【作者】 周朝彬；

【导师】 龚伟；

【作者基本信息】 四川农业大学 ， 森林培育， 2019， 博士

【摘要】 梭梭(Haloxylon ammodendron)是苋科(Amaranthaceae)梭梭属(Haloxylon Bunge)植物,为古尔班通古特沙漠植被建群种,对干旱荒漠生态系统的极端高/低温、干旱以及盐碱等逆境具有极强的适应性。由于树木在长期生长发育过程中,木材(木质部)结构可调整适应不同的生态环境;同时,储存在木质部薄壁组织(射线和轴向薄壁组织)中的非结构性碳(Nonstructural carbohydrates,NSC)可能是树木个体生长发育和存活潜在的限制因子。因此,研究木质部解剖特征和射线的NSC贮存及其径向运输功能,将有助于理解梭梭种群动态及其对环境的进化适应性。本文以梭梭木质部为研究对象,在古尔班通古特沙漠南缘的精河、乌苏、石河子、蔡家湖和奇台等五个地区设置样地,选择砾石、沙土和土质土壤类型,通过野外调查和盆栽试验,研究梭梭木质部生态解剖和射线功能。研究结果如下:(1)梭梭生长轮内深棕色带和浅棕色带之间的过渡明显,属于急变,梭梭木质部具射线组织,单列或多列排列,射线细胞壁有明显增厚现象,厚度2.85μm～3.08μm。导管由直径较大的导管和直径较小的导管组成,2～18个导管聚集分布形成管孔团,可保证梭梭植株体内水分运输的安全性和有效性。管间纹孔互列式或近对列式,导管内呈典型螺纹加厚,导管壁厚3.15μm～5.53μm,螺纹间纹孔单列。纤维细胞壁较厚,为2.64μm～2.97μm。梭梭木质部解剖特征表现出超强的旱生特性,且沙质土壤类型比土质土壤类型具有更强的抗旱性。(2)梭梭大多数木质部解剖特征的地区间变异显著高于地区内树木个体间变异。随着降水量的减少,梭梭木射线密度、射线高度、导管直径和导管壁厚值显著增加(P<0.05),然而,射线细胞壁厚度却降低(P<0.05)。在降水更少的精河地区,梭梭木质部射线密度和射线高度值更大,这有利于梭梭储存更多淀粉和水分,降低水分胁迫。更干旱条件下,梭梭木质部导管直径和导管壁厚度值更大,可有利于提高传导能力的同时减少木质部对干旱导致的空穴化的敏感性。1月均温和4月～6月最大风速与纤维壁厚值显著相关(P<0.05),表明在低温和强风环境中,更厚壁的纤维细胞为梭梭茎杆直立和导管传导提供更强的力学支撑。梭梭木质部解剖特征对气候条件的高度适应性解释了其在亚非沙漠地理上的广泛分布。(3)盆栽模拟试验表明,梭梭幼苗1月龄时出现木射线,此时梭梭茎杆半木质化;在幼苗期,梭梭木射线高度、宽度、细胞壁厚度以及细胞面积在4月～6月迅速增加,7月和8月趋于稳定,这可能是由于环境因子的季节变化所致。从髓心向外,随着树轮年龄增加,成年梭梭木质部射线宽度以及细胞面积显著增加(P<0.05),梭梭木射线解剖特征呈现显著季节和年动态变化。(4)随梭梭树龄增大,木质部的NSC、可溶性糖以及淀粉的径向运输速率呈现出不断增加的规律。梭梭木质部NSC径向运输速率表现为5月和10月高于7月(P<0.05)。可溶性糖径向运输速率的季节变化呈现出5月为最高、7月为最低的规律(P<0.05)。淀粉径向运输速率从5月到10月呈逐渐降低趋势(P<0.05)。可溶性糖径向运输速率与导管长度(P<0.05)、导管直径以及射线高度表现为显著正相关(P<0.01);淀粉径向运输速率与木质部导管长度和直径间关系表现为极显著正相关(P<0.01);NSC径向运输速率与木质部导管直径以及射线高度间表现为极显著正相关关系(P<0.01)。由此表明,梭梭木质部射线的径向运输功能与木射线以及导管的结构相关,且呈明显季节和年际动态。(5)砾石土壤类型中,梭梭木质部的射线密度(4.16条/mm～2)、射线组织比量(7.0%)、NSC含量(5.87%)、可溶性糖含量(1.87%)以及淀粉含量(4.0%)最高,土质土壤类型刚好相反。木质部射线组织比量与NSC(P<0.01)和淀粉含量(P<0.05)间表现出显著正相关关系,木质部射线细胞壁厚度与NSC含量间表现出显著负相关关系(P<0.01)。表明梭梭通过降低射线细胞壁厚度、增加射线比量和NSC含量来适应沙漠的恶劣条件。(6)精河地区梭梭木射线细胞壁厚度(2.85μm)显著低于石河子地区(3.08μm);导管壁厚度(5.53μm)显著高于石河子地区(5.15μm)。在石河子地区,共发现795个上调差异蛋白点和421个下调差异蛋白点。苯丙素生物合成通路、光合作用、糖酵解/糖异生、碳代谢、淀粉和蔗糖代谢、代谢通路、植物激素信号转导、半胱氨酸和蛋氨酸代谢、氨基酸糖和核苷酸糖代谢通路等为细胞壁合成提供底物或能量,促进梭梭木质部细胞壁生物合成。在梭梭木质部细胞壁生物合成过程中,PREDICTED:non-specific lipid-transfer protein-like protein At5g64080-like[Vitis vinifera]、PREDICTED:probable non-specific lipid-transfer protein AKCS9-like[Citrus sinensis])和β-膨胀素EXPB2.1使细胞壁松弛、延展和扩展,木葡聚糖转葡糖苷酶/水解酶对细胞壁木葡聚糖进行剪切和链接;随后,光系统I P700脱辅基蛋白A1、可逆糖基化多肽1以及GDP-甘露糖-3′,5′-异构酶等提供构造成分或能量,促进细胞壁的纤维素、半纤维素、果胶质等合成;最后,苯丙素生物合成通路中差异蛋白促进细胞壁木质化,完成梭梭木质部细胞壁生物合成过程。总之,梭梭木质部解剖特征及射线贮存和径向运输功能表现出对沙漠环境变化的高度适应。环境变化会导致梭梭木质部细胞壁相关的蛋白质表达发生改变。未来可进一步发掘与梭梭木质部细胞壁加厚(尤其是射线)有关的调控基因并进行功能鉴定,并将其应用到人工用材林品种改良中,对于提高人工林木材品质具有重要应用价值。更多还原

【Abstract】 Haloxylon ammodendron,belongs to Amaranthaceae,Haloxylon Bunge,is the constructive species of vegetation in the Guerbantunggut desert.The plant is highly adaptable to extremely high/low temperature,drought and salinity in arid desert ecosystem.The structure of wood(xylem)can be adapted to different ecological environments during the long-term growth and development of trees.Moreover,Nonstructural carbohydrates(NSC)stored in xylem parenchyma tissues(ray parenchyma and axial parenchyma)may be the potential limiting factors for the growth,development as well as survival of trees.Consequently,studies on xylem anatomy,NSC storage and radial transport function of xylem ray will be helpful to understand the population dynamics of H.ammodendron and its evolutionary adaptation to the desert environment.This paper takes the H.ammodendron xylem as the research materials,sample plots are set up in five regions,including Jinghe,Wusu,Shihezi,Caijiahu and Qitai,on the southern Guerbantunggut desert,three edaphic types(gravel soil,sandy soil and loam)are selected,the ecological anatomy and ray function of the H.ammodendron xylem are studied by field investigation and pot experiment.The results are as follows.The transition between dark brown layer and light brown layer is distinct in the growth rings of H.ammodendron,which belongs to abrupt change.The xylem of H.ammodendron has ray tissues,uniseriate or multiseriate.The wall of ray cells is obvious thick with the thickness of 2.85μm～3.08μm.Both wide vessels and narrow vessels exist in the plant xylem,2～18 vessels are aggregated to form pore clusters,which can ensure the safety and efficiency of water transport in H.ammodendron.Intervessel pits are alternate or near opposite,there is spiral thickening in inner wall with wall thickness of 3.15μm～5.53μm,the pits between spiral thickening are uniseriate.The fibers are thick-walled,ranging from 2.64μm～2.97μm.The anatomy of H.ammodendron xylem shows superstrong xerophytic characteristics,and the sandy soil type has stronger drought resistance than the loam type.For most anatomical characteristics,more variation is explained by region than by tree(within-region variation).With the decrease of precipitation,the ray density,ray height,diameter of vessel and wall thickness of vessel in H.ammodendron raise significantly(P<0.05),but the wall thickness of ray cell reduce(P<0.05).Xylem responds to low precipitation by increasing ray density and ray height to improve the storage of water and starch to combat drought stress in Jinghe.In an arid region(Jinghe),H.ammodendron has wide vessels to improve conductivity.Moreover,they increase the vessel wall thickness to decrease its sensitivity to embolism caused by drought stress.Both average temperature in January and maximum wind velocity from April to June are significantly related to the wall thickness of the fiber(P<0.05),indicating that a thicker fiber cell wall could provide higher mechanical resistance to steady stems and improve vessel conduction in low temperature and strong wind conditions.These results indicate that there is high adaptation in the xylem anatomical structures of H.ammodendron in response to different desert climates and also explain the adaptation of the plant to a wide range of Asian and African deserts.The simulated pot experiment shows that rays appear when the H.ammodendron seedlings at the 1-month-old age,and the stem of H.ammodendron is semi-lignified.During the seedling stage,the ray height and width,wall thickness of ray cell and area of ray cell in H.ammodendron enhance rapidly from April,May to June,and stabilize in July and August,which may be caused by seasonal changes in environmental factors.From pith to outside in xylem of H.ammodendron adults,the ray width and area of ray cell enhance significantly with the increases of tree ring ages(P<0.05).The anatomical characteristics of rays in H.ammodendron show significantly seasonal and annual dynamic changes.The radial transport rates of NSC,soluble sugar and starch in H.ammodendron xylem increase significantly with the tree age(P<0.05).In different seasons,the radial transport rate of NSC is higher in May and October than in July(P<0.05).The radial transport rate of soluble sugar in H.ammodendron is the highest in May,and then in July,and there is a significant difference exists among seasons(P<0.05).The starch radial transportation rate decreases from May to October,and a significant difference is found among the seasons(P<0.05).There is a significant positive correlation between vessel length and the radial transport rate of soluble sugar(P<0.05),vessel diameter and the radial transport rate of soluble sugar(P<0.01),ray height and the radial transport rate of soluble sugar(P<0.01),vessel length as well as diameter and the radial transport rate of starch(P<0.01),vessel diameter and the radial transport rate of NSC(P<0.01)as well as ray height and the radial transport rate of NSC(P<0.01).The radial transport function of H.ammodendron xylem is related to the anatomical structure of xylem ray and vessel,and shows obvious seasonal dynamics.The highest values of ray density(4.16 n/mm～2),ray proportion(7.0%),NSC(5.87%),soluble sugar(1.87%)and starch(4.0%)are found in gravel soil,the values in loam are just the opposite.The ray proportion is positively correlated with NSC(P<0.01)and starch(P<0.05),and a negative correlation is found between the wall thickness of ray cell and NSC(P<0.01).These results indicate that H.ammodendron cope with the severe conditions,through decreasing the wall thickness of ray cell,increasing ray proportion and NSC.The wall thickness of ray cell in Jinghe(2.85μm)is significantly lower than that in Shihezi(3.08μm)(P<0.01),but the wall thickness of vessel in Jinghe(5.53μm)is significantly higher than that in Shihezi(5.15μm).In Shihezi region,totally 795differentially expressed proteins are upregulated and 421 differentially expressed proteins are downregulated.The phenylpropanoid biosynthesis,photosynthesis,glycolysis/gluconeogenesis,carbon metabolism,starch and sucrose metabolism,metabolic pathways,plant hormone signal transduction,cysteine and methionine metabolism,amino sugar as well as nucleotide sugar metabolism etc.promote cell wall biosynthesis of H.ammodendron xylem through providing substrates or energy.During the process of cell wall biosynthesis in the H.ammodendron xylem,the proteins(including PREDICTED:non-specific lipid-transfer protein-like protein At5g64080-like[Vitis vinifera],PREDICTED:probable non-specific lipid-transfer protein AKCS9-like[Citrus sinensis]and beta expansin EXPB2.1[Mirabilis jalapa])first make the cell wall loosening,extension as well as expansion,and the xyloglucan endotransglycosylase/hydrolase 1 cut off and link the xyloglucan chains.Then the photosystem I P700 apoprotein A1,reversibly glycosylated polypeptide 1 and GDP-mannose-3′,5′-epimerase etc.involve in the cellulose,hemicellulose and pectin biosynthesis of the cell wall through providing the components or energy.Finally,the proteins in the phenylpropanoid biosynthesis promote the lignification of cell walls and complete the biosynthetic process of cell walls.In conclusion,our results indicate that significant adaptation of both the anatomical features and ray storage as well as radial transport function in H.ammodendron xylem to variations of desert environment.Environment variations can also result in the changes of differentially expressed proteins associated with the cell walls of the H.ammodendron xylem.The regulatory genes related to thick-walled tissues(especially ray cell)in H.ammodendron can be further explored and their functions be identified,and the genes can be applied to the improvement of timber forest,which is of great practical value in improving the wood properties of timber forest.更多还原