近70年来黄土高原典型植物δ13C值变化研究

对黄土高原地区 4种典型C3 植物狼牙刺 (Sophoraviciifolia) 、辽东栎 (Quercusliaotungensis) 、虎榛子 (Os tryopsisdavidiana) 和酸枣 (Zizyphusjujubavar.spinosa) 样品稳定性碳同位素组分 (δ¹³ C) 进行分析, 研究了从 2 0世纪 30年代至今近 70年中不同年代植物δ¹³ C值的变化。结果表明, 在近 70年中, 4种植物δ¹³ C值变化范围为- 2 5.0 5‰~ - 2 9.75‰, 平均值为 - 2 7.0 4‰。 4种植物叶片δ¹³ C值均呈下降趋势, 表明随气候环境变化, 近 70年4种植物的水分利用效率 (WUE) 均呈降低趋势。但不同植物叶片δ¹³ C值下降幅度不同 :狼牙刺和辽东栎叶片δ¹³ C值下降非常明显, 虎榛子叶片δ¹³ C值下降也较明显, 而酸枣叶片δ¹³ C值下降不明显。 4种植物δ¹³ C值的降低率分别为 14.6 5 %、14.4 6 %、11.99%和 2.4 4 %, 说明不同植物对气候环境因子的敏感性不同, 具有不同的适应环境变化的策略, 酸枣是 4种植物中耐旱能力较强, WUE较高的物种。     

新的C4及CAM光合途径植物

以稳定性碳同位素比(δ~(13)C)鉴别禾本科、莎草科、苋科和萝摩科共46种植物的光合作用途径,发现了36种新的C_4植物(δ~(13)C-10.43到-13.66‰)和1种CAM植物(δ~(13)C-15.24‰)。根据Hattersley区分C_4植物三种亚类型的不同δ~(13)C值,提出在36种C_4中有8种具δ_(13)C值-10.4到-10.9‰者是NADP-ME型,6种具δ~(13)C值-13‰左右的是NAD-ME型,其余种类可能是NADP-ME或PCK型。     

不同生活型绿化植物叶片碳同位素组成的季节特征

通过测定北京地区不同生活型绿化植物叶片的碳同位素组成(δ13C值),从植物种和生活型两个方面研究植物水分利用效率的自然可变性。结果表明:所测定的75种植物(隶属于35科65属)的叶片的δ13C值变幅,春季为-30.7‰--23.4‰,夏季为-31.5‰--25.1‰,秋季为-31.4‰--23.9‰;落叶灌木种间差异不显著(p=0.114),而常绿乔木(p=0.005)、落叶乔木(p0.001)、常绿灌木(p=0.022)、草本植物(p0.001)和藤本植物(p=0.001)的种间差异显著或极显著;同一生活型植物叶片的δ13C季节差异显著,春季叶片的δ13C值显著大于夏秋两季(常绿乔木除外),不同生活型植物叶片的δ13C值在春、夏、秋3个季节差异都达到了极显著水平(春季p=0.001、夏季p0.001、秋季p0.001),且叶片的δ13C值表现出乔木树种灌木树种藤本植物草本植物、常绿植物落叶植物的规律。因此,植物种和生活型均会引起植物叶片δ13C值的变化,但δ13C受生活型变化的影响较大,表明不同生活型植物的水分利用效率具有明显差异。     

中国北方干湿气候区C_3草本植物δ~（13）C值及其与湿润指数的关系

通过对中国北方C3草本植物稳定性碳同位素的测定以及有关该区植被碳同位素资料的收集,共获取了47个样点的地理位置、气候因子和325个植物样品的碳同位素数据;计算了中国北方不同气候分区的湿润指数,分析了C3草本植物δ13C值的空间特征以及与湿润指数等环境因子之间的关系。在所调查的范围内,中国北方地区C3草本植物δ13C值的分布区间为-29.9‰--25.4‰,平均值为-27.3‰。C3草本植物δ13C的平均值从半湿润地区到半干旱地区再到干旱地区显著变重;3个气候分区植物δ13C值的变化范围分别是-29.9‰--26.7‰（半湿润区）、-28.4‰--25.6‰（半干旱区）和-28.0‰--25.4‰（干旱区）。一元回归分析表明,各气候分区C3草本植物δ13C值与湿润指数的关系存在差异,在半干旱区、半湿润区和整个北方地区,C3草本植物δ13C值与湿润指数均呈显著线性负相关（P〈0.05）,随着湿润指数的增加,C3植物δ13C平均值均变轻,但下降幅度不同。而在北方干旱气候区内,C3草本植物δ13C与湿润指数呈显著正相关（P〈0.05）,湿润指数每升高0.1,植物δ13C平均值增加1.3‰。年均温度可能是决定该区内各样点湿润指数和C3植物对13C分馏能力差别的主要原因。     

不同生境胡杨叶片δ~(13)C和δ~(15)N及其对环境因子的响应

以新疆南北疆8个不同生境林龄群体的胡杨叶片为材料,测定幼树和成熟胡杨叶片的天然稳定碳、氮同位素组成值(δ~(13)C、δ~(15)N)以及碳含量、氮含量和比叶面积,分析叶片δ~(13)C、δ~(15)N值与海拔、经纬度、叶片碳氮含量、比叶面积以及水分利用效率之间的相互关系。结果表明:(1)胡杨幼树和成熟林叶片δ~(13)C平均值分别为-27.863‰(-28.776‰～-26.695‰)和-28.230‰(-29.717‰～-26.033‰),不同生境胡杨叶片间的δ~(13)C值具有显著差异(P0.05),并且幼树林叶片δ~(13)C均大于对应成熟林;幼树和成熟林叶片δ~(15)N平均值分别为3.259‰(-1.842‰～9.082‰)和3.651‰(0.798‰～5.779‰)。(2)胡杨幼树和成熟林叶片碳含量平均值分别为46.225‰(44.573‰～49.056‰)和45.720‰(43.226‰～47.349‰),它们叶片氮含量平均值分别为1.708‰(1.327‰～2.116‰)和1.823‰(1.164‰～2.450‰);成熟林叶片碳含量与其δ~(13)C和δ~(15)N值分别呈极显著负相关和极显著正相关关系(P0.01),而其氮含量与δ~(13)C值呈不显著正相关关系(P0.05),与δ~(15)N值呈显著正相关关系。(3)胡杨幼树林叶片的比叶面积平均值(91.565 cm~2/g)小于成熟林叶片(103.141 cm~2/g)。(4)幼树和成熟林胡杨叶片δ~(13)C、δ~(15)N值均与纬度呈极显著正相关关系,幼树林叶片δ~(13)C、δ~(15)N值与海拔也呈极显著正相关关系,幼树林叶片δ~(15)N值与经度也呈显著正相关关系。(5)幼树和成熟胡杨林水分利用率的平均值分别为77.618μmol/mol(68.070～91.069μmol/mol)和72.463μmol/mol(62.809～97.111μmol/mol),不同林龄的胡杨水分利用率均与其叶片δ~(13)C呈极显著正相关关系(P0.001),各生境中于田县(阿日系马扎)的幼树和成熟林叶片具有较高的δ~(13)C值(-26.695‰和-26.033‰)和水分利用效率(91.069和97.111μmol/mol)。     

华北低丘山区栓皮栎人工林冠层CO2浓度和δ13C变化及其影响因素

采用离轴积分腔输出光谱技术测定华北低丘山区栓皮栎人工林冠层上缘(11 m)和下部(6 m)大气CO2浓度和δ13C值,在小时尺度上分析冠层CO2浓度和δ13C变化及其影响因素.结果表明:冠层CO2浓度呈先高后低再升高的日变化趋势,而δ13C值没有明显一致的日变化规律.白天大气不稳定状态出现的频率为70.2%,在光合作用和林内湍流的共同作用下,栓皮栎冠层下部CO2浓度高于冠层上缘约1.70μmol·mol-1,而δ13C值低于冠层上缘约0.81‰.晚上大气稳定状态出现的频率为76.2%,湍流弱,冠层叶片呼出的CO2不易流动,导致冠层下部CO2浓度高于上缘约1.24μmol·mol-1,δ13C值低于冠层上缘约0.58‰.白天和晚上冠层上下缘的CO2浓度差值与δ13C差值均呈显著的相关关系.逐步回归分析表明,白天太阳辐射和相对湿度是影响冠层CO2浓度和δ13C值差异的主要环境因子,晚上温度显著影响冠层下部与上缘δ13C值的变化,这些环境因子通过增强或减弱光合和呼吸作用来影响冠层大气中CO2浓度和δ13C值的变化.     

内蒙古锡林河流域植物功能群组成及其水分利用效率的变化--依水分生态类群划分

依照植物水分生态类群,将锡林河流域主要植物种划分为6个植物功能群:呈生植物、中旱生植物、旱中生植物、中生植物、湿中生植物和湿生植物.沿土壤水分梯度,我们调查了8个植物群落的功能群组成及其δ13C值.结果表明:1)在水分状况不同的8个群落中,植物功能群的组成有很大差异.在较湿润生境中(沼泽化草甸和盐化草甸),湿中生和湿生植物成为优势种并构成地上生物量的主要部分;在干旱生境中(草甸草原、典型草原和退化草原),旱生和中旱生植物占绝对优势并构成群落生物量的90%以上;2)不同功能群δ13C值表现为:旱生植物(26.38‰)=中旱生植物(26.51‰)＞旱中生植物(-27.02‰)＞中生植物(-27.56‰)=湿中生和湿生植物(-27.80‰),表明随着不同水分生态类群所适应生境从干旱到湿润逐渐转变,植物的水分利用效率显著降低;3)在土壤水分状况不同的生境下,旱生植物始终维持相对较高的δ13C值和水分利用效率;而中旱生植物的δ13C值表现出较大的变化幅度,表明其对土壤水分的改变更敏感;4)旱生植物叶片脯氨酸含量最高;旱中生、中旱生和中生植物次之;湿中生和湿生植物脯氨酸含量最低.不同水分生态类群脯氨酸含量与其δ13C值和地上生物量呈显著正相关关系.     

4种乔木叶片光合特性和水分利用效率随树高的变化

叶片是植物主要的光合器官并对外界环境条件的改变最为敏感.水分亏缺对叶片的生理特性的影响尤为显著,主要表现在叶片的光合特性以及水分利用效率的改变.由于木质部通道增长引起的重力作用和通道阻力的增大,高大乔木叶片的生理指标随树高增加而发生变化.通过测定北京地区4种高大乔木悬铃木(Platanus hispanica)、刺槐(Robinia pseudoacacia)、白腊(Fraxinus chinensis)和银杏(Ginkgo biloba)的叶片的光合特性和碳稳定同位素比率(δ13C)等随树高的变化,得出叶片的光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Cond)和胞间CO2浓度(Ci)等均随着树高的增大而降低,而叶片的δ13C等则随着树高的增大而增大,其中悬铃木、刺槐、白腊、以及银杏的树冠上部比树冠下部的δ13C值分别增加了1.126‰、2.310‰、2.290‰和2 276‰.方差分析和多重比较结果表明,除个别指标外,4种乔木上下部叶片的光合特性和δ13C等指标均差异明显(P<0 05).光合能力随树高下降而δ13C值随树高增加表明树顶叶片确实受到水分胁迫的影响,支持了树高极限的水分限制假说.     

海拔梯度对巴郎山奇花柳叶片δ13C的影响

2010年在四川卧龙自然保护区选择海拔为2350、2700、3150和3530 m的4个分布地点,研究了巴郎山海拔梯度对奇花柳叶片13C、光合、CO2扩散导度、氮含量、光合氮利用效率( PNUE)和比叶面积(SLA)的影响.结果表明:随着海拔的升高,目标树种叶片氮含量(尤其是单位面积氮含量)及PNUE增加,叶片δ13C值也随之显著增加,且海拔每升高1000 m,δ13C增加1.4‰;CO2扩散导度(气孔导度和叶肉细胞导度)的增加,在一定程度上阻碍了叶片δ13C值随海拔升高,但不足以改变δ13C值随海拔升高的趋势;羧化能力是羧化位点与外界CO2分压比( Pc/Pa),甚至δ13C的限制因子.在海拔2350～2700m,奇花柳光合系统内部氮素分配主要受温度的影响,而2700～3530 m的光照作用可能更大.奇花柳的SLA随海拔无显著变化.     

内蒙古草原常见植物叶片δ~(13)C和δ~(15)对环境因子的响应

在中国东北样带沿线的内蒙古草原地区采集了一些常见植物的叶片样品,并测定其δ~(13)C和δ~(15)N值,分析了其统计学特征以及对环境因子(年平均降雨量和温度)的响应模式。发现东北样带草原区同时存在C_3和C_4两种不同光合途径的植物,但是C_3植物占主导地位,C_4植物数量有限。C_3植物叶片δ~(13)C随着年平均降雨量和年平均温度的升高而显著降低,反映了此区域C_3植物δ~(13)C受控于降水量和温度。C_4植物的叶片δ~(13)C值随着降雨量的增多而有轻微升高的趋势,但是C_4植物的叶片δ~(13)C值对年平均温度的响应不敏感。不论对C_3植物还是C_4植物而言,叶片δ~(15)N都随降雨量增加而显著降低,即干旱区的植物叶片δ~(15)N大于湿润地区,这说明降水是影响植物叶片δ~(15)N的一个重要因素。然而两者叶片δ~(15)N对温度的响应不敏感。     

Temperature response of photosynthesis in C3, C4, and CAM plants: temperature acclimation and temperature adaptation

Most plants show considerable capacity to adjust their photosynthetic characteristics to their growth temperatures (temperature acclimation). The most typical case is a shift in the optimum temperature for photosynthesis, which can maximize the photosynthetic rate at the growth temperature. These plastic adjustments can allow plants to photosynthesize more efficiently at their new growth temperatures. In this review article, we summarize the basic differences in photosynthetic reactions in C₃, C₄, and CAM plants. We review the current understanding of the temperature responses of C₃, C₄, and CAM photosynthesis, and then discuss the underlying physiological and biochemical mechanisms for temperature acclimation of photosynthesis in each photosynthetic type. Finally, we use the published data to evaluate the extent of photosynthetic temperature acclimation in higher plants, and analyze which plant groups (i.e., photosynthetic types and functional types) have a greater inherent ability for photosynthetic acclimation to temperature than others, since there have been reported interspecific variations in this ability. We found that the inherent ability for temperature acclimation of photosynthesis was different: (1) among C₃, C₄, and CAM species; and (2) among functional types within C₃ plants. C₃ plants generally had a greater ability for temperature acclimation of photosynthesis across a broad temperature range, CAM plants acclimated day and night photosynthetic process differentially to temperature, and C₄ plants was adapted to warm environments. Moreover, within C₃ species, evergreen woody plants and perennial herbaceous plants showed greater temperature homeostasis of photosynthesis (i.e., the photosynthetic rate at high-growth temperature divided by that at low-growth temperature was close to 1.0) than deciduous woody plants and annual herbaceous plants, indicating that photosynthetic acclimation would be particularly important in perennial, long-lived species that would experience a rise in growing season temperatures over their lifespan. Interestingly, across growth temperatures, the extent of temperature homeostasis of photosynthesis was maintained irrespective of the extent of the change in the optimum temperature for photosynthesis (T _opt), indicating that some plants achieve greater photosynthesis at the growth temperature by shifting T _opt, whereas others can also achieve greater photosynthesis at the growth temperature by changing the shape of the photosynthesis–temperature curve without shifting T _opt. It is considered that these differences in the inherent stability of temperature acclimation of photosynthesis would be reflected by differences in the limiting steps of photosynthetic rate.     

The temperature response of C(3) and C(4) photosynthesis

We review the current understanding of the temperature responses of C(3) and C(4) photosynthesis across thermal ranges that do not harm the photosynthetic apparatus. In C(3) species, photosynthesis is classically considered to be limited by the capacities of ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco), ribulose bisphosphate (RuBP) regeneration or P(i) regeneration. Using both theoretical and empirical evidence, we describe the temperature response of instantaneous net CO(2) assimilation rate (A) in terms of these limitations, and evaluate possible limitations on A at elevated temperatures arising from heat-induced lability of Rubisco activase. In C(3) plants, Rubisco capacity is the predominant limitation on A across a wide range of temperatures at low CO(2) (<300 microbar), while at elevated CO(2), the limitation shifts to P(i) regeneration capacity at suboptimal temperatures, and either electron transport capacity or Rubisco activase capacity at supraoptimal temperatures. In C(4) plants, Rubisco capacity limits A below 20 degrees C in chilling-tolerant species, but the control over A at elevated temperature remains uncertain. Acclimation of C(3) photosynthesis to suboptimal growth temperature is commonly associated with a disproportional enhancement of the P(i) regeneration capacity. Above the thermal optimum, acclimation of A to increasing growth temperature is associated with increased electron transport capacity and/or greater heat stability of Rubisco activase. In many C(4) species from warm habitats, acclimation to cooler growth conditions increases levels of Rubisco and C(4) cycle enzymes which then enhance A below the thermal optimum. By contrast, few C(4) species adapted to cooler habitats increase Rubisco content during acclimation to reduced growth temperature; as a result, A changes little at suboptimal temperatures. Global change is likely to cause a widespread shift in patterns of photosynthetic limitation in higher plants. Limitations in electron transport and Rubisco activase capacity should be more common in the warmer, high CO(2) conditions expected by the end of the century.     

High temperature biocatalysis by chemically modified cytochrome C

Chemically modified cytochrome c with poly(ethylene glycol) (PEG) showed activity at temperatures higher than 100 degrees C and to be highly thermostable. The molecular size of PEG moieties and the coupling site affected the thermal stabilization. An optimal PEG/protein mass ratio of 2.8 was found, producing a fully thermostable biocatalyst at 80 degrees C. Site-directed mutagenesis on yeast cytochrome c showed an increased thermostabilization when lysine 79 residue, localized at the edge of the active site, was replaced by a nonreactive residue. Tertiary, secondary, and active-site structures were analyzed by fluorescence, CD, and UV/visible spectroscopies. Besides its disordered structure, the pegylated protein showed a lower unfolding rate at the active-site than the unmodified ones. A shell-like structure seems to protect the heme environment, in which PEG is coiled on the protein surface with a primary shield of rigid water molecules solvating the hydrophilic region of bound-PEG, and the PEG hydrophobic regions interacting with the hydrophobic clusters on protein surface.     

Effects of irradiance and temperature on photosynthesis in C3, C4 and C3/C4 Panicum species

Species in the Laxa and Grandia groups of the genus Panicum are adapted to low, wet areas of tropical and subtropical America. Panicum milioides is a species with C₃ photosynthesis and low apparent photorespiration and has been classified as a C₃/C₄ intermediate. Other species in the Laxa group are C₃ with normal photorespiration. Panicum prionitis is a C₄ species in the Grandia group. Since P. milioides has some leaf characteristics intermediate to C₃ and C₄ species, its photosynthetic response to irradiance and temperature was compared to the closely related C₃ species, P. laxum and P. boliviense and to P. prionitis. The response of apparent photosynthesis to irradiance and temperature was similar to that of P. laxum and P. boliviense, with saturation at a photosynthetic photo flux density of about 1 mmol m^-2 s^-1 at 30°C and temperature optimum near 30°C. In contrast, P. prionitis showed no light saturation up to 2 mmol m^-2 s^-1 and an optimum temperature near 40°C. P. milioides exhibited low CO₂ loss into CO₂-free air in the light and this loss was nearly insensitive to temperature. Loss of CO₂ in the light in the C₃ species, P. laxum and P. boliviense, was several-fold higher than in P. milioides and increased 2- to 5-fold with increases in temperature from 10 to 40°C. The level of dark respiration and its response to temperature were similar in all four Panicum species examined. It is concluded that the low apparent photorespiration in P. milioides does not influence its response of apparent photosynthesis to irradiance and temperature in comparison to closely related C₃ Panicum species.Abbreviations AP apparent photosynthesis - I CO₂ compensation point - gl leaf conductance; gm, mesophyll conductance - PPFD photosynthetic photon flux density - PR apparent photorespiration rate - RuBPC sibulose bisphosphate carboxylase     

Effect of temperature on the structure of trout troponin C

Adaptation for life at different temperatures can cause changes in many aspects of an organism. One example is the expression of different protein isoforms in species adapted to different temperatures. The calcium regulatory protein cardiac troponin C (cTnC), from rainbow trout (Oncorhynchus mykiss), is a good model for studying temperature effects, both because of its low physiological temperature and because mammalian cTnC, extensively studied at higher temperatures, can be used for comparison. We determined the structure and studied the backbone dynamics of the regulatory domain of trout cardiac troponin C (ScNTnC) with one Ca(2+) bound at 7 and 30 degrees C, using nuclear magnetic resonance spectroscopy (NMR). The overall fold of the regulatory domain of trout cTnC at both temperatures is similar to the regulatory domain of mammalian (human, bovine, and porcine isoform) cTnC bound to one Ca(2+). By comparing the trout structures at the two temperatures, we identify differences between the positions of the helices flanking the calcium binding loops, and the overall structure at 7 degrees C is more compact than that at 30 degrees C. The structure at 7 degrees C is more similar to the mammalian cTnC, which was determined at 30 degrees C, indicating that they have the same conformation at their respective physiological temperatures. The dynamic properties of the regulatory domain of trout cTnC are similar at the two temperatures that were used in these studies.     

Deformation of helix C in the low temperature L-intermediate of bacteriorhodopsin

X-ray and electron diffraction studies of specific reaction intermediates, or reaction intermediate analogues, have produced a consistent picture of the structural mechanism of light-driven proton pumping by bacteriorhodopsin. Of central importance within this picture is the structure of the L-intermediate, which follows the retinal all-trans to 13-cis photoisomerization step of the K-intermediate and sets the stage for the primary proton transfer event from the positively charged Schiff base to the negatively charged Asp-85. Here we report the structural changes in bacteriorhodopsin following red light illumination at 150 K. Single crystal microspectrophotometry showed that only the L-intermediate is populated in three-dimensional crystals under these conditions. The experimental difference Fourier electron density map and refined crystallographic structure were consistent with those previously presented (Royant, A., Edman, K., Ursby, T., Pebay-Peyroula, E., Landau, E. M., and Neutze, R. (2000) Nature 406, 645-648; Royant, A., Edman, K., Ursby, T., Pebay-Peyroula, E., Landau, E. M., and Neutze, R. (2001) Photochem. Photobiol. 74, 794-804). Based on the refined crystallographic structures, molecular dynamic simulations were used to examine the influence of the conformational change of the protein that is associated with the K-to-L transition on retinal dynamics. Implications regarding the structural mechanism for proton pumping by bacteriorhodopsin are discussed.