生长光强对4种热带雨林树苗光合机构的影响

于雾凉季研究了西双版纳热带雨林 4种植物幼苗对光抑制及光破坏的防御。发现不同光强下生长的玉蕊和滇南红厚壳日间光抑制均较团花树和滇南插柚紫重 ,在中光强下还发生了长期光抑制。中光强下生长的团花树和滇南插柚紫叶绿素含量降低 ,光合能力升高 ,同时增加热耗散量 ,维持光能平衡 ,避免了光破坏的发生。中光强下玉蕊和滇南红厚壳减少光能吸收、提高热耗散的同时 ,发生了光系统II光化学量子产量长期下调。中光强下生长的 4种植物叶片的类胡罗卜素的绝对含量并不高 ,但单位叶绿素的类胡罗卜素含量显著升高 ,相对保护作用增强。先锋树种团花树类胡罗卜素含量低于另 3种植物 ,这与其较低的热耗散速率相一致 ,光合能力的提高对其光破坏的防御有重要的作用     

七种热带雨林树苗叶片气孔特征及其可塑性对不同光照强度的响应

对生长在荫棚3种不同光照条件下和全自然光下的热带雨林4个冠层种(望天树、绒毛番龙眼、团花、红厚壳)和3个中层种(玉蕊、藤黄、滇南风吹楠)树苗叶片气孔特征以及它们的可塑性进行了研究、结果表明,这些植物的气孔全部着生在远轴面．7种植物中,玉蕊和绒毛番龙眼的气孔密度较大,滇南红厚壳和团花的保卫细胞最长．随光强的增大,气孔密度和气孔指数增大,单位叶气孔数在低光强下较大．除团花外,其它植物叶片气孔导度在50％光强处最大,而光强对保卫细胞的长度影响不显著．相关分析表明,气孔密度与植物单位叶的面积呈负相关。而与气孔导度的相关性不显著、尽管两种不同生活型植物气孔指数和单位叶气孔数在不同光强下的可塑性差异较小,但冠层树种气孔密度和气孔导度的可塑性显著高于中层树种．     

热带雨林蒲桃属3个树种的幼苗光合作用对生长光强的适应

 测定了生长于3种光强下（100％、42％和14％自然光强） 热带雨林演替早期（思茅蒲桃Syzygium latilimbum）、中期（乌墨S.cumini）和后期（阔叶蒲桃S. szemaoense）出现的蒲桃属 （Syzygium）3个树种幼苗叶片气体交换参数和叶绿素荧光参数的日变化、比叶重和叶绿素含量。发现演替早期树种光合能力和光合可塑性最大、中期树种次之,后期树种光合能力最弱且在强光下受到显著抑制。但是,生长在强光下,3个树种均未发生长期光抑制和光破坏。随生长光强增加,3个树种热耗散速率都升高。不过在强光下,中期和后期树种通过热耗散消耗的过剩光能较多,通过叶黄素循环的热耗散可能对于这两个树种在强光下避免光合机构的光破坏起到了重要作用。14％光强下,3个树种最大净光合速率、光合作用的光饱和点、光补偿点、暗呼吸速率、比叶重降低,叶片单位干重叶绿素含量提高,对低光环境有了较好的形态学和生理学适应。但是,在4％光强下思茅蒲桃和乌墨幼苗全部死亡,只有阔叶蒲桃幼苗仍能存活,说明阔叶蒲桃幼苗适应弱光环境的能力高于思茅蒲桃和乌墨,与它们的演替状态一致。     

不同生态习性热带雨林树种的幼苗对光能的利用与耗散

研究了生长于100％、25％和8％光照条件下的热带雨林先锋树种团花、演替顶极阶段的冠层树种绒毛番龙眼和中下层树种滇南风吹楠幼苗的光合能力及光能分配特性对光强的响应。与绒毛番龙眼和滇南风吹楠相比,团花具有较高的最大光合速率和最大电子传递速率,从光能分配对光强的响应曲线可以看出,随着光强的增加,3个树种幼苗叶片吸收的光能分配到光化学反应的比例减少,分配到热耗散的比例增加,光能在光化学反应与热耗散之间的分配呈显著负相关,与其它两个种相比,100％光下的团花幼苗将较多的光能分配到光化学反应中,热耗散较弱且未达到饱和。过剩光能少,没有引起长期光抑制,绒毛番龙眼和滇南风吹楠将叶片吸收的较多光能分配到热耗散中,但生长于100％光下的幼苗过剩光能仍然较多,导致幼苗遭受长期光抑制,结果表明,不同生态习性热带雨林树种幼苗更新对光环境的要求与这些幼苗对光能的利用和耗散特性密切相关。     

四种热带雨林树种光合和形态解剖特征对不同生长光强的适应

研究了西双版纳热带雨林2种喜光树种中平树(Macaranga denticulata)、倒樱木(Pnravallaris macrophylla)和2种耐荫树种云南肉豆蔻(Myristica yunnanensis)、金丝李(Garcinia paucinervis)幼苗叶片光合和形态解剖特征对3种不同生长光强(5％、25%和50％相对光强)的适应。研究结果表明,与强光下相比,弱光下生长的4种植物最大净光合速率、光饱和点、光补偿点、暗呼吸速率、叶绿素a／b、叶片和栅栏组织厚度、气孔密度和比叶重都降低,而海绵组织／栅栏组织和叶绿素含量升高。在相同光强下,与2种耐荫树种相比,2种喜光树种有较大的最大净光合速率、暗呼吸速率、气孔密度和较低的叶绿素含量。在不同光强下,4种植物均表现出了对光适应有利的生理和形态解剖可塑性,而喜光树种比耐荫树种有较大的生理和形态可塑性,表明喜光树种具有比耐荫树种对强光有更强的适应能力。4种植物的生理指标的可塑性均大于叶片解剖结构的可塑性。     

夜间低温对不同光强下生长的两种热带树苗光合作用的影响

于雾凉季测定了叶片叶绿素荧光和气体交换参数、H2 O2 和丙二醛 (MDA)含量 ,探讨了 4～ 6℃夜间低温对 3种相对光强 (太阳光的 8%、2 5 %和 5 0 % )下生长的 2种山地雨林树苗光合作用的影响。夜间低温处理导致 3种光强下生长的 2种植物叶片日间和胁迫诱导的光抑制加剧 ,净光合速率 (Pn)和光呼吸速率降低 ,H2 O2 和MDA含量升高。生长环境光强升高可加剧夜间低温的效应 ,弱光下 2种植物受夜间低温影响较小 ,间接表明雾使光强减弱可缓解自然夜温降低对西双版纳热带植物的危害。处理期间滇南插柚紫Pn 主要受气孔限制 ,滇南红厚壳Pn 降低与活性氧增加引起的羧化效率降低有关 ,两种植物Pn 的降低均与光抑制关系不大。夜间低温后滇南红厚壳气孔导度降低较少 ,H2 O2 和MDA含量较高 ,光抑制较重 ,5 0 %相对光强下其未做夜间低温处理的对照植株发生了胁迫诱导的光抑制 ,表明它对夜间低温较敏感。     

四种亚高山针叶林树种的表型可塑性对不同光照强度的响应

以青藏高原东缘亚高山针叶林群落演替后期种岷江冷杉、演替中后期种粗枝云杉和青榨槭、及先锋树种红桦为材料，研究了不同光强下生长的4种树苗生长、生物量分配、叶片形态和光合特性，探讨植物幼苗的形态和生理特征的表型可塑性与光适应的关系。结果表明：（1）弱光环境中生长的4种植物的基茎、相对生长速率、叶片厚度、根重比、最大净光合速率、光饱和点、光补偿点、暗呼吸速率较低，而比叶面积、地上／地下生物量、茎长／茎重、叶重比和茎重比较高。（2）大部分光环境下岷江冷杉幼苗的最大净光合速率和暗呼吸速率低于粗枝云杉，青榨槭幼苗的最大净光合速率和暗呼吸速率略低于红桦。（3）高光强下生长的粗枝云杉和红桦幼苗的相对生长速率分别大于岷江冷杉和青榨槭，但在低光强下则与之相反。（4）粗枝云杉和红桦幼苗的11种可塑性指数平均值则分别大于岷江冷杉和青榨槭。岷江冷杉适应弱光环境的能力略强于粗枝云杉和红桦，但适应强光的能力较差。生理适应的可塑性指数大于形态适应的可塑性指数，表明前者在4种植物幼苗光适应方面起到了重要的作用。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。     

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。     

夜间低温对不同光强下生长的两种沟谷雨林树苗荧光参数的影响

 于雾凉季测定了叶片叶绿素荧光参数,探讨了4～6 ℃夜间低温对4种相对光强下生长的两种西双版纳沟谷雨林树苗光系统Ⅱ（PSⅡ）活性的影响及雾对植物的可能保护机制。随夜间低温处理时间延长,不同光强下生长的团花树（Anthocephalus chinensis）和玉蕊（Barringtonia macrostachya）叶片日间和长期光抑制,以及PSⅡ反应中心的可逆失活或破坏加剧,生长环境光越强夜间低温的效应越明显,弱光下其效应不显著。间接表明雾使光强减弱利于缓解自然夜温降低对本区热带植物的影响。中光强下玉蕊对照植株发生了胁迫诱导的光抑制;相同处理条件下玉蕊的光抑制程度均比团花树重,表明玉蕊对夜间低温引起的光抑制更敏感。夜间低温处理后,中等和低光强下团花树的热耗散多于玉蕊,表明其光保护作用较强。夜间低温处理期间两种植物的光抑制与热耗散增多和PSⅡ反应中心的可逆失活或破坏的加剧有关。     

两种热带雨林树苗对环境光强变化的生理响应和适应机制

干季末雨季初以西双版纳热带雨林中木奶果和玉蕊2种树苗为材料,研究了将生长于12.5%自然光（相当于小林窗的光强）和36%自然光（相当于大林窗的光强）下的这2种树苗分别移至36%自然光和12.5%自然光下之后各自叶片最大净光合速率（Pmax）、叶绿素荧光参数、光合色素含量、比叶重（LMA）以及叶片悬挂角（MA）的变化过程,探讨了2种植物幼苗在生长环境光强改变后其形态和生理生态特性做出的相应调整以适应新的光环境的过程与机制。结果表明,这2种树苗均不适宜生长在大林窗的强光环境下,但木奶果对光环境的增强表现出一定的耐受力,光合适应潜力强于玉蕊,2种树苗对低光环境都能较好地适应;新叶的生成在整株植物对生长光环境变化的适应过程中也起到至关重要的作用。     

Photosynthetic Characteristics,Dark Respiration,and Leaf Mass Per Unit Area in Seedlings of Four Tropical Tree Species Grown Under Three Irradiances

We investigated the effect of growth irradiance (I) on photon-saturated photosynthetic rate (P _max), dark respiration rate (R _D), carboxylation efficiency (CE), and leaf mass per unit area (LMA) in seedlings of the following four tropical tree species with contrasting shade-tolerance. Anthocephalus chinensis (Rubiaceae) and Linociera insignis (Oleaceae) are light-demanding, Barringtonia macrostachya (Lecythidaceae) and Calophyllum polyanthum (Clusiaceae) are shade-tolerant. Their seedlings were pot-planted under shading nets with 8, 25, and 50 % daylight for five months. With increase of I, all species displayed the trends of increases of LMA, photosynthetic saturation irradiance, and chlorophyll-based P _max, and decreases of chlorophyll (Chl) content on both area and mass bases, and mass-based P _max, R _D, and CE. The area-based P _max and CE increased with I for the light-demanders only. Three of the four species significantly increased Chl-based CE with I. This indicated the increase of nitrogen (N) allocation to carboxylation enzyme relative to Chl with I. Compared to the two shade-tolerants, under the same I, the two light-demanders had greater area- and Chl-based P _max, photosynthetic saturation irradiance, lower Chl content per unit area, and greater plasticity in LMA and area- or Chl-based P _max. Our results support the hypothesis that light-demanding species is more plastic in leaf morphology and physiology than shade-tolerant species, and acclimation to I of tropical seedlings is more associated with leaf morphological adjustment relative to physiology. Leaf nitrogen partitioning between photosynthetic enzymes and Chl also play a role in the acclimation to I.     

Light requirements of Australian tropical vs. cool-temperate rainforest tree species show different relationships with seedling growth and functional traits

Background and Aims

A trade-off between shade tolerance and growth in high light is thought to underlie the temporal dynamics of humid forests. On the other hand, it has been suggested that tree species sorting on temperature gradients involves a trade-off between growth rate and cold resistance. Little is known about how these two major trade-offs interact.

Methods

Seedlings of Australian tropical and cool-temperate rainforest trees were grown in glasshouse environments to compare growth versus shade-tolerance trade-offs in these two assemblages. Biomass distribution, photosynthetic capacity and vessel diameters were measured in order to examine the functional correlates of species differences in light requirements and growth rate. Species light requirements were assessed by field estimation of the light compensation point for stem growth.

Results

Light-demanding and shade-tolerant tropical species differed markedly in relative growth rates (RGR), but this trend was less evident among temperate species. This pattern was paralleled by biomass distribution data: specific leaf area (SLA) and leaf area ratio (LAR) of tropical species were significantly positively correlated with compensation points, but not those of cool-temperate species. The relatively slow growth and small SLA and LAR of Tasmanian light-demanders were associated with narrow vessels and low potential sapwood conductivity.

Conclusions

The conservative xylem traits, small LAR and modest RGR of Tasmanian light-demanders are consistent with selection for resistance to freeze–thaw embolism, at the expense of growth rate. Whereas competition for light favours rapid growth in light-demanding trees native to environments with warm, frost-free growing seasons, frost resistance may be an equally important determinant of the fitness of light-demanders in cool-temperate rainforest, as seedlings establishing in large openings are exposed to sub-zero temperatures that can occur throughout most of the year.     

两种木兰科植物叶片光合作用的光驯化

测定了生长在全日、54%和21%日光强下需光植物火力楠(Michelia meachurei)和耐荫植物华东拟单性木兰(Parakmerialotungensis)叶片气体交换参数,用以估测降低光强对光合作用的限制和对低光的光驯化.生长在全日光强下火力楠的光饱和光合速率较华东拟单性木兰高.当日光强降低到54%,火力楠叶片光合速率降低幅度较华东拟单性木兰大.当日光降低至21%,华东拟单性木兰的表观量子产率和光能转换率较火力楠高.在全日光强下,火力楠的Vcmax较华东拟单性木兰高.随着日光强降低,两种木兰植物的Vcmax降低,当日光强降低至54%和21%,火力楠的Vcmax降幅较华东拟单性木兰大,火力楠Vcmax对光强降低较华东拟单性木兰敏感.生长光强降低,两种木兰植物内部CO2传导度(gi)降低.在低光强下火力楠仍保持较华东拟单性木兰高的gi.生长光强降低到全日光强的54%,火力楠gi对光合速率限制(Li)与在全日光强的条件下没有区别(p＞0.05),表现火力楠gi对54%日光强的驯化;在54%的光条件下,华东拟单性木兰的呼吸速率对光合速率的限制(Lr)与全日光照无差别(p＞0.05),显示呼吸速率对低光的驯化.两种木兰植物气孔导度对光合速率的限制(Ls)随光强降低而增大.在遮荫条件下种间叶特性差别明显,这亦反映出两种植物物种光合驯化的差异.火力楠gi对低光驯化,而华东拟单性木兰叶片对较高光强驯化更甚于对低光强.     

Seedling growth strategies in Bauhinia species: comparing lianas and trees

BACKGROUND AND AIMS: Lianas are expected to differ from trees in their growth strategies. As a result these two groups of woody species will have different spatial distributions: lianas are more common in high light environments. This study determines the differences in growth patterns, biomass allocation and leaf traits in five closely related liana and tree species of the genus Bauhinia. METHODS: Seedlings of two light-demanding lianas (Bauhinia tenuiflora and B. claviflora), one shade-tolerant liana (B. aurea), and two light-demanding trees (B. purpurea and B. monandra) were grown in a shadehouse at 25% of full sunlight. A range of physiological, morphological and biomass parameters at the leaf and whole plant level were compared among these five species. KEY RESULTS: The two light-demanding liana species had higher relative growth rate (RGR), allocated more biomass to leaf production [higher leaf mass fraction (LMF) and higher leaf area ratio (LAR)] and stem mass fraction (SMF), and less biomass to the roots [root mass fraction (RMF)] than the two tree species. The shade-tolerant liana had the lowest RGR of all five species, and had a higher RMF, lower SMF and similar LMF than the two light-demanding liana species. The two light-demanding lianas had lower photosynthetic rates per unit area (A(area)) and similar photosynthetic rates per unit mass (A(mass)) than the trees. Across species, RGR was positively related to SLA, but not to LAR and A(area). CONCLUSIONS: It is concluded that the faster growth of light-demanding lianas compared with light-demanding trees is based on morphological parameters (SLA, LMF and LAR), and cannot be attributed to higher photosynthetic rates at the leaf level. The shade-tolerant liana exhibited a slow-growth strategy, compared with the light-demanding species.     

Fluorescence imaging of light acclimation of brazilian atlantic forest tree species

In the pursuit of knowledge on the biological behavior of Brazilian Atlantic Forest tree species, this study evaluated the susceptibility of the light-demanding species, Schinus terebinthifolia Raddi., Pseudobombax grandiflorum (Cav.) A. Robyns and Joannesia princeps Vell., and of the shade-tolerant species, Hymenaea courbaril L. var. stilbocarpa and Lecythis pisonis Camb, to photoinhibition and acclimation capacity. These species were first cultivated under two irradiance conditions, I₂₀ (20% direct sunlight radiation) and I₁₀₀ (all-sky or direct sunlight) and then transferred from I₂₀ to I₁₀₀. The effects of the sudden increase in light radiation intensity on photosynthetic activity were then evaluated through chlorophyll (Chl) fluorescence imaging, HPLC xanthophylls analysis, and cell membrane lipid peroxidation measurements. Light-demanding species were found to present a higher photochemical efficiency and higher acclimation capacity under high light irradiance than shade-tolerant species. The higher photoinhibition tolerance observed in light-demanding species was associated to their higher capacity for photochemical dissipation and dissipation of excess excitation energy via the xanthophyll cycle, leading to a lower ROS generation. The obtained results suggested that a knowledge of acclimation capacity, by means of Chl fluorescence imaging yields, is a useful indicator of species successional grouping.     

Photosynthetic responses of Miconia species to canopy openings in a lowland tropical rainforest

We examined the photosynthetic acclimation of three tropical species of Miconia to canopy openings in a Costa Rican rainforest. The response of photosynthesis to canopy opening was very similar in Miconia affinis, M. gracilis, and M. nervosa, despite differences in growth form (trees and shrubs) and local distributions of plants (understory and gap). Four months after the canopy was opened by a treefall, photosynthetic capacity in all three species had approximately doubled from closed canopy levels. There were no obvious signs of high light damage after treefall but acclimation to the gap environment was not immediate. Two weeks after treefall, A_max, stomatal conductance, apprarent quantum efficiency, and dark respiration rates had not changed significantly from understory values. The production of new leaves appears to be an important component of light acclimation in these species. The only variables to differ significantly among species were stomatal conductance at A_max and the light level at which assimilation was saturated. M. affinis had a higher stomatal conductance which may reduce its water use efficiency in gap environments. Photosynthesis in the more shade-tolerant M. gracilis saturated at lower light levels than in the other two species. Individual plant light environments were assessed after treefall with canopy photography but they explained only a small fraction of plant variation in most measures of photosynthesis and growth. In conclusion, we speculate that species differences in local distribution and in light requirements for reproduction may be more strongly related to species differences in carbon allocation than in carbon assimilation.