Clonal Differences in Photosynthesis in Hevea Brasiliensis Müll. Arg.

The objective of the present investigation was to examine the extent of variations in single leaf net photosynthetic rate (P_N) and its relative dependence on stomatal conductance (g_s) and the mesophyll capacity to fix carbon in 12 clones of the natural rubber plant. There were significant variations in P_N measured at low and saturating photon flux density (PFD); the extent of variation was larger at low than at saturating PFD. The compensation irradiance (CI) and apparent quantum yield of CO₂ assimilation (φ_c) calculated from the P_N/PFD response curves showed significant variations among the clones. P_N at low irradiance was positively correlated with φ_c. Thus a clone with large P_N at low irradiance, high φ_c, and low CI may tolerate shade better and thus produce a high tree stand per hectare. A strong positive correlation existed between P_N saturated with radiant energy (P_sat) and carboxylation efficiency (CE) estimated from the response curves of P_N on intercellular CO₂ concentration (C_i), but g_s showed a poor correlation with P_sat High CO₂ compensation concentration (Γ) led to low CE in Hevea clones. A clone with large P_sat, high CE, low g_s, and low Γ is the one in which photosynthesis is more dependent on the mesophyll factors than stomata. Such a clone may produce relatively high biomass and maintain high water use efficiency. This revised version was published online in September 2006 with corrections to the Cover Date.     

Comparative Anatomical,Morphological, and Physiological Parameters Controlling Photosynthesis in Two Populusxeuramericana Clones During Short-Term Osmotic Treatment

The relationships between drought response and anatomical/physiological properties were assessed in two poplar clones belonging to the Aigeros section: Populusxeuramericana clone Dorskamp (drought-tolerant) and clone Luisa Avanzo (drought-sensitive). Cuttings of both clones were exposed for 12 h to 0 mM (control). 50 mM (osmotic potential −0.112 MPa), and 150 mM (−0.336 MPa) mannitol. In control, Dorskamp had smaller stomata than Luisa Avanzo, one or two layers of palisade cells, a spongy mesophyll, and high concentrations of antioxidative compounds (ascorbate, glutathione). After exposure to 50 or 150 mM mannitol, both clones closed their stomata: leaf conductance and opening of stomata decreased. When exposed to 50 mM mannitol, net photosynthetic rate (P _N) and chlorophyll (Chl) and total solute contents remained stable; ribulose-1,5-bisphosphate carboxylase/-oxygenase activity, Chl synthesis and turn-over, ascorbate peroxidase and glutathione reductase activities were less affected in Dorskamp than in Luisa Avanzo. Following an exposure to 150 mM mannitol, Dorskamp exhibited higher P _N and higher contents of antioxidants (ascorbate, glutathione) and antioxidative enzymes (ascorbate peroxidase, glutathione reductase) than Luisa Avanzo. Hence the drought-tolerant poplar was able to better avoid and tolerate osmotic stress. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of light intensity on partitioning of photosynthetic electron transport to photorespiration in four subtropical forest plants

Photosynthetic rate (P_n) and the partitioning of noncyclic photosynthetic electron transport to photorespiration (J_O) in seedlings of four subtropical woody plants growing at three light intensities were studied in the summer time by measurements of chlorophyll fluorescence and CO₂ exchange. ExceptSchima superba, an upper canopy tree species, the tree speciesCastanopsis fissa and two understory shrubsPsychotria rubra, Ardisia quinquegona had the highestP _n at 36% of sunlight intensity. The total photosynthetic electron transport rate (J_F) and the ratio ofJ _O/J_F were elevated in leaves under full sunlight.J _O/J_F ratio reached 0.5–0.6 and coincided with the increasing of oxygenation rate of Rubisco (V_O), the activity of glycolate oxidase and photorespiration rate at full sunlight. It is suggested that an increasing partitioning proportion of photosynthetic electron transport to photorespiration might be one of the protective regulation mechanisms in forest plant under strong summer light and high temperature conditions.     

油菜叶片气体交换对O３浓度和熏蒸方式的响应

运用CIRAS-1型便携式光合作用测定系统,在田间原位比较研究了不同O3浓度(CF,50 nl.L-1和100 nl.L-1)和熏蒸方式(恒定和动态)油菜叶片的气体交换特征及其对光强、CO2浓度升高的响应。结果表明(1)恒定熏气下,O3浓度增加导致叶片的蒸腾速率降低,水分利用效率提高,但动态熏蒸则引起蒸腾速率增加,水分利用效率下降,而且明显导致光合速率和气孔导度的降低;(2)高浓度的O3(100 nl.L-1)引起叶片的表观量子产额、暗呼吸饱和光强和最大净光合速率显著降低,光呼吸和CO2补偿点显著升高;熏蒸方式对叶片的暗呼吸、光补偿点、饱和光强、最大光合速率、羧化效率的影响差异显著;(3)不论何种熏蒸方式,高浓度的O3都引起下叶位的Fv/Fo、Fv/Fm显著降低,对上叶位没有影响。相同剂量下,动态熏蒸对叶片气体交换的影响更大,不利于植物生长和干物质的积累。     

玉米、花生及其间作茬口与施磷对冬小麦光合特性及产量的影响机制

该试验在玉米单作茬口、玉米-花生间作茬口(间作茬口)、花生单作茬口共3种茬口,以及0 kg P_2O_5·hm~(-2)(P_0)和180 kg P_2O_5·hm~(-2)(P_1) 2个磷水平下,研究了间作茬口与施磷对冬小麦分蘖、叶面积指数(LAI)、干物质积累、光合特性及产量的影响机制,为玉米花生间作与小麦-玉米复种轮作提供理论依据。结果表明:(1)间作茬口较玉米茬口显著提高了冬小麦有效分蘖数、LAI、净光合速率和干物质积累量,并提高了冬小麦旗叶的SPAD值、CO_2饱和点、光饱和点及最大净光合速率(P_(nmax))、表观量子效率(AQY)、羧化效率(CE)、最大羧化速率(V_(cmax))、最大RUBP再生的电子传递速率(J_(max))和最大磷酸丙糖利用速率(V_(TPU)),且CE、V_(cmax)、V_(TPU)的增幅均达到显著水平(P0.05),有效改善了冬小麦产量构成,显著提高籽粒产量(P0.05)。(2)间作茬口较花生茬口提高了冬小麦乳熟期的P_(nmax)、AQY、CE,增加了穗粒数和粒重,提高了产量。(3)与不施磷相比,施磷180 kg P_2O_5·hm~(-2)显著促进间作茬口冬小麦生长,显著提高冬小麦旗叶的SPAD值、P_(nmax)、AQY、CE、V_(cmax)、J_(max)、V_(TPU)和籽粒产量(P0.05)。研究发现,间作茬口较玉米茬口能有效增强冬小麦旗叶表观量子效率和CO_2羧化能力,显著提高小麦花后光合能力,促进冬小麦生长,从而增加穗粒数、粒重和籽粒产量,且间作茬口结合施磷180 kg P_2O_5·hm~(-2)效果更好。     

入侵植物马缨丹(Lantana camara)及其伴生种的光合特性

马缨丹(Lantana camara L.)是粤东地区的入侵植物之一.采用LI-6400光合作用仪对马缨丹及其常见主要伴生种鬼针草(Bidens pilosa L.)、肖梵天花(Urena lobata L.)、土牛膝(Achyranthes aspera L.)在不同有效光合辐射(PAR)和不同CO2浓度下的光合生理指标进行测定,结果表明:(1)马缨丹的光饱和点(LSP)与光补偿点(LCP)分别为1225、13.58 μmol·m-2·s-1,均低于伴生种,且和伴生种差异达到显著水平,光饱和点时的最大净光合速率(Pmax)为13.89μmol·m-2·s-1,表观量子效率(AQY)为0 0503 μmol·m-2·s-1,与土牛膝相当,而显著高于肖梵天花;(2) 马缨丹的CO2饱和点(CSP)与CO2补偿点(CCP)分别为1350、61.78 μmol·mol -1,CO2饱和点时马缨丹的最大净光合速率(Pmax)为20.08 μmol·mol-1,显著高于土牛膝,马缨丹的表观羧化效率(CE)与鬼针草相当,为0.0424 μmol·mol -1;(3)有效光合辐射与CO2浓度的增加,对马缨丹气孔导度(Gs)、蒸腾速率(Tr)影响不明显,但大大提高了其水分利用率(WUE),提示马缨丹对于环境中光强和CO2的变化具有良好的适应能力.这些信息对马缨丹生理生态学特性的认识是一个补充,并能为马缨丹入侵机制的研究提供一些有价值的参考.     

高效Rubisco羧化活性筛选体系的设计与构建

【背景】广泛存在于植物、藻类及其他自养微生物中的核酮糖-1,5-二磷酸羧化/加氧酶(Rubisco)是卡尔文循环中固定CO2的关键酶及限速酶,在生物质合成和全球碳循环中扮演着重要角色。鉴于Rubisco的重要性以及极低的固碳羧化活性,对Rubisco的筛选进化研究具有重要意义。【目的】构建一种适用于筛选高效Rubisco羧化活性的筛选体系。【方法】分析现有筛选体系对Rubisco羧化活性筛选压力缺失的原因,设计构建适用于高效Rubisco羧化活性的筛选体系,以BWLac产乳酸菌株为宿主,在含有5%CO2的N2环境下厌氧培养,比较不同羧化活性Rubisco对细胞生长的影响,通过HPLC及LCMS检测总乳酸及固定CO2生成乳酸的产量评估筛选体系。【结果】通过终端代谢产物乳酸产生下拉力,以及甘油代谢产生的剩余还原力需要平衡消耗掉的设计靶点,增强Prk和Rubisco的固碳支路代谢通量,加强RuBP对细胞的毒性抑制作用,使细胞生长与Rubisco活性有效偶联,构建高通量筛选办法。在新构建的筛选体系中,Rubisco失活突变体BWLac/197不能生长,Rubisco和Prk双失活突变体BWLac/197-2021生长未受影响,菌落大小约1.58 cm。粗酶液羧化活性相差2倍以上的RBC1和7002,其细胞生长在筛选条件下受不同程度抑制,菌落大小分别有1.06 cm和0.65 cm。通过检测乳酸产量及甘油消耗量对筛选体系验证评估,RBC1消耗甘油1.39 g/L,产乳酸2.82 g/L,其中来自于NaH13CO3的标记乳酸含量为18.05μmol/L,比7002的相应检测结果高1.3-1.6倍,检测结果与筛选体系设计原理相符,即乳酸产量越高,甘油消耗越多,Rubisco羧化活性越高,细胞生长得越好。【结论】成功设计构建了高效Rubisco羧化活性筛选体系,为进化或探索更高羧化活性Rubisco提供有效的高通量筛选办法。     

Effects of above- and below-ground competition from shrubs on photosynthesis, transpiration and growth in Quercus robur L. seedlings

For a tree seedling to successfully establish in dense shrubbery, it must maintain function under heterogeneous resource availability. We evaluated leaf-level acclimation in photosynthetic capacity, seedling-level transpiration, and seedling morphology and growth to gain an understanding of the effects of above- and below-ground competition on Quercus robur seedlings. Experimental seedlings were established in a typical southern Swedish shrub community where they received 1 of 4 competition levels (above-ground, below-ground, above- and below-ground, or no competition), and leaf-level responses were examined between two growth flushes. Two years after establishment, first-flush leaves from seedlings receiving above-ground competition showed a maximum rate of photosynthesis (A_max) 40% lower than those of control seedlings. With the development of a second flush above the shrub canopy, A_max of these seedlings increased to levels equivalent to those of seedlings free of light competition. Shrubby competition reduced oak seedling transpiration such that seedlings exposed to above- and below-ground competition showed rates 43% lower than seedlings that were not exposed to competition. The impaired physiological function of oak seedlings growing amid competition ultimately led to a 60-74% reduction in leaf area, 29-36% reduction in basal diameter, and a 38-78% reduction in total biomass accumulation, but root to shoot ratio was not affected. Our findings also indicate that above-ground competition reduced A_max, transpiration and biomass accumulation more so than below-ground competition. Nevertheless, oak seedlings exhibited the ability to develop subsequent growth flushes with leaves that had an A_max acclimated to utilize increased light availability. Our findings highlight the importance of flush-level acclimation under conditions of heterogeneous resource availability, and the capacity of oak seedlings to initiate a positive response to moderate competition in a shrub community.     

Modelling ¹⁸O₂ and ¹⁶O₂ unidirectional fluxes in plants: II. analysis of rubisco evolution

The studies of Rubisco characteristics observed during plant evolution show that the variation of the Rubisco specificity factor only improved by two times from cyanobacteria to modern C3 plants. However we note important variations of the ratio between the maximum rates of oxygenation and carboxylation (V_O/V_C). Modelling in vivo¹⁸O₂ data in plant gas exchange shows that the oxygenation reaction of Rubisco plays a regulating role when the photochemical energy exceeds the carboxylation capacity. A protective index ‘oxygenation capacity’ is postulated, related to the ratio V_O/V_C of Rubisco, and hence to the sink energy effect of photorespiration. Analysing the trends of Rubisco parameters along the evolutionary scale, we show: (1) the increase of both V_C and V_O; (2) the enhancement of CO₂ affinity; and (3) the rise in oxygenation capacity at the expense of the CO₂ specificity. Hence, the factors of evolutionary pressure have not only directed the enzyme towards a more efficient utilisation of CO₂, but mainly to positively use the unavoidable great loss of energy and assimilated carbon in the process of photorespiration. These observations reinforce the hypothesis of plant-atmosphere co-evolution and of the complex role of Rubisco, which seems to be selected to develop both better CO₂ affinity and oxygenation capacity. The latter increases the capacity of sink of photorespiration, in particular, during water stress or under high irradiance, the two conditions experienced by plants in terrestrial environments. These observations help to explain some handicaps of C4 plants, and the supremacy of CAM and C3 perennial higher plants in arid environments.     

Variations in the relationship between maximum leaf carboxylation rate and leaf nitrogen concentration

叶片最大羧化速率是表征植物光合能力的关键参数, 受到光照、温度、水分、CO₂浓度、叶片氮含量等多个要素的控制。准确地模拟植物叶片最大羧化速率对环境因子的响应是预测未来植被生产力和碳循环过程的前提。目前大多数陆地碳循环过程模型以Farqhuar光合作用模型为基础模拟植物的光合作用, 关于植物叶片的最大羧化速率与叶氮含量关系的模拟方法却各不相同。该文汇总了1990-2013年国内外植物叶片光合速率观测研究文献中叶片最大羧化速率与叶氮含量的关系式及相关数据, 分析了叶片最大羧化速率与叶氮含量关系随不同植被功能型和时间的变化特征, 以及环境因子变化条件下最大羧化速率与叶氮含量关系的变化特征, 探讨了二者关系变异性的可能原因以及影响因子。结果表明: 1)不同功能型植物叶片的最大羧化速率和叶氮含量的关系存在较大差异, 二者线性关系式的斜率平均值变化范围为16.29-50.25 μmol CO₂·g N^-1·s^-1。落叶植被叶片的最大羧化速率随叶氮含量的变化率和光合氮利用效率一般都高于常绿植被, 其变异主要源于植物的比叶重和叶片内部氮素分配的差异。2)叶片最大羧化速率随叶氮含量的变化存在季节和年际变异。在没有受到水分胁迫的年份中, 叶片最大羧化速率随叶氮含量变化的速率一般在春季或夏季最高, 其季节变异与比叶重和叶氮在Rubisco的分配比例的季节变化有关。受到干旱的影响, 叶片最大羧化速率随叶氮含量的变化率会升高。3)当大气CO₂浓度增加时, 由于叶片中Rubisco含量的降低, 多年生针叶叶片最大羧化速率和叶氮关系斜率值会出现降低; 当供氮水平增加时, 叶片最大羧化速率和叶片氮含量均表现出增加趋势, 二者线性关系的斜率也相应增加。在此基础上, 该文指出在模拟叶片最大羧化速率与叶氮含量的关系时, 应考虑叶片比叶重和叶氮在Rubisco中的分配比例的季节变异、水分胁迫、大气CO₂浓度和供氮水平变化对二者关系的影响。囿于数据的有限性, 今后应进一步加强多因子控制实验研究, 深入探讨叶片最大羧化速率与叶氮含量关系的变异性机理, 并获得更系统的观测数据, 以助生态系统过程模型的改进, 提高模型的模拟精度。