二倍体、四倍体和六倍体小麦产量及水分利用效率

试验选用了6个不同染色体倍性的小麦进化材料（3个二倍体、2个四倍体和1个六倍体）,分别在不同水肥条件下研究其根系、地上生物量、产量、蒸腾耗水量和水分利用效率等指标,旨在阐明小麦进化材料产量及水分利用效率的差异及水肥条件对这些特性的影响。试验表明：不同倍性小麦进化材料的生物量、产量和水分利用存在显著的差异,而且水肥条件对其有显著影响。在染色体倍性由2n→4n→6n的进化过程中,小麦根系及地上生物量均先增加后降低,而产量却显著增加,这与收获指数的增加有关。小麦产量的大小顺序为：T.aestivum〉T.dicoccum〉T.dicoccoides〉Ae.squarrosa〉Ae.speltoides〉T.boeoticum。水分亏缺显著降低小麦的生物量、产量和收获指数;在不同水分条件下,增加施肥量有利于这些指标的增加。但是水分亏缺下,增加施肥却降低各小麦材料的根系生物量。随小麦的进化,蒸腾耗水量显著降低,这与其生育期缩短有关;而生物量水分利用效率和产量水分利用效率却显著升高,且后者的差异要大于前者。各小麦产量水分利用效率的大小排序与产量的完全一致。水分亏缺处理显著减少各小麦进化材料的蒸腾耗水量47％～52％，而显著增加生物量水分利用效率3％～40％；但水分亏缺对产量水分利用效率的促进作用却随染色体倍性的增加而降低，甚至降低六倍体小麦T.aestivum的产量水分利用效率19％。不同水分条件下，高肥处理均有利于蒸腾耗水量、生物量水分利用效率和产量水分利用效率的增加。     

三峡库区岸边共存松栎树种水分利用策略比较

对三峡库区木鱼岛上马尾松(Pinus massoniana)、槲栎(Quercus aliena)和栓皮栎(Q. variabilis)组成的针阔混交林成林和幼林的光合速率(P_n)、气孔导度(G_s)、清晨和中午水势(ψ_pd和ψ_md)以及叶片稳定碳同位素(δ¹³C)进行了测定。实验结果表明:针叶树马尾松P_n、G_s均低于阔叶树槲栎和栓皮栎(差异达到极显著水平,p<0.001),但马尾松内在水分利用效率(WUE_i, P_n/G_s)却高于槲栎(p=0.003)和栓皮栎(p=0.025)。反映了裸子植物和被子植物木质部不同的水力特性。针阔叶树幼树的P_n和G_s高于成年树,但WUE_i和δ¹³C却低于成年树。表明水分利用效率与水分在树体内传输的距离有关。幼树属于挥霍型水分利用策略,成年树属保守型水分利用策略。三峡大坝的建设所造成的生态环境的改变可能会对三峡库区针阔混交林的演替产生一定的影响,但这需要长期的研究。     

灌浆期水分亏缺条件下二、四、六倍体小麦收获指数和水分利用效率的演化

为揭示不同倍性小麦生长发育、产量性状及水分利用对灌浆期水分亏缺响应的差异,选用二倍体野生一粒小麦(Triticum boeoticum)、栽培一粒小麦(T.monococcum),四倍体野生二粒小麦(T.dicoccoides)、栽培二粒小麦(T.dicoccon),和两个普通六倍体小麦(T.aestivum)品种‘长武134’和‘陕253’6个小麦品种作为供试材料。采用盆栽控水的方法,测定和分析了不同灌浆期土壤水分条件下小麦株高、旗叶叶面积、穗长、根干重、地上生物量、根冠比、千粒重、粒数、产量、收获指数、蒸腾耗水量和水分利用效率等性状的变化。在小麦染色体倍体由二倍体向六倍体进化的过程中,小麦地上生物量、千粒重、穗粒数、产量、收获指数和水分利用效率都显著增加。随着土壤水分从正常→中度亏缺→重度亏缺的减少,收获指数先增大后减小,分别为41.26%、42.48%和38.19%;生物量水分利用效率逐渐增大,分别为2.39、2.43和2.53g·kg–1;产量水分利用效率分别为1.05、1.10和1.04g·kg–1。在灌浆期水分条件是影响收获指数和水分利用效率的关键因素之一。灌浆期的水分亏缺有利于六倍体小麦的收获指数和四倍体的生物量水分利用效率的提高。中度的水分亏缺有利于四倍体和六倍体产量水分利用效率的提高。     

不同去趋势方法对基于Dendrometer数据的茎干水分动态分析的影响——以白扦为例

树木茎干半径变化记录仪(Dendrometer)监测的高精度数据不仅包括木质部的年内径向生长过程, 还包含由茎干水分的消耗和补充引起的可逆变化。然而, 不同的年内生长去趋势方法获得的茎干水分波动之间的差异性仍缺乏对比研究。基于芦芽山北坡针叶林下限白扦(Picea meyeri) 2015年生长季的茎干半径变化和环境因子的实时监测数据, 使用Gompertz生长模型(GPZ)、线性生长模型(LG)、零生长模型(ZG)、日值法(D)和茎干循环法(SC)模拟并去除茎干年内的生长趋势, 然后提取5种不同类型树木水分缺乏引起的茎干收缩(TWD_GPZ、TWD_LG、TWD_ZG、TWD_D和TWD_SC)以表征茎干水分亏缺, 并进一步对比分析了不同茎干水分亏缺序列对环境中水分状况的响应特征。研究发现: (1)不同去趋势方法计算的茎干水分亏缺的趋势和幅度有所差异, 可聚类为3组: TWD_LG和TWD_ZG、TWD_GPZ以及TWD_D和TWD_SC。同组或聚类距离接近的序列在生长季内每个月份都展现出显著的相关性。然而, TWD_LG、TWD_ZG和TWD_GPZ与TWD_D和TWD_SC在8月份相关性较弱。(2) TWD_D和TWD_SC与空气饱和水汽压差(VPD)的正相关关系比TWD_GPZ、TWD_LG和TWD_ZG更加稳定, 且具有更大的相关系数。5种茎干水分亏缺序列和土壤含水量(SWC)的关系在生长季内变化很大。(3)不同去趋势方法的茎干水分亏缺都随着水分胁迫程度(VPD/SWC)升高而显著增长。当胁迫程度较低时, TWD_SC对VPD/SWC的变化最为敏感(R² = 0.39, p < 0.001), 但是与TWD_ZG差别不大(R ² = 0.37, p < 0.001); 当胁迫程度较高时, TWD_ZG对VPD/SWC的敏感性最高(R ² = 0.59, p < 0.001)。综合对比来看, 零生长模型是比较适合研究区白扦生长季内茎干水分波动的去趋势方法, 其可为干旱胁迫条件下预测研究区树木的茎干水分动态及特征提供科学 依据。     

我国抗虫转基因杨树生态安全性研究进展

转基因树木与农作物相比, 人们更关注其长时间种植可能导致转基因扩散到周围野生近缘种。由于生长周期长, 转基因树木会增加转基因不稳定性, 对非靶标生物的影响, 靶标害虫对转基因植物产生抗性, 增加树木入侵性(杂草化), 以及由于基因漂移或基因逃逸对环境产生的负面影响或新的环境风险。过去十几年, 针对我国抗食叶害虫的两个商业化转Bt基因欧洲黑杨(Populus nigra)和转双抗虫基因741杨[P. alba× (P. davidiana + P. simonii) × P. tomentosa], 已开展了有关生态安全性方面的多项研究。本文围绕抗虫转基因树木生态安全性研究进展进行了综述。抗虫转基因杨树对节肢动物种群和群落结构产生了一定影响, 使昆虫的多样性提高, 但对土壤微生物区系未见明显影响。转基因欧洲黑杨通过花粉和种子发生的基因漂移几率很低。转基因杨树通过内生菌发生的水平转移可能会对环境造成的潜在危险也进行了评价。文章最后指出对抗虫转基因杨树农林复合生态系统开展生物安全研究的必要性。     

铅胁迫对欧美杂交杨幼苗碳、氮和磷积累与分配的影响

为深入了解欧美杂交杨(Populus deltoids × Populus nigra)在不同铅(Pb)胁迫条件下的生长适应特性, 采用盆栽控制试验, 研究了长江上游典型酸性紫色土和钙质紫色土上欧美杂交杨碳(C)、氮(N)和磷(P)积累与分配特征对不同浓度Pb胁迫(CK: 0 mg·kg^-1; T1: 200 mg·kg^-1; T2: 450 mg·kg^-1; T3: 2000 mg·kg^-1)的响应。欧美杂交杨总C、N和P积累量在两种土壤中均表现出随Pb胁迫程度的增加而降低的趋势, 且钙质紫色土中欧美杂交杨总C、N和P积累量在各处理浓度下均高于酸性紫色土。Pb胁迫处理明显改变了欧美杂交杨各器官C、N和P的分配格局。与对照相比, Pb胁迫处理使酸性紫色土中欧美杂交杨细根C、N和P积累量的比例明显增加, 叶C、N和P积累量的比例则呈现出降低的趋势。相对于酸性紫色土, 钙质紫色土中欧美杂交杨细根C、N和P积累量的比例明显降低, 其叶C、N和P积累量的比例则表现出增加的趋势。两种土壤中欧美杂交杨P的利用效率均表现出随Pb胁迫程度的增加而增加的趋势, 而T2、T3处理下两种土壤中N的利用效率均显著降低。这些结果表明, 在N素缺乏的情况下, 酸性紫色土中欧美杂交杨P的利用效率显著低于钙质紫色土, 因此酸性紫色土中植物C、N和P积累、分配与利用更易受到Pb胁迫的影响。同时也表明, 钙质紫色土中欧美杂交杨通过改变养分分配格局将资源更多地分配于养分利用器官维持自身的生长, 能更好地适应Pb胁迫环境。     

调亏灌溉对菘蓝水分利用及产量的影响

通过探究水分调亏对河西地区膜下滴灌菘蓝(Isatis indigotica)各项生理指标、产量和水分利用的影响, 为菘蓝高效节水种植提供理论指导。于2016年在河西走廊中部张掖市民乐县益民灌溉试验站进行菘蓝水分调亏研究, 在保持苗期和肉质根成熟期充分灌溉的情况下, 在菘蓝营养生长期和肉质根生长期分别进行轻度、中度和重度的水分亏缺处理, 并测定各项光合生理指标、产量和水分利用率。结果表明, 营养生长期和肉质根生长期的中度与重度水分亏缺显著降低了菘蓝叶片净光合速率、叶面积指数、株高及主根长, 并且随水分亏缺程度加重降幅增大; 而轻度水分亏缺与对照组的差异不显著。营养生长期和肉质根生长期轻度水分亏缺处理的菘蓝产量与水分利用效率最高, 分别达到8 239.56 kg·hm^-2和24.11 kg·hm^-2·mm^-1; 其它水分亏缺处理组产量和水分利用效率均有所降低, 与对照组之间差异显著(P<0.05), 重度水分亏缺处理各项指标均最低。因此, 最优的菘蓝水分调控处理为营养生长期和肉质根生长期的轻度水分调亏, 能够降低菘蓝耗水量, 提高水分利用效率且其产量不会降低。     

降雨格局变化对内蒙古典型草原优势种大针茅幼苗的影响

大针茅(Stipa grandis)是内蒙古草原的优势物种, 研究其幼苗在不同降雨格局下的响应特征, 可以为进一步研究降雨格局变化下内蒙古典型草原的响应特征提供科学依据。在中国科学院内蒙古草原生态系统定位研究站, 利用开顶式生长室进行控制试验模拟降雨格局变化, 研究了大针茅幼苗对总降雨量和降雨间隔时间变化的响应。结果表明: 1)总降雨量增加50%使大针茅幼苗生长季末的地上生物量平均增加23% (p < 0.05), 而降雨间隔时间由5天增长为15天使地上生物量平均增加48.8% (p < 0.001)。2)总降雨量对大针茅幼苗的地下生物量没有显著影响; 而在低降雨量条件下, 降雨间隔时间增长使地下生物量增加56.2% (p < 0.001), 在高降雨量条件下作用不显著。3)总降雨量和降雨间隔时间对根冠比的效应都依赖于对方水平的高低, 总降雨量增大只在较长降雨间隔条件下使根冠比发生改变(-28.4%, p < 0.05), 降雨间隔时间增长只在高降雨量条件下使根冠比发生改变(-28.8%, p < 0.05)。4)处理期间, 在处理时间分别为30天和45天时, 大针茅幼苗地上生物量、地下生物量和总生物量的差异都主要取决于总降雨量; 而在处理时间为75天时, 其差异则都主要取决于降雨间隔时间。该研究得到以下主要结论: 1)降雨间隔时间与总降雨量一样, 是影响大针茅幼苗生长的关键因素之一。2)总降雨量对大针茅幼苗生长的效应与降雨间隔时间的长短紧密相关。3)降雨格局对大针茅幼苗生长的影响机制随着幼苗的生长期不同而改变。     

灌水量与密度互作对冬小麦籽粒产量和水分利用效率的影响

为明确协同提高冬小麦产量和水分利用效率的适宜灌水量和种植密度,选用大穗型品种‘泰农18’(T18)和中穗型品种‘山农22’(S22)为试验材料,设置4个灌溉水平(不灌水、每次灌水45、60、75 mm)和4个种植密度,其中泰农18选用135×10⁴、270×10⁴、405×10⁴、540×10⁴ 株·hm^-2,山农22选用90×10⁴、180×10⁴、270×10⁴、360×10⁴株·hm^-2,研究了籽粒产量、麦田耗水特性和水分利用效率对灌水量和密度互作效应的响应。结果表明: 籽粒产量、总耗水量、土壤贮水消耗量和水分利用效率均受到灌溉水平、种植密度及两者互作效应的显著影响。每次灌水量为45 mm,泰农18种植密度为405×10⁴株·hm^-2、山农22种植密度为270×10⁴株·hm^-2时,两品种籽粒产量均达到最高,拔节后棵间蒸发量占阶段农田总耗水量的比例最小,1 m以下土壤水消耗比例、水分利用效率高。种植密度与灌溉量合理组合,有利于降低水分无效损耗,提高水分利用效率。     

采用稳定碳同位素法分析白羊草在不同干旱胁迫下的水分利用效率

本研究以黄土高原乡土草种白羊草(Bothriochloa ischaemum(L.)Keng.)为研究对象,采用盆栽控制实验,比较白羊草在3个水分处理(CK80%FC、MS60%FC和SS 40%FC)下的生物量积累和分配模式、瞬时水分利用效率(WUE)、不同部位(新叶、老叶、茎、细根、粗根)的稳定碳同位素组成(δ~(13)C)和碳同位素分辨率(Δ~(13)C)及其相互关系,以及干旱胁迫下影响水分利用效率的主导环境因子。结果表明:1)重度干旱胁迫显著降低植物整体生物量,显著增加根冠比和细根生物量比例;2)随着干旱胁迫加剧,白羊草各器官的δ~(13)C均呈上升趋势,Δ~(13)C呈减小趋势,SS处理不同器官δ~(13)C和Δ~(13)C没有显著差异,CK和MS处理的各器官δ~(13)C均值表现分别为细根粗根老叶新叶茎、细根新叶老叶粗根茎,CK和MS处理Δ~(13)C的值总体呈根叶茎。3)新叶的δ~(13)CNL和Δ~(13)CNL与WUE的相关系数均最大,说明利用稳定碳同位素方法测定白羊草水分利用效率具有可行性。4)不同水分处理的WUE的主导影响因子不同,CK、MS、SS水分处理WUE分别受到叶面温度、大气水汽压亏缺和空气温度的影响最大。为采用稳定碳同位素方法指示白羊草水分利用效率可行性及阐明植物的胁迫响应机制提供理论依据。     

准噶尔荒漠早春短命植物的光合特性及生物量分配特点

准噶尔荒漠分布的早春短命植物不仅具有十分独特的生物学特点,而且在荒漠植物群落演替、物种多样性维持及土壤改良与防治水土流失等方面具有重要的生态学价值。该文运用Li-6400开放式气体交换光合作用测定系统,对分布于准噶尔荒漠的16种早春短命植物生长盛期的净光合速率(P_n)、蒸腾速率(T_r)、水分利用效率(WUE)等特征进行了测定,并对其中7种植物与生长相关的生物量分配特征进行了分析。结果表明:1)16种植物的最大P_n、 最大T_r及WUE分别为8.07~35.96 μmol CO₂·m^-2·s^-1、3.16~29.64 mmol H₂O·m^-2·s^-1、0.54~4.26 μmol CO₂·mmol^-1H₂O;种间最大P_n与最大气孔导度(Stomatal conductance, G_s)之间存在正相关关系,其相关系数为0.77(p<0.05),线性回归斜率为26.36 μmol·mmol^-1;从光合速率对胞间CO₂浓度及光量子通量密度的响应曲线来看,这类植物的表观CO₂补偿点均在4~5 Pa之间(28~30 ℃),表观羧化效率为0.64~1.86 μmol CO₂·m^-2·s^-1·Pa^-1,表观量子效率为0.05~0.06。2)从生物量分配来看,所测植物的个体生物量为0.05~0.39 g;单株总叶面积为 3.24~51.40 cm²;单位叶面积干重为0.40~0.77 g·m^-2,根在总生物量中所占比例为5.72%~19.43%,单株叶面积比在2.92~9.00 m²·kg^-1之间。种间根所占生物量的比与对应的WUE之间的比较分析结果表明,二者之间存在显著的正相关关系,其相关系数r为0.93(p<0.01)。这些结果表明,所观测的早春短命植物具有典型的C₃植物特征,相比其它类型的荒漠植物具有较高的单位叶面积P_n、高T_r及低WUE,并且在生长发育过程中表现出很低的根/地上生物量比、较高的叶面积比和单位叶面积干重,说明它们具有相对高的生长速率,这与其生长发育节律相一致,反映了它们与准噶尔荒漠环境相适应的特点。     

硅对生姜叶片水、二氧化碳交换特性的影响

为探讨硅对生姜植株的生理效应,以莱芜大姜为试材,研究了水培营养液中不同硅素水平对生姜植株生长、硅含量及叶片光合作用和蒸腾作用的影响.结果表明：植株各器官硅含量及生物量均随营养液硅素水平的升高而显著增加,1.0 (T₁)、1.5 (T₂)、2.0 (T₃) mmol·L^-1硅(Si)处理植株叶片硅 (SiO₂) 含量分别比CK增加604.4%、834.8%和1130.4%,单株生物量分别比CK增加9.4%、19.4%和22.8%.随着硅素水平的升高,叶片Mg²⁺ TPase、Ca²⁺ ATPase活性及光合速率(P_n)和水分利用效率(WUE)提高,蒸腾速率(T_r)降低.一天中在11:00时,T₁、T₂、T₃处理的生姜叶片P_n和WUE分别比CK提高11.2%、21.8%、28.2%和23.1%、55.9%、54.8%,T_r分别比CK降低6.3%、17.1%和19.2%.此外,硅素还显著提高了生姜叶片光合作用饱和光强、CO2羧化效率及类胡萝卜素含量,但对叶绿素含量无显著影响.本试验条件下,以15～20 mmol·L-1硅素(Si)处理效果最好.     

Water Use Efficiency and Biomass Partitioning of Three Different Miscanthus Genotypes with Limited and Unlimited Water Supply

Miscanthus species, which are C₄perennial grasses, have a highbiomass potential but yields at many sites in Europe can belimited by insufficient water supply and plant survival is endangeredunder extreme summer drought. A pot experiment was conductedto measure the influence of reduced water supply on the wateruse efficiency (WUE) and biomass partitioning of three Miscanthusgenotypes (M. x giganteus, M. sacchariflorus, and a M. sinensishybrid) in a controlled environment. The experiment consistedof three phases (phase 1 = 0–20 d; phase 2 = 21–39d; phase 3 = 40–54 d) punctuated by destructive harvests.In phase 1, soil moisture was non-limiting. In the second andthird phases, lowered soil moisture contents induced water deficits.Air vapour pressure deficit (VPD) was 0.49 ± 0.05 kPa.Water deficits caused leaf senescence in M. x giganteus andM. sacchariflorus, but not in the M. sinensis hybrid. Greenleaf conductances were lowest in M. sinensis under water deficit,indicating stomatal regulation. Water use efficiency for wholeplants of each genotype ranged from 11.5 to 14.2 g dry matter(DM) kg^-1H₂O but did not differ significantly between genotypesor water treatments under the conditions of this experiment.However, differences in dry matter partitioning to the shoot(the harvestable component) resulted in genotypic differencesin WUE, calculated on a harvestable dry matter basis, whichranged from 4.1 g DM kg^-1H₂O for M. sacchariflorus to 2.2 gDM kg^-1H₂O for M. x giganteus. Copyright 2000 Annals of BotanyCompany Miscanthus sinensis, Miscanthus sacchariflorus, Miscanthus x giganteus, water use efficiency, biomass, C₄plants, drought     

Drought tolerance in three hybrid poplar clones submitted to different watering regimes

Aims Poplars grown in North China may experience water-deficient periods in their life cycle. The aim of the present paper was to quantify the response of three clones to different watering regimes and to determine which clone among the three is the best adapted to drought conditions.Methods Three hybrid poplar clones (clone DN-34, R-247 and OP-367) were used in the present experiment. The seedlings of the three clones were grown under four watering regimes: control (well watered, 100% field water capacity (FC)) and three drought treatments (drought stress I, 50% FC; drought stress II, 40% FC; drought stress III, 30% FC). Changes in morphological, physical and biochemical indicators of the three hybrid poplar clones were investigated.Important findings Drought treatment (50%, 40% and 30% FC) decreased net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs), shoot height, total biomass and chlorophyll (Chl) content in all the three clones and it increased activities of antioxidant enzymes and free proline content. The highest values of the above-mentioned morphological and physiological parameters were recorded in clone OP-367 under 30% FC, followed by clone DN-34 and R-247. Relative leaf water content (RWC) and stem diameter (sd) markedly declined in clone R-247 and DN-34 under drought stress I, II and III, whereas RWC and sd declined in clone OP-367 only under drought stress II and III. Clone OP-367 had more RWC and sd than DN-34 and R-247. Only the 30% FC induced an increase in the root-to-shoot ratio (rs) and water use efficiency (WUE) in all the three clones. OP-367 was the most efficient clone in water absorption and use, for plants of the clone had the highest values of rs and WUE. Our data demonstrate that among the three clones, OP-367 was better able to maintain photosynthesis and growth and lower the damage caused by drought.     

Impact of drought on productivity and water use efficiency in 29 genotypes of Populus deltoides x Populus nigra

We examined the relationships among productivity, water use efficiency (WUE) and drought tolerance in 29 genotypes of Populus x euramericana (Populus deltoides x Populus nigra), and investigated whether some leaf traits could be used as predictors for productivity, WUE and drought tolerance. At Orléans, France, drought was induced on one field plot by withholding water, while a second plot remained irrigated and was used as a control. Recorded variables included stem traits (e.g. biomass) and leaf structural (e.g. leaf area) and functional traits [e.g. intrinsic water use efficiency (Wi) and carbon isotope discrimination (Delta)]. Productivity and Delta displayed large genotypic variability and were not correlated. Delta scaled negatively with Wi and positively with stomatal conductance under moderate drought, suggesting that the diversity for Delta was mainly driven by stomatal conductance. Most of the productive genotypes displayed a low level of drought tolerance (i.e. a large reduction of biomass), while the less productive genotypes presented a large range of drought tolerance. The ability to increase WUE in response to water deficit was necessary but not sufficient to explain the genotypic diversity of drought tolerance.     

Leaf Abscission and Stem Lesions (Intumescences) on Poplar Clones after SO2 and O3 Fumigation: A Link with Ethylene Release?

Differences in premature leaf abscission and in visible steminjury in genetic lines of poplar followed continuous fumigationswith air pollutant levels of SO₂ (90–100 nl l^–1)and O₃ (70–80 nl l^–1) either separately or together.The clones used were: Populus deltoides var. missiouriensisMarsh., P. nigra cv. ‘italicd’ L., and the hybridsP. nigra cv. ‘italica’ xP. deltoides (He-X/3) andP. nigra cv.‘italica’ x P. nigra cv. ‘Serres’(He-K/7). While most leaf abscission occurred within 20 d fromthe start of fumigation, stem lesions (intumescences), appearedonly after 72 d. Their anatomical characteristics include theformation of lysigenous aerenchyma in the lower parts of theintumescence, the sloughing of superficial cells from the injuredarea, and the development of crystalline formations on the surfaceof the lesions. P. deltoides exhibited the least morphologicalresponse to the gases. Ethylene released from fumigated leaves was determined at thesame gas concentration of SO₂ (100 nl l^–1), O₃ (75 nll^–1) and their mixture. Leaves of P. deltoides consistentlyshowed the lowest ethylene production after the gas treatments.P. ‘italica’ production was higher but was littlealtered by the treatments. The two hybrids He-X/3 and He-K/7showed the greatest increases in ethylene evolution with time.With He-K/7 exposed to the gas mixture the production of ethylenedecreased after the initial sharp rise during days 1–2,and reflected the considerable leaf damage observed after day3. The results suggest that sensitivity to air pollution, (as shownby leaf abscission and the formation of stem intumescences)can be correlated with the level of pollutant-induced ethyleneevolution from leaves. Initially high levels could induce abscission,whilst prolonged production could be responsible for intumescenceinitiation. The discussion proposes a series of events fromSO₂ and/or O₃ entry into the leaf and the physiological reasonsfor the clonal differences. Key words: Sulphur dioxide, ozone, ethylene, poplar, leaf abscission, stem lesions     

The Interaction of Ultraviolet-B Radiation and Water Deficit in Two Arabidopsis thaliana Genotypes

It has been demonstrated, in both herbaceous and woody species,that tissue hydration resulting from exposure to drought isless pronounced if plants are concurrently exposed to ultraviolet-Bradiation (UV-B). An explanation for the mechanisms underlyingthis phenomenon has been elusive. Arabidopsis thaliana(L.) Heynh.genotypes, defective in specific defences against UV-B exposure,may permit more insightful study of drought-UV-B interactionsthan is possible with genetically uniform plants. Arabidopsishas a rosette stature and has predominantly abaxial stomata.Thus, it is difficult to investigate its stomatal behaviourand gas exchange using conventional techniques and instrumentation.In this study, the relative abundance of¹³C and¹²C in leaf tissue(¹³C) was used as a means of determining water use efficiency(WUE) and the relative balance, at the site of carbon fixation,between CO₂supply and demand. UV-B insensitive (L er) and sensitive(fah1)Arabidopsis genotypes were raised in a growth chamberand exposed to 6 kJ m^-2 d^-1UV-B irradiation and subjected todrought. In both genotypes, leaf desiccation was less pronouncedthan that of control plants that were subjected to drought butnot exposed to UV-B. The relatively low (more negative) leaf¹³C values (indicating low WUE), but high dry matter productionof the UV-B exposed plants suggest that their higher leaf watercontent was not primarily due to stomatal closure. We proposethat the mechanisms underlying the maintenance of higher leafwater content involved UV-B and water stress induced biosynthesisof stress proteins and compatible osmolytes. Copyright 2000Annals of Botany Company Arabidopsis thaliana, ultraviolet-B, water deficit, stable carbon isotopes, ¹³C, stomatal opening, tissue dehydration, dehydrin     

Effects of Different CO2 Environments on the Photosynthesis-Yield Relationship and the Carbon and Water Balance of a White Clover (Trifolium repens L. cv. Blanca) Sward

Effects of atmospheric CO₂ enrichment to a level above 600 parts10^–6 on leaf and canopy gas exchange characteristics wereinvestigated in Trifolium repens, using an open system for gasexchange measurement. The cuvettes of the system served as growthchambers, allowing continuous measurement in a semi-controlledenvironment of ±350 and ±600 parts 10^–6CO₂, respectively. Carbon balance data were compared with cropyield and effects on the canopy level were compared with measuredleaf responses of photosynthesis and stomatal behaviour. Photosyntheticstimulation by high CO₂ was stronger at the canopy level (103%on average) than for leaves (90% in full light), as a consequenceof accelerated foliage area development. The latter increasedabsolute water consumption by 16%, despite strong stomatal closure.The overall result was a 63% improvement in canopy water useefficiency (WUE), while leaf WVE increased almost 3-fold insaturating light. The stomatal response was such that, whilethe internal CO₂ concentration in the leaf, ch increased withrising atmospherical CO₂ concentration, c_a, ci/c_a was somewhatdecreased. Total canopy resistance, R_c, was generally lowerat high CO₂ levels, despite higher leaf resistance. Higher canopyCO₂ loss at night and faster light extinction in a larger-sizedhigh CO₂ canopy were major drawbacks which prevented a furtherincrease in dry matter production (the harvest index was increasedby a factor 1.83). Key words: CO₂ enrichment, canopy CO₂ exchange, carbon balance, water use efficiency, leaf and canopy resistance     

Water use efficiency by alfalfa: Mechanisms involving anti-oxidation and osmotic adjustment under drought

Water use and mechanisms relating to osmotic adjustment and anti-oxidation were investigated in alfalfa (Medicago sativa L.) plants under reduced water availability. Water use efficiency (WUE), MDA and proline contents, and antioxidant enzyme activities were measured in three alfalfa cultivars under three levels of soil water availability in a greenhouse pot experiment. WUE was determined indirectly using discriminating carbon isotope composition. WUE increased with the severity of water deficit. Under all water regimes examined, cv. Longdong showed the greatest WUE values and the least reduction in biomass production under a 50% soil field water capacity. Stomatal density increased with increasing water deficit, but stomatal conductance decreased. This suggests that water stress can increase WUE by modifying stomatal regulation of the balance between the rates of CO₂ assimilation and water loss. The maintenance of leaf physiological function and leaf water status suggests that alfalfa has some mechanisms to maintain cell function when the plant is subjected to water deficit. The increase in the MDA content under drought conditions indicates that some degree of damage to cell membranes is unavoidable, whereas other results showing increases in the contents of proline and soluble sugars and activities of superoxide dismutase, peroxide dismutase, and catalase indicate how cell function may be to some extent maintained to result in the higher WUE. Alfalfa is shown to exhibit cultivar-specific differences in WUE with the maintenance of cell function under water deficit being related to anti-oxidation and osmotic adjustment.     

Growth and Physiology of One-year old Poplar (Populus) Under Elevated Atmospheric CO2 Levels

The effects of elevated atmospheric CO₂ concentrations on theecophysiological responses (gas exchange, chlorophyll a fluorescence,Rubisco activity, leaf area development) as well as on the growthand biomass production of two poplar clones (i.e. Populus trichocarpax P. deltoides clone Beaupré and P. x euramericana cloneRobusta) were examined under open top chamber conditions. Theelevated CO₂ treatment (ambient + 350 µmol mol^-1) stimulatedabove-ground biomass of clones Robusta and Beaupré afterthe first growing season by 55 and 38%, respectively. This increasedbiomass production under elevated CO₂ was associated with asignificant increase in plant height, the latter being the resultof enhanced internode elongation rather than an increased productionof leaves or internodes. Both an increased leaf area index (LAI)and a stimulated net photosynthesis per unit leaf contributedto a significantly higher stem biomass per unit leaf area, andthus to the increased above-ground biomass production underthe elevated CO₂ concentrations in both clones. The larger LAIwas caused by a larger individual leaf size and leaf growthrate; the number of leaves was not altered by the elevated CO₂treatment. The higher net leaf photosynthesis was the resultof an increase in the photochemical (maximal chlorophyll fluorescenceFm and photochemical efficiency Fv/Fm) as well as in the biochemical(increased Rubisco activity) process capacities. No significantdifferences were found in dark respiration rate, neither betweenclones nor between treatments, but specific leaf area significantlydecreased under elevated CO₂ conditions.Copyright 1995, 1999Academic Press Biomass, chlorophyll a fluorescence, elevated CO₂, growth, Populus, poplar, photosynthesis, respiration, Rubisco