菊花及其近缘种属植物耐涝评价体系建立及耐涝性鉴定

为发掘耐涝种质资源,建立了菊花近缘种属植物苗期耐涝性评价体系.根据盆栽淹水处理过程菊花近缘种属植物表型变化,将涝害指数划分为7级;采用叶色、叶形态、茎色、茎形态4个外观形态指标,并将其定量分级,制定等级得分标准及评价方案,然后以各指标得分的总和对耐涝性进行综合评价,建立评价体系.对57个菊花近缘种属植物进行了苗期耐涝性鉴定,结果表明,耐涝性鉴定时间以淹水6d为宜;菊花近缘种属植物对水涝较为敏感,大部分材料属于较不耐涝级,同种不同种源存在耐涝性差异;初步筛选出8份耐涝性强的菊花优异种质.     

涝渍胁迫下5种菊花近缘种属植物生理特性

采用土培模拟涝害的方法,对5种菊花近缘种属植物的根系活力、叶绿素含量和光合生理特性以及涝渍胁迫后的形态表现进行研究和观察,比较了其耐涝能力.结果表明:涝渍胁迫下,5种菊花近缘种属植物根系活力急剧下降,但紫花野菊在胁迫初期表现出强的根系活力;5种植物叶绿素含量总体呈现先升后降的趋势;涝渍胁迫15d时纪伊潮菊、泡黄金菊的光合强度明显降低,CO2同化作用下降,并出现负值,叶片已丧失光合作用能力,其次是大岛野路菊和那贺川野菊,而紫花野菊维持了一定水平的净光合速率.结合叶片外观形态观察发现,紫花野菊最为耐涝,泡黄金菊最不耐涝,而大岛野路菊、纪伊潮菊和那贺川野菊的耐涝性介于两者之间.     

栽培菊花与菊属-近缘属属间杂种杂交后代耐盐性的遗传分析

为了解菊花近缘种属植物耐盐性的遗传规律,对栽培菊花与菊属-近缘属属间杂种杂交后代耐盐性进行了遗传分析。以栽培菊花'韩2’为母本,大岛野路菊×芙蓉菊属间杂种为父本进行杂交,以盐害指数作为指标,通过水培法对获得的F₁群体进行耐盐性鉴定,并应用植物数量性状主基因+多基因混合遗传模型,采用单个F₂世代的分离分析方法对F₁群体耐盐性进行混合遗传分析。结果发现:F₁群体的耐盐性出现广泛分离,变异系数达53.63%,盐害指数的变异范围为3.33%-96.67%;中亲优势为2.47,未达到显著水平;将后代的耐盐性分为5个级别,其中高耐的占14.52%,耐盐的占38.70%,中耐的占30.65%,敏盐的占9.68%,高敏的占6.45%。F₁群体的耐盐性符合B-2模型,由两个主效基因控制,加性效应均表现正向增效,分别为18.06和19.13,显性效应表现负向效应,分别为-17.99和-1.44,主基因遗传率为61.14%,属高度遗传力。综合分析表明:菊花近缘种属植物耐盐性可通过杂交导入栽培菊花,实现栽培菊花耐盐性遗传改良;菊花近缘种属植物盐害指数受两对主基因的控制,主基因在F₁群体的遗传率属高度遗传力,耐盐性选育可在早期世代进行。     

遮阴对闽楠叶绿素含量和光合特性的影响

为探讨闽楠对不同光环境的光合适应机制,以2年生闽楠幼苗为材料,设置3个光照处理(全光照、遮光率50%和遮光率78%),适应6个月后,测定其叶绿素含量、气体交换和叶绿素荧光同步数据,研究不同光环境处理对闽楠叶片叶绿素含量、叶绿素荧光参数和光合特性的影响.结果表明: 3种光照处理下,闽楠叶片叶绿素a、叶绿素b、叶绿素(a+b)和类胡萝卜素含量大小次序为78%遮光率>50%遮光率>全光照,但不同光照处理对闽楠叶绿素a/b值没有显著影响.遮阴条件下,闽楠叶片光补偿点(LCP)降低,光饱和点(LSP)和表观量子效率(AQY)升高,说明遮阴条件下闽楠叶片对弱光和强光的利用能力均有所提高;最大净光合速率(P_{n max})、光下暗呼吸速率(R_d)和最大电子传递速率(J_max)均增大.在不同处理间,闽楠叶片净光合速率(P_n)、CO₂气孔导度(g_sc)、胞间CO₂浓度(C_i)和叶肉导度(g_m)均存在显著差异.P_n和g_m的大小顺序为: 78%遮光率>50%遮光率>全光照.78%遮光率处理下g_sc显著大于全光照.50%遮光率条件和78%遮光率条件下C_i均显著小于全光照.78%遮光率条件下PSⅡ实际光量子产量(F_v′/F_m′)、PSⅡ光化学效率(Φ_PSⅡ)和电子传递速率(J)均显著大于50%遮光率条件和全光照.由此可知,在遮阴条件下闽楠可以通过增加叶绿素含量、AQY、J、g_sc和g_m来增大光合能力.     

遮荫对13种盆栽棕榈植物生长的影响

研究13种盆栽棕榈植物在不同遮荫处理条件下的生长、叶片叶绿素含量、含水量及比叶重的变化,并通过系统聚类分析及主分量分析,将13种棕榈植物的耐阴性分为三类,其中缨络椰子、散尾葵和小琼棕较耐阴,国王椰子、假槟榔、金帝葵和美丽针葵耐阴性较差,短穗鱼尾葵、袖珍椰子、雪佛里椰子、穗花轴榈、蒲葵和棕竹等棕榈植物耐阴性居中.     

遮光对野扇花生长特性和生理指标的影响

以2年生野扇花为试验材料,研究了遮光率分别为0%、30%、60%、95%条件下其生长发育和生理指标的变化,以分析野扇花生长发育和生理指标与光照条件的关系,为其合理引种栽培提供理论依据.结果表明:随光强的减弱,野扇花的株高、地径、冠幅、分枝量都有一定程度的增加,最长枝枝长、叶长、叶宽、叶面积逐渐增大,且在60%遮光条件下植株的地径、分枝量、最长枝叶片数和节间长,以及叶鲜重和叶干重均表现出最佳状态;同时叶片含水量逐渐上升,比叶重显著下降,叶绿素a、叶绿素b、叶绿素(a+b)和胡萝卜素的含量显著增加,而叶绿素a/b值下降;其可溶性糖、可溶性蛋白的含量逐渐下降,淀粉和游离氨基酸的含量变化规律不明显,且全光照处理有利于初生代谢产物含量的积累.研究发现,野扇花在60%遮光处理下生长发育最好,其形态和观赏价值最佳,极度遮光不会抑制其正常生长;野扇花生长最适条件与其初级代谢产物积累最适条件不相同,它与植物所处的生长季节有密切关系.     

不同遮光处理对平茬后厚朴萌蘖株部分形态及生理指标的影响

以自然光照(遮光率0.0%)为对照,对遮光率20.0%、52.5%和78.6%条件下平茬后厚朴(Magnolia officinalis Rehd.et Wils)萌蘖株的部分形态和生理指标进行比较.结果表明:随遮光率提高,3个遮光处理组萌蘖株的株高呈现逐渐增大的趋势,萌蘖株叶中的叶绿素a、叶绿素b、类胡萝卜素和总叶绿素含量也基本上呈现逐渐增大的趋势,但萌蘖株的地径却呈现逐渐减小的趋势.萌蘖株的冠幅,单桩的萌蘖株数、叶片总数和叶芽总数,叶长和叶宽,单叶的干质量和叶面积,叶中叶绿素a含量与叶绿素b含量的比值(Chla/Chlb)和可溶性糖含量均在遮光率52.5%条件下最大,但仅冠幅、单桩叶片总数、单叶面积和叶中可溶性糖含量显著大于对照,分别较对照增加156.21%、28.18%、129.02%和64.31%;并且,多数指标在遮光率20.0%条件下居中、在遮光率78.6%条件下最小.然而,萌蘖株的叶长宽比、比叶质量及叶的相对含水量和可溶性蛋白质含量则在遮光率52.5%条件下最小,但仅比叶质量显著小于对照,较对照减少37.43%;并且,多数指标在遮光率20.0%条件下居中、在遮光率78.6%条件下最大.研究结果显示:适当的遮光处理能够促进平茬后厚朴萌蘖株的生长,遮光率52.5%为最优的遮光处理条件.     

“741杨”扦插苗耐阴性的研究

 用黑色遮阴网遮光,研究了741杨嫩枝扦插苗的耐阴性。共设置全日照(对照)、全日照的24.5％、7.5％和2.5％等4种光量。研究了光强对叶生长、叶解剖构造、叶绿素含量、光-光合曲线、新梢生长和生物量等指标。结果表明,741杨是一种喜光树种,在全日照下生长,其生物量等多项指标都高于各种遮光处理。741杨对24.5％光量有较强的适应补偿能力,其单片叶面积、新梢生长率、叶绿素含量、叶柄长度等都超过对照,但生物量还是低于对照34.4％。7.5％光量处理已接近741杨的耐阴极限。741杨扦插苗不能长期在2.5％的光量下生活。     

AM真菌增强孔雀草耐阴性的效应

于温室盆栽不同光照条件（遮光率分别为0%、24%、48%、72%、96%）下,对孔雀草Tagetes patula进行接种丛枝菌根（arbuscular mycorrhiza,AM）真菌幼套近明球囊霉Claroideoglomus etunicatum、摩西斗管囊霉Funneliformis mosseae、球状巨孢嚢霉Gigaspora margarita和不接种对照处理,测定孔雀草菌根侵染率、生长指标和生理指标,旨在评价AM真菌对孔雀草耐阴性的影响。结果表明,供试AM真菌均能侵染孔雀草根系形成典型的丛枝菌根,不同遮光处理均以接种F. mosseae的侵染效果最佳,强光及弱光均不利于AM真菌侵染,当遮光率为24%时,孔雀草生长状况最佳。与不接种对照相比,接种F. mosseae显著提高了孔雀草株高、茎粗、叶面积、根冠比、比叶重、着花数和花茎,单花花期延长,提高了根系活力、叶绿素a、叶绿素b、总叶绿素和可溶性糖含量,降低了脯氨酸含量,光补偿点下降,光饱和点升高,最大净光合速率增大。结果表明,适当遮荫有利于孔雀草生长发育,接种AM真菌能增强孔雀草对光照的适应能力,促进植株生长发育,减缓弱光造成的损伤,增强其耐阴性,且以接种F. mosseae效果最好。     

玉米苗期耐低铁能力的综合评价及其预测

为了筛选和鉴定耐低铁玉米品种应用于生产,本研究以23个玉米品种为材料,测定低铁胁迫和正常供铁(对照)玉米幼苗的株高、茎粗、可见叶、展叶、叶面积、根长、根体积、总干重、活性铁、含铁量、铁积累量和叶绿素含量等15个性状,以各性状的相对值作为衡量指标,利用主成分分析、隶属函数分析和聚类分析对其进行耐低铁能力的综合评价。结果表明不同玉米品种耐低铁能力存在明显的基因型差异;邡玉1号、福康玉909、正大619、正红102、福得2号、正红2号耐低铁能力较强;展叶数、叶面积、根长、根干重、铁积累量可作为玉米耐低铁品种苗期筛选指标;可利用玉米苗期耐低铁能力的回归模型:D=(-384.23+2.71X4+2.50X5+3.22X6+1.70X9+4.86X14)×10-3对玉米苗期耐低铁能力进行预测。     

Field assessment of sub-epidermal leaf anthocyanin, PSII photochemistry,and the xanthophyll-cycle as photoprotective mechanisms in two morphs of Agave striata

We tested the hypothesis that leaf epidermal pigments screen light of particular wavelengths from reaching the photosynthetic machinery, reducing dependence on the xanthophyll-cycle as an energy dissipation process. Under field conditions, photosynthesis and water relations were studied in two morphs of Agave striata that differ in leaf coloration (green vs. reddish-purple). Titratable acidity, chlorophyll fluorescence, and internal and surface leaf temperatures were measured under low irradiance by shading (30%) and full sunlight (100%) for six days. We also measured the reflectance ratio (R_RED: R_GREEN), an index of anthocyanin content and the change in photochemical reflectance index (ΔPRI), an index of xanthophyll-cycle de-epoxidation state (xanthophyll conversion). Our results showed that both morphs expressed typical CAM-activity with no significant differences under sun vs. shade. However, shading did reduce titratable acids in both morphs. Both morphs were well hydrated, with the relative water content (RWC) being greater than 93%. Leaf surface temperature was found to be significantly higher during the day in the green morph compared to the red morph under sun and shade. Dark level fluorescence (Fo), photochemical efficiency of PSII (Fv/Fm), and the quantum yield of PSII electron transport (Φ_PSII) were higher in the red morph under sun compared to the green morph. The value of qN (non-photochemical quenching) was significantly higher during the day for the green morph compared to the red morph and this higher qN value was associated with a greater xanthophyll conversion and surface leaf temperature. However, sunlight did not predispose either of the morphs to photoinhibition. It is clear that the sub-epidermal anthocyanins serve as a photoprotective mechanism in the red morph, screening light energy from reaching the photosynthetic machinery and reducing dependence on the xanthophyll-cycle. We concluded that under natural light conditions the leaves of two morphs tested utilized differential photoprotective mechanisms.     

Effect of partial shading on the photosynthetic apparatus and photosystem stoichiometry in sunflower leaves

The partial shading effect on the photosynthetic apparatus of the sunflower (Helianthus annuus L.) was examined by monitoring oxygen evolution, maximum quantum yield of PSII photochemistry in dark-adapted leaves (F_v/F_m), the chlorophyll (Chl) concentrations and the Rubisco contents, and leaf mass per area (LMA) at the leaf level and by determining the concentrations of cytochrome (Cyt) f and the reaction centres of photosystem (PS) I and PSII at the thylakoid level. In this experiment, partial shading was defined as the shading of 2^nd leaves with shade cloths, and the whole treatment was defined as the covering of the whole individuals with shade cloths. In the leaf level responses, oxygen evolution, LMA, Chl concentrations and Rubisco contents decreased in all shade treatments administered for six days. F_v/F_m remained constant irrespective of the shade treatments. On the other hand, in the thylakoid-level responses, the concentrations of the thylakoid components per unit Chl and the stoichiometry of the two photosystems showed no statistical difference among the shade treatments. The data obtained from the present study indicate that the partial shading affected the leaf-level responses rather than the thylakoid-level responses. The light received at the lower leaves might serve as a factor in the regulation of the leaf properties of the upper leaves due to the whole plant photosynthesis, while this factor did not have an effect at the thylakoid level.     

Dodonaea viscosa var. angustifolia leaf: New source of polysaccharide and its anti-oxidant activity

Ultrasonic technology was applied for polysaccharide extraction from the leaves of Dodonaea viscosa and response surface methodology (RSM) was used to optimize the effects of processing parameters on polysaccharide extraction yield. Three independent variables were extraction time (X₁), extraction temperature (X₂) and ultrasonic power (X₃), respectively. The statistical analysis indicated the independent variables (X₁, X₂, X₃), the quadratic terms (X₁₁ and X₃₃) and the interaction terms (X₁X₂, X₁X₃, X₂X₃) had significant effects on the yield of polysaccharides (P < 0.05). The optimal extraction conditions of D. viscosa leaf were determined as follows: extraction time 50.54 min, extraction temperature 85 °C and ultrasonic power 400 W. Under these conditions, the experimental yield of polysaccharides was 9.455 ± 0.24%, which was agreed closely with the predicted value (9.398%). The evaluation of anti-oxidant activity suggested that the polysaccharide exhibited significant protection against DPPH and hydroxyl radicals and could be explored as a nutraceutical agent.     

Effect of drought and ABA on growth, photosynthesis and antioxidant system of Cotinus coggygria seedlings under two different light conditions

We exposed seedlings of Cotinus coggygria var. cinerea to drought and exogenous abscisic acid (ABA) under two different light conditions. Two watering regimes (well-watered and drought), two exogenous ABA applications (no ABA and with ABA) and two light regimes (full sunlight and shade) were employed. Compared with well-watered treatment, drought treatment significantly reduced the relative growth rate, relative water content (RWC), net photosynthesis rate (A) and transpiration (E), but increased chlorophyll a (chla), carbon isotope (δ¹³C), endogenous ABA, malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents, and guaiacol peroxidase (POD) and catalase (CAT) activities. There was an apparent alleviation of drought effects by shade, as indicated by the lower relative growth rate, and chlorophyll, MDA and H₂O₂ contents, and increases in indoleacetic acid (IAA) and reduced glutathione (GSH) contents. On the other hand, the exogenous ABA application under shade induced protective effects on drought-stressed seedlings, as visible in RWC, MDA, A, stomatal conductance (g_s), E, δ¹³C, ABA and IAA values. In all, our results suggest that seedlings of C. coggygria are more sensitive to drought under full-light than under shade.     

Carbon and nitrogen translocation in response to shading of the seagrass Posidonia sinuosa

Translocation of carbon (C) and nitrogen (N) was investigated in response to shading of the seagrass Posidonia sinuosa in control (ambient light) and shade (below minimum light requirement) treatments after 10 d shading. A mature leaf was incubated in situ in ¹³C- and ¹⁵N-enriched seawater for 2 h and the appearance of the isotopes in the young leaf and adjacent rhizome monitored over 29 d. C and N isotopes gradually reduced in the mature leaf: of ¹⁵N contained in the entire shoot (mature leaf, young leaf and 4 cm rhizome), 95% (control) and 97% (shade) was found in the mature leaf after 2 h incubation and only 75% and 60% remained in the mature leaf after 29 d; 98% and 94% of ¹³C was found in the mature leaf after 2 h, and it had reduced to 36% and 44% after 29 d. This corresponded to an equal increase in the young leaf + rhizome indicating that the mature leaf is a source of these nutrients to the young leaf and rhizome. C translocation from mature leaves was not significantly affected by the shade treatment. In contrast, there was an increase in ¹⁵N taken up by the mature leaves (1.9× higher in the shade), the percent of ¹⁵N translocated to the young leaf and rhizome (24% in control and 40% in shade) and N concentration in the young leaf (1.24% control and 1.41% shade) and rhizome (0.86% control and 0.99% shade). Resorption of C and N was also estimated from changes in the total C and N content of the mature leaf over 29 d. N resorption from the mature leaf contributed up to 63% of young leaf N requirements in the control treatment but only 41% in the shade treatment. We conclude that uptake and translocation of N by mature leaves is a response to shading in P. sinuosa and would provide additional N to growing leaves, enhancing light harvesting efficiency.     

Acclimation responses of mature Abies amabilis sun foliage to shading

This paper addresses two main questions. First, can evergreen foliage that has been structurally determined as sun foliage acclimate physiologically when it is shaded? Second, is this acclimation independent of the foliage ageing process and source-sink relations? To investigate these questions, a shading and debudding experiment was established using paired branches on opengrown Abies amabilis trees. For each tree, one branch was either shaded, debudded, or both, from before budbreak until the end of summer, while the other branch functioned as a control. Foliage samples were measured both prior to and during treatment for photosynthesis at light saturation (A _max), dark respiration, nitrogen content, chlorophyll content, chlorophyll-to-nitrogen ratio and chlorophyll a:b ratio. All age classes of foliage responded similarly during the treatment, although pre-treatment values differed between age classes. Within 1 month after the treatment began, A _max was lower in shaded foliage and remained lower throughout the treatment period. For debudded branches, A _max was lower than the controls only during active shoot elongation. At the end of the treatments in September, A _max in shade-treated sun foliage matched the rates in the true shade-formed foliage, but nitrogen remained significantly higher. By 1.5 months after treatment, chlorophyll content in shaded foliage was higher than in controls, and the chlorophyll a:b ratio was lower for the shaded foliage. On debudded branches, chlorophyll content and chlorophyll a:b ratio were similar to the values in control samples. Shading lowered the rate of nitrogen accumulation within a branch, while removing debudding decreased the amount of sequestered N that was exported from the older foliage to supply new growth. By September, chlorophyll content in shade-treated foliage was higher than that in the control sun foliage or in true shade foliage. The chlorophyll increase as a result of shading was unexpected. However, the chlorophyll-to-nitrogen ratio was identical for the shade-treated sun foliage and the true shade foliage while being significantly lower than the control sun foliage. It appears that acclimation to shading in mature foliage involves a reallocation of nitrogen within the leaf into thylakoid proteins. A redistribution of resources (nitrogen) among leaves is secondary and appears to function on a slower time scale than reallocation within the leaf. Thus, A. amabilis foliage that is structurally determined as sun foliage can acclimate to shade within a few months; this process is most likely independent of ageing and is only slightly affected by source-sink relations within a branch.     

A morphophysiological analysis of the effects of drought and shade on <Emphasis Type="Italic">Catalpa bungei</Emphasis> plantlets

The interactive effects of shade and drought on the morphological and physiological traits of Catalpa bungei plantlets were assessed. Seedling growth, biomass, biomass allocation, leaf morphology, chlorophyll (Chl) content and gas-exchange parameters were measured in plants raised for 3 months under three light levels [80% (HI), 50% (MI), 30% (LI)] and two water levels [moisture (M) and drought (D)]. The results showed that shade greatly decreased growth, biomass, leaf area (LA) and Chl a/b; increased specific leaf area (SLA) and Chl content; and reduced photosynthetic rate (P _n). Drought reduced the growth, biomass, LA, SLA, Chl a/b, P _n, stomatal conductance (G _s), transpiration rate (T _r) and intercellular carbon dioxide concentration (C _i) and increased the Chl content. Stomatal closure was an early physiological response to water stress. Light, water and their interaction significantly affected plant traits and their bivariate relationships. The phenotypic plasticity index of light (0.47) was much higher than that of water (0.21), indicating that light was the main driver of the variations observed. Under drought stress, growth, biomass, leaf and stem biomass allocation significantly decreased in the HI and MI environments, whereas no significant difference was observed in growth or biomass parameters under the LI condition. Furthermore, no significant difference was observed in P _n, G _s, or T _r under the LI condition under water stress. Our results showed that shade did not alter the negative effects caused by drought stress in MI but did alleviate the negative effects of the LI condition. In summary, the effect of drought on C. bungei plantlets depends on the irradiance conditions.     

荆条叶性状对野外不同光环境的表型可塑性

光照是影响植物生长和分布的重要环境因子。对生长在野外5种不同光环境下(林外、阔叶林林缘、阔叶林林下、针叶林林窗和针叶林林下)的荆条的叶片进行取样研究,通过对光合作用光响应曲线、叶绿素荧光、叶绿素含量、叶片氮磷含量以及叶片形态的测量,来反映荆条对不同光环境的表型可塑性。研究结果表明,荆条叶片对于野外不同的光环境具有很好的适应机制,叶片功能性状受到结构性状的调节。低光下通过高的比叶面积(SLA)、单位质量叶绿素含量、光系统II最大量子产量,低的暗呼吸速率、光饱和点、光补偿点、叶绿素a,b的比值来提高对光能的利用效率,维持生长;高光下则通过与SLA有关的叶片结构的变化对光合作用进行调节。大多数的叶性状只受到日光照总量的影响,SLA的大小与日最高光强有关,可以对不同日变化模式的光照做出迅速的响应,是适应不同光照的敏感指标。尽管光照是不同光环境下影响荆条叶性状的主要环境因子,土壤养分含量同样会对叶性状产生影响,高土壤养分下的高叶长与叶柄长的比值体现了植物对资源获取和支撑结构之间分配的权衡。     

遮荫对金莲花光合特性和叶片解剖特征的影响

以金莲花为材料,系统研究了不同遮荫处理(全光照、40%、60%和80%遮荫)对金莲花叶片光合特性和叶解剖结构的影响,为金莲花引种驯化和抚育管理提供理论依据。结果表明:全光照下金莲花叶净光合速率有明显光合"午休"现象,遮荫处理下"午休"现象不明显。其中,40%遮荫处理显著促进了金莲花叶片净光合速率,80%遮荫处理则起抑制作用;40%和60%遮荫处理促进金莲花叶蒸腾速率和气孔导度的提高,降低了蒸汽压亏缺,有利于光合作用的进行;80%遮荫处理下胞间CO2浓度提高,气孔限制值和蒸汽压亏缺均显著高于其它处理,抑制了金莲花叶蒸腾作用和光合作用;遮荫处理降低了金莲花叶光补偿点和暗呼吸速率,40%和60%遮荫处理下表观量子效率和最大净光合速率提高,说明金莲花有一定耐荫性;金莲花叶光合特性与解剖结构关系密切。遮荫降低了金莲花叶气孔密度和气孔指数,但气孔纵轴长和横轴长显著高于对照。40%和60%遮荫处理下,单叶气孔数量没有明显变化;遮荫下金莲花叶片增厚。栅栏组织厚度和细胞层数减少,栅栏细胞宽度加大,且第二层栅栏细胞有向海绵组织过度的趋势。海绵组织厚度增加,栅栏组织/海绵组织比值减小。随遮荫度增高,栅栏组织和海绵组织细胞间隙增大。该结构有利于提高对光能的利用效率;遮荫处理促进维管束的发育,维管束数量增加,木质部、韧皮部分化明显,其中中脉导管直径和导管数目增加,有利于蒸腾作用和光合作用的进行。     

Physiological and growth characteristics of Ginkgo biloba L. exposed to open field and shade enclosure during the reproductive stage

The current study compares responses to open field and shade enclosure condition (plastic shading nets were used to imitate a natural shading rate) to test the possible benefit of shading in terms of physiological and growth characteristics in Ginkgo biloba L. during the reproductive stage in summer. Compared with the net shade treated plants (NS-plants), the open-field plants (O-plants) contained lower chlorophyll (Chl) a + b content and Chl a/b ratio, and exhibited a decreased ratio of Chl/Car. Results showed that the chlorophyll fluorescence characteristics including maximum PSII photochemical efficiency (F _v /F _m ), potential electron transport per excited leaf cross-section (ET₀/CS₀), potential electron transport per PSII reaction center (ET₀/RC), dissipation per excited leaf cross-section (DI₀/CS₀), dissipation per PSII reaction center (DI₀/RC), and overall performance index of PSII photochemistry on absorbtion basis (PI_ABS) were altered by the net shade treatment. It was observed that the grana were illegible and difficult to distinguish by transmission electron microscopy, especially, in the cells of O-plants in which phenols were observed in the vacuole. The phenomenon of photoinhibition induced by excessive irradiance was confirmed by the abnormally high levels of the reactive oxygen species. Moreover, antioxidant enzymes activities were induced by high irradiance in the ginkgo leaves. In addition, significant differences were observed in the fresh weight and dry weight of leaves and seeds. Comparison of the variation of underlying physiological and biochemical mechanisms suggested that there was a better efficiency of ginkgo plants under artificial net shade conditions. Therefore, ginkgo plant would be best grown at 30–35 % of natural irradiance in summer months to be more profitably harvested and then meet the increasing demand of leaves and seeds.