热带雨林剑叶凤尾蕨(Pteris ensiformis)对光强变化的适应

野外调查表明剑叶凤尾蕨能适应不同的光环境,本研究测定剑叶凤尾蕨在两种不同光环境下的适应能力,在热带雨林林下和林窗生长40d后,林下生长的剑叶凤尾蕨比林窗生长的植株有较多的叶片数,大的冠幅,高的叶绿素含量和表观量子效率。同时。林下生长的剑叶凤尾蕨有高的光化学效率和较低的非光化学耗散能力,这说明低光植物表现出有较高的能量转换能力,而两种光强生长的剑叶凤尾蕨最大光合放氧速率相似。这可能与在高光下的非辐射耗散的提高和光合机构的损伤有关,研究结果表明,剑叶凤尾蕨通过光合器官的调整对不同光强的适应。以促进剑叶凤尾蕨在不同光环境的生长能力。     

4种木本植物叶片的光合电子传递和吸收光能分配特性对光强？…

以气体交换和叶绿素荧光测定相结合的方法研究了亚热带自然林乔木荷树、黧蒴和林下灌木九节、罗伞幼苗的光合电子传递及激发能利用的分配对生长光强的适应特性。４种植物生长于１００％、３６％和１６％的自然光下８个月,叶片的光化学速率和热能耗散速率随光强增大而提高,热能耗散占总的光能吸收的比例也因光强不同而改变,１６％光下的相对热耗散率约为４０％－４５％,１００％自然光下增大至５０％－７５％。叶片总的非环式电子     

4种木本植物叶片的光合电子传递和吸收光能分配特性对光强的适应

以气体交换和叶绿素荧光测定相结合的方法研究了亚热带自然林乔木荷树、黧蒴和林下灌木九节、罗伞幼苗的光合电子传递及激发能利用的分配对生长光强的适应特性。4种植物生长于100%、36%和16%的自然光下8个月,叶片的光化学速率和热能耗散速率随光强增大而提高,热能耗散占总的光能吸收的比例也因光强不同而改变,16%光下的相对热耗散率约为40%～45%,100%自然光下增大至50%～75%。叶片总的非环式电子流速率及其分配到光呼吸的比例在100%光强下最高。乔木和灌木的电子传递和光能分配特性在16%光下相似,在100%光下差别较明显。除灌木种有较高的热耗散比例之外,其余的参数皆比乔木的低。结果表明乔木与灌木皆可通过提高激发能热耗散比例和提高光合电子传递向光呼吸的比例来适应于高光强条件。     

光强对两种硅藻光合作用、碳酸酐酶和RubisCO活性的影响

为研究海洋浮游硅藻光合固碳能力与光强的关系, 以三角褐指藻和威氏海链藻为实验材料, 测定了不同光强培养下三角褐指藻和威氏海链藻生长、光合特性、碳酸酐酶和核酮糖-1, 5-二磷酸羧化/氧化酶活性(RubisCO)的变化, 结果显示高光强促进两种硅藻的生长, 但对威氏海链藻的影响更明显。高光强导致两种硅藻叶绿素a、c含量、光系统Ⅱ的最大光化学效率和实际光化学效率明显下降, 非光化学淬灭系数明显升高, 但对光化学淬灭系数并没有明显影响。在高光下威氏海链藻和三角褐指藻胞内外碳酸酐酶活性明显升高。在高光强下培养的威氏海链藻RubisCO活性明显高于低光下培养, 但三角褐指藻正好相反, 不管高光还是低光培养威氏海链藻RubisCO活性始终高于三角褐指藻。以上结果表明不同硅藻对光强变化的响应存在差异, 它们可以通过调节光合生理特征、光合固碳关键酶和CO2供应以适应光强的变化。       

生长环境光强对两种热带雨林树种幼苗光合作用的影响

以西双版纳热带雨林中演替后期种绒毛番龙眼和先锋树种山黄麻为材料 ,于雾凉季测定了不同光强下生长的 2种树苗叶片最大净光合速率 (Pmax)、叶绿素荧光参数以及光合色素含量和比叶重 (L MA) ,探讨了不同生态习性热带雨林树种幼苗对光强的适应及光保护机制。发现在一定光强范围内随生长环境光强的增加 ,2种树苗 L MA、荧光的非化学猝灭 (N PQ)、类胡萝卜素(Car)含量、Car与叶绿素 (Chl)之比升高 ,光饱和点和光补偿点也有随生长环境光强的增大而升高的趋势 ,Chl含量降低 ,2种树苗均能通过形态和生理特性的变化适应不同的光强环境。相同的生长光强下 ,绒毛番龙眼光抑制明显比山黄麻重 ,山黄麻适应强光的能力强。随生长环境光强的增加 ,山黄麻 N PQ增加不显著 ,热耗散较少 ,相同光强下其 Pmax显著高于绒毛番龙眼。绒毛番龙眼则相反 ,其热耗散随生长环境光强的升高显著增多 ,但 Pmax差异不显著。表明先锋种山黄麻主要通过提高 Pmax利用光能防止光合机构光破坏 ,而演替后期种绒毛番龙眼却较大程度通过增强非光化学猝灭来耗散过量光能。上午人为降低光强度对先锋种山黄麻影响不大 ,但可以明显缓解绒毛番龙眼的光抑制 ,表明上午一定程度的遮光 (如有雾 )可减缓绒毛番龙眼光抑制     

民勤沙生植物园4种云杉属植物光化学特性的趋同适应

采用叶绿素荧光图像分析手段,结合叶绿素含量和主枝生长量测定,研究了沙地云杉、青海云杉、蓝云杉、白扦PSⅡ光化学效率和非光化学能量耗散的光响应特性及对稳态光强的适应性。结果表明:在相同生境和管理条件下,15a苗龄的4种云杉属植物生长势态良好,均能适应民勤荒漠气候环境;蓝云杉针叶的叶绿素含量较高,而青海云杉的叶绿素a、b比值(Chl a/b)较低;4种植物PSⅡ光化学效率的光响应曲线相似,但蓝云杉PSⅡ非光化学猝灭系数(NPQ)的光响应明显有别于其余3种;150μmol m~(-2)s~(-1)低光强下4种植物间NPQ的差异与PSⅡ最大光化学量子效率(Fv/Fm)一致,是内禀光合特性的反映;1500μmol m~(-2)s~(-1)高光强下的NPQ和PSⅡ最大效率(Fv'/Fm')在4云杉属植物间没有差异,呈现光合生理的趋同适应。综合比较分析可知,蓝云杉和白扦在低光强具有略低的PSⅡ非光化学猝灭能力,在高光强具有相对高的PSⅡ运行效率(Fq'/Fm'),光驯化适应能力较大;沙地云杉和青海云杉具有几乎一致的PSⅡ光化学和非光化学猝灭特性,其耐荫性和喜光性相近;4种云杉属植物光合机构对干旱荒漠生境的驯化适应具有趋同性,可作为我国北方防护林建设和城市绿化的重要树种。     

飞机草和兰花菊三七光合作用对生长光强的适应

测定了干季不同光强下生长的飞机草和兰花菊三七叶片最大净光合速率(Pmax)、荧光动力学参数、叶绿素含量和比叶重(LMA),研究了两种植物适应光环境的策略,探讨了其与入侵性的关系.100%光强下,两种植物主要通过降低捕光色素复合体Ⅱ的含量减少光能吸收,提高Pmax增加光能利用维持叶片能量平衡,而它们的热耗散能力并不强,均显著低于其它光强下的值.100%光强下,提高类胡萝卜素含量是飞机草耗散过剩能量的有效策略,而兰花菊三七可能有其它耗散途径.4.5%光强下仅飞机草能够存活,它通过降低LMA、维持很低的日间热耗散和较高的光合系统Ⅱ非环式电子传递效率适应了弱光环境.推测对强光环境较强的适应能力是入侵植物的共性之一,但这种能力强不一定入侵性大.     

光照对两种热带雨林树种幼苗光合能力、热耗散和抗氧化系统的影响

 研究了生长于不同光照条件下（100%、25%和8%光强）热带雨林冠层树种绒毛番龙眼（Pometia tomentosa）和中层树种滇南风吹楠（Horsfieldia tetratepala）幼苗的光合能力、热耗散、活性氧和保护性酶的活性。结果表明,绒毛番龙眼的最大光合速率随着生长光强的增加而提高,而滇南风吹楠在全光条件下的最大光合速率反比25%光照条件下的低。全光条件下两个树种光系统II的最大光化学效率（Fv/Fm）都显著降低,表明发生了长期光抑制。当把生长于遮荫条件下的幼苗移到全光下,从凌晨到中午随着光强的增加光抑制加剧,日落时生长于8%光照条件下的绒毛番龙眼及生长于8%和25%光照条件下的滇南风吹楠的光抑制不能完全恢复。非光化学猝灭对光强的响应曲线表明,随着生长光强的增加滇南风吹楠的热耗散能力增强,而生长在全光和25%光照条件下的绒毛番龙眼的热耗散能力都比滇南风吹楠的弱。两个树种叶片中O-[]·2、H2O2含量、SOD和CAT活性均随着生长光强的增加而提高;在同一光照条件下,绒毛番龙眼叶片中O-[]·2、H2O2含量、SOD和CAT活性显著高于滇南风吹楠。上述结果表明,在光抑制条件下,冠层树种绒毛番龙眼较大程度通过提高保护性酶的活性来保护光合机构免受损伤,而中层树种滇南风吹楠却较大程度通过增强非光化学猝灭来耗散过量光能;滇南风吹楠对强光的适应性差。     

不同光照强度下谢君魔芋的光合作用及能量分配特征

为了探讨喜阴植物谢君魔芋(Amorphophallus xiei)对不同光强的适应策略,测量和分析了不同透光率(高光,透光率100%;中光,透光率32.6%;低光,透光率5.98%)下谢君魔芋对光、CO₂、光斑的响应特征及响应过程中叶绿素a荧光和能量分配特征.结果表明: 随着生长光强的增大,谢君魔芋最大净光合速率(P_max)、暗呼吸速率、表观量子产额、羧化效率显著降低,光补偿点、CO₂补偿点显著升高.中光处理的谢君魔芋对光合诱导的响应更迅速(P<0.05);随着生长光强的增加,暗适应初始气孔导度(g_s-i)显著升高;完成光合诱导中最大净光合速率30%(t_30%P)、50%(t_50%P)和90%(t_90%P)所需的时间与g_s-i呈负相关.高光处理的植株PSⅡ实际光化学效率(ΔF/F_m′)、光化学猝灭(q_P)和电子传递速率(ETR)较高,且在光合诱导过程中所对应的非光化学猝灭(NPQ)值相对较高,而低光处理具有较高的反应中心激发能捕获效率(F_v′/F_m′).高光处理非光化学耗散途径比例(Ф_NPQ)较低,而低光处理Ф_NPQ则相对较高.表明喜阴植物谢君魔芋在中低光下生长时受到高光胁迫能够启动快速耗散机制来保护自身光合机构,长期处于高光环境则采用增加热耗散成本和形成淬灭复合物的策略在一定程度上应对高光胁迫,这可能是其不能很好适应高光环境的原因之一.     

遮荫和全光下生长的棉花光合作用和叶绿素荧光特征

 遮荫条件下（遮荫下光强相当于自然光强的40％左右）棉花(Gossypium hirsutum)叶片光合速率明显降低,仅为自然光强下生长叶片的30%～40％,叶片中RuBP羧化酶活性降低,而表观量子效率(AQY)较高。不同光照条件下生长的棉花叶片对短时间持续光强的光合诱导过程有明显的差异,由弱光转到强光下,自然光强下生长的叶片的Pn、Gs、ΦPSⅡ及非光化学猝灭系数(NPQ)都能在较短的时间内达到最大值,而遮荫叶片需要的时间较长;遮荫下生长的棉花叶片的实际光化学效率,随光强的增加下降幅度较大,而自然光照下生长的叶片下降幅度较小;自然光照下生长的叶片的NPQ随光强的升高达到较高水平,而遮荫叶片在较低的光强下即达到最大值,此时NPQ较低,遮荫叶片依赖于叶黄素循环的能量耗散水平较低。遮荫叶片较低的光合速率以及过剩光能耗散能力是其转入自然强光后光抑制严重的主要原因。     

Ecophysiological responses of Fagus sylvatica seedlings to changing light conditions. I. Interactions between photosynthetic acclimation and photoinhibition during simulated canopy gap formation

Natural regeneration of European beech (Fagus sylvatica L.) establishes under shade, but sudden exposure to high irradiance may occur due to openings in the canopy. To elucidate ecophysiological mechanisms associated with survival of European beech seedlings, the gas exchange, chlorophyll concentrations, and chlorophyll a fluorescence parameters of two different beech populations were studied under changing light conditions. Plants were grown both in a growth chamber and at a natural site (one population) where the seedlings were raised in containers placed in understory and in simulated canopy gaps. Upon exposure to high light in the growth chamber, photosynthetic rates of shade-acclimated leaves of seedlings from both populations increased severalfold and then decreased over several days to the rates of the low-light control seedlings. High-light seedlings always had the highest photosynthetic rates. Initial fluorescence displayed a trend opposite that of photosynthesis; it increased over time, and relative fluorescence and half-time rise declined continuously until the end of experiment to very low values. Exposure to high light of shade-acclimated seedlings resulted in a shift in chlorophyll concentrations to levels intermediate between high-light and low-light seedlings. The light treatment effects were statistically greater than population effects; however, seedlings from the Abetone population were found to be more susceptible to changing light conditions than seedlings from Sicily. Reciprocal light treatments on plants growing at the natural site confirmed the results obtained in the growth chamber experiment. Overall, beech seedlings grown in the field appeared to have a fairly large acclimation potential achieved by plasticity in the photosynthetic apparatus. The lack of pronounced acclimation to high light in seedlings grown in the growth chamber was ascribed to a threshold-type relationship between the acclimation capacity and the level of damage. These observations on the limited potential for acclimation to high light in leaves of European beech seedlings which show a clear capability to exploit sunflecks, are discussed in relation to regeneration following canopy gap formation and reinforce the view of the central role of gap formation in forest dynamics. We conclude that small forest gaps (in which sunflecks play a major role) may present a favorable environment for survival and growth of beech because of their limited ability to acclimate to a sudden increase in irradiance and because of the moderate levels of light stress found in small gaps.     

Photosynthetic responses to dynamic light under field conditions in six tropical rainforest shrubs occuring along a light gradient

 We examined in the field the photosynthetic utilization of fluctuating light by six neotropical rainforest shrubs of the family Rubiaceae. They were growing in three different light environments: forest understory, small gaps, and clearings. Gas exchange techniques were used to analyse photosynthetic induction response, induction maintenance during low-light periods, and lightfleck (simulated sunfleck) use efficiency (LUE). Total daily photon flux density (PFD) reaching the plants during the wet season was 37 times higher in clearings than in the understory, with small gaps exhibiting intermediate values. Sunflecks were more frequent, but shorter and of lower intensity in the understory than in clearings. However, sunflecks contributed one-third of the daily PFD in the understory. Maximum rates of net photosynthesis, carboxylation capacity, electron transport, and maximum stomatal conductance were lower in understory species than in species growing in small gaps or clearings, while the reverse was true for the curvature factor of the light response of photosynthesis. No significant differences were found in the apparent quantum yield. The rise of net photosynthesis during induction after transfer from low to high light varied from a hyperbolic shape to a sigmoidal increase. Rates of photosynthetic induction exhibited a negative exponential relationship with stomatal conductance in the shade prior to the increase in PFD. Leaves of understory species showed the most rapid induction and remained induced longer once transferred to the shade than did leaves of medium- or high-light species. LUE decreased rapidly with increasing lightfleck duration and was affected by the induction state of the leaf. Fully induced leaves exhibited LUEs up to 300% for 1-s lightflecks, while LUE was below 100% for 1–80 s lightflecks in uninduced leaves. Both induced and uninduced leaves of understory species exhibited higher LUE than those of species growing in small gaps or clearings. However, most differences disappeared for lightflecks 10 s long or longer. Thus, understory species, which grew in a highly dynamic light environment, had better capacities for utilization of rapidly fluctuating light than species from habitats with higher light availability. Received: 4 January 1997 / Accepted: 28 April 1997     

Contrasting behavior of higher plant photosystem I and II antenna systems during acclimation

In this work we analyzed the photosynthetic apparatus in Arabidopsis thaliana plants acclimated to different light intensity and temperature conditions. Plants showed the ability to acclimate into different environments and avoid photoinhibition. When grown in high light, plants had a faster activation rate for energy dissipation (qE). This ability was correlated to higher accumulation levels of a specific photosystem II subunit, PsbS. The photosystem II antenna size was also regulated according to light exposure; smaller antenna size was observed in high light-acclimated plants with respect to low light plants. Different antenna polypeptides did not behave similarly, and Lhcb1, Lchb2, and Lhcb6 (CP24) are shown to undergo major levels of regulation, whereas Lhcb4 and Lhcb5 (CP29 and CP26) maintained their stoichiometry with respect to the reaction center in all growth conditions. The effect of acclimation on photosystem I antenna was different; in fact, the stoichiometry of any Lhca antenna proteins with respect to photosystem I core complex was not affected by growth conditions. Despite this stability in antenna stoichiometry, photosystem I light harvesting function was shown to be regulated through different mechanisms like the control of photosystem I to photosystem II ratio and the association or dissociation of Lhcb polypeptides to photosystem I.     

The excess light energy that is neither utilized in photosynthesis nor dissipated by photoprotective mechanisms determines the rate of photoinactivation in photosystem II

Photoinactivation of PSII is thought to be caused by the excessive light energy that is neither used for photosynthetic electron transport nor dissipated as heat. However, the relationship between the photoinactivation rate and excess energy has not been quantitatively evaluated. Chenopodium album L. plants grown under high-light and high-nitrogen (HL-HN) conditions show higher tolerance to photoinactivation and have higher photosynthetic capacity than the high-light and low-nitrogen (HL-LN)- and low-light and high-nitrogen (LL-HN)-grown plants. The rate of photoinactivation in the LL-HN plants was faster than that in the HL-LN, which was similar to that in the HL-HN plants, while the LL-HN and HL-LN plants had similar photosynthetic capacities [Kato et al. (2002b) Funct. Plant Biol. 29: 787]. We quantified partitioning of light energy between the electron transport and heat dissipation at the light intensities ranging from 300 to 1,800 micromol m(-2) s(-1). The maximum electron transport rate was highest in the HL-HN plants, heat dissipation was greatest in the HL-LN plants, and the excess energy, which was neither consumed for electron transport nor dissipated as heat, was greatest in the LL-HN plants. The first-order rate constant of the PSII photoinactivation was proportional to the magnitude of excess energy, with a single proportional constant for all the plants, irrespective of their growth conditions. Thus the excess energy primarily determines the rate of PSII photoinactivation. A large photosynthetic capacity in the HL-HN plants and a large heat dissipation capacity in the HL-LN plants both contribute to the protection of PSII against photoinactivation.     

四种热带雨林树种幼苗比叶重,光合特性和暗呼吸对生长光环境的适应

雾凉季研究了西双版纳热带雨林4种植物幼苗对生长光环境的适应,其中两个树种幼苗喜光（团花和滇南插柚紫）,两个树种幼苗耐荫（滇南红厚壳和玉蕊）发现弱光环境中生长的4种植物比叶重、光合能力、光饱和点、光补偿点暗呼吸速度、叶绿素a/b比较低,叶绿素含量较高。玉蕊和滇南红厚壳幼苗的光合能力和呼吸速度 于团花树和滇南插柚紫。团花树和滇南插机紫的比叶重和光合作用的可塑性大于玉蕊和滇南红厚壳。高光强下生长的团花树和滇南插机紫增加叶氮分配给羧化酶的比较。减少分配给叶绿素的比例。滇南红厚壳和玉蕊适应弱光环境的能力略强于团花树和滇南插机紫,但适应强光的能力较差。研究结果支持树种的生理生态特性决定了其演替状况和生境选择的假说,单位干重叶的光合能力和呼吸速率并未表现出利于光适应的可塑性,表明4种植物生理适应能力较差,形态学上的适应在4种热带雨林树种幼苗光适应方面起到了重要的作用,叶氮分配也是它们光适应的策略之一。     

Seasonal and habitat differences affect the impact of food and predation on herbivores: a comparison between gaps and understory of a tropical forest

Herbivore populations are influenced by a combination of food availability and predator pressure, the relative contribution of which is hypothesized to vary across a productivity gradient. In tropical forests, treefall gaps are pockets of high productivity in the otherwise less productive forest understory. Thus, we hypothesize that higher light availability in gaps will increase plant resources, thereby decreasing resource limitation of herbivores relative to the understory. As a result, predators should regulate herbivore populations in gaps, whereas food should limit herbivores in the understory. We quantified potential food availability and compared arthropod herbivore and predator densities in large forest light gaps and in the intact understory in Panama. Plants, young leaves, herbivores and predators were significantly more abundant per ground area in gaps than in the understory. This pattern was similar when we focused on seven gap specialist plant species and 15 shade-tolerant species growing in gaps and understory. Consistent with the hypothesis, herbivory rates were higher in gaps than the understory. Per capita predation rates on artificial caterpillars indicated higher predation pressure in gaps in both the dry and late wet seasons. These diverse lines of evidence all suggest that herbivores experience higher predator pressure in gaps and more food limitation in the understory.