走廊风沙区和戈壁区红砂根系分形维数均较小，分别为1.1778、1.1169；而半干旱的黄土丘陵沟壑区分形维数相对较大，为1.3104，且干旱的河西走廊红砂根系总分支率均比半干旱的黄土丘陵沟壑区要小，表明在半干旱的黄土丘陵沟壑区红砂根系分支能力相对较强，随着干旱的增加其分支能力有所减弱。不同生境条件下红砂根系的连接长度都较大，但生境不同却表现出明显差异，其中武威民勤干旱风沙区根系平均连接长度最长。可见，红砂为适应干旱的环境通过减少根系次级分支和根系的重叠、增加根系连接长度，使其根系的分支模式向鱼尾分支模式发展以降低根系内部对营养物质的竞争，提高根系贫瘠土壤水分和养分的吸收效率，保证其正常生长的有效营养空间，从而适应干旱瘠薄的土壤环境。4.自然条件下2种荒漠植物细根的形态结构具有明显的差异，但均以1级侧根数目为最多，占所有序级根数的比例也最大，回归分析表明2种荒漠植物各级细根数量与序级之间均呈现出较好的指数关系。2种荒漠植物随着序级的升高，细根直径、根长均增加，而比根长、组织密度则降低，细根直径和根长随序级的升高呈有规律的变化，均可用指数函数很好的表征；而比根长和组织密度随序级的变化则可用二次函数表征。2种荒漠植物随着根序的上升，C含量和C/N比逐渐增加，而N含量逐渐降低，且2种荒漠植物1级根C、N含量与2、3级根之间差异显著，表明末端根系（1级根）因呼吸作用强主要承担水分和养分的吸收功能，而相对较高级根序细根，因木质化程度较高主要担负运输功能，并贮存碳水化合物。5.人工模拟水分梯度下红砂幼苗根系具有明显的形态可塑性，随土壤水分胁迫程度和根序的不同而各异。首先随着土壤水分胁迫程度的增加红砂幼苗主根的伸长生长受到抑制，但促进了各级侧根的伸长生长并导致了根系总长度的增加；土壤水分胁迫使红砂幼苗根系直径变细、根体积减少，比表面积和比根长增加，且主要是通过低级根系（1级根和2级根）来实现的，表明在土壤水分胁迫下红砂主要是通过低级侧根伸长，根表面积增加，根体积和根直径减少等形态特征的改变来适应逆境环境。然而，随着根序的变化红砂幼苗根系具有明显的形态可塑性，随根序的升高各土壤水分条件下红砂幼苗根长、比根长均显著减少，相反，直径和体积却随根序的升高而显著增加；总根表面积和比表面积随根序的变化略有不同，表现为随根序的升高呈先增加后减少的变化趋势，但较低级根（1级和2级）比表面积占总比表面积的比例较大，表明红砂细根内部具有高度的形态异质性。6.人工模拟水分梯度下红砂幼苗细根的养分特征也随土壤水分胁迫程度和根序的不同而各异，全C含量均随土壤水分胁迫程度的增加而呈减少的变化趋势，而N含量随土壤水分胁迫程度的增加呈现出先减少后增加的趋势；表明在中度土壤水分胁迫条件下红砂细根呼吸作用有所降低。各土壤水分条件下红砂细根全C含量和C/N比随着根序上升而逐渐增加，而细根全N含量呈现出随着根序上升而逐渐降低，表明较低级根序具有较强的呼吸作用与代谢活性。在土壤水分胁迫条件下红砂幼苗根系总生物量和各级侧根生物量均有所增加，且侧根对总根系生物量的增加的贡献最大。然而，在土壤水分胁迫条件下，红砂地上部分生长受到了抑制，特别是叶片开始脱落其生物量降低最大，因而增大了根冠比。土壤水分胁迫程度的增加显著降低了红砂幼苗的蒸腾耗水量，但提高了其水分利用效率。7.土壤水分胁迫对红砂幼苗根系并未形成伤害，随土壤水分胁迫增加红砂幼苗根系活力呈增加趋势，与对照相比，中度土壤水分胁迫和重度土壤水分胁迫根系活力分别提高了12.89%、17.42%，表明在土壤水分胁迫条件下，红砂幼苗仍能保持较高的根系TTC还原力，在逆境环境中为地上部分提供生长所需的养分和水分，保证其正常生长。随土壤水分胁迫的增加根系SOD活性和POD活性有所降低，但差异不显著，然而CAT活性、脯氨酸含量随土壤水分胁迫程度的增强而增加，表明红砂幼苗根系在土壤水分胁迫条件下主要通过增加CAT活性来减轻干旱胁迫中膜脂过氧化作用，清除细胞内过多的H2O2，使其维持在低水平上，保护膜的结构，同时通过增加脯氨酸含量来增强渗透调节能力，表现出更强的抗旱性。在土壤水分胁迫条件下红砂幼苗仍保持较低的MDA含量，表明其细胞膜的并没有出现膜脂过氧化。可见，在土壤水分胁迫下红砂幼苗主要通过能维持较高根系活力、CAT活性、脯氨酸含量以及保持较低的MAD含量来适应土壤干旱胁迫，表现出较强的抗旱特性，这也是红砂能在干旱半干旱区能大量生存和分布的主要原因。更多还原

【Abstract】 The root system is the vegetative organ from which the plants absorb water and nutrition;moreover, it offers the partial material base for photosynthesis. The root system’smorphological characteristics, spatial distribution and architecture show a great difference indifferent habitats conditions. The study of morphology structure, nutrition characteristics andphysiological characteristics against drought of root system in different habitats conditionsplay a significant role in understanding the root morphological structure and functions inresponding mechanism to environmental factors and the strategy of physiological adaptationwithin the different environments.Based on the typical desert plants Reaumuria soongorica and Nitraria tangutorun in aridand semi-arid regions of northwestern China, according to the precipitation gradient, themethod which combined trenching with root-tracking method were used to mine thewhole-plant roots in this research, and its morphological characteristics and architectureparameters were measured, and its root distribution was drew. At the same time, fine rootsunder different habitats were collected and classificated according to the Pregitzer,sclassification method, and then the root analysis software was used to measure themorphology parameters, and the nutrient characteristics（the content of C、N）of the fine rootwas measured. Under different habitats, morphological characteristics and architectureparameters of two desert plants were discussed, and the response mechanism of them toenvironmental variations was revealed, fine root architecture and morphology and functionalcharacteristics were also clarified. Combined with the water gradient experiment of artificialcontrol conditions, the morphology and function of R. soongorica root were compared underdifferent soil moisture conditions. We further prove the response strategy of the morphologycharacteristics and functions of R. soongorica root to soil moisture variations.1. The taproot growth of the two types of desert plants was restrained with the decrease inprecipitation and increase in drought stress. However, there were some discrepancies amongdifferent species, among which the taproot growth of R.soongorica is evidently restrained.These two types of desert plants can adapt the environmental stress through the morphologicalchange in arid and semi-arid regions in Northwest, China. These two types of desert plants inloess hilly and gully region can adapt the environmental stress through the increase of lateralbranches, the increase of the number of lateral branches and the total root length. Nevertheless, these two types of desert plants in sandy area of Hexi Corridor can adapt the bioticenvironment mainly through prolong the average connecting length which demonstrate theobvious morphological plasticity of the two types of desert plants.2. The root topological indices of the two desert plants were small, and the root branchingpatterns were herringbone-like. The roots of the two desert plants had obvious fractalcharacteristics, with the fractal dimension of R.soongorica and N.tangutorum being (1.18±0.04) and (1.3±0.06), respectively. The root fractal dimension and fractal abundance weresignificantly positively correlated with the root average link length. The root average linklengths of the two plants were long，which enlarged the plants’ effective nutrition space，andthus, made the plants adapt to the dry and infertile soil environment. The sums of the rootcross-sectional areas before and after the root bifurcation of the two desert plants were equal,which verified the principle of Leonardo da Vinci. A total of17parameters of rootarchitecture were analyzed by the principal component analysis. The parameters of roottopological structure，numbers of root links，stepwise branching ratio，and root diameter couldwell present the root architecture characteristics of the two desert plants.3. Topological indices of R.soongorica root system are small at all the habitats, and rootbranching pattern tends to be dichotomous. The topological indices of R.soongorica rootsystem gradually increase in the Minqin windblown sand region and the Zhangye Gobi regionin Hexi Corridor, which indicates that drought makes root branching pattern tend to beherringbone-like. Fractal dimension values of R.soongorica root system all are small in theMinqin windblown sand region and the Zhangye Gobi region in Hexi Corridor and the valuesare1.1778and1.1169, respectively. While the fractal dimension values are relative large inJiuzhoutai semi-arid hilly and gully region of the Loess Plateau and the values is11.3104.Total branching ratios of the R.soongorica root system in arid region of Hexi Corridor aresmaller than that in the Jiuzhoutai semi-arid hilly and gully region of the Loess Plateau. Itshows that the root branching ability in the semi-arid region is stronger, and it decreases atsome degree with drought increase. The root link lengths of R.soongorica root system arelong at all the habitats, but there are significant differences between the different habitats. Theroot link length at the Minqin windblown sand region is the longest. It is concluded thatR.soongorica adapts to arid environment by decreasing root branching, decreasing rootoverlap and increasing the root link length, which makes its root branching pattern tend to beherringbone-like to reduce compete degree in root internal environment for nutrients and toenhance root absorption rate to nutrients, and ensure the effective nutrition space, thus it can absorb enough water and nutrients in resource-poor settings to ensure its normal physiologicalrequirements.4. The morphology structure of fine root of two desert plants had an obvious differenceunder the natural condition, but the first order lateral root had high proportion in all the rootorders. Regression analysis showed that there was an exponential relationship between all fineroots of every order and the order for two desert plants. With increasing root order, thediameter and length of fine roots of two desert plants increased, whereas the specific rootlength (SRL) and tissue density decreased. The diameter and root length of fine roots indicateda regular change with increasing of root order, and had a good character with exponentialfunctions, while the change of the specific root length and tissue density could be depicted asthe quadratic function. With increasing root order, the C content and C/N of two desert plantsincreased gradually, whereas the N concent decreased. Moreover, C content and N concenthad significant differences between the first order and order of2ndand3rd. This showed thatfirst order roots mainly undertook the function of absorbing nutrient and water due to theirhigh respiration, while higher order of fine roots played an important role in nutrient andwater transportation and carbohydrate storage owing to the high degree of lignifications.5. The morphological characteristics of R.soongorica seedling roots demonstrated greatvariations under different water gradient and root order. The growth of taproot was inhibitedwith the increase of stress of soil water, but the total length of lateral roots increasedobviously under higher water stress. The diameters and volumes of root also influenced by thedegree of water stress, and specific surface area and specific root length increased with theincrease of water stress, especially for the roots of order1and order2, this results indicatedgreater lateral root length, root surface area, root volumes, and smaller root diameters appearto be important indicators of morphological adaptation of root system in an extreme soilcondition. The morphological characteristics of R.soongorica seedling roots also weredifferent with the change of root orders, and the root length and specific root length decreasedwith increase of root orders, however, the root with higher order has greater root diameter andvolume. The total root surface area and specific surface area showed a more complexvariability under different root orders, and increased in lower order root, followed by adecrease in higher order root. These phenomena indicated the highly morphological variationof fine root system of R. soongorica, and the high development of lateral root with lowerorder was an important strategy in response to the water stress conditions.6. The nutrient characters of fine roots of R. soongorica seedling changed with the different degree of drought stress and root order. The total carbon content decreased with theincrease of soil water stress, but the total nitrogen content firstly decreased and then increasedwith the increase of soil water stress. This showed that respiration of fine roots ofR.soongorica seedling was restrained under different soil water stress condition. Under samesoil water stress condition, the total carbon content and C/N of fine roots of R.soongoricaseedling gradually increased with the increase of root order, but the total nitrogen contentgradually decreased with the increase of root order. This showed that the low roots havestronger respiration and metabolic activity. Under different soil water stress condition, thetotal fine roots and lateral root biomass of R.soongorica seedling were all increased, andlateral root made the greatest contribution to the increase of the total roots biomass, however,under soil water stress condition, the growth of aerial parts of R.soongorica seedling wasrestrained, especially, abscission of the leaves caused the decrease of aerial parts biomass. Sothe root shoot ratio was increased. With the increasing of soil water stress, water consumptionof R.soongorica seedling deceased, but water use efficiency was improved.7. Soil water stress has not done hurt to the root of R.soongorica seedling to some extent,and the root activity of R.soongorica seedling increased with the increase of soil water stress.In compared with the control, the root activities under middle and severe water stress wereincreased by12.89%and17.42%, respectively. This showed, under soil water stresscondition, that the root of R.soongorica seedling still had relatively high TTC deoxidizingability which provides water and nutrients for the growth of the aerial portion to ensure thenormal growth of plant in the hostile environment. SOD and POD activity of roots issomewhat reduced with the increase of soil water stress, but the differences were notsignificant, however, CAT activity and proline content increased with the increase of soilwater stress. This showed, under soil water stress condition, that the root of R.soongoricaseedling mainly decreased lipid peroxidation and clear intracellular excess H2O2by increasingCAT activity to make it maintain at a low level, in order to protect the construction of the cellmembrane under soil water stress, in the meantime, increased ability of osmotic regulation byincreasing proline content, the higher drought resistance ability was represented. R.soongoricaseedling still remained low MDA content under soil water stress condition, and this showedits membranes did not produce lipid peroxidation. So, under soil water stress condition,R.soongorica seedling mainly adapt to soil drought stress by maintaining high root activity,CAT activity and proline content and remaining low MDA content, the high droughtresistance ability was represented. This is main reason why R.soongorica can largely exist anddistribute on arid or semi-arid.更多还原