干旱胁迫与施氮对麻疯树幼苗渗透调节物质积累的影响

采用盆栽控水的方法,研究干旱胁迫(80％ FC、60％ FC、40％ FC和20％ FC)及施氮(N0 0 g·pot-1、N1 1.2 g·pot1、Nm3.6 g·pot-1和Nh6.0 g·pot-1)对麻疯树幼苗叶、茎和根部主要渗透调节物质积累的影响.结果表明:干旱胁迫条件下,麻疯树幼苗茎和根部的游离脯氨酸、可溶性蛋白和茎部可溶性糖大量积累,叶片中脯氨酸含量也随干旱胁迫程度的增加大幅度上升;Na+、Ca2+和Mg2+在麻疯树幼苗叶、茎和根中大量积累,而K+仅在茎中大量积累,叶片和根部K+含量略微上升.施氮对植株渗透调节物质的影响与干旱胁迫强度和施氮水平有关.在80％ FC和60％ FC水分条件下,增加N肥施用量能明显促进麻疯树幼苗各组分渗透调节物质的积累;在40％ FC水分条件下,Nh处理对渗透调节物质积累的促进作用减弱;而在20％ FC条件下,N1处理植株的渗透调节能力较高,Nm和Nh处理对植株渗透调节的促进作用不明显甚至转为抑制.     

不同施氮水平对巨桉幼树耐旱生理特征的影响

采用盆栽方法,研究了巨桉幼树在N0(不施氮)、N1(1.4g尿素·盆-1)、N2(2.8g尿素·盆-1)3个氮处理水平下,连续干旱不同时间[分别停水0(D0)、3、6、9、12、15、18d]时巨桉的生理响应。结果显示:(1)除D0外,试验期内N1和N2处理的巨桉叶片含水量(LWC)、叶片相对含水量(LRWC)和叶片保水力(LWHC)基本低于N0水平,尤其在干旱中期最为明显,表明在干旱胁迫前施氮可能对巨桉叶片水分生理产生负面作用。(2)干旱初期,氮处理间的可溶性蛋白(SP)和可溶性糖(SS)含量的差异不大,而干旱处理后期(9~18d),N0处理的SP和SS较初期明显增加,但N1和N2处理相对于N0变化较为平缓,表明施氮不利于SP和SS积累;N1和N2处理下脯氨酸(Pro)含量的增幅随着干旱胁迫时间的延长明显大于N0处理。(3)随干旱时间延长干旱程度加重,N1、N2处理巨桉叶片过氧化氢(H2O2)和丙二醛(MDA)含量明显高于N0处理,表明施氮使得巨桉在干旱条件下水分缺乏更为严重,产生更多的活性氧(ROS)。(4)整个干旱处理期内,施氮并未显著改变巨桉的超氧化物歧化酶(SOD)活性和抗坏血酸(AsA)含量,但N1和N2的过氧化物酶(POD)活性明显高于N0。(5)施氮增加了巨桉叶片的色素含量并在干旱初期和中期保持较高水平,在干旱初期(0~3d)增加了巨桉叶片的净光合速率(Pn),但随着干旱时间的延长而迅速下降;施氮(N1、N2)的蒸腾速率(Tr)和气孔导度(Gs)在干旱初期均显著小于N0,但在干旱中后期(6d以后)各处理间差异不显著且均处于极低水平。研究表明,水分充足时施氮有助于增强巨桉的光合同化能力,促进其生长,但遇到持续干旱时施氮更易面临水分亏缺,降低其抵抗干旱的能力,因此在巨桉人工林的经营管理过程中,不应在干旱或季节性干旱即将到来之前施氮,若干旱过程中需施氮则应采取灌溉等途径保证其充足的水分供应。     

施氮量对不同肥力水平下夏玉米碳氮代谢及氮素利用率的影响

以郑单958为材料,在高产田和中产田两种地力水平下,利用15N标记法研究了施氮量对夏玉米氮素分配率、利用率和碳氮代谢的影响.结果表明:高产田适量施氮可以提高玉米产量,过量施氮没有表现出进一步增产效果,其氮肥利用率较低(29 04%).中产田随施氮量的增加产量提高,但氮素利用率却降低.各个器官15N积累量依次为籽粒>叶片>茎>根>叶鞘>穗轴.在高产田,当施氮量超过300kg·hm-2时,玉米籽粒和叶片中积累15N有所下降,而茎和根中积累15N的量随施N量的增加而增加;在中产田,随着施N量的增加,籽粒和穗轴积累15N量均相应增加.高产田叶片的硝酸还原酶活性、谷氨酰胺合成酶活性和蔗糖磷酸合成酶活性以及籽粒中蔗糖合成酶活性和酸性转化酶活性均是施氮300kg·hm-2时最大,施氮450 kg·hm-2则抑制了其活性的增强,而中产田的各个酶活性则随着施氮量的增加而增加.     

施氮水平对库尔勒香梨光合产物分配的影响

以6年生库尔勒香梨为材料,用¹³C脉冲标记技术研究了150、300、450 kg N·hm^-2(分别用N₁、N₂、N₃表示)3个施氮水平下树体各器官生物量、碳积累量以及¹³C同化物的吸收分配特性。结果表明: 库尔勒香梨树体整株的生物量、碳积累量、¹³C固定量以及叶片的同化能力均随着施氮水平的提高而增加;根冠比则随施氮水平的提高而降低。生殖器官果实的生物量、碳积累量在N₂处理下最高。树体各器官¹³C含量和分配率随施氮量的增加发生动态变化。新梢旺长期,叶片和根系对光合同化物的竞争能力较强,且¹³C分配率均为N₁处理下最高;果实膨大期和成熟期,叶片和果实的竞争能力较强,叶片¹³C含量和分配率在N₃处理下最高,而果实¹³C含量和分配率则在N₂处理下最大。综上,根据不同施氮水平各器官对碳同化物的吸收分配特征,以提高产量为目标,建议6年树龄的库尔勒香梨果园最佳施氮量为300 kg·hm^-2。     

内蒙古温带草原大针茅叶片光合生理特性对氮添加的响应

大气氮沉降增加生态系统氮有效性，优势种植物对不同水平氮输入的响应影响草原生态系统结构和功能。研究设置4个氮添加水平，分析内蒙古温带草原优势种大针茅（Stipa grandis）光合生理特性对不同梯度氮添加的响应。结果表明：低氮（0-2 g m^-2 a^-1）处理时，大针茅叶片氮含量较低，叶绿素含量和1，5-二磷酸核酮糖羧化/加氧酶的活性不高，光能利用效率低，导致光系统II出现过剩激发能，光合器官受到抑制，净光合速率相对较低。适量氮添加（5-10 g m^-2 a^-1）提高了大针茅叶片羧化系统和电子传递系统的氮分配，进而提高了1，5-二磷酸核酮糖羧化/加氧酶的活性以及电子传递速率，净光合速率增大。高氮（25 g m^-2 a^-1）处理时，叶片氮含量较高，但光合氮分配比例下降，降低了光合氮利用效率。大针茅光抑制程度增大，叶绿素含量、1，5-二磷酸核酮糖羧化/加氧酶的活性下降，不利于生物量积累。研究结果有助于进一步了解全球变化背景下草原生态系统优势种的生理响应机制，并为草原的可持续发展提供一定的理论依据。     

氮添加对内蒙古温带草原羊草光合特性的影响

受人类活动和气候变化的影响,大气氮(N)沉降日益加剧,使得草地生态系统正从自然N限制转向富营养化甚至饱和,进而影响了草地的生长。然而,关于优势种植物在N添加下的光合生理潜在机制的研究仍然不足。该研究以内蒙古温带典型草原优势种植物为研究对象,通过不同水平的N养分添加实验,探讨优势种羊草(Leymus chinensis)对N添加的光合生理响应机制。结果表明:地上生物量随着N添加先增加后降低,以10 g N·m~(–2)·a~(-1)处理增加最多。尽管25 g N·m~(–2)·a~(-1)处理出现下降趋势,但与对照相比仍然显著增加了地上生物量。低N时,植物通过把较少的N分配给羧化系统,并降低比叶质量(LMA)使叶片获得更多的光能来适应低N生境。适量的N添加通过增加总叶绿素(Chl)的含量,降低Chl a/b的比值来捕获更多光能;同时增加LMA、羧化效率、最大羧化速率(Vcmax)、最大电子传递速率(Jmax),并降低Jmax/Vcmax,把更多的N分配给羧化系统,提高羧化能力;通过增加实际光化学效率、电子传递效率和光化学猝灭系数,提高了光系统II(PSII)的光化学活性。过量的N添加对羊草的生理指标有一定抑制作用,羧化能力降低,导致净光合速率有所降低,在一定程度上抑制PSII的光化学活性,而非光化学猝灭系数以及类胡萝卜素增加起到了耗散过剩激发能的作用。N添加对羊草光合特性的影响总体表现为"适量促进,过量抑制"。该地区羊草最适的N添加范围是5–10 g N·m~(–2)·a~(-1)。     

遮光和施氮对暗紫贝母生长和C-N平衡的影响

为了了解暗紫贝母对资源变化的适应策略,本研究通过田间控制试验,研究了遮光和施氮对暗紫贝母生物量、生物量分配,以及叶、根C、N状态的影响。结果表明：遮光和施氮处理后,暗紫贝母生物量均减少;遮光下叶片的生物量分配相对增加,叶根生物量比显著升高（P<0.05）,但施氮处理下叶根生物量比的变化不明显;遮光和施氮后,暗紫贝母叶、根N含量均显著升高（P<0.05）,叶片和根的C：N显著降低（P<0.05）;相关分析显示,叶片N、C：N与暗紫贝母总生物量、叶根生物量比有极显著的相关性（P<0.01）。本研究表明,与生物量分配相比,C-N平衡,尤其是叶片的C：N比能更好的解释暗紫贝母对资源变化的适应。     

不同光照条件下喜阴植物谢君魔芋对稳态和动态光源的响应特征

谢君魔芋(Amorphophallus xiei)是起源于云南西南地区热带雨林的典型喜阴植物,近年来得到了广泛种植和推广,在种植过程中,谢君魔芋需要采用遮荫栽培模式。为了揭示谢君魔芋对光照强度的适应策略,该研究探讨了生长在不同光照强度下(透光率为50%、29%、17%、7%)谢君魔芋叶片的光合作用特征、光合诱导特征、光合色素含量以及叶片氮素(N)含量和N分配。结果表明:随着生长环境光照强度的降低,单位叶面积和单位叶质量最大净光合速率、光合色素含量、最大羧化速率、最大电子传递速率及比叶面积均增大,而暗呼吸和光补偿点均减小。在光合诱导过程中,生长在透光率为17%光环境中的谢君魔芋完成50%光合诱导所需的时间最短,约为81.4 s;在光诱导进行10 min时,诱导状态最高,为87.3%。完成50%和90%光合诱导所需的时间与低光下初始气孔导度呈负相关关系。随着生长光照强度降低,叶片中的N分配到羧化组分和生物能转化组分中的比例先增大后减小,在透光率为17%的光环境下具有最大值;而叶片中的N分配到捕光色素组分中的比例随着生长环境光照强度降低而增加。该研究结果表明,喜阴植物谢君魔芋通过加强对低光和动态光源的利用能力及有效的N资源分配策略来适应低光照环境。     

外源施N对干旱河谷白刺花（Sophora davidii）幼苗生长，生物量及C、N、P积累与分配的影响

干旱气候条件下改善土壤养分能否提高植物抗旱能力,促进植物生长一直是一个争论性的问题.为了解外源施N是否可提高岷江上游干旱河谷优势灌木白刺花(Sophora davidii)幼苗适应干旱贫瘠环境的能力,研究了不同施N(0、92 mg N · kg-1土和184 mg N · kg-1土)处理下一个生长季节内白刺花幼苗生长、生物生产量、C、N和P的积累与分配特性,以及N和P利用效率.研究结果表明:轻度施N(92 mg N ·kg-1土)处理促进了植物生长,增加了生物生产量,强化了C的固定和N、P等资源的吸收和积累,提高了其它受限资源的利用效率(如P),降低了N利用效率;但并不显著改变幼苗生物生产量及C、N和P等资源的分配格局,从而维持了资源的吸收、分配与利用的相对平衡,可能改善白刺花幼苗适应干旱贫瘠环境能力.而重度施N(184 mg N · kg-1土)处理虽然也相对于对照增加了叶片数目、生物生产量和C、N、P的积累量,但显著降低了幼苗根系的长度,抑制了根系的生长,并导致生物量及资源(生物量、C、N、P)较多地分配给地上部分(主要是叶片),不利于干旱环境下水分的吸收和利用,因而可能会加重幼苗受胁迫伤害的程度.综合分析表明,适当施加N肥可以促进白刺花幼苗的生长,一定程度上提高幼苗抗旱能力,改善幼苗定居,但也应避免过度施N.     

峨眉冷杉幼苗叶片功能特征及其N、P化学计量比对模拟大气氮沉降的响应

通过人工施氮模拟大气氮沉降,研究了施氮对峨眉冷杉(Abies fabiri)幼苗叶片功能特征、氮和磷含量及其化学计量比的影响,以及幼苗对氮素的积累效应。结果表明:经过2个生长季节的施氮处理(2009年和2010年,N2)幼苗的总生物量、叶干重、叶重比、叶片氮和磷含量及其N:P分别高于对照处理11.29%、46.70%、41.40%、37.30%、22.33%和6.43%,而比叶面积则降低了6.61%,其中叶干重、叶重比和叶片氮含量与对照处理差异显著(P<0.05),N:P差异极显著(P<0.01),并且叶干重与叶片氮含量具有较强的线性相关;与经1个生长季节施氮处理(2009年,N1)的幼苗总生物量、叶干重、叶重比、比叶面积、叶片氮和磷含量及其N:P的比较分析表明,除叶重比和比叶面积外,其他指标N2均高于N1;人工施氮显著促进了幼苗叶片的生长,提高了叶片氮、磷含量及其N:P,但也反映幼苗生长仍受氮素限制,同时,峨眉冷杉幼苗具有氮素积累效应。     

Photosynthesis or persistence: nitrogen allocation in leaves of evergreen and deciduous Quercus species

Photosynthetic nitrogen use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) is one of the most important factors for the interspecific variation in photosynthetic capacity. PNUE was analysed in two evergreen and two deciduous species of the genus Quercus. PNUE was lower in evergreen than in deciduous species, which was primarily ascribed to a smaller fraction of nitrogen allocated to the photosynthetic apparatus in evergreen species. Leaf nitrogen was further analysed into proteins in the water‐soluble, the detergent‐soluble, and the detergent‐insoluble fractions. It was assumed that the detergent‐insoluble protein represented the cell wall proteins. The fraction of nitrogen allocated to the detergent‐insoluble protein was greater in evergreen than in deciduous leaves. Thus the smaller allocation of nitrogen to the photosynthetic apparatus in evergreen species was associated with the greater allocation to cell walls. Across species, the fraction of nitrogen in detergent‐insoluble proteins was positively correlated with leaf mass per area, whereas that in the photosynthetic proteins was negatively correlated. There may be a trade‐off in nitrogen partitioning between components pertaining to productivity (photosynthetic proteins) and those pertaining to persistence (structural proteins). This trade‐off may result in the convergence of leaf traits, where species with a longer leaf life‐span have a greater leaf mass per area, lower photosynthetic capacity, and lower PNUE regardless of life form, phyllogeny, and biome.     

全球变化下植物的碳氮关系及其环境调节研究进展——从分子到生态系统

在全球变化条件下,温度的升高和降水格局的变化,导致淡水资源更加匮乏。环境因子胁迫,如干旱和高温等,它们单独或联合的作用将导致作物大幅度减产,引发自然生态系统退化。植物的碳氮代谢及其分配相互联系、不可分割,其生物过程及外界环境调节共同决定着植物的净生产力和营养水平。该文试图从分子、组织、器官、个体和生态系统等层面上,就植物的碳氮关系及其环境调节(温度、水分和CO₂浓度等)进行综述,并提出了进一步展开相关研究应重点关注的几个方面。     

干旱胁迫对不同施氮水平麻疯树幼苗光合特性及生长的影响

采用盆栽控水的方法,研究了干旱胁迫（连续干旱0 d,5 d,10 d,…,45 d）对不同施氮水平(对照 0 kg N·hm^-2、低氮 96 kg N·hm^-2、中氮 288 kg N·hm^-2、高氮 480 kg N·hm^-2)麻疯树幼苗光合特性及其生长的影响.结果表明: 随干旱胁迫强度的增加,各施氮水平麻疯树幼苗叶片相对含水量、苗高生长量、地径生长量、叶面积、净光合速率、蒸腾速率和气孔导度均降低,且各水分处理间差异极显著(P<0.01);随干旱时间的延长,叶绿素含量和水分利用效率表现出先升高后降低的趋势,而胞间CO₂浓度呈先降低后升高的趋势.正常供水时,施氮处理均不同程度提高了麻疯树幼苗的光合能力,促进了麻疯树幼苗的生长,且施氮量越高效果越好;干旱条件下,氮素营养对植株光合能力和生长的影响与干旱程度和施氮水平有关.轻度干旱时,提高施氮水平对植株光合能力和生长具有明显的促进作用;中度干旱时,中氮的促进作用明显高于其他施氮水平;严重干旱时,低氮的促进效果最好,高氮的促进作用减弱并逐渐转向抑制.     

氮肥对风箱果幼苗形态和生理特性的影响

采用盆栽实验的方法,设置4种水平氮肥处理,研究不同氮肥处理对风箱果1年生幼苗的生长表现、生物量积累和分配、光合生理特征、非结构性碳（NSC）积累等的影响。结果表明：施用氮肥促进了风箱果幼苗的地径、分枝数和冠幅的生长,促进了茎、叶和总生物量的积累（P<0.05）,提高了茎的生物量分配比例,减少了根生物量的分配比例;施用氮肥显著提高了净光合速率、叶氮含量、茎中的可溶性糖和NSC的积累（P<0.05）,但减少了根中的可溶性糖和NSC含量（P<0.05）。不同水平氮肥处理间（N1、N2、N3）的大部分指标差异并不显著,说明风箱果幼苗对土壤养分的变化并不敏感。     

Photosynthetic nitrogen-use efficiency of species that differ inherently in specific leaf area

Factors that contribute to interspecific variation in photosynthetic nitrogen-use efficiency (PNUE, the ratio of CO₂ assimilation rate to leaf organic nitrogen content) were investigated, comparing ten dicotyledonous species that differ inherently in specific leaf area (SLA, leaf area:leaf dry mass). Plants were grown hydroponically in controlled environment cabinets at two irradiances (200 and 1000 μmol m^–2 s^–1). CO₂ and irradiance response curves of photosynthesis were measured followed by analysis of the chlorophyll, Rubisco, nitrate and total nitrogen contents of the leaves. At both irradiances, SLA ranged more than twofold across species. High-SLA species had higher in situ rates of photosynthesis per unit leaf mass, but similar rates on an area basis. The organic N content per unit leaf area was lower for the high-SLA species and consequently PNUE at ambient light conditions (PNUE_amb) was higher in those plants. Differences were somewhat smaller, but still present, when PNUE was determined at saturating irradiances (PNUE_max). An assessment was made of the relative importance of the various factors that underlay interspecific variation in PNUE. For plants grown under low irradiance, PNUE_amb of high-SLA species was higher primarily due to their lower N content per unit leaf area. Low-SLA species clearly had an overinvestment in photosynthetic N under these conditions. In addition, high SLA-species allocated a larger fraction of organic nitrogen to thylakoids and Rubisco, which further increased PNUE_amb. High-SLA species grown under high irradiance showed higher PNUE_amb mainly due to a higher Rubisco specific activity. Other factors that contributed were again their lower contents of N_org per unit leaf area and a higher fraction of photosynthetic N in electron transport and Rubisco. For PNUE_max, differences between species in organic leaf nitrogen content per se were no longer important and higher PNUE_max of the high SLA species was due to a higher fraction of N in␣photosynthetic compounds (for low-light plants) and a higher Rubisco specific activity (for high-light grown plants). Received: 11 October 1997 / Accepted: 9 April 1998     

Effects of soil water and nitrogen on growth and photosynthetic response of Manchurian ash (Fraxinus mandshurica) seedlings in northeastern China

Background

Soil water and nitrogen (N) are considered to be the main environmental factors limiting plant growth and photosynthetic capacity. However, less is known about the interactive effects of soil water and N on tree growth and photosynthetic response in the temperate ecosystem.

Methods/Principal Findings

We applied N and water, alone and in combination, and investigated the combined effect of different water and N regimes on growth and photosynthetic responses of Fraxinus mandshurica seedlings. The seedlings were exposed to three water regimes including natural precipitation (CK), higher precipitation (HW) (CK +30%) and lower precipitation (LW) (CK −30%), and both with and without N addition for two growing seasons. We demonstrated that water and N supply led to a significant increase in the growth and biomass production of the seedlings. LW treatment significantly decreased biomass production and leaf N content, but they showed marked increases in N addition. N addition could enhance the photosynthetic capability under HW and CK conditions. Leaf chlorophyll content and the initial activity of Rubisco were dramatically increased by N addition regardless of soil water condition. The positive relationships were found between photosynthetic capacity, leaf N content, and SLA in response to water and N supply in the seedling. Rubisco expression was up-regulated by N addition with decreasing soil water content. Immunofluorescent staining showed that the labeling for Rubisco was relatively low in leaves of the seedlings under LW condition. The accumulation of Rubisco was increased in leaf tissues of LW by N addition.

Conclusions/Significance

Our study has presented better understanding of the interactions between soil water and N on the growth and photosynthetic response in F. mandschurica seedlings, which may provide novel insights on the potential responses of the forest ecosystem to climate change associated with increasing N deposition.     

Sex-specific carbon and nitrogen partitioning under N deposition in Populus cathayana

Key message

Females of Populus cathayana allocated increased N to soluble proteins, while males keep N allocation pattern unchanged under N enrichment.

Abstract

In our study, Populus cathayana as a model species is employed to detect the sex-specific responses in growth, photosynthetic nitrogen (N) use efficiency (PNUE), carbon (C) and N partitioning when exposed to 0, 7.5 and 15 g N m^?2 year^?1 on the basis of local N deposition level. Our results showed that females had higher responses in photosynthesis and growth than males when exposed to N deposition, and also exhibited higher PNUE than males when exposed to high level of N deposition, suggesting that plasticity in the females may enhance the capacity of young seedlings to acquire resources. Moreover, we found that females mainly allocated increased N to soluble proteins and detergent-soluble proteins, but not to cell-wall proteins, while males maintained original partitioning pattern of N and also accumulated excessive N in the form of free amino acids. Females also allocated more fraction of leaf N to carboxylation (P _C), bioenergetics (P _B), and then more fraction of leaf N to all components of photosynthetic machinery (P _T) than males under high level of N deposition. Such sex-specific N allocation strategy may correlate with sex-related PNUE. These results indicated that there is a higher critical N demand in females, and females could use N nutrient more efficiently than males under high N deposition. We also found that higher shift from starch to soluble sugars, such as sucrose, occurred in females than in males under N enrichment. By contrast, excessive accumulation of starch and non-structural carbohydrate in females relative to males was observed under control conditions, which might inhibit female photosynthesis rate. Accordingly, we suggested that the different leaf C and N partitioning patterns could explain the sex-specific responses in growth. Therefore, females may obtain advantageous position in the process of intraspecific competition when exposed to high level of N deposition because they have higher light capture (total leaf area) ability and utilization efficiency (PNUE) than the males that confer the ability for fast growth and thus are likely to be more responsive to N enrichment. Our results suggested that it could be important to look at the stronger growth response of the females over the males under N enrichment at both the leaf and the plant scale.     

干旱胁迫条件下AMF促进小马鞍羊蹄甲幼苗生长的机理研究

采用温室水分控制试验,在干旱胁迫条件下,定量化研究优势丛枝菌根真菌(AMF)影响优势乡土植物小马鞍羊蹄甲(Bauhinia faberi var.microphylla)幼苗生长的机理,主要通过研究干旱胁迫条件下摩西球囊霉菌(Funneliformis mosseae)与小马鞍羊蹄甲的共生关系,阐明AMF在植物生长初期的作用。结果表明,干旱胁迫条件下,摩西球囊霉菌能够很好地侵染幼苗,侵染率高达89%—97%,并且不受水分条件影响。接种的幼苗最大光合速率、水分利用效率随着干旱胁迫程度从重度到轻度(水分从低到高)逐渐增大,相反地,叶片脯氨酸含量逐渐减小。接种显著地促进幼苗株高、叶片数、叶面积、根长、根面积等生长指标,提高幼苗各部分生物量、地上地下磷(P)含量。当含水量为60%田间持水量时,AMF促进小马鞍羊蹄甲幼苗吸收P的效果最好。接种还显著影响幼苗的生物量分配,在重度干旱胁迫时影响P分配,水分条件也显著影响幼苗的生物量分配。此外,接种和水分的交互作用对叶生物量、总生物量、生长指标以及地上部氮(N)总量影响显著。结果表明干旱胁迫条件下菌根效应显著,并在干旱条件下显著促进了小马鞍羊蹄甲幼苗的生长,这为进一步干旱河谷植被恢复提供了理论依据。     

The role of Rubisco and cell walls in the interspecific variation in photosynthetic capacity

Photosynthetic capacity is known to vary considerably among species. Its physiological cause and ecological significance have been one of the most fundamental questions in plant ecophysiology. We studied the contents of Rubisco (a key enzyme of photosynthesis) and cell walls in leaves of 26 species with a large variation in photosynthetic rates. We focused on photosynthetic nitrogen-use efficiency (PNUE, photosynthetic rate per nitrogen), which can be expressed as the product of Rubisco-use efficiency (RBUE, photosynthetic rate per Rubisco) and Rubisco nitrogen fraction (RNF, Rubisco nitrogen per total leaf nitrogen). RBUE accounted for 70% of the interspecific variation in PNUE. The variation in RBUE was ascribed partly to stomatal conductance, and other factors such as mesophyll conductance and Rubisco kinetics might also be involved. RNF was also significantly related to PNUE but the correlation was relatively weak. Cell wall nitrogen fraction (WNF, cell wall nitrogen per total leaf nitrogen) increased with increasing leaf mass per area, but there was no correlation between RNF and WNF. These results suggest that nitrogen allocation to cell walls does not explain the variation in PNUE. The difference in PNUE was not caused by a sole factor that was markedly different among species but by several factors each of which was slightly disadvantageous in low PNUE species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Short-term effects of fertilization on loblolly pine (Pinus taeda L.) physiology

Fertilization commonly increases biomass production in loblolly pine (Pinus taeda L.). However, the sequence of short‐term physiological adjustments allowing for the establishment of leaf area and enhanced growth is not well understood. The effects of fertilization on photosynthetic parameters, root respiration, and growth for over 200 d following the application of diammonium phosphate were intensively investigated in an effort to establish a relative sequence of events associated with improved growth. Root respiration, foliar nitrogen concentration [N]_f, and light‐saturated net photosynthesis (A_sat) temporarily increased following fertilization. A_sat was correlated positively with [N]_f when non‐fertilized and fertilized treatments were pooled (R² = 0.47). Increased photosynthetic capacity following fertilization was due to both improved photochemical efficiency and capacity and enhanced carboxylation capacity of Rubisco. Positive effects of fertilization on growth were observed shortly after A_sat increased. Fertilized seedlings had 36.5% more leaf area and 36.5% greater total dry weight biomass at 211 d following fertilization. It is concluded that fertilization temporarily increased photosynthetic capacity, which resulted in a pool of photo‐assimilate used to build leaf area. The N from fertilizer initially invested in photosynthetic structures and enzymes probably re‐translocated to newly developing foliage, explaining the reduction in [N]_f and A_sat that was observed after peak levels were achieved following fertilization.