不同抗旱性青稞LEA2/LEA3蛋白基因的克隆与表达

作物的抗旱性是一个多基因控制的、极为复杂的数量性状，植物对干旱在分子水平上的差异反应通过植物组织生理和细胞生物学水平，最终表现为植物抗旱性的不同。在我国，旱地农业超过耕地面积的50%，但水资源短缺，因此培育和选育抗旱高产作物是发展节水型农业最有效的途径。 青藏高原气候恶劣、年均降雨量少，也是世界大麦初生起源中心，因而蕴藏了十分丰富的与抗逆相关的种质资源材料，从这些特殊的资源材料克隆抗旱基因，不仅对培育抗旱、优质、高产大麦新品种具有重要理论意义和经济价值，而且对整个作物抗旱基础和育种应用研究都具重大促进作用。 为了筛选青稞（裸大麦，Hordeum vulgare ssp. vulgare）抗旱性材料，本研究选用来自青藏高原不同地区的84份青稞为材料，在叶片失水率(water loss rate, WLR)检测分析的基础上，选择失水率值差异显著的12个品种，通过相对含水量（relative water content, RWC）和反复干旱法评价其抗旱性，并通过植株对干旱胁迫下的丙二醛（MDA）含量和游离脯氨酸（free-proline）含量变化，了解不同抗旱性材料的生理反应特性。选择抗旱性强弱不同的品种各两份进行LEA2蛋白基因(Dhn6基因)、LEA3蛋白基因(HVA1基因)的克隆，比较LEA蛋白结构差异与作物抗旱性之间的关系。同时，对抗旱性不同的青稞品种受到干旱时间不同的失水变化率（dynamics water loss rate, DWLR）进行了检测；对抗旱性不同的青稞对照材料进行2 h、4 h、8 h和12 h的快速干旱处理，通过SYBR Green实时荧光定量RT-PCR技术对Dhn6基因、Dhn11基因、Dhn13基因和HVA1基因在不同抗旱性材料受到不同干旱时间处理后的相对表达水平进行了检测。本研究对LEA蛋白基因在抗旱性不同的青稞材料中的干旱胁迫分子水平上的差异反应进行了研究，也对植物的抗旱机理进行了初步探讨。主要研究结果如下： 1. 青稞苗期进行离体叶片失水率测定结果表明，来自青藏高原的84份青稞材料的WLR在0.086~0.205gh-1g-1DW之间。选择WLR低于0.1gh-1g-1DW和WLR高于0.18gh-1g-1DW的品种各6份，并对苗期分别进行未干旱及干旱12小时的处理。相对含水量检测结果表明，低失水率青稞材料干旱后的具有更高的相对含水量，盆栽缺水试验也显示叶片失水率低的材料耐旱能力强于失水率高的材料。通过水合茚三酮法测定离体叶片游离脯氨酸的含量，结果表明，所有品种未干旱处理时，游离脯氨酸含量差异不大（17.10~25.74 µgg-1FW）；干旱12小时后，低失水率的品种游离脯氨酸含量明显增高（32.99~53.45µgg-1FW），高失水率品种的游离脯氨酸含量与干旱前变化不明显(P<0.05)。硫代巴比妥酸法测定离体叶片丙二醛(MDA)含量，结果显示，12份所选对照品种中，丙二醛的含量在0.97~2.74nmolg-1FW，干旱12小时后丙二醛的含量显著上升（1.46~4.74nmolg-1FW），高失水率的6个品种的丙二醛含量在未干旱和干旱处理时都明显高于低WLR品种。本研究结果表明青稞的低失水率、低丙二醛含量、高相对含水量和高脯氨酸含量具相关性（P<0.05）。综上研究，我们认为作物失水率的测定可以作为快速检测作物抗旱性的指标之一，因此，强抗旱品种喜玛拉10号(TR1)、品比14号(TR2)和弱抗旱品种冬青8号(TS1)、QB24 (TS2)被选作抗旱基因克隆和表达分析的研究材料。 2. 高等植物胚胎发育晚期丰富蛋白(late embryogenesis abundant proteins, LEA proteins)与植物耐脱水性密切相关，为了探讨青稞LEA蛋白结构差异性与植物抗旱性的关系，本研究以强抗旱品种（喜玛拉10号、品比14号）和弱抗旱品种（冬青8号、QB24）为材料，利用同源克隆法，通过RT-PCR，分别克隆了与抗旱性密切相关的Dhn6基因和HVA1基因。Dhn6基因序列分析结果表明，强抗旱品种品比14号和弱抗旱品种冬青8号Dhn6基因所克隆到的序列为1026bp，它们之间只有5个碱基的差异；喜玛拉10号和QB24克隆到的序列长963bp。在强弱不同的抗旱品种中有22个核苷酸易突变位点，相应的脱水素氨基酸序列推导结果表明，22个核苷酸突变位点中，仅有8个位点导致相应的氨基酸残基的改变，其余的位点系同义突变，另外，21个富含甘氨酸序列的缺失并没有联系作物抗旱性特征。推测这些同义突变位点的氨基酸残基对维持青稞DHN6蛋白的正常结构和功能起着非常重要的作用，也可能DHN6蛋白对青稞长期适应逆境胁迫和遗传进化的结果。对HVA1基因的序列分析结果表明，冬青8号、QB24、品比14号和喜玛拉10号的目的基因核苷酸序列全长分别为661bp、697bp、694bp和691bp，它们都包含1个完整的开放阅读框。相应的LEA3蛋白氨基酸序列结果表明，11个高度保守的氨基酸残基组成基元重复序列的拷贝数与青稞抗旱性之间没有必然关系，在强抗旱品种（喜玛拉10号、品比14号）中三个共同的氨基酸突变位点Gln32、Arg33和Ala195可能对抗旱蛋白的结构和功能有影响；另外，强抗旱青稞品种LEA3蛋白质中11-氨基酸保守基元序列拷贝数和极性氨基酸占蛋白的比例更高，推测LEA3蛋白中基元序列拷贝数和极性氨基酸占蛋白的比例对该蛋白的结构和功能影响更大。 3. LEA蛋白基因的表达水平的上调与植物的耐脱水性密切相关，我们对强抗旱性材料（喜玛拉10号、品比14号）和弱抗旱材料（冬青8号、QB24）进行干旱处理2 h、4 h、6 h、8 h和10 h的失水变化率进行测定，结果表明弱抗旱品种在2~4小时之间失水率变化最明显，而四个对照品种的失水率在8小时后和24小时的失水率值变化不大。进一步提取青稞苗期进行2 h、4 h、8 h和12 h的干旱处理后的总RNA，通过SYBR Green实时荧光定量RT-PCR技术对青稞脱水素基因(Dhn6、Dhn11和Dhn13)和LEA3蛋白基因(HVA1)的相对表达水平受干旱时间和作物抗旱性的影响进行了检测。研究发现，抗旱性不同的青稞品种随干旱处理的时间延长，Dhn6、Dhn11、Dhn13和HVA1基因的相对表达水平不同。 Dhn6基因的相对表达水平在强抗旱青稞品种干旱8小时后快速上升，但在弱抗旱青稞品种干旱处理12小时后检测到更高表达量；Dhn11基因在对照青稞抗旱品种的表达累积水平随干旱时间的延长持续下降；整个干旱过程中，Dhn13基因的相对表达水平在弱抗旱品种持续上升，在强抗旱品种中干旱处理8小时快速上升并达到最高，干旱12小时后降低。与脱水素基因相比较，强抗旱青稞品种在干旱2小时后HVA1基因的相对表达水平显著升高，相对表达量随干旱处理的时间持续上升，在干旱12小时后达到最高；与之相比较，在整个干旱过程中，弱抗旱品种的相对表达水平显著低于强抗旱品种，在干旱8小时之前弱抗旱品种的相对表达水平变化不明显；在干旱8~12小时后却显著上升。上述结果表明，不同的LEA蛋白在植物耐脱水过程中的干旱表达累积水平不同；干旱不是诱导高等植物Dhn11基因表达的主要因素；植物的抗旱性不同，不同LEA蛋白基因对干旱的反应有差异。推测某些LEA蛋白基因的干旱胁迫早期表达累积程度与植物的抗旱性直接相关；其中，Dhn11基因和Dhn12基因不同的表达模式可能与干旱调控表达顺式作用成分(dehydration responsive element, DRE)的有无或结构上的差异有关。 本研究结果认为，(1)失水率和相对含水量可作为植物抗旱性检测的指标之一；(2) DHN6同义突变位点的氨基酸残基对维持该蛋白的正常结构和功能起着重要作用；(3) 11-氨基酸保守基元序列拷贝数和极性氨基酸的比例对LEA3蛋白结构和功能有重要影响；(4)LEA蛋白表达随着干旱胁迫程度而增加，但Dhn11基因并不受干旱诱导表达；(5)作物的抗旱性不同，LEA蛋白对干旱的累积反应并不相同，干旱早期LEA蛋白的累积程度可能会影响植物的抗旱性。 Drought resistance was a complex trait which involved multiple physiological and biochemical mechanisms and regulation of numerous genes. Because its complex traits, it is difficult to understand the mechanisms of drought resistance in plants. Plants respond to water stress through multiple physiological mechanisms at the cellular, tissue, and whole-plant levels. Tibetan hulless barley, a pure line, is a selfing annual plant that has predominantly penetrated into the Qinghai-Tibetan Plateau and remains stable populations there. The wide ecological range of Tibetan hulless barley differs in water availability, temperature, soil type and vegetation, which makes it possess a high potential of adaptive diversity to abiotic stresses. This adaptive genetic diversity indicates that the potential of Tibetan hulless barley serves as a good source for drought resistance alleles for breeding purposes. 12 contrasting drought-tolerant genotypes were selected to measure relative water content (RWC), maldondialdehyde (MDA) and proline content, based on values of water loss rate (WLR) and repeated drought methods from Tibetan populations of cultivated hulless barley. As a result of the screening, sensitive and tolerant genotypes were identified to clarify relationships between characteristics of LEA2/LEA3 genes sequences and expression and drought-tolerant genotypes, associated with resistance to water deficit. In addition, dynamics water loss rate (DWLR) was measured to observe the changes on diffrential drought-tolerant genotypes. Real-time quantitative RT-PCR was applied to detect relative expression levels of Dhn6, Dhn11, Dhn13 and HVA1 genes in sensitive and tolerant genotypes with 2 h, 4 h, 8h and 12 h of dehydration. In the present study, differential sequences and expression of LEA2/LEA3 genes were explored in Tibetan hulless barley, associated with phenotypically diverse drought-tolerant genotypes. 1. The assessments of WLR and RWC were considered as an alternative measure of plant water statues reflecting the metabolic activity in plants, and the parameters of MDA and proline contents were usually consistent with the resistance to water stress. The values of detached leaf WLR of the tested genotypes were highly variable among 84 genotypes, ranging from 0.086 to 0.205 g/h.g DW. The 12 most contrasting genotypes (6 genotypes with the lowest values of WLR and 6 genotypes with the highest values of WLR) were further validated by measuring RWC, MDA and free-proline contents, which were well watered and dehydrated for 12 h. Results of RWC indicated that the values of 12 contrasting genotypes RWC ranged from 89.94% to 93.38% under condition of well water, without significant differences, but 6 genotypes with lower WLR had higher RWC suffered from 12 h dehydration. The results indicated that lower MDA contents, lower scores of WLR and higher proline contents were associated with drought-tolerant genotypes in hulless barley. Remarkably, proline amounts were increased more notable in 6 tolerant genotypes than 6 sensitive genotypes after excised leaves were dehydrated for 12 h, with control to slight changes under condition of well water. Results of MDA contents showed that six 6 tolerant genotypes had lower MDA contents than the 6 sensitive genotypes under both stressed and non-stressed conditions. As a result of that screening, drought- resistant genotypes (Ximala 10 and Pinbi 14) and drought-sensitive genotypes (Dongqing 8 and QB 24) were chosen for comparing the differential characteristics of LEA2/LEA3 genes and their expression analysis. It was conclusion that measurements of WLR could be considered an alternative index as screening of drought-tolerant genotypes in crops. 2. Late embryogenesis abundant (LEA) proteins were thought to protect against water stress in plants. To explore the relationships between configuration of LEA proteins and phenotypically diverse drought-tolerant genotypes, sequences of LEA genes and their deduced proteins were compared in Tibetan hulless barley. Results of comparing Dhn6 gene in Ximala 10 and QB24 indicated that absence of 63bp was found, except that only 5 mutant nucleotides were found. While 22 mutant sites were taken place in Dhn6 gene between sensitive and tolerant lines, 14 synonymous mutation sites appeared in the contrasting genotypes. The additional/absent polypeptide of 21 polar amino acid residues was not consistent with phenotypically drought-tolerant genotypes in hulless barley. It was deduced that synonymous mutation sites would play important roles in holding out right configurations and functions on DHN6 protein. The sequencing analysis results indicated that each cloned HVA1 gene from four selected genotypes contained an entire open reading frame. The whole sequence of HVA1 gene from Dongqing 8, QB24, Pinbi 14 and Ximala 10 was respectively 661bp, 697bp, 694bp and 691bp. Results of DNA sequence analyses showed that the differences in nucleotides of HVA1 gene in sensitive genotypes were not consistent with that of tolerant genotypes, except for absence of 33 nucleotides from +154 to +186 (numbering from ATG) in QB24. Database searches using deduced amino acid sequences showed a high homology in LEA3 proteins in the selected genotypes. Multiple sequence alignments revealed that LEA3 protein from Dongqing 8 was composed of 8 repeats of an 11 amino acid motif, less the fourth motif than Pinbi 14, Ximala 10 and QB24. Consistent mutant amino acid residues appeared in contrasting genotypes by aligning and comparing the coding sequence region, including Gln32, Arg33 and Ala195 in tolerant genotypes as compared to Asp32, Glu33 and Thr195 (Thr184 in Dongqing 8) in sensitive lines. It was concluded that consistent appearance of Gln32, Arg33 and Ala195 would contributed to functions of LEA3 protein in crops, as well as higher proportion of 11-amino-repeating motifs and polar amino acid residues. 3. Most of the LEA genes are up-regulated by dehydration, salinity, or low temperature, are also induced by application of exogenous ABA, which increases in concentration in plants under various stress conditions and acts as a mobile stress signal. Higher levels of proteins of LEA group 3 accumulated was correlated well with high level of desiccation tolerance in severely dehydrated plant seedlings. Dehydrins (DHNs), members of LEA2 protein, are an immunologically distinct protein family, and Dhn genes expression is associated with plant response to dehydration. Dynamic water loss rate was measured between sensitive genotypes and tolerant genotypes after they were dehydrated for 2 h, 4 h, 6h and 8 h. Detailed measurements of WLR at the early stage of dehydration (2, 4, 6, and 8 h) showed that WLR was stabilizing after 8 h, and there were no significant changes between these values and WLR after 24 h. Drought stress was applied to 10-day-old seedlings by draining the solution from the container for defined dehydration periods. Leaf tissues of the selected genotypes were harvested from control plants (time 0); and after 2, 4, 8, and 12 h of dehydration. Differential expression trends of Dhn6, Dhn11, Dhn13 and HVA1 genes were detected in phenotypically diverse drought-tolerant hulless barleys, related to different time of dehydration. Results of quantitative real-time PCR indicated that relative level of HVA1 expression was always higher in tolerant genotypes, rapidly increasing at the earlier stages (after 2-4 h of dehydration). However, HVA1 expressions of sensitive genotypes had a fast increase from 8 h to 12 h of stress. Significant differences in expression trends of dehydrin genes between tolerant genotypes and sensitive lines were detected, mainly in Dhn6 and Dhn13 gene, depending on the duration of the dehydration stress. The relative expression levels of Dhn6 gene were significantly higher in tolerant genotypes after 8 h dehydration, by control with notable higher expression levels after 12 h water stress in sensitive ones. The relative expression levels of Dhn13 gene tended to ascend during exposure to dehydration in drought-sensitive genotypes. However, fluctuate trends of Dhn13 expression level were detected in drought-resistant lines, including in lower expression levels of 12 h dehydration as compared to 8 h water stress. It was conclusion that (1) diverse LEA proteins would play variable roles in resisting water stress in plants; (2) expression of Dhn11 gene was not induced by dehydrated signals because of the trends of expression descended in contrasting genotypes suffered from water deficit and (3) variable accumulations on LEA proteins would be appear in diverse drought-tolerant genotypes during dehydrations. It is deduced that higher accumulations of Dhn6 and Dhn13 expression in 8 h dehydration are related to diverse drought-tolerant lines in crops. The present results indicated that different dehydrin genes would play variable functional roles in resisting water stress when plants were suffered from water deficit. The authors suggest physiologically different reactions between resistant and sensitive genotypes may be the results of differential expression of drought-resistant genes and related signal genes in plants. In addition, contrarily induced expression of Dhn11 and Dhn12 was related to dehydration responsive element (DRE) in barleys. The present study indicated that (1) measurements of WLR and RWC could be considered as one index of drought-tolerant screenings; (2) synonymous mutation sites would play important roles in holding out right configurations and functions on DHN6 protein, (3) higher proportion of 11-amino-repeating motifs and polar amino acid residues would contribute to functions on LEA3 protein, (4) the longer drought, the more accumulation on LEA proteins, except for Dhn11 gene in crops and (5) differential responses on expression of LEA protein genes would result in physiological traits of drought tolerance in plants.

水分亏缺对番茄生理特性及水分生产效率的影响

根据番茄的生长发育特点,分别以50%、60%、75%田间持水量作为苗期、开花坐果期、结果期的土壤水分下限,每个生育期的土壤水分上限设置3个水分水平,研究不同生育期水分亏缺和亏缺程度对番茄生长发育及生理特性的影响。结果表明,不同生育期的水分亏缺对番茄株高、茎粗、叶绿素相对含量、日光合及蒸腾速率变化等均有不同程度的影响,呈现明显的生长与生理补偿效应,水分胁迫处理的日光合速率峰值提前出现,蒸腾速率随水分亏缺程度的增加而减少,这有助于调控番茄无用的蒸腾耗水。通过对番茄不同生育期的灌水量和产量关系的研究得出,当全生育期灌水量为4025.80 m3/hm2时,番茄可以获得最高产量12.84×104kg/hm2。

冠层温度-气温差与作物水分亏缺关系的研究

试验研究了冬小麦在不同土壤水分条件下拔节～抽穗期冠层温度-气温差变化规律及其随作物生长发育期的变化状况。结果表明,作物在充分供水条件下冠层温度-气温差变化较平缓;缺水时变化较大。冠层温度-气温差随作物生长发育期的变化趋势为低水分处理高于高水分处理。冠层温度-气温差可较合理反映土壤水分变化状况和作物水分亏缺程度。

水肥交互作用对黄土高原南瓜光合特性及其产量的影响

通过不同的灌水和施肥处理,研究水肥交互作用对南瓜光合特性日变化及产量的影响,结果表明:水分与施肥因子对南瓜叶片的光合特性和产量有重要影响,在水分胁迫的情况下,肥水交互作用不显著,在水分较低的情况下,二者表现互为限制条件的协同作用;在水分较高的情况下,肥水交互作用转变成顺序加和作用。其中单因素效应大小表现为:氮>水>磷,耦合效应大小表现为:氮与水耦合>氮与磷耦合>磷与水耦合。在水分适宜时,适宜的施肥量(施氮量50kg/hm2、施磷量35 kg/hm2)可以提高南瓜光合速率和产量,不施肥或施肥量过高都会影响南瓜光合速率和产量。

干旱和复水条件下转基因甘薯的光合特性

以转铜锌超氧化物歧化酶(Cu/Zn SOD)和抗坏血酸过氧化物酶(APX)基因甘薯(TS)及未转基因甘薯(NT)为实验材料,研究在旱后复水条件下转基因甘薯及未转基因甘薯抗氧化酶活性和光合特性变化。结果显示,连续36 h胁迫条件下,TS和NT的SOD活性都先降低后升高,但TS的SOD活性始终高于NT。胁迫至24 h时,TS的SOD活性约为NT的1.2倍,复水后二者SOD活性都下降。持续胁迫,TS的APX活性先升高后降低,NT与之相反,复水后TS和NT的APX活性都是先升高后降低,复水12 h,TS的APX活性是NT的1.5倍。水分胁迫条件下TS的膜质受伤害程度要轻于NT,胁迫24 h,复水12 h,NT的MDA含量均约为TS的1.2倍。胁迫12 h,TS和NT净光合速率都下降,继续胁迫,TS净光合速率开始上升,NT几乎保持不变,胁迫36 h,TS的净光合速率约为NT的1.5倍。复水后二者净光合速率都开始上升,复水12 h,TS净光合速率约为NT的3倍。胁迫时TS、NT胞间CO2浓度(Ci)都逐渐增大,胁迫36 h时NT胞间CO2浓度显著高于TS,是其1.4倍。实验结果表明,同时转入SOD、APX抗氧化基因后,在...

土壤水分与短期遮光对棉花光合及其气孔响应的影响

以陆地棉 (Gossypium hirsutum L.Zhongmain No.2 3)为供试材料 ,探讨了在充分供水-水分胁迫 -复水的处理过程中 ,短期不同遮光水平对棉花光合特性及其气孔响应的影响。结果表明 ,在水分处理过程中 ,所有不同遮光水平的棉花叶片对短期遮光具有相似的基本响应规律 :短期遮光使净光合速率迅速降低 ,气孔导度减少 ,但减少速率缓慢 ;遮阳网去掉后 ,叶片气孔重新开放速率和光合恢复被延迟。水分胁迫期间 ,所有遮光处理的水分利用效率均最高 ,但净光合速率均较低 ,光合及其气孔响应受到严重限制 ,遮光 75%受到的影响大于遮光 40 %的处理。复水后水分胁迫带来的残留影响仍然存在 ,结果使水分利用效率在整个水分处理过程中最低 ,遮光 75%的处理尤为明显。上述表明 ,土壤水分与短期遮光对棉花光合及其气孔响应的影响十分显著

水分处理对油菜叶位光合速率、蒸腾速率及水分利用效率的影响

通过对不同水分处理下油菜不同叶位叶片光合速率(Pn)、蒸腾速率(E)和水分利用效率(WUE)的测定表明,油菜主茎叶片的光合速率、蒸腾速率和水分利用效率随叶位的降低而降低;干旱胁迫下油菜水分利用效率显著提高,光合速率变化不明显,但上部、下部叶间光合速率差异大。充分供水时叶片的蒸腾速率提高,水分利用效率则降低,从上到下叶片水分利用效率、光合速率降低不剧烈,而蒸腾速率表现为上部和下部叶高,而中部叶低。据测定,干旱处理下油菜单株生物量为37.45g,充分供水时为38.76g,干旱导致油菜生物量降低;水分胁迫能提高作物水分利用效率;在充分供水条件下叶片蒸腾速率较高,这可能是气孔行为的结果。

土壤干旱胁迫下沙棘休眠、萌芽期内源激素变化及外源GA_3的调节

研究了２年生中国沙棘（Ｈｉｐｐｏｐｈａｅ ｒｈａｍｎｏｉｄｓ）在土壤干旱胁迫下苗木含水量、内源激素水平与萌芽率关系以及萌芽关键期喷施外源ＧＡ３的作用。结果表明：土壤干旱胁迫使冬季休眠与春季萌芽期苗木含水量、内源ＧＡ１／３降低，内源ＡＢＡ明显提高，ＧＡ１／３ＡＢＡ下降，达到萌动所需的调控阈值的时间延迟，重度干旱下苗木萌芽延迟约２５ｄ，且萌芽后的枝生长十分缓慢；中度干旱下苗木萌芽延迟１０ｄ，萌芽后生长亦有所抑制。喷施８０ｍｇ／Ｌ外源ＧＡ３溶液可有效提高重度干旱下苗木内源ＧＡ１／３，降低ＡＢＡ含量，使ＧＡ１／３／ＡＢＡ提高，促进苗木提早萌芽及萌芽后生长；在适宜水分及中度干旱下，沙棘苗木外施ＧＡ３对萌芽及其生长作用不明显。

不同生育期干旱对冬小麦产量及水分利用效率的影响

用盆栽对冬小麦不同生育阶段进行不同程度水分调亏试验结果表明 :拔节—孕穗期、抽穗—扬花期和灌浆—成熟 3个阶段内 RW上限为 4 0 %、5 0 %、60 %的水分亏缺均引起了产量的极显著下降 ,而且水分亏缺越严重 ,产量降低越大。在 3个生育阶段内进行 RW上限为 4 0 %的水分调亏减产幅度都很大 ,而且 3个生育阶段之间差异不明显 ;进行 5 0 %、60 %水分调亏 ,其减产程度则与生育期有关。灌浆—成熟期的减产程度大于前二个时期 ,这可能与前二个阶段复水后作物的补偿生长有关。不同生育期水分亏缺对冬小麦产量构成因素的影响也不同 ,拔节—扬花期水分亏缺主要减少了穗粒数 ,灌浆—成熟阶段的水分亏缺主要减少了千粒重

Probabilistic modelling of soil moisture dynamics of irrigated cropland in the North China Plain

A probabilistic soil moisture dynamic model is used to estimate the soil moisture probability distribution and plant water stress of irrigated cropland in the North China Plain. Soil moisture and meteorological data during the period of 1998 to 2003 were obtained from an irrigated cropland ecosystem with winter wheat and maize in the North China Plain to test the probabilistic soil moisture dynamic model. Results showed that the model was able to capture the soil moisture dynamics and estimate long-term water balance reasonably well when little soil water deficit existed. The prediction of mean plant water stress during winter wheat and maize growing season quantified the suitability of the wheat-maize rotation to the soil and climate environmental conditions in North China Plain under the impact of irrigation. Under the impact of precipitation fluctuations, there is no significant bimodality of the average soil moisture probability density function.

CO2H2O and energy exchange of an Inner Mongolia steppe ecosystem during a dry and wet year

We used an eddy covariance technique to measure evapotranspiration and carbon flux over two very different growing seasons for a typical steppe on the Inner Mongolia Plateau, China. The rainfall during the 2004 growing season (344.7 mm) was close to the annual average (350.43 mm). In contrast, precipitation during the 2005 growing season was significantly lower than average (only 126 mm). The wet 2004 growing season had a higher peak evapotranspiration (4 mm day(-1)) than did the dry 2005 growing season (3.3 mm day(-1)). In 2004, latent heat flux was mainly a consumption resource for net radiation, accounting for similar to 46% of net radiation. However, sensible heat flux dominated the energy budget over the whole growing season in 2005, accounting for 60% of net radiation. The evaporative rate (LE/R-n) dropped by a factor of four from the non-soil stress to soil water limiting conditions. Maximum half-hourly CO2 uptake was -0.68 mg m(-2) s(-1) and maximum ecosystem exchange was 4.3 g CO2 m(-2) day(-1) in 2004. The 2005 drought growing stage had a maximum CO2 exchange value of only -0.22 mg m(-2) s(-1) and a continuous positive integrated-daily CO2 flux over the entire growing season, i.e. the ecosystem became a net carbon source. Soil respiration was temperature dependent when the soil was under non-limiting soil moisture conditions, but this response declined with soil water stress. Water availability and a high vapor pressure deficit severely limited carbon fixing of this ecosystem; thus, during the growing season, the capacity to fix CO2 was closely related to both timing and frequency of rainfall events. (c) 2007 Published by Elsevier Masson SAS.

Defoliation, nitrogen, and competition: effects on plant growth and resource allocation of Cleistogenes squarrosa and Artemisia frigida

Two species, Artemisia frigida Willd. (C-3, semishrub, and dominant on overgrazed sites) and Cleistogenes squarrosa (Trin.) Keng (C-4, perennial bunchgrass, and dominant or codominant on moderately grazed sites) were studied to determine the effects of defoliation, nitrogen (N) availability, competition, and their interactions on growth, biomass, and N allocation in a greenhouse experiment. The main treatments were: two nitrogen levels (NO = 0 mg N pot(-1), N1 = 60 mg N pot(-1)), two defoliation intensities (removing 60% of total aboveground biomass and no defoliation), and three competitive replacement series (monocultures of each species and mixtures at 0.5:0.5). Our results were inconsistent with our hypothesis on the adaptive mechanisms of A. frigida regarding the interactive effects of herbivory, N, and competition in determining its dominant position on overgrazed sites. Cleistogenes squarrosa will be replaced by A. frigida on over-grazed sites, although C. squarrosa had higher tolerance to defoliation than did A. frigida. Total biomass and N yield and N-15 recovery of C. squarrosa in mixed culture were consistently lower than in monocultures, whereas those of A. frigida grown in mixtures were consistently higher than in monocultures, suggesting higher competitive ability of A. frigida. Our results suggest that interspecific competitive ability may be of equal or greater importance than herbivory tolerance in determining herbivore-induced species replacement in semi-arid Inner Mongolian steppe. In addition, the dominance of A. frigida on overgrazed sites has been attributed to its ability to shift plant-plant interactions through (lap colonization, root niche differentiation, and higher resistance to water stress.

Depression of net ecosystem CO2 exchange in semi-arid Leymus chinensis steppe and alpine shrub

Uptake and release of carbon in grassland ecosystems is very critical to the global carbon balance and carbon storage. In this study, the dynamics of net ecosystem CO2 exchange (FNEE) of two grassland ecosystems were observed continuously using the eddy covariance technique during the growing season of 2003. One is the alpine shrub on the Tibet Plateau, and the other is the sem-arid Leymus chinensis steppe in Inner Mongolia of China. It was found that the FNEE of both ecosystems was significantly depressed under high solar radiation. Comprehensive analysis indicates that the depression of FNEE in the L. chinensis steppe was the results of decreased plant photosynthesis and increased ecosystem respiration (R-eco) under high temperature. Soil water stress in addition to the high atmospheric demand under the strong radiation was the primary factor limiting the stomatal conductance. In contrast, the depression of FNEE in the alpine shrub was closely related to the effects of temperature on both photosynthesis and ecosystem respiration, coupled with the reduction of plant photosynthesis due to partial stomatal closure under high temperature at mid-day. The R,c of the alpine shrub was sensitive to soil temperature during high turbulence (u* > 0.2 m s(-1)) but its FNEE decreased markedly when the temperature was higher than the optimal value of about 12 degrees C. Such low optimal temperature contrasted the optimal value (about 20 degrees C) for the steppe, and was likely due to the acclimation of most alpine plants to the long-term low temperature on the Tibet Plateau. We inferred that water stress was the primary factor causing depression of the FNEE in the semi-arid steppe ecosystem, while relative high temperature under strong solar radiation was the main reason for the decrease of FNEE in the alpine shrub. This study implies that different grassland ecosystems may respond differently to climate change in the future. (c) 2006 Elsevier B.V All rights reserved.

Leaf orientation, incident sunlight, and photosynthesis in the alpine species Suassurea superba and Gentiana straminea on the Qinghai-Tibet Plateau

The extremely high level of solar radiation on the Qinghai-Tibet Plateau may induce photoinhibition and thus limit leaf carbon gain. To assess the effect of high light, we examined gas exchange and chlorophyll fluorescence for two species differing in light interception: the prostrate Saussurea superba and the erect-leaved Gentiana straminea. In controlled conditions with favorable water and temperature, neither species showed apparent photoinhibition in gas exchange measurements. In natural environment, however, their photosynthetic rate decreased remarkably at high light. Photosynthesis depression was aggravated under high leaf temperature or soil water stress. Relative stomatal limitation was much higher in S. superba than in G. straminea and it remarkably increased in the later species at midday when soil was dry. F-v/F-m as an indicator for photoinhibition was generally higher in S. superba than in the other species. F-v/F-m decreased significantly under high light at midday in both species, even when soil moisture was high. F-0 linearly elevated with the increment of leaf temperature in G. straminea, but remained almost constant in S. superba. Electron transport rate (ETR) increased with photosynthetically active photon flux density (PPFD) in S. superba, but declined when PPFD was high than about 1000 mumol m(-2) s(-1) in G. straminea. Compared to favorable environment, the estimated daily leaf carbon gain at PPFD above 800 mumol m(-2) s(-1) was reduced by 32% in S. superba and by 17% in G. straminea when soil was moist, and by 43% and 53%, respectively, when soil was dry. Our results suggest that the high radiation induces photoinhibition and significantly limits photosynthetic carbon gain, and the limitation may further increase at higher temperature and in dry soil.