The Effect of Shading on the Photosynthetic Rate and Longevity of Grass Leaves

The rate at which the net photosynthesis of grass leaves grownin bright light (119 W m^–2) decreased as they aged wasincreased by severe shading (to 21 W m^–2 or less). However,less severe shading (light intensities of 36 W m^–2 ormore) had no effect. The decrease in photosynthesis was unaffectedby whether the whole plant was shaded or only the leaf whosephotosynthesis was measured. In both shaded and unshaded leaves, photosynthesis measuredin bright light fell faster as the leaf aged than did photosynthesisin dim light. Both mesophyll and stomatal diffusion resistancesrose as the leaf aged but the former rose faster. The chlorophyllcontent fell only towards the end of the life of the leaves.     

Effect of Flowering on the Photosynthetic Capacity of Ryegrass Leaves Grown With and Without Natural Shading

The photosynthetic capacity of newly expanded leaves of vernalizedor non-vernalized plants of S24 perennial ryegrass (Lolium perenneL.), grown in long or short photoperiods, was measured in twoexperiments. In the first, leaves were protected from shadingduring development, while in the second, the natural shade ofneighbouring tillers in a sward was allowed. In the first experiment there was little effect of vernalization,day length or flowering, and leaves in all treatments had photosyntheticrates at 250 W m^–2 of between 28 and 32 mg CO₂ dm^–2h_–1.In the second experiment the photosynthetic rate of successiveleaves fell as sward leaf area increased. This downward trendwas reversed, however, in flowering tillers in the vernalizedlong-day treatment, while in the other treatments, which didnot flower, photosynthetic capacity continued to fall. It isconcluded that the leaves of reproductive tillers have highphotosynthetic capacities because stem extension carries themto the top of the canopy where they are well illuminated duringexpansion. Lolium perenneL, ryegrass, photosynthetic capacity, flowering, shading, vernalization     

遮荫对甜瓜叶片光合特性的影响

以适宜不同栽培条件的3个甜瓜品种为材料,研究了遮荫对其光合色素含量、净光合速率及比叶重等叶片特性的影响。结果表明:与正常光照相比,遮光处理能诱使甜瓜叶片叶绿素和类胡萝卜素含量显著提高,叶绿素a/b显著降低。全光照条件下,3个甜瓜品种的净光合速率日变化曲线均呈双峰型,有明显的"光合午休"现象,而在遮荫条件下则呈单峰曲线变化,且光合峰值出现的时间比全光照下推迟;遮光条件下甜瓜叶片气孔导度日变化曲线与其净光合速率日变化类似。3个品种间比叶重在全光照条件下差异不显著,但遮荫显著降低了壮龄叶片的比叶重,且遮荫强度越重,比叶重越小;品种‘黄河蜜3号’壮龄叶的比叶重降幅(31.83%)显著大于‘银帝’(27.22%)和‘玉金香’(26.01%)。可见,遮荫降低了甜瓜叶片的净光合速率和功能叶片的比叶重,植株通过增加自身叶片光合色素含量以增强对环境的适应性,缓解遮荫对其的影响,品种‘银帝’表现出较强的耐弱光性。     

遮荫对雪茄外包皮烟生长和光合特性的影响

采用全光照(Lck)与遮荫处理———透光率为71%(L1)、63%(L2)和22%(L3),对雪茄外包皮烟生长发育及其光合特性进行了研究.结果显示:(1)随着透光率的降低,烟株茎变细,叶片变薄;株高和叶面积各处理均先增加后降低,且在L2遮荫条件下株高和叶面积显著高于其它处理,分别达最大值(32.5 cm,47 620 cm2);根系干重显著降低,总干重先增加至透光率为63%时达最大值,当透光率降至22%时又显著降低;净光合效率(Pn)呈先增加后降低趋势,且在透光率为71%的遮荫条件下达最大值;(2)遮荫处理可显著提高雪茄外包皮烟叶绿素含量和Fv/F0值,使ΦpsⅡ、Fv/Fm和QP值增大、QN和Chl a/b的值降低.研究表明,透光率为63%的遮荫处理下雪茄外包皮烟植株地上部分生长最好.     

遮荫对黑茶藨子叶片形态结构和光合特性的影响

以黑茶藨子为试验材料,通过人工遮荫的方式,研究了不同遮荫强度（全光照、20%和60%遮荫）和遮荫时间（初期、中期和后期）对黑茶藨子叶片形态解剖结构和光合特性的影响。结果表明：（1）20%、60%遮荫处理的叶片厚度均显著低于全光照处理,上下表皮厚度则高于全光照处理;随着遮荫强度的加大,栅栏组织与海绵组织厚度比值大小均呈减少趋势,随着遮荫时间的延长,呈增加趋势。（2）遮荫初期和中期,20%遮荫处理的叶片净光合速率（P_n）比全光照和60%遮荫处理的值略高,但差异并不显著（P>0.05）,其蒸腾速率（T_r）、水分利用效率（WUE）也略有增加;但是,60%遮荫处理的叶片净光合速率（P_n）显著低于全光照处理（P<0.05）。遮荫后期,60%遮荫处理的叶片净光合速率（P_n）显著高于全光照处理,且水分利用效率（WUE）、气孔导度（G_s）、蒸腾速率（T_r）均显著高于全光照和20%遮荫处理。综上所述,遮荫处理导致叶片厚度减少,海绵组织比例增加,有利于减少透射光中的光量子丧失,提高光能利用效率;生长早期和中期作20%轻度遮荫处理,后期作60%中度遮荫处理能提高植株对光和水分的利用效率、维持较高的光合速率、延缓衰老。     

遮阳对白花前胡叶片光合特性的影响

为规范白花前胡(Peucedanum praerupterum)种植和提高产量,对不同光强下白花前胡的光合特性进行了研究.结果表明,与遮阳40％和60％相比,对照(CK)和遮阳20％的白花前胡叶片具有更高的最大电子传递速率[分别为247.129和266.866μmol/(m2·s)]和最大净光合速率[分别为25.621...     

遮荫对半夏叶片光合色素与保护酶活性的影响

对半夏进行不同程度遮荫处理,研究了其生长过程中叶组织的光合色素含量、叶绿素a/b值、保护酶体系(SOD、POD、CAT)活性和丙二醛(MDA)含量的变化及其生理特性.结果表明:不同处理的半夏在生长过程中,光合色素的含量呈先升后降的趋势;与全光照相比,遮荫处理的叶绿素含量较高,叶绿素a/b值较低,类胡萝卜素含量在生长发育中早期较低而后期较高;SOD、POD、CAT活性呈由低到高再降低的趋势,MDA含量持续升高;遮荫处理的SOD、POD活性和MDA含量均低于全光照处理,CAT活性则表现为先高于后低于全光照处理.适度的遮荫可以提高半夏叶绿素的含量,降低膜系统受到的伤害,改善半夏的倒苗状况,为半夏叶片的生长提供较好的环境.     

不同光照梯度的遮荫处理对绒毛番龙眼幼苗生长的影响

在不同光照梯度,即100%自然全光照(natural sunlight,NS)、37.3%NS、15.5%NS、4.2%NS、1.6%NS和0.6%NS的人工遮荫条件下,研究了西双版纳季节雨林冠层树种绒毛番龙眼(Pometia tomentosa)幼苗的早期生长和定居后的生长特点。结果表明,光照是影响幼苗生长的重要环境因子。生长早期的幼苗基径和复叶数随遮荫程度的增加而降低;主根长、根冠比、总干重和单株叶面积均以37.3%NS处理最大;比叶面积随遮荫程度的增加而增大,而相对生长率则降低;幼苗株高在0.6%NS下增长最快,表明种子中贮藏的营养物质对幼苗的早期生长可能具有重要作用。37.3%NS处理对定居后绒毛番龙眼幼苗的生长最有利,幼苗的株高、基径、复叶数、叶轴长、复叶最多小叶数、单株叶面积、相对生长率和净同化率均在37.3%NS处理下获得最大增长;幼苗总干重随光照强度的减弱而降低;比叶面积在15.5%NS处理时最大。幼苗比叶面积和根冠比在生长过程中的波动可能是光照和土壤水分共同作用的结果。     

遮荫对油用牡丹植株生长和光合特性的影响

设置100%全光照(L0)、50%全光照(L1)、25%全光照(L2)和15%全光照(L3)4种光环境,分析不同遮荫环境对油用牡丹的生长、光合作用及叶绿素荧光参数的影响。结果表明:(1)油用牡丹的花朵数量、比叶重、气孔密度在L2和L3处理下显著低于L0处理,但L1较L0无显著变化;随着遮荫水平增加,油用牡丹种子数量、气孔器面积百分比逐渐下降,且在4个不同处理间差异显著。(2)油用牡丹叶片最大净光合速率(Pmax)、光补偿点(LCP)和光饱和点(LSP)在遮荫条件下均有不同程度降低,L2和L3处理的Pmax和LSP显著低于L0,但L1较L0无显著变化。(3)L3处理的光系统Ⅱ(PSⅡ)的最大量子效率(Fv/Fm)为0.76,显著低于其余3个光照处理;随光化光诱导时间的增加,开放的PSⅡ反应中心的激发能捕获效率(Fv′/Fm′)呈逐渐下降并趋于稳定的趋势,而PSⅡ的实际量子产量效率(ΦPSⅡ)、光化学猝灭系数(qP)、非光化学猝灭系数(NPQ)呈逐渐增加并趋于稳定的趋势,稳定后的Fv′/Fm′、ΦPSⅡ值表现为L0L1L2L3,NPQ大小顺序为L3L2L1L0,但不同处理间的qP无显著差异。研究发现:过度遮荫(15%~25%自然光强)严重抑制了油用牡丹的净光合速率,而且与产量直接相关的花朵数量和种子数量也显著下降,最终造成严重减产;在云南昆明地区50%~100%之间的自然光可能是油用牡丹较为合适的生长光强。     

Photosynthetic Characteristics of Spinach Leaves Grown with Different Nitrogen Treatments

Spinach plants (Spinacia oleracea L.) were grown hydroponicallywith different concentrations of nitrate nitrogen, ranging from0.5 to 12 mM, in a glasshouse under full sunlight. Using anopen gas exchange system, the rate of CO₂ assimilation, A, wasdetermined as a function of intercellular partial pressure ofCO₂, P_i, with a constant amount of absorbed light per unit Chl.When expressed on a leaf area basis, A measured at high irradianceand at p_i=500 µbar, was proportional to the in vitro rateof uncoupled whole-chain electron transport as well as to Chlcontent. There was a curvilinear relationship between the mesophyllconductance (the slope of the A : P_i curve near the CO₂ compensationpoint) and the in vitro RuBP carboxylase activity. The curvaturedid not appear to be due to enzyme inactivation in vivo in leaveswith high nitrogen contents. The curvature suggested the presenceof a CO₂ transfer resistance between the intercellular spacesand the site of carboxylation of 2.2 m² s bar mol^–1 CO₂,which is similar to that previously observed in wheat. Thisimplied that, while nitrogen deficiency increased the ratioof in vitro activity of electron transport to that of RuBP carboxylase,the two activities remained balanced in vivo. Irradiance response curves were determined by both net CO₂ andO₂ exchange. The two methods gave reasonable agreement at lightsaturation. The quantum yield measured by O₂ evolution was 0.090?0.003mol O₂ mol^–1 absorbed quanta, whereas after correctingfor p_i = 500µbar, the quantum yield for CO₂ assimilationwas only 82% of that measured by oxygen evolution. ²Present address: Plant Environmental Biology Group, ResearchSchool of Biological Sciences, The Australian National University,G.P.O. Box 475, Canberra, A.C.T. 2601, Australia. (Received July 29, 1987; Accepted November 2, 1987)     

The Effect of Shading During Vegetative and Reproductive Growth on the Photosynthetic Capacity of Leaves in a Grass Sward

The decline in photosynthetic capacity of successive newly expandedleaves, which occurs as a vegetative grass sward increases inleaf area, was prevented in a field sward of S24 perennial ryegrass(Lolium perenne L.) by protecting tillers from shading by theirneighbours. This adds support for the view that the declineis caused by the shading of leaves during their expansion. However, in a flowering sward where there is no such decline,the photosynthetic capacity of leaves was not reduced by shadingthem with a plastic mesh during expansion, although it was bypegging down tillers so that they developed at the bottom ofthe sward. Lolium perenne, perennial rye-grass, photosynthetic capacity, growth, shading     

不同遮光处理对猫须草生长及光合特性的影响

本文探讨全光照、遮光50%、遮光75%、遮光90%等4种处理对猫须草植株生长及光合特性的影响。结果表明,与全光照相比,3种遮光处理植株叶片净光合速率、蒸腾速率减少,叶片厚度及栅栏组织变薄,比叶鲜质量下降,植株分枝数减少,节间距、株高显著增加,植株根、茎、叶的生长量明显下降。从而表明,猫须草植株生长最适宜的光照条件为全光照。     

遮荫对风箱果幼苗光合能力和碳水化合物积累的影响

以1年生风箱果幼苗为材料,采用人工遮荫方式设置CK （全光）、轻度遮荫L1（60%全光）和重度遮荫L2（20%全光）3种光环境,测定不同光环境下风箱果幼苗的光合特性、光合色素含量、非结构性碳水化合物（NSC）积累等,分析风箱果幼苗对不同遮荫环境的适应性。结果表明：风箱果属于阳生树种,对光环境的变化非常敏感;遮荫显著降低了表观量子效率（AQY）、最大净光合速率（P_max）、暗呼吸速率（R_d）、光补偿点（LCP）、光饱和点（LSP）和类胡萝卜素含量（Car）（P<0.05）,显著提高了叶绿素a （Chla）、叶绿素b （Chlb）、总叶绿素（Chl）含量和叶绿素/类胡萝卜素（P<0.05）;遮荫显著减少了根、茎、叶中NSC含量（P<0.05）,尤其是L2时,分别比CK减少了52.5%、44.9%和43.9%。综上所述,风箱果幼苗对于遮荫环境的适应和调节能力较差,生产实践中应栽植在阳光充足的环境中。     

遮荫对紫叶李幼苗叶片色素含量及光合速率的影响

以露地栽培的1年生紫叶李和绿叶李为试材,研究了全光照(CK)、中度遮荫(透光率为43%)、重度遮荫(透光率为27%)处理下叶片色素含量及净光合速率的变化.结果表明:在夏季,各处理紫叶李幼苗叶片叶绿素含量、类胡萝卜素含量随遮荫时间的延长逐渐升高,花色素苷含量、花色素苷含量/叶绿素含量比值降低;在秋季,各处理紫叶李幼苗叶片叶绿素含量、类胡萝卜素含量先升高后降低,而花色素苷含量、花色素苷含量/叶绿素含量比值则先降低后升高.在夏秋两季,紫叶李3种色素含量均高于绿叶李,全光照下的紫叶李叶片花色素苷含量、花色素苷含量/叶绿素含量比值及净光合速率日积分值均高于遮荫处理.紫叶李具备一定的喜光性,全光照环境有利于其彩色的呈现和光合性能的发挥.     

遮光处理对山杏幼苗光合特性的影响

以3年生山杏苗木为材料,用CIRAS-2型光合仪测定70%和40%遮光处理下其叶片光合生理参数的光响应和日变化特征,以探讨山杏光合特性对光照条件的适应机制.结果表明:(1) 随着遮光处理的加重,山杏叶片净光合速率(Pn)、光补偿点、光饱和点、暗呼吸速率及生物量等均呈下降趋势,70%和40%遮光处理下山杏叶片最大Pn分别比全光照显著下降58%和38%,而其表观量子效率分别显著提高31%和22%.(2)遮光处理下,山杏叶片Pn日变化呈"单峰"曲线,70%和40%遮光处理山杏叶片Pn日均值分别比全光照显著下降68%和49%;随着环境光照的增强,山杏叶片Pn下降的原因逐渐由气孔限制转变为非气孔限制为主.(3) 随光照强度的增加,山杏叶片蒸腾速率表现为增大趋势,70%和40%遮光处理的均值分别比全光照下降55%和16%;弱光环境下山杏具有降低蒸腾作用来提高水分利用效率的生理特性,水分利用效率均值和最大值均表现为70%遮光>全光照>40%遮光.研究发现,山杏较喜光,但对弱光也有一定适应能力,光照生态幅较宽,在干旱缺水的黄土丘陵区适当遮荫可提高其对有限水分的利用效率.     

遮荫对闽楠幼苗光合及其叶片解剖特性的影响

以2年生闽楠幼苗为材料,探讨不同遮荫处理［0(CK,全光照) 和30%、50%、70%遮荫］对闽楠［Phoebe bournei (Hemsl.) Yang］幼苗光合作用及其叶片解剖结构的影响,为闽楠的合理栽培及人工林混交树种的配置提供理论依据。结果表明：(1)与全光照处理(CK)相比,闽楠幼苗叶片净光合速率(P_n)、蒸腾速率(T_r)、气孔导度(G_s)、最大净光合速率(P_nmax) 、光饱和点(LSP)、光补偿点(LCP)及暗呼吸速率(Rd)均随遮荫强度的增加而显著下降;在30%和50%遮荫下,幼苗能通过提高水分利用效率(WUE)和表观量子效率(AQY),增加叶绿素含量来充分利用弱光环境;70%遮荫处理则影响闽楠幼苗的正常生长。(2)遮荫降低了闽楠幼苗叶片的气孔密度,但单个气孔器的面积显著增加;遮荫处理下,闽楠叶片和主脉明显变薄;栅栏组织和海绵组织厚度降低,排列稀疏,栅海比减小,有利于提高对光能的利用效率。(3)闽楠幼苗根、茎、叶及总生物量均在全光照下最大,遮荫抑制了植株生物量的积累。研究发现,闽楠幼苗在遮荫处理下生物量积累和光合效率降低,但同时在叶片解剖结构和功能上表现出对遮荫的适应性,从而表现出一定的耐荫性。     

The Effects of Increased Illumination and Shading on the Low-Light-Induced Decline in Photosynthesis in Cotton Leaves

An experiment was carried out to study whether low-light-induced damage to the photosynthetic system in leaves of cotton (Gossypium hirsutum cv. Deltapine) which are below the compensation point in the canopy can be arrested and reversed by increased illumination. In addition it was intended to find out whether the photosynthetic system in leaves of shade plants show a greater resistance to low-light-induced damage than leaves of plants from more exposed habitats. The plants were grown at high density, and increased illumination to the shade leaves in the canopy was achieved by thinning the stand. Thinning was carried out at two stages and its effects on the decline in the photosynthetic capacity of the 4th leaf were followed. An early thinning was carried out shortly after the 4th leaf dropped below the compensation point and a late thinning 2 weeks later. Comparison was also made between the low-light-induced damage to the photosynthetic capacity of the 4th leaf in plants grown under two light regimes during the progressive increase in self-shading of the 4th leaf within the canopy. It was observed that both types of thinning arrested the low-light-induced damage to the photosynthetic system in shade leaves. The decline in photosynthetic capacity of the 4th leaf was stopped after both early and late thinning. The dry weight of the shoot system in the early and late thinned plants was not significantly different. It was double that of the control plants. The plants thinned early did not have higher shoot weight than the late thinned plants since there was a rapid shedding of flowers and fruits after early thinning. The 4th leaf in the early thinned plants showed a 30% increase in chlorophyll content and dry weight per unit leaf area. It is suggested that shedding of flowers and fruits, and increases in chlorophyll and dry weight per unit leaf area in the early thinned plants were caused by a change in the hormonal balance of the plants. The photosynthetic system in leaves of shade plants showed a greater resistance to damage by low light intensity than the photosynthetic system in leaves of plants grown at higher light intensities.     

The Effects of Copper Supply and Shading on Retranslocation of Copper from Mature Wheat Leaves

Plants of Gamenya wheat (Triticum aestivum L.) were grown inpots of a Cu-deficient sand at two levels of Cu (deficient andsufficient), and harvested on days 13, 22, 28 and 38. In 50per cent of the pots in each Cu treatment, the oldest leaf andleaf 2 of the main stem were shaded when they reached full expansion. The Cu content of the oldest leaf of Cu-sufficient, unshadedplants was high at day 13 and declined rapidly to day 38. Thatof Cu-deficient, unshaded plants was initially relatively lowand declined much more slowly, so that at day 38 it resembledthat of Cu-sufficient plants. Shading the oldest leaf acceleratedthe loss of its Cu in both Cu-deficient and Cu-sufficient plants.The effects of shading and of Cu supply on the loss of Cu fromthe oldest leaf paralleled their effects on the loss of N andchlorophyll. The results suggest that most of the Cu in theoldest leaf does not move out until the leaf senesces. In Cu-deficient plants retention of Cu by old green leaves accentuatedCu deficiency. The release of Cu, resulting from shading theold leaves of Cu-deficient plants, stimulated the growth ofnew leaves. In Cu-sufficient plants, shading depressed growth. copper, shading, retranslocation, wheat, Triticum aestivum L.     

遮荫对月季光合特性及生长发育的影响

采用人工遮荫法研究不同程度遮荫(75%、50%和25%全光照,以全光照为对照)处理对月季的生长发育、光合特性及叶绿素荧光参数的影响。结果表明:(1)随着遮荫程度的增加,月季的叶片厚度、花径、成花率均呈降低趋势,叶绿素含量呈增加趋势;净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、胞间CO2浓度(Ci)降低,气孔限制值(Ls)升高,Pn下降的主要原因可能为气孔限制。(2)月季在遮荫条件下的光饱和点和光补偿点、暗呼吸速率下降,表现出其对光照降低的生理适应机制;其光饱和点在600~1 200μmol·m-2·s-1,光补偿点在29.89~62.95μmol·m-2·s-1,CO2补偿点在78.16~89.41μmol·mol-1,CO2饱和点在1 100μmol·mol-1左右,潜在光合能力13.06~25.63μmol·m-2·s-1,其对光的适应范围较宽,光照和CO2浓度对其光合能力的影响较大。(3)各处理条件下叶绿素荧光参数显示,月季在自然光和低光下(50%和25%全光照)叶片PSⅡ受到了明显伤害,光合作用原初反应过程受到抑制,光合电子传递受到影响。研究发现,月季虽是阳生植物,但光照生态幅较宽,轻度遮荫(75%全光照)能促进其光合作用效率,减少光抑制,植株长势好,成花率高。     

谷子叶片光合速率日变化及水分利用效率

通过降低空气湿度（ 从约３０ ％ 减少到５ ％ ） 、增加ＣＯ２ 浓度（ 从４００ μｌ ＣＯ２／Ｌ增加到７３０ μｌ ＣＯ２／Ｌ） 、烫叶鞘破坏韧皮部等处理对谷子叶片光合速率日变化和水分利用效率（ＷＵＥ） 进行了研究, 发现中午光合速率降低与光合产物积累有关; 虽然低大气相对湿度（５ ％ ） 使光合速率有所降低,但提高了ＷＵＥ。而烫叶鞘使光合物质积累既抑制了光合速率,又降低了ＷＵＥ。