The physiological ecology of haemocyanin in some selected crabs. II. The characteristics of haemocyanin in relation to terrestrialness

The haemocyanins of five crabs ranging in habit from aquatic to terrestrial have been investigated.

The mean P₅₀ values of the respiratory pigments were determined at 0 mm Hg CO₂ and 28 °C (the average environmental temperature of all the species). Comparison of these data adjusted to the individual mean physiological pH indicate an increase in P₅₀ with terrestrialization, perhaps related to the greater abundance of oxygen in the aerial than in some the aquatic habits, and the progressive elaboration of lung breathing with terrestrialization.

The Bohr shifts (Δ log P₅₀/ΔpH) were determined (using different P_CO2 values to vary pH) and were found to decrease with terrestrialization, perhaps in adaptation to an associated rise in internal P_CO2 (6–8-fold between the aquatic Callinectes sapidus Rathbun and the terrestrial Cardisoma guanhumi Latreille and probably resulting from progressive gill reduction.

The temperature shifts (ΔH cal/mol) of the haemoeyanins were found and it is suggested that they diminish with increasing evironmental temperature and temperature fluctuation accompanying terrestrialization.     

粳稻生育后期剑叶光合日变化和光合色素对大气CO2浓度和温度升高的响应——FACE研究

为研究水稻叶片光合色素和光合日变化对大气CO₂浓度和气温升高的响应,我们采用在开放空气中控制升高CO₂浓度和温度的方法,以常规粳稻南粳9108为试验材料,设置了环境CO₂和高大气CO₂浓度(增加200 μmol·mol^-1)、环境温度和增温(增加1～2 ℃)交互的4个处理,测定了灌浆中期和后期水稻剑叶的光合日变化特征和光合色素含量.结果表明: 水稻剑叶净光合速率(P_n)为双峰曲线,发生了光合“午休”现象;大气CO₂浓度升高提高了剑叶P_n,灌浆中期和后期平均分别增加了47.6%和39.1%;高温有降低P_n的趋势,但相关性未达到显著水平.大气CO₂浓度和温度升高导致水稻剑叶生育后期气孔导度(g_s)平均分别降低了17.0%和11.8%.高CO₂浓度水稻剑叶生育后期蒸腾速率(T_r)、叶绿素a、叶绿素b、类胡萝卜素、总叶绿素和叶绿素a/b值显著降低,平均降幅分别为5.9%、50.4%、21.3%、41.4%、39.4%和21.4%,明显增加了剑叶水分利用率(WUE),平均增幅达47.9%.与之相反,生育后期增温使水稻剑叶T_r增加了10.2%,使WUE平均降低了20.4%.综上所述,大气CO₂浓度升高对粳稻生育后期剑叶P_n、g_s和光合色素含量的影响明显大于增温效应.因此,应重视大气CO₂浓度和温度对水稻光合作用和光合色素的综合效应,减弱增温的负效应.     

粳稻生育后期剑叶光合日变化和光合色素对大气CO2浓度和温度升高的响应——FACE研究

为研究水稻叶片光合色素和光合日变化对大气CO₂浓度和气温升高的响应,我们采用在开放空气中控制升高CO₂浓度和温度的方法,以常规粳稻南粳9108为试验材料,设置了环境CO₂和高大气CO₂浓度(增加200 μmol·mol^-1)、环境温度和增温(增加1～2 ℃)交互的4个处理,测定了灌浆中期和后期水稻剑叶的光合日变化特征和光合色素含量.结果表明: 水稻剑叶净光合速率(P_n)为双峰曲线,发生了光合“午休”现象;大气CO₂浓度升高提高了剑叶P_n,灌浆中期和后期平均分别增加了47.6%和39.1%;高温有降低P_n的趋势,但相关性未达到显著水平.大气CO₂浓度和温度升高导致水稻剑叶生育后期气孔导度(g_s)平均分别降低了17.0%和11.8%.高CO₂浓度水稻剑叶生育后期蒸腾速率(T_r)、叶绿素a、叶绿素b、类胡萝卜素、总叶绿素和叶绿素a/b值显著降低,平均降幅分别为5.9%、50.4%、21.3%、41.4%、39.4%和21.4%,明显增加了剑叶水分利用率(WUE),平均增幅达47.9%.与之相反,生育后期增温使水稻剑叶T_r增加了10.2%,使WUE平均降低了20.4%.综上所述,大气CO₂浓度升高对粳稻生育后期剑叶P_n、g_s和光合色素含量的影响明显大于增温效应.因此,应重视大气CO₂浓度和温度对水稻光合作用和光合色素的综合效应,减弱增温的负效应.     

渭河平原农田冬小麦土壤呼吸及其影响因素

基于对半湿润易旱区的渭河平原农田2013—2014年冬小麦生长期土壤呼吸(SR)及环境因子和生物因子的观测,研究了冬小麦土壤呼吸日变化、季节变化特征,综合分析了温度(T)、土壤含水量(W)、总初级生产力(GPP)和叶面积指数(LAI)对土壤呼吸的影响.结果表明: 冬小麦土壤呼吸日变化呈单峰型,呼吸速率变化范围为1.5～6.94 μmol CO₂·m^-2·s^-1,最大值出现在12:00—14:00;温度是影响土壤呼吸日变化的驱动因子,其中地表温度(T_s)能解释土壤呼吸时间变异的80.9%;土壤呼吸速率与温度的昼夜变化对应关系呈顺时针近椭圆曲线.冬小麦土壤呼吸速率从出苗后到冬季呈下降趋势,在冬季时保持较低水平,进入返青期后迅速增加,在抽穗期和灌浆期达到最大,成熟期后有所下降,变化范围为0.65～4.85 μmol CO₂·m^-2·s^-1;土壤呼吸季节变化与温度、土壤含水量、GPP、LAI均呈显著(P<0.01)正相关关系;土壤温度和水分是影响土壤呼吸季节变化的关键因素,使用复合模型SR=e^{(a+bT_{5 cm}}+cW10 cm+dW_{10 cm²}),可以解释土壤呼吸时间变异的82.6%,比单因子模型(不超过65.7%)的解释能力显著提高.经模型计算,该区域2013—2014年冬小麦生长期平均土壤呼吸速率为1.67 μmol CO₂·m^-2·s^-1.     

梭梭和多枝柽柳的枝干光合及其主要影响因子

荒漠植物长期演化过程中保留了枝干光合(Pg)的特性,枝干光合有效减少局部碳损失,且在维持植物正常生理代谢方面发挥重要作用.本研究以古尔班通古特沙漠南缘荒漠植物梭梭和多枝柽柳为对象,利用Li-Cor 6400便携式光合仪与特制叶室相结合监测枝干与叶片光合速率,同时辅以枝干/叶片功能性状(叶绿素含量、含水量、叶/枝面积、碳...     

油蒿资源利用效率在生长季的相对变化及对环境因子的响应

为了探明西北半干旱区典型沙生植物油蒿(Artemisia ordosica)叶水平资源利用效率的相对变化及对环境因子的响应机制, 该研究于2018年5-10月, 使用LI-6400XT便携式光合仪测定了毛乌素沙地油蒿叶片的净光合速率(P_n)、蒸腾速率(E)、叶表面光合有效辐射(PAR_l)、叶表面温度(T_l)、叶表面相对湿度(RH_l), 在实验室计算叶片单位面积氮含量(N_area), 分析了叶片氮利用效率(NUE)、水分利用效率(WUE)、光利用效率(LUE)与环境因子之间的关系及NUE、WUE、LUE之间的相对变化。研究结果表明, 在充足且稳定光强下油蒿的P_n主要受温度的影响, NUE、WUE与VPD_l、T_l之间具有显著负相关关系, NUE、WUE与LUE间为正相关关系, NUE、WUE和LUE最大值分别发生在5、7和9月, 分别为9.43 μmol CO₂·g^-1·s^-1、3.86 mmol·mol^-1、0.04 mol·mol^-1, 资源利用效率的变化主要受P_n的影响。温度通过影响植物N分配来改变P_n, 进而影响着资源利用效率, WUE与LUE显著正相关, 对构建荒漠区生态系统能量交换过程模型有重要意义。     

开放式空气CO2浓度增高试验中的NO和NO2地气交换观测研究

介绍了农田FACE(free-air CO₂ enrichment)试验中的NO和NO₂地气交换观测方法,即静态暗箱采样—NO和NO₂化学发光分析法,并对观测结果进行了分析讨论.此观测方法简单、易于操作,并可获得可靠的NO和NO₂净交换通量观测结果.在稻麦轮作农田的旱地阶段,无论FACE还是对照处理,NO主要表现为地面净排放,NO₂主要表现为地面净吸收.逐日的NO净排放不依赖于土壤温度,但却与土壤含水量呈线性负相关(R²=0.82,P<0.001).NO₂净吸收具有明显的季节变化特征,逐日的净吸收通量随土壤温度和土壤含水量的变化可分别用抛物线方程拟合(温度:R²=0.74,P<0.001;含水量:R²=0.69,P<0.001).大气CO₂浓度升高200±40μmol·mol^-1使NO净排放减弱19%(t检验P=0.096),NO₂净吸收减弱10%(t检验P=0.26),这主要是植物生长受到促进的缘故.     

Electron paramagnetic resonance saturation studies of P-700 reaction center chlorophyll in plant photosynthesis

Electron paramagnetic resonance (EPR) power saturation and saturation recovery methods have been used to determine the spin lattice, T₁, and spin-spin, T₂, relaxation times of P-700⁺ reaction-center chlorophyll in Photosystem I of plant chloroplasts for 10 K T 100 K. T₁ was 200 μs at 100 K and increased to 900 μs at 10 K. T₂ was 40 ns at 40 K and increased to 100 ns at 10 K. T₁ for 40 K T 100 K is inversely proportional to temperature, which is evidence of a direct-lattice relaxation process. At T = 20 K, T₁ deviates from the 1/T dependence, indicating a cross relaxation process with an unidentified paramagnetic species. The individual effects of ascorbate and ferricyanide on T₁ of P-700⁺ were examined: T₁ of P-700⁺ was not affected by adding 10 mM ascorbate to digitonin-treated chloroplast fragments (D144 fragments). The P-700⁺ relaxation time in broken chloroplasts treated with 10 mM ferricyanide was 4-times shorter than in the untreated control at 40 K. Ferricyanide appears to be relaxing the P-700⁺ indirectly to the lattice by a cross-relaxation process. The possibility of dipolar-spin broadening of P-700⁺ due to either the iron-sulfur center A or plastocyanin was examined by determining the spin-packet linewidth for P-700⁺ when center A and plastocyanin were in either the reduced or oxidized states. Neither reduced center A nor oxidized plastocyanin was capable of broadening the spin-packet linewidth of the P-700⁺ signal. The absence of diplolar broadening indicates that both center A and plastocyanin are located at a distance at least 3.0 nm from the P-700⁺ reaction center chlorophyll. This evidence supports previous hypotheses that the electron donor and acceptor to P-700 are situated on opposite sides of the chloroplast membrane. It is also shown that the ratio of photo-oxidized P-700 to photoreduced centers A and B at low temperature is 2 : 1 if P-700 is monitored at a nonsaturating microwave power.     

六盘山南侧华北落叶松人工林冠层蒸腾及其影响因子的坡位差异

2014年5—10月,在宁夏六盘山香水河小流域选择了一个东南坡向的典型华北落叶松人工林坡面,设立上、中上、中、中下、下5个坡位的样地(P_1、P_2、P_3、P_4、P_5),利用热扩散探针法监测树干液流,并同步监测气象、土壤水势等环境因子.结果表明:研究期间林分日蒸腾(T_r,mm·d^-1)存在显著的坡位差异,不同坡位T_r为:P_2(0.975)>P_4(0.876)>P_3(0.726)>P_1(0.653)>P_5(0.628).T_r与日最高气温(T_max)、日均太阳辐射强度(SR)、日均饱和水汽压差(VPD)、日潜在蒸散(PET)、日均土壤水势(Ψ)呈显著正相关,与日均大气相对湿度(RH)、日降水量(P)、日最低气温(T_min)呈显著负相关.基于边界线的斜率绝对值分析表明,从坡上到坡下,T_r对日均气温(T)、RH、VPD、PET和Ψ的响应呈现逐渐减小的趋势,而对SR、土壤体积含水量(VSM)的响应程度则逐渐增大.进一步回归分析和偏相关分析表明,VPD、PET和RH对不同坡位T_r的影响均占主导地位,Ψ和T对上坡样地T_r影响较大,而下坡样地T_r受SR、T_min和VSM的影响较大.总体来看,T_r的坡位差异是土壤水分和气象条件共同作用的结果,在利用特定观测样地的液流速率尺度外推计算坡面T_r时,需同时考虑土壤水分和气象因子随坡位的变化.     

The use of pleopods for shell water circulation and respiration by hermit crabs

The use of the pleopods was investigated in two species of Diogenid hermit crabs, Dardanus arrosor and D. calidus. A transparent glass shell was used to observe the movements of the pleopods in hermit crabs. The movements consisted of periodic, irregular beating, which generated an irregular flow of the water within the shell.

A strong, regular beating movement was elicited when there was detritus or faeces in the shell, as was occupation of a new shell. Injection of water with a low oxygen concentration into the shell failed to induce any variation in the pleopod beating frequency (PBF), while the injection of water with a high CO₂ concentration induced a sudden PBF increase. When pH was varied and CO₂ concentration held at normal atmospheric level, there was a change in PBF. However, CO₂ variation alone, at constant pH, did not trigger any visible reaction. This suggests that there is a receptor for pH, which acts independently of the CO₂ concentration.

The function of males hermit crabs pleopods has always been obscure. However, at least in Dardanus, they are actively involved in water circulation within the shell for shell-cleaning and probably for ventilation.     

Ventilation in the shore crab Carcinus maenas (L.) as a function of ambient oxygen and carbon dioxide: Field and laboratory studies

Ventilatory responses of crabs Carcinus maenas (L.) to changes in ambient oxygen and carbon dioxide were studied in field and laboratory experiments, over a range of Pw_O2 and Pw_co2 conditions encompassing natural variations observed in intertidal rock-pools. Ventilatory activity was assessed by recording gill chamber hydrostatic pressure and estimating the specific ventilation, Vw/M_O2, the reciprocal of the difference of oxygen concentrations in inspired and expired waters.

Variations in ambient oxygenation always induced large changes of ventilatory activity, hyperventilation in hypoxia, hypoventilation in hyperoxia. Conversely, Pw_CO2 changes either at constant P_O2 or in combination with different P_O2 values (hypoxic hypercapnia or hyperoxic hypocapnia) led only to small or even non-significant ventilatory responses. In the field, strong hyperventilation developed during tidal exposure at night, when the pool water became hypoxic and hypercapnic, whereas during the day the animals hypoventilated in progressively more hyperoxic and hypocapnic conditions.

Thus, in a typical intertidal animal such as C. maenas, the only ventilatory stimulus of ecological significance appears to be the ambient water oxygenation.     

不同氧浓度下C2C12细胞的Nrf2抗氧化系统对H2O2刺激的反应*

目的:探讨不同氧浓度下小鼠骨骼肌卫星细胞系(C2C12细胞)对H₂O₂刺激反应的变化及其机制。方法:小鼠骨骼肌卫星细胞系(C2C12细胞),经培养复苏后,将细胞分为7组,每组设8个复孔,各组分别加入浓度为0.1 mmol/L、0.25 mmol/L、0.5 mmol/L、0.75 mmol/L、1 mmol/L、2 mmol/L的H₂O₂,分别作用1 h、2 h后测细胞活力,选择细胞H₂O₂刺激的最佳作用时间和浓度;C2C12细胞分为不同氧浓度组:21% O₂、12% O₂、8% O₂、5% O₂每组设8个复孔,12 h后,H₂O₂作用1 h,收集细胞;检测细胞Nrf2蛋白荧光和蛋白表达量,测定Nrf2和抗氧化酶SOD1、SOD2、CAT、NQO-1、HO-1、GPX-1 的mRNA表达量及细胞ROS水平。结果:选择H₂O₂作用时间相对较短的1 h和浓度0.5 mmol/L作为本实验的H₂O₂刺激条件。与21%O₂组相比,12%O₂组细胞Nrf2蛋白荧光增强,Nrf2 的mRNA和蛋白表达以及抗氧化酶SOD1、SOD2、CAT、NQO-1、HO-1、GPX-1的 mRNA表达均显著增加(P＜0.05或P＜0.01),细胞 ROS水平明显降低(P＜0.01);8%O₂组仅GPX-1 mRNA显著增加(P＜0.05),其他指标变化不大;5%O₂组细胞 Nrf2 mRNA和蛋白表达以及抗氧化酶SOD1、SOD2、NQO-1、GPX-1的 mRNA表达均明显降低(P＜0.05或P＜0.01),细胞 ROS水平则明显升高(P＜0.01)。结论:不同氧浓度下C2C12细胞中Nrf2介导的抗氧化系统对H₂O₂刺激反应不同,12 h的12% O₂浓度可促进C2C12细胞Nrf2的抗氧化作用,而5% O₂浓度的严重低氧则作用相反。     

The differential regulation of aldosterone output in hamster adrenal by angiotensinII and adrenocorticotropin.

Aldosterone was isolated from hamster adrenal cells and was identified by high performance liquid chromatography and thermospray mass spectroscopy analysis. Basal outputs from adrenal cell suspensions were of the same order of magnitude, 8.4 ± 1.9 ng and 8.0 ± 0.7 ng/2 h/50,000 cells, for aldosterone and corticosteroid, respectively. The outputs of aldosterone and corticosteroid increased with K⁺ concentrations to reach maxima of 3.3- and 1.6-fold at 10 meq/l of K⁺. Angiotensin_II (A_II) produced dose-dependent increases in aldosterone and corticosteroid outputs with maxima of 3- and 4-fold, respectively. In contrast, ACTH induced relatively no changes in aldosterone output, whereas dose-dependent increases in corticosteroid output were found. In time study experiments, with 10⁻⁸ M A_II, aldosterone and corticosteroid outputs were maximally increased after 1 h (6-fold) and 3 h (1.8-fold), respectively. At 10⁻⁸ M, ACTH had a small stimulatory effect on aldosterone output after 6 h, whereas it provoked a gradual increase in corticosteroid output (up to 7-fold after 8 h of incubation). The effects of A_II and ACTH on adrenal cytochrome P-450_11β involved in the last steps of aldosterone formation were evaluated by c combined in vivo andin vitro experiments. The P-450_11β mRNA level was increased by a low sodium intake but not by a 24 h ACTH stimulus. These results taken together indicate that ACTH and A_II differentially regulate P-450_11β. It is postulated that these two regulatory peptides regulate the hamster adrenal steroidogenesis by different P-450 genes.     

佛甲草(Sedum lineare)在干旱条件下的气体交换

在干旱条件下,测定了广州市1、4、5和年期屋顶绿化植物佛甲草叶片的气体交换参数、相对含水量(RWC)和比叶重(LMA),探讨了佛甲草在屋顶绿化中的生理生态适应性.结果表明不同生长期佛甲草叶片的RWC和LMA相对较低,分别在81.79%～87.58%和0.059～0.072 kg·m^-2之间,RWC和LMA在不同生长期的差异不显著(P>0.05).不同生长期佛甲草的气体交换参数CO₂同化速率(A)、气孔导度(g_s)和蒸腾速率(E)均呈现相似的日变化格型,A、g_s和E的日均值差异不显著(P>0.05).A、g_s和E之间的日变化呈明显的正相关关系(P<0.01).根据植物的RWC和气体交换参数的特征,推断佛甲草属兼性CAM植物,不同生长期佛甲草的主要生理生态指标相似.     

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.     

Some kinetic properties of polyphenol oxidase from Thymbra spicata L. var. spicata

Polyphenol oxidase (PPO) of Thymbra (Thymbra spicata L. var. spicata) was isolated by (NH₄)₂SO₄ precipitation and dialysis. A diphenolase from Thymbra plant, active against 4-methylcatechol, catechol and pyrogallol was characterized in detail in terms of pH and temperature optima, stability, kinetic parameters and inhibition behaviour towards some general PPO inhibitors. 4-Methylcatechol was the most suitable substrate, due to the lowest K_m and the biggest V_max/K_m values, followed by catechol and pyrogallol. The Thymbra PPO had maximum activity at pH 5.0, 7.0 and 8.0 with 4-methylcatechol, catechol and pyrogallol substrates, respectively. The optimum temperature of activity for Thymbra PPO was 30, 40 and 50 °C for 4-methylcatechol, catechol and pyrogallol substrates, respectively. It was found that optimum temperature and pH were substrate-dependent studied. The enzyme activity decreased due to heat denaturation of the enzyme with increasing temperature and inactivation time. Inhibition of Thymbra PPO was investigated with inhibitors such as l-cysteine and glutathione using 4-methylcatechol, catechol and pyrogallol as substrates. It was found that l-cysteine was a more effective inhibitor than glutathione owing to lower K_i. The type of inhibition depended on the origin of the PPO studied and also on the substrate used. Furthermore, the IC₅₀ values of inhibitors sudied on PPO were determined by means of activity percentage (I) diagrams.     

低温对离体大鼠心室肌复极时程的影响及其机制

目的: 观察低温对离体大鼠心室肌复极时程及Kir2.1蛋白表达的影响,探讨Kir2.1蛋白在其中的作用。 方法:18只健康雄性SD大鼠, 随机分为3组(n=6),即正常对照组(C组)、35℃低温组(H₁组)和32℃低温组(H₂组)。制备Langendorff离体心脏灌注模型,37℃ K-H液平衡灌注15 min后,C组继续灌注37℃ K-H液30 min;H₁组继续灌注35℃的K-H液30 min,H₂组继续灌注32℃的K-H液30 min。记录各组平衡灌注15 min(T₁)和继续灌注30 min(T₂)时HR、左心室前壁三层心肌单相动作电位,计算单相动作电位复极50％、90％的时程(MAPD₅₀、MAPD₉₀)和跨室壁复极离散度(TDR),同时记录心律失常发生情况。取测量电生理的心室肌部位组织以Western blot测定Kir2. 1蛋白表达,以免疫组织化学法测量Kir2. 1蛋白的平均光密度值(AOD)及分布情况。结果: 与T₀比较,T₁时H₁组和H₂组HR显著减慢(P＜0.05), MAPD₅₀、MAPD₉₀显著延长(P＜0.05),TDR显著增大(P＜ 0.05);与C组比较,T₁时H₁组和H₂组HR显著减慢(P＜0.05),MAPD₉₀显著延长(P＜0.05),TDR显著增大(P＜ 0.05),Kir2.1蛋白表达显著减少(P＜0.05), AOD值显著减少(P＜0.05)。与H₁组比较,T₁时H₂组心率显著减慢(P＜0.05),MAPD₅₀、MAPD₉₀显著延长(P＜0.05),TDR显著增大(P＜0.05)。C组Kir2.1蛋白分布正常,H₁、H₂组蛋白分布紊乱。结论: 低温会延长心室复极时程,增加复极离散度,其机制与低温下调Kir2.1蛋白表达、改变Kir2.1蛋白分布有关。     

水杨酸和油菜素内酯对低温胁迫下黄瓜幼苗光合作用的影响

为了探明外源水杨酸(SA)和2,4-表油菜素内酯(EBR)对低温胁迫下黄瓜幼苗光合作用的调控机理,以‘优博1-5’黄瓜为试材,用1 mmol·L^-1SA和0.1 μmol·L^-1EBR喷施预处理幼苗,每天喷1次,连喷2 d后置于低温下[10 ℃/5 ℃,光强(PFD)80 μmol·m^-2·s^-1]处理.结果表明: 低温胁迫下黄瓜幼苗生长量及净光合速率(P_n)下降;喷施SA和BER显著提高了P_n、光系统Ⅱ最大光化学效率(F_v/F_m)、光系统Ⅱ实际光化学效率(Φ_PSⅡ)和光化学猝灭系数(q_P),减缓了非光化学猝灭系数(NPQ)增加的幅度,同时核酮糖-1,5-二磷酸羧化/加氧酶(Rubisco)、景天庚酮糖-1,7-二磷酸酯酶(SBPase)、转酮醇酶(TK)和果糖-1,6-二磷酸醛缩酶(FBA)活性明显升高.说明SA和EBR可以通过调节光合关键酶的活性,缓解低温对黄瓜幼苗光合作用的影响,增强其对低温的适应性.     

A comparison of measured and calculated net community CO2 exchange: Scaling from leaves to communities

Leaf net photosynthesis is crucial for detecting the mechanism of photosynthesis, whereas community net photosynthesis is useful for understanding the photosynthetic capacity of communities and its relationship with environmental factors. In particular, we need to scale up eco-physiological models from leaf scale to canopy level to study carbon cycling at regional or global scale. We hypothesized that accumulated leaf net photosynthetic rate (P_c) at community scale, i.e., calculated based on leaf net photosynthetic rate (P_n) and leaf area index (LAI), equals to measured net community CO₂ exchange (NCE). The purpose of this study is to verify this hypothesis. Our field study was carried out in Duolun, Nei Mongol, China, where we constructed single-species communities by sowing Medicago sativa ‘Aohan’ seeds in three plots (3 m × 5 m) on May 30, 2012. On August 16, 2014, P_n of five healthy leaves of M. sativa ‘Aohan’ in each plot were measured with a LI-6400 portable photosynthesis system at 10:00, and net ecosystem CO₂ exchange (NEE) in each plot was measured simultaneously with a LI-8100 system connected with a assimilation chamber (0.5 m × 0.5 m × 0.5 m). P_c was calculated based on P_n, number of leaves (n), LAI percentage of healthy leaves (r) and percentage of received effective light by leaves (m). NCE was derived from NEE and ecosystem respiration rate (R_eco). P_c was 3.52 μmol CO₂·m^-2·s^-1, and very close to NCE (3.56 μmol CO₂·m^-2·s^-1), suggesting that leaf-scale photosynthesis may accurately predict community-scale photosynthesis. However, our method could not separate community respiration from soil respiration, and future studies, should be designed to counteract this effect. Scaling up from leaf photosynthesis to community photosynthesis should also consider vertical structure of communities and nonlinear responses of leaf photosynthesis to changes in light quantum.