在水生与气生状态下石莼光合作用对无机碳的响应

潮间带海藻光合作用总是处于水生(高潮时)与气生(低潮时)两种连续变化的环境状态下进行.对汕头沿岸常见的潮间带海藻石莼(Ulva lactuca L.)在水生和气生不同状态下光合作用对无机碳的响应特性进行了比较研究.在水生状态下,现有海水中溶解性无机碳浓度能充分饱和(10 ℃和20 ℃时)或接近饱和(30 ℃时)石莼的光合作用;而在气生状态下,石莼光合作用受大气CO2浓度的限制,且这种限制作用在较高温度(20-30 ℃)下比在低温(10 ℃)下更严重.在10 ℃和20 ℃时,石莼在气生状态下比在水生状态下具有更高的碳饱和最大光合速率;而在30 ℃时,石莼在这两种状态下的碳饱和光合速率相似.石莼光合作用的Km (CO2)值在气生状态下比在水生状态下高;而在气生状态下石莼对CO2的表观光合导度远小于其在水生状态下的值.认为大气CO2浓度升高将通过促进石莼在气生状态下的光合作用而增加其初级生产力.     

在水生与气生状态下石莼光合作用对光照和温度的响应

如何对付由于高潮时的水生状态与低潮时的气生状态高频率循环所导致的不同环境条件,是潮间带海藻的光合作用所面临的独特问题。对采自汕头沿岸的石莼(Ulva lactuca)在水生和气生不同状态下光合作用对光照和温度的响应特性进行了测定,以探讨这种常见的潮间带绿藻在潮汐循环背景下的光合特性。在气生状态下,光饱和净光合速率(Pmax)随气生暴露时间的变化模式可以很好地用三次方程进行描述,而温度影响方程的系数;当水分损失为15％时,石莼的Pmax增加至最大值,然后Pmax随进一步脱水而下降,在水分损失为80％时下降至0。温度对Pmax的影响在水生状态下比在气生状态下更大。气生状态下(充分水化)Pmax在10℃时显著小于水生状态下的值,而在30％时则相反。在10℃时,气生干出时间在6h以内,或在20％时,气生干出时间在2．2h以内,石莼的净碳固定量在气生状态下比在水生状态下要大;而在30％时,在气生状态下的净碳固定量比总是小于在水生状态下的净碳固定量。认为石莼在低潮气生状态下与在高潮水生状态下光合特性及净碳固定存在差异,但这种差异与环境温度及叶状体的水分状态有关。     

在水生与气生状态下石莼光合作用对光照和温度的响应

如何对付由于高潮时的水生状态与低潮时的气生状态高频率循环所导致的不同环境条件,是潮间带海藻的光合作用所面临的独特问题。对采自汕头沿岸的石莼(Ulva lactuca)在水生和气生不同状态下光合作用对光照和温度的响应特性进行了测定,以探讨这种常见的潮间带绿藻在潮汐循环背景下的光合特性。在气生状态下,光饱和净光合速率(Pmax)随气生暴露时间的变化模式可以很好地用三次方程进行描述,而温度影响方程的系数;当水分损失为15％时,石莼的Pmax增加至最大值,然后Pmax随进一步脱水而下降,在水分损失为80％时下降至0。温度对Pmax的影响在水生状态下比在气生状态下更大。气生状态下（充分水化）Pmax在10℃时显著小于水生状态下的值,而在30℃时则相反。在10℃时,气生干出时间在6 h 以内,或在20℃时,气生干出时间在2.2 h 以内,石莼的净碳固定量在气生状态下比在水生状态下要大;而在30℃时,在气生状态下的净碳固定量比总是小于在水生状态下的净碳固定量。认为石莼在低潮气生状态下与在高潮水生状态下光合特性及净碳固定存在差异,但这种差异与环境温度及叶状体的水分状态有关。     

低潮干出状态下石莼的光合作用特性（简报）

在低潮时（即干出状态下）汕头广澳湾潮间带海藻石莼的光合速率和呼吸速率都有随水分损失增加而下降的趋势。PSⅡ光化学效率、表观量子产额、光饱和点、以及表观羧化效率都随水分损失增加而下降;而光补偿点、CO2补偿点则随水分损失增加而增高,低潮时的干出状态下空气中CO2浓度限制石莼的光合作用,如果大气CO2浓度升高,则会促进其暴露于空气中的光合作用。     

CO2浓度升高对干旱胁迫下小麦光合作用和抗氧化酶活性的影响

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蛋白核小球藻生长和无机碳利用对不同光照强度和CO2浓度的响应

为了探讨光照强度和CO₂浓度对蛋白核小球藻(Chlorella pyrenoidosa)生长、无机碳利用的复合效应, 丰富绿藻中无机碳浓缩机制的资料, 该文设置两种光照强度(40和120 µmol photons•m^-2•s^-1)和两种CO₂浓度(0.04%和0.16%)组合成4种条件, 比较了蛋白核小球藻生长、无机碳浓度、pH补偿点、光合放氧速率、碳酸酐酶(CA)活性和α-CA基因转录表达对这4种培养条件的响应。结果发现: 蛋白核小球藻在高光强高CO₂浓度组生长最快; 低光强高CO₂浓度组培养体系中总无机碳浓度为1163.3 µmol•L^-1, 显著高于其他3组; 高光强低CO₂浓度组藻的pH补偿点最高(9.8), 而低光强高CO₂浓度组藻的pH补偿点最低(8.6); 低光强高CO₂浓度组藻的最大光合速率(V_max)和最大光合速率一半时的无机碳浓度(K_0.5)最高, 分别是其他3组的1.28-1.91倍和1.61-2.00倍; 高光强低CO₂浓度组藻的胞外CA活性最高; 而低光强低CO₂浓度组藻的胞外α-CA基因表达量显著高于其他3组。以上结果表明低CO₂浓度可促进蛋白核小球藻的pH补偿点和无机碳亲和力的提高, 诱导胞外CA活性及α-CA基因的表达; 该藻主要以HCO₃^-为无机碳源, 其对无机碳的利用受光照的调节。     

中国东北样带土壤活性有机碳的分布及其对气候变化的响应

 基于中国东北样带2001年考察采集土样的实测数据及CO2浓度升高和干旱胁迫的模拟试验资料,分析了土壤活性有机碳的分布特征及其对气候变化的响应。结果表明,样带土壤活性有机碳与土壤有机碳之间呈极显著正相关关系（相关系数Ｒ=0.993,p<0.001）。表层土壤活性有机碳平均为(3.5     

氮素对高大气CO2浓度下小麦叶片光合作用的影响

通过测定小麦拔节期叶片的光合气体交换参数和光强-光合速率（P_n）响应曲线,研究了氮素对长期高大气CO₂浓度（760 μmol·mol^-1）下小麦叶片光合作用的影响.结果表明：在长期高大气CO₂浓度下,增施氮肥能提高小麦叶片P_n、蒸腾速率（T_r）和瞬时水分利用效率（WUE_i）;与正常大气CO₂浓度相比,高大气CO₂浓度下小麦叶片的P_n和WUE_i增加,气孔导度（G_s）和胞间CO₂浓度(C_i）降低.随光合有效辐射的增强,高大气CO₂浓度下小麦叶片的P_n和WUE_i均高于正常大气CO₂浓度处理,G_s则较低,而C_i和T_r无显著变化.高氮水平下小麦叶片G_s与P_n、T_r、WUE_i呈线性正相关,G_s与C_i在正常大气CO₂浓度下呈线性负相关,但高大气CO₂浓度下二者无相关性;低氮水平下小麦叶片的G_s与P_n、WUE_i无相关性,而与C_i和T_r呈线性正相关,表明高大气CO₂浓度下低氮水平的小麦叶片P_n由非气孔因素限制.     

厚壁毛竹光合作用对CO2浓度倍增的短期响应

采用Li-6400P光合测定仪对比测定了大气CO2浓度和短期CO2浓度倍增下不同季节厚壁毛竹的光合特性,结果表明:CO2浓度加倍促使最大净光合速率、净光合速率、水分利用率、光合量子效率和光饱和点升高,年平均增幅分别为62.79%、48.74%、94.41%、8.70%和16.67%;CO2浓度加倍促使蒸腾速率、暗呼吸速率和光补偿点下降,年平均降幅分别为17.60%、37.25%和40.50%。不同季节厚壁毛竹光合生理特性参数在CO2浓度加倍后的增加幅度或降低幅度与叶片生理活性和气候变化密切相关。CO2浓度的倍增并未明显改变厚壁毛竹光合特性的季节变化规律,除光补偿点外,其它光合参数的季节大小顺序仍与大气CO2浓度下的相同。厚壁毛竹光合作用对短期CO2浓度升高的响应特征与C3植物光合作用对短期CO2浓度升高响应的普遍规律相符。     

土壤有机碳和氮分解对温度变化的响应趋势与研究方法

总结了土壤中碳和氮贮量与温度的关系、土壤碳和氮分解对温度时空差异和直接加热升温的响应,以及土壤碳和氮分解对低温冻结及冻融循环的响应趋势,讨论了其研究方法的误差和不确定性,并对今后的研究提出了一些建议．气候变暖在短期内将使土壤碳和氮分解加速并引起CO2释放量增加,而长期过程中却并不一定会引起土壤碳和氮分解加速．合理解释不同研究结果的差异,除了需要系统分析土壤碳和氮分解对温度变化响应的机制外,还需要充分认识土壤碳和氮分解对温度变化响应的长期过程和短期过程的差异,以及研究方法、植被、土壤和气候等因素的影响．     

Two modes of bicarbonate utilization in the marine green macroalga Ulva lactuca

The green marine macroalga Ulva lactuca L. was found to be able to utilize HCO₃^? from sea water in two ways. When grown in flowing natural sea water at 16°C under constant dim irradiance, photosynthesis at pH8.4 was suppressed by acetazolamide but unaffected by 4,4′-diisothiocyanostilbene-2,2′-disulphonate. These responses indicate that photosynthetic HCO₃^? utilization was via extracellular carbonic anhydrase (CA) -mediated dehydration followed by CO₂ uptake. The algae were therefore described as being in a ‘CA state’. If treated for more than 10 h in a sea water flow-through system at pH9.8, these thalli became insensitive to acetazolamide but sensitive to 4,4′-diisothiocyanostilbene-2,2′-disulphonate. This suggests the involvement of an anion exchanger (AE) in the direct uptake of HCO₃^?, and these plants were accordingly described as being in an ‘AE state’. Such thalli showed an approximately 10-fold higher apparent affinity for HCO₃^? (at pH9.4) than those in the ‘CA state’, while thalli of both states showed a very high apparent affinity for CO₂. These results suggest that the two modes of HCO₃^? utilization constitute two ways in which inorganic carbon may enter the Ulva lactuca cells, with the direct entry of HCO₃^?, characterizing the ‘AE state’, being inducible and possibly functioning as a complementary uptake system at high external pH values (e.g. under conditions conducive to high photosynthetic rates). Both mechanisms of entry appear to be connected to concentrating CO₂ inside the cell, probably via a separate mechanism operating intracellularly.     

Carbonate ions appear to neither inhibit nor stimulate use of bicarbonate ions in photosynthesis by Ulva lactuca

Rates of photosynthesis by the marine macroalga Ulva lactuca were measured in a factorial experiment at five concentrations of HCO₃^? and CO₃^2- between 0·20 and 1·26 mol m^?3, but very low concentrations of CO₂. The results demonstrated that HCO₃^? was available for use, but an analysis of variance showed that CO₃^2- had neither an inhibiting nor a stimulating effect on rates of photosynthesis over this concentration range. Over the experiment, pH varied from 8·46 to 10·06 and this also had no significant effect on rates of photosynthesis. The lack of a stimulatory effect of high concentrations of CO₃^2- on the rate of photosynthesis at low concentrations of HCO₃^? was taken as circumstantial evidence for direct uptake of HCO₃^? rather than proton extrusion and external production of CO₂. In the rockpools in which U. lactuca grows, pH values up to 10·35 have been recorded, and for much of the time, CO₃^2- was the major form of inorganic carbon available. The apparent lack of an ability to use CO₃^2- under these conditions suggests that direct use of CO₃^2- as a source of inorganic carbon for photosynthesis is unlikely to be widespread.     

Effects of ocean acidification on growth and physiology of Ulva lactuca (Chlorophyta) in a rockpool‐scenario

Rising atmospheric CO₂‐concentrations will have severe consequences for a variety of biological processes. We investigated the responses of the green alga Ulva lactuca (Linnaeus) to rising CO₂‐concentrations in a rockpool scenario. U. lactuca was cultured under aeration with air containing either preindustrial pCO₂ (280 μatm) or the pCO₂ predicted by the end of the 21st century (700 μatm) for 31 days. We addressed the following question: Will elevated CO₂‐concentrations affect photosynthesis (net photosynthesis, maximum relative electron transport rate (rETR(max)), maximum quantum yield (Fv/Fm), pigment composition) and growth of U. lactuca in rockpools with limited water exchange? Two phases of the experiment were distinguished: In the initial phase (day 1–4) the Seawater Carbonate System (SWCS) of the culture medium could be adjusted to the selected atmospheric pCO₂ condition by continuous aeration with target pCO₂ values. In the second phase (day 4–31) the SWCS was largely determined by the metabolism of the growing U. lactuca biomass. In the initial phase, Fv/Fm and rETR(max) were only slightly elevated at high CO₂‐concentrations, whereas growth was significantly enhanced. After 31 days the Chl a content of the thalli was significantly lower under future conditions and the photosynthesis of thalli grown under preindustrial conditions was not dependent on external carbonic anhydrase. Biomass increased significantly at high CO₂‐concentrations. At low CO₂‐concentrations most adult thalli disintegrated between day 14 and 21, whereas at high CO₂‐concentrations most thalli remained integer until day 31. Thallus disintegration at low CO₂‐concentrations was mirrored by a drastic decline in seawater dissolved inorganic carbon and HCO₃^?. Accordingly, the SWCS differed significantly between the treatments. Our results indicated a slight enhancement of photosynthetic performance and significantly elevated growth of U. lactuca at future CO₂‐concentrations. The accelerated thallus disintegration at high CO₂‐concentrations under conditions of limited water exchange indicates additional CO₂ effects on the life cycle of U. lactuca when living in rockpools.     

Affinity, capacity and oxygen sensitivity of two different mechanisms for bicarbonate utilization in Ulva lactuca L. (Chlorophyta)

Ulva lactuca, collected on the west coast of Sweden at the end of May, was able to utilize the HCO₃ ^? pool of seawater only through extracellular dehydration via carbonic anhydrase, followed by uptake of the CO₂ formed. A decrease in the CO₂ supply via this mechanism resulted in the gradual development of an additional method of HCO₃ ^? utilization, namely a direct uptake of HCO₃ ^? . Photosynthesis could then be supported by either a ‘HCO₃ ^? dehydration mechanism’ or a ‘HCO₃ ^? uptake mechanism’. Through selective inhibition of either of these mechanisms, the physiological properties of the other could be assessed. These properties suggest that the HCO₃ ^? uptake mechanism of U. lactuca is important under conditions when low concentrations of inorganic C, high pH and high external O₂ concentrations would limit photosynthesis supported by the HCO₃ ^? dehydration mechanism. Such conditions may occur during intense irradiation of the alga in rockpools or in shallow bays with low rates of water exchange. The results are discussed in relation to a possible coupling between mechanisms for inorganic C acquisition and cell structure (or even morphology) of green macroalgae. They also illustrate some necessary precautions when using Michaelis–Menten kinetics for estimations of V_max and K_1/2 values.     

Research note: Irradiance of photosynthetically active radiation determines ultraviolet-susceptibility of photosynthesis in Ulva lactuca L.(Chlorophyta)

The respective ratio of photosynthetically active to ultraviolet radiation is of crucial importance to results obtained in ultraviolet (UV)‐research on photoautotrophic organisms. Specimens of the green macroalga Ulva lactuca L. were exposed to a constant irradiance of UV‐radiation at increasing irradiances of photosynthetically active radiation (PAR). The effects of experimental irradiance and spectral composition on photoinhibition of photosynthesis and its recovery were monitored by chlorophyll fluorescence measurements and the activity of the xanthophyll cycle was assessed by high performance liquid chromatography‐(HPLC) based pigment analysis. Results indicate a UV‐induced delay in recovery from PAR‐induced photoinhibition and a deceleration of violaxanthin conversion within the xanthophyll cycle due to the presence of UV‐radiation. Also the concentration of the protective pigment lutein increased considerably and could be indicative of the existence of an additional light‐protective mechanism, as, for example, the lutein‐epoxid cycle in Ulva. In total, results clearly show that the extent of UV‐induced inhibition of photosynthesis to be found in UV‐exposure experiments is highly dependent on the irradiance of background photosynthetically active radiation: with increasing irradiance of PAR the UV‐effects were diminished. Exemplified by the green algae Ulva lactuca this study demonstrates the crucial importance of the ratios of PAR:UV applied in UV‐research, particularly when conducting laboratory experiments in an ecological context.     

The effect of temperature and oxygen on the CO2 compensation point of the marine alga Ulva lactuca

Abstract The CO₂ compensation point of Ulva lactuca frond sections has been measured in artificial seawater using a sensitive gas-chromatographic method. Under nitrogen the compensation point remained relatively constant at 3–6 cm³ m⁻³ at temperatures from 10 to 30°C while in air-saturated medium (0.3 kg m⁻³ O₂) the compensation point rose from 5 cm³ m⁻³ at 10°C to 11 cm³ m⁻³ at 30°C. These responses of the compensation point to temperature and oxygen concentration indicate that there is little photorespiratory CO₂ loss in this marine macroalga, and the low values of these compensation points indicate that inorganic carbon is actively accumulated by the plant.     

水生生态系统的碳循环及对大气CO2的汇

水生生态系统,特别是海洋无疑是大气CO2的一个巨大的汇。海洋对大气CO2的汇以及大气圈和海洋之间碳的变换量在很大程度上取于混合层碳酸盐化学、水中溶解碳的平流传输、CO2通过空气－－海水界面的扩散、海洋生物生产和所产生的有面碳化合物的沉隆等,现在已建立和发展了多种海洋碳子模型以对CO2的汇进行估测。根据国内外研究资料,综述了水生生态系统碳循环过程及“生物泵”作用机制等方面的研究进展;介绍了两大类主要的海洋碳子模型：厢式模型和普通环流模型,采用这些模型对海洋碳汇的估算约为1.2-2.4GtC/a;分析了湖泊、河流等对大气CO2汇的特点及向海洋的转移,并对影响水体生态系统碳循环和大气CO2汇的因素进行了讨论。