蛋白核小球藻生长和无机碳利用对不同光照强度和CO_2浓度的响应

为了探讨光照强度和CO_2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120μmol photons×m–2×s–1)和两种CO_2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CO_2浓度组生长最快;低光强高CO_2浓度组培养体系中总无机碳浓度为1 163.3μmol×L–1,显著高于其他3组;高光强低CO_2浓度组藻的p H补偿点最高(9.8),而低光强高CO_2浓度组藻的p H补偿点最低(8.6);低光强高CO_2浓度组藻的最大光合速率(Vmax)和最大光合速率一半时的无机碳浓度(K0.5)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CO_2浓度组藻的胞外CA活性最高;而低光强低CO_2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CO_2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HCO_3~–为无机碳源,其对无机碳的利用受光照的调节。     

CO2浓度变化对拟柱胞藻生长与光合作用的影响

为了探讨大气CO₂浓度升高对水华藻类的影响,利用水华蓝藻-拟柱胞藻作为实验材料,研究了CO₂浓度升高对其生长生理和光合作用的影响,结果表明CO₂浓度升高,导致拟柱胞藻的生物量、最大光合放氧速率、光合效率显著增加。当CO₂浓度为700 mg/L以下,暗呼吸速率和光饱和点无明显影响,而CO₂浓度为1000 mg/L时,暗呼吸速率和光饱和点显著提高。随着CO₂浓度增加,藻细胞光合作用对无机碳的亲和力降低,同时胞外碳酸酐酶活性显著下降。这表明大气CO₂浓度的增加,有利于拟柱胞藻的生长和光合,进而增加了水华发生的风险。     

光强调控三角褐指藻对海洋酸化的生理学响应

光和海洋酸化(CO₂浓度升高)分别对海洋硅藻的光合能力具有不同程度的影响, 但两者的耦合响应被较少关注。研究以三角褐指藻作为实验材料, 测定了不同光强下CO₂浓度升高对三角褐指藻的生长、净光合速率、生化组分、胞外碳酸酐酶(eCA)活性和核酮糖-1,5-二磷酸羧化/氧化酶(Rubisco)活性的影响。结果显示在低光下, CO₂浓度对三角褐指藻的生长和净光合速率(P_n)并没有显著影响, 而在高光下, 具有明显的影响。无论是在高光或是低光下, eCA活性、叶绿素和可溶性蛋白的含量都随着CO₂浓度的升高而降低。在低光下, 高浓度CO₂ (HC)培养下的Rubisco活性分别是低浓度CO₂ (LC)和中浓度CO₂ (MC)的2.42和1.39倍, 而在高光下, HC培养下的Rubisco活性分别是LC和MC的6.72和3.45倍。以上结果表明硅藻能够通过调节光合生理特征和CCM运行中能量的分配来适应环境中光强和CO₂浓度的变化。     

花生幼苗光合特性对弱光的响应

在苗期用黑色遮阳网对丰花1号和丰花2号进行不同遮光处理(不遮光,遮光27%、43%和77%),研究了苗期遮光及恢复对花生叶片光合特性的影响.结果表明： 遮光后,随遮光程度增强,叶片叶绿素含量显著增加,实际光化学效率(Ф_PSⅡ)和最大光化学效率(F_v/F_m)升高,叶绿素a/b和净光合速率(P_n)降低.恢复自然光照后1 d,在高光强下测定时,随前期遮光程度增强,P_n、气孔导度(G_s)下降,细胞间隙CO₂浓度(C_i)升高;在低光强下测定时,P_n显著升高,G_s和C_i下降;低光强与高光强下测定的P_n比值显著升高;恢复自然光照后,随前期遮光程度增强,光补偿点、光饱和点、CO₂补偿点、CO₂饱和点和羧化效率显著降低,表观量子效率显著升高.恢复自然光照后,P_n、Ф_PSⅡ和F_v/F_m先迅速下降,3～5 d后逐渐回升;恢复15 d后,遮光27%处理的各项指标恢复到对照水平,其他处理的恢复程度则因遮光程度和品种而异.丰花1号各处理叶绿素含量、P_n、Ф_PSⅡ均高于丰花2号.苗期遮光提高了花生利用弱光的能力,降低了其利用强光的能力.     

稳定表达人源GABAAR-CHO细胞株的建立

目的: 构建α₁亚基诱导表达、β₂和γ_2L亚基稳定表达的人源α₁β₂γ_2L-GABA_AR-CHO(Chinese hamster ovary)细胞株。方法: 从人cDNA文库中扩增α₁、β₂、γ_2L亚基编码基因,分别构建亚基表达载体;将三个亚基表达载体共转染CHO-K1细胞,通过抗性筛选、膜电位检测法进行稳定表达克隆筛选;通过qPCR、Western blot对亚基表达进行鉴定;以激动剂GABA、阳性变构调节剂地西泮(diazepam,Dia)、拮抗剂荷包牡丹碱(bicuculine)为工具药,采用全细胞膜片钳方法及膜电位检测法对稳定表达细胞的药理学功能进行鉴定。结果: 经克隆筛选获得表达量较高的α₁β₂γ_2L-GABA_AR-CHO并对其亚基表达鉴定,结果显示该细胞稳定表达α₁、β₂、γ_2L亚基,构建的α₁β₂γ_2L-GABA_AR-CHO细胞仅在加入四环素(tetracyclin)诱导的情况下表达α₁亚基并与β₂、γ_2L组装成具有功能活性的α₁β₂γ_2L-GABA_AR;对其进行全细胞膜片钳检测研究发现,GABA可对其产生激动效应,引起α₁β₂γ_2L-GABA_AR-CHO细胞产生氯离子通道特征性电流变化,Dia可剂量依赖性地增强GABA对α₁β₂γ_2L-GABA_AR的激动效应;在膜电位检测研究中,获得GABA激动效应EC₅₀为(177.72 ± 15.92)nmol/L,Dia变构效应EC₅₀为(3.63±0.52)μmol/L,拮抗剂Bicuculine拮抗效应IC₅₀为(538.83±29.55)nmol/L。结论: 通过采用诱导表达策略,成功构建了α₁β₂γ_2L-GABA_AR-CHO稳定表达细胞株,该细胞株具有对激动剂、阳性变构剂、拮抗剂特异性检测的药理学功能。     

太湖两种大型沉水植物无机碳利用效率差异及其机理

该文通过pH值漂移实验比较了太湖常见的两种沉水植物菹草(Potamogeton crispus)和马来眼子菜(P. malaianus)对无机碳利用效率的差异,并测定两者无机碳吸收关键酶——碳酸酐酶的活性,探讨了两者无机碳吸收效率差异的原因。根据太湖自然水体的无机碳条件设定了3种不同碱度条件,测定起点pH值和无机碳条件。不同碱度下pH值漂移变化和总无机碳/碱度比值的结果表明,两个种均能利用${HCO_{3}}^{-}$,适应低无机碳条件。两者对${HCO_{3}}^{-}$的吸收速率决定于其浓度大小,该离子浓度越大,光合速率越高。但是对${HCO_{3}}^{-}$的吸收速率存在差异:马来眼子菜在各碱度下终点pH值显著高于菹草,整体光合速率较高。CO₂-光合速率响应曲线表明,在高pH值(CO₂受到限制)时,马来眼子菜对CO₂亲和力较大。尽管菹草在pH值较低(6.5~7.0)时有相对较高的光合速率,但是基于太湖自然水体夏季高pH值(>8.5)条件,马来眼子菜具有更大的生长优势,成为优势种群。两者无机碳吸收速率的差异是造成它们生活史差异和时间生态位的一重要原因。同时,马来眼子菜碳酸酐酶活性明显高于菹草,表明在相同无机碳条件下,前者催化${HCO_{3}}^{-}$与CO₂之间的转化效率更高,这可能是造成两者无机碳吸收速率差异的原因。     

碳酸酐酶在中肋骨条藻光合作用中的作用

探讨了在正常空气条件下生长的中肋骨条藻(Skeletonema costatum)的碳酸酐酶(CA)在其光合固碳中的作用.在中肋骨条藻的胞内和胞外均有CA活性,但胞外CA活性很低.CA抑制剂AZ(乙酰唑磺胺)对中肋骨条藻的光合放氧速率没有明显影响,而CA抑制剂EZ(乙氧苯唑胺)对其光合放氧速率有强烈的抑制作用.EZ的抑制作用使细胞最大光合速率、饱和光强和无机碳亲和力下降,无机碳的补偿点和光呼吸提高,使强光下光抑制作用增强.这些结果表明:中肋骨条藻的胞外CA在其光合作用中所起的作用较小,而其胞内CA通过催化胞内碳库中的HCO-3快速转化成CO2,提高胞内CO2的有效供给,从而提高细胞光合固碳能力和对逆境(高O2、强光和低CO2)的适应能力.     

四种作物光下暗呼吸速率降低的原因

以C₃作物(小麦, Triticum aestivum和大豆, Glycine max)和C₄作物(玉米, Zea mays和千穗谷, Amaranthus hypochondriacus)为例, 探讨了其光下暗呼吸速率降低的原因。结果表明, 2% O₂条件下, CO₂浓度为0时, 叶室CO₂浓度维持在0左右, 而胞间CO₂浓度(C_i)显著高于叶室CO₂浓度。分析认为这是由于此时植物的暗呼吸仍在正常进行。因此, 该测量条件下的表观光合速率应为CO₂浓度为0时的光下暗呼吸速率(R_d)。CO₂浓度为0时, 不同光强下的R_d均随光强的升高而降低, 且在低光强(50 μmol·m^-2·s^-1)和高光强(2000 μmol·m^-2·s^-1)之间存在显著差异, 说明光强对R_d具有较大影响。在2% O₂条件下, 经饱和光强充分活化而断光后, 以上4种作物叶片的暗呼吸速率(R_n)均随着时间的推移而下降, 说明光强并未抑制暗呼吸速率。试验结果表明, R_d的降低是由于CO₂被重新回收利用所导致, CO₂回收利用率随光强的升高而增大, 从低光强(50 μmol·m^-2·s^-1)到高光强(2000 μmol·m^-2·s^-1), 小麦、大豆、玉米和千穗谷的回收利用率范围变动分别为22.65%-52.91%、22.40%-55.31%、54.24%-87.59%和72.43%-90.07%。     

水稻光合碳在植物-土壤系统中的分配及其对CO2升高和施氮的响应

采用¹³C-CO₂进行连续标记,研究水稻分蘖期和孕穗期光合碳在植株-土壤系统中的分配及其对大气CO₂浓度升高(800 μL·L^-1)和施氮(100 mg·kg^-1)的响应.结果表明: CO₂浓度升高显著提高分蘖期根系生物量和孕穗期地上部生物量,并使生物量根冠比在分蘖期增加,而在孕穗期减小.CO₂浓度升高条件下,施氮使水稻地上部分生物量增加,却显著降低了孕穗期水稻根系生物量.CO₂浓度升高使光合¹³C在孕穗期向土壤的输入显著增加,然而施肥并没有促进由CO₂浓度升高驱动的光合¹³C在土壤中的积累,而且还降低了土壤中的光合¹³C的分配比例.综上,CO₂浓度升高显著提高了稻田土壤光合碳输入,促进稻田有机碳周转;施氮促进了水稻地上部的生长,却降低了光合碳向地下的分配比例.     

水稻光合碳在植物-土壤系统中的分配及其对CO2升高和施氮的响应

采用¹³C-CO₂进行连续标记,研究水稻分蘖期和孕穗期光合碳在植株-土壤系统中的分配及其对大气CO₂浓度升高(800 μL·L^-1)和施氮(100 mg·kg^-1)的响应.结果表明: CO₂浓度升高显著提高分蘖期根系生物量和孕穗期地上部生物量,并使生物量根冠比在分蘖期增加,而在孕穗期减小.CO₂浓度升高条件下,施氮使水稻地上部分生物量增加,却显著降低了孕穗期水稻根系生物量.CO₂浓度升高使光合¹³C在孕穗期向土壤的输入显著增加,然而施肥并没有促进由CO₂浓度升高驱动的光合¹³C在土壤中的积累,而且还降低了土壤中的光合¹³C的分配比例.综上,CO₂浓度升高显著提高了稻田土壤光合碳输入,促进稻田有机碳周转;施氮促进了水稻地上部的生长,却降低了光合碳向地下的分配比例.     

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.     

Consumption of O2 in the light by Chlorella pyrenoidosa and Chlamydomonas reinhardtii

A mass spectrometer has been used to measure O₂ production and consumption and net CO₂ exchange near the CO₂ compensation point in Chlorella pyrenoidosa and Chlamydomonas reinhardtii grown in air and in 2% (v/v) and 5% (v/v) CO₂ in air. Some experiments were run in presence of -hydroxy-2-pyridinemethanesulfonic acid and, for others, data are presented from parallel assays for enzymic glycolate oxidation. Although the glycolate-oxidising enzyme was present in cells grown with and without CO₂ enrichment, the activities measured were not compatible with direct measurements of O₂ consumption in the light. This and other evidence argues against glycolate being the primary substrate for light-induced O₂ consumption by these organisms.     

荒漠草原猪毛蒿种群繁殖特征的土壤驱动因子分析

繁殖是植物生命活动的重要环节, 了解植物的繁殖特征是解释植物生态适应性和制定有效管理措施的重要依据。该研究以荒漠草原猪毛蒿(Artemisia scoparia)种群为研究对象, 通过测定不同土壤类型的理化性质和猪毛蒿的繁殖特征, 以期探讨影响其繁殖特征的主要土壤驱动因子。结果表明: 灰钙土、风沙土和基岩风化残积土的水溶性碳含量、全氮含量、全磷含量、全盐含量、土壤水分含量、土壤硬度存在显著差异。猪毛蒿平均个体大小、单株头状花序的平均质量和数量均以灰钙土生境下最大, 基岩风化残积土最小。繁殖分配在不同土壤类型下无显著差异, 但与单个头状花序质量、单株头状花序数量和质量间呈极显著正相关关系。单株头状花序数量与单个头状花序质量间呈负相关关系。在风沙土生境下, 单株头状花序质量主要受到土壤水溶性碳含量、土壤水分含量以及pH值的共同影响; 单株头状花序数量受全盐含量的影响最大; 繁殖分配和单个头状花序质量主要受全碳含量的影响。灰钙土生境下, 单株头状花序质量与土壤水溶性碳含量、土壤水分含量和有机碳含量呈正相关关系; 速效氮含量显著影响着单株头状花序数量。而基岩风化残积土生境下, 繁殖特征的变异主要受到土壤水溶性碳含量、土壤硬度、土壤水分含量、全磷和速效磷含量的影响。综合分析发现, 土壤因子对猪毛蒿繁殖特征的影响程度不同, 其中单株头状花序数量和质量极显著地受到土壤水溶性碳含量和土壤水分含量的影响, 繁殖分配和单个头状花序质量与土壤水溶性碳含量、土壤水分含量呈负相关关系。因此, 土壤水溶性碳含量和土壤水分是荒漠草原地区影响猪毛蒿种群繁殖特征的主要土壤因子。     

Effluxes of nitrous oxide,methane and carbon dioxide and their responses to increasing nitrogen deposition in the Gurbantünggüt Desert of Xinjiang,China

Aims Desert soils play an important role in the exchange of major greenhouse gas (GHG) between atmosphere and soil. However, many uncertainties existed in understanding of desert soil role, especially in efflux evaluation under a changing environment. Methods We conducted plot-based field study in center of the Gurbantünggüt Desert, Xinjiang, and applied six rates of simulated nitrogen (N) deposition on the plots, i.e. 0 (N0), 0.5 (N0.5), 1.0 (N1), 3.0 (N3), 6.0 (N6) and 24.0 (N24) g·m^-2·a^-1. The exchange rates of N₂O, CH₄ and CO₂ during two growing seasons were measured for two years after N applications. Important findings The average efflux of two growing seasons from control plots (N0) were 4.8 μg·m^-2·h^-1, -30.5 μg·m^-2·h^-1 and 46.7 mg·m^-2·h^-1 for N₂O, CH₄ and CO_2, respectively. The effluxes varied significantly among seasons. N0, N0.5 and N1 showed similar exchange of N₂O in spring and summer, which was relatively higher than in autumn, while the rates of N₂O in N6 and N24 were controled by time points of N applications. The uptake of CH₄ was relatively higher in both spring and summer, and lower in autumn. Emission of CO₂ changed minor from spring to summer, and greatly decreased in autumn in the first measured year. In the second year, the emission patterns were changed by rates of N added. N additions generally stimulated the emission of N₂O, while the effects varied in different seasons and years. In addition, no obvious trends were found in the emission factor of N₂O. The uptake of CH₄ was not significantly affected by N additions. N additions did not change CO₂ emissions in the first year, while high N significantly reduced the CO₂ emissions in spring and summer of the second year, without affected in autumn. Structure equation model analysis on the factors suggested that N₂O, CH₄ and CO₂ were dominantly affected by the N application rates, soil temperature or moisture and plant density, respectively. Over the growing seasons, both the net efflux and the global warming potential caused by N additions were small.     

Inorganic carbon uptake kinetics of the stream macrophyte Callitriche cophocarpa Sendt.

Photosynthetic carbon uptake of Callitriche cophocarpa Sendt. was examined in plants collected from six Danish streams and in plants grown under variable inorganic carbon conditions in the laboratory. Both field and laboratory plants showed a low affinity for inorganic carbon (CO₂ compensation points ranging from 0.7 to 22 μM, and K_0.5(CO₂) from 51 to 121 μM), consistent with C-3 photosynthesis and use of CO₂ alone. Variation in inorganic carbon uptake characteristics was low in both groups of plants. Only in laboratory-grown plants was a coupling found between carbon uptake and the inorganic carbon regime of the medium. The carbon extraction capacity, expressed as a percentage of the initial amount of dissolved inorganic carbon (DIC) assimilated in PH-drift experiments, increased from −1.4 to 11.8% with declining external carbon availability, and the initial slope of the CO₂ response curve increased from 6.4 to 15.3 g⁻¹ h⁻¹ dm³. The plasticity of the inorganic carbon uptake system of C. cophocarpa was very low compared to the plasticity observed for submerged macrophytes with accessory carbon uptake systems (i.e. HCO₃⁻ use or C-4 photosynthesis), suggesting that the plasticity of the C-3 photosynthetic apparatus as such is restricted. The low carbon affinity of C. cophocarpa indicates that this species depends on CO₂ oversaturation for a sufficient supply of CO₂ for photosynthesis and growth.     

Construction of CO2-response model of electron transport rate in C4 crop and its application

准确估算光合电子流对CO₂响应的变化趋势对深入了解光合过程具有重要意义。该研究在植物光合作用对CO₂响应新模型(模型I)的基础上构建了电子传递速率(J)对CO₂的响应模型(模型II), 并对用LI-6400-40便携式光合仪测量的玉米(Zea mays)和千穗谷(Amaranthus hypochondriacus)的数据进行了拟合。结果表明, 模型II可以很好地拟合玉米和千穗谷叶片J对CO₂浓度的响应曲线(J-C_a曲线), 得到玉米和千穗谷的最大电子传递速率分别为262.41和393.07 mmol·m ^-2·s ^-1, 与估算值相符合。在此基础上, 对光合电子流分配到其他路径进行了探讨。结果显示, 380 mmol·mol ^-1 CO₂浓度下玉米和千穗谷碳同化所需的电子流为247.92和285.16 mmol·m ^-2·s ^-1, 分配到其他途径的光合电子流为14.49和107.91 mmol·m ^-2·s ^-1(考虑植物CO₂的回收利用)。比较两种植物的其他途径光合电子流分配值发现, 两者相差6倍之多。分析认为这与千穗谷和玉米的催化脱羧反应酶种类以及脱羧反应发生的部位不同密切相关。该发现为人们研究C₄植物中烟酰胺腺嘌呤二核苷磷酸苹果酸酶型和烟酰胺腺嘌呤二核苷酸苹果酸酶型两种亚型之间的差异提供了一个新的视角。此外, 构建的电子传递速率对CO₂的响应模型为人们研究C₄植物的光合电子流的变化规律提供了一个可供选择的数学工具。     

Correlation between vein density and water use efficiency of Salix matsudana in Zhangye Wetland,China

Aims The correlation between vein density and water use efficiency (WUE) affects the balance between water supply and demand of plant leaves, which is significant for comprehending the ecological adaptation strategies of plants. The objective of this study was to study how Salix matsudana modulated vein density and WUE along a soil moisture gradient in Zhangye Wetland, China. Methods The study was conducted in floodplain wetland near Heihe River in Zhangye City, Gansu Province, China. Three sample plots, at a spatial interval of 70 m, were set up along a soil moisture gradient ordinally from the area near the water body to the wetland edge, plot I (69.23%), spot II (48.38%) and spot III (35.27%). Community traits were investigated by using diagonal method, and all individuals of S. matsudana were used for measurements of height and canopy. At each plot, 5 individuals of S. matsudana at 4 vertices and diagonal intersection were selected for measurements of vein density, WUE, net photosynthetic rate (P_n), transpiration rate (T_r), photosynthetically active radiation (PAR), saturated vapor pressure differences (VPD), specific leaf area, stomatal conductance (G_s) and intercellular CO₂ concentration (C_i). We used mathematical methods of correlation analysis and standardized major axis to investigate relationships between vein density and WUE. Important findings With decreasing soil moisture, the height, canopy, specific leaf area, G_s and C_i of S. matsudana decreased gradually, while the vein density, WUE, P_n, T_r, PAR and VPD increased gradually. The correlation between vein density and WUE was positive in all the three plots, but the relationship varied along the soil moisture plots gradient. There was a highly significant positive correlation (p < 0.01) between the vein density and WUE at plot I and III, whereas the correlation only reached a significant level (p < 0.05) at plot II; The correlation coefficient between vein density and WUE is significantly smaller than 1 at plot I (p < 0.05), while the correlation coefficient is significant greater than 1 at plot II and III (p < 0.05). We can conclude that varied relationships between vein density and WUE of S. matsudana along a soil moisture gradient could reflect plant acclimation.     

CO2浓度倍增对红松幼苗根尖和叶解剖结构及生理功能的影响

大气CO₂浓度升高对植物的影响是目前植物生态学研究中普遍关注的问题。以往的研究主要关注植物地上部分叶解剖结构及生理功能的改变, 而对根解剖结构和生理功能变化以及根与叶变化之间潜在联系的研究较少。该文以三年生红松(Pinus koraiensis)幼苗为研究对象, 通过CO₂浓度倍增(从350 µmol·mol^-1增加到700 µmol·mol^-1)试验, 研究当年生针叶和根尖解剖结构及生理功能的变化。结果表明: (1) CO₂浓度倍增处理的红松幼苗, 气孔密度显著降低, 叶肉组织面积、木质部及韧皮部面积明显增加; (2) CO₂浓度倍增导致红松幼苗根尖直径增粗, 皮层厚度和层数显著增加, 管胞直径变小; (3)高CO₂浓度处理下, 叶气孔导度和蒸腾速率降低, 光合速率和水分利用效率提高, 同时根尖的导水率显著下降, 但管胞的抗栓塞能力显著提高。这些结果显示, 叶和根解剖结构及生理功能在CO₂浓度升高条件下具有一致的响应。未来研究中应该同时关注全球气候变化对植物地上和地下器官结构与功能的影响。     

Greenhouse gas fluxes of typical northern subtropical forest soils: Impacts of land use change and reduced precipitation

Aims It is important to study the effects of land use change and reduced precipitation on greenhouse gas fluxes (CO₂, CH₄ and N₂O) of forest soils. Methods The fluxes of CO₂, CH₄ and N₂O and their responses to environmental factors of primary forest soil, secondary forest soil and artificial forest soil under a reduced precipitation regime were explored using the static chamber and gas chromatography methods during the period from January to December in 2014. Important findings Results indicate that CH₄ uptake of primary forest soil ((-44.43 ± 8.73) μg C·m^-2·h^-1) was significantly higher than that of the secondary forest soil ((-21.64 ± 4.86) μg C·m^-2·h^-1) and the artificial forest soil ((-10.52 ± 2.11) μg C·m^-2·h^-1). CH₄ uptake of the secondary forest soil ((-21.64 ± 4.86) μg C·m^-2·h^-1) was significantly higher than that of the artificial forest ((-10.52 ± 2.11) μg C·m^-2·h^-1). CO₂ emissions of the artificial forest soil ((106.53 ± 19.33) μg C·m^-2·h^-1) were significantly higher than that of the primary forest soil ((49.50 ± 8.16) μg C·m^-2·h^-1) and the secondary forest soil ((63.50 ± 5.35) μg C·m^-2·h^-1) (p < 0.01). N₂O emissions of the secondary forest soil ((1.91 ± 1.22) μg N·m^-2·h^-1) were higher than that of the primary forest soil ((1.40 ± 0.28) μg N·m^-2·h^-1) and the artificial forest soil ((1.01 ± 0.86) μg N·m^-2·h^-1). Reduced precipitation (-50%) had a significant inhibitory effect on CH₄ uptake of the artificial forest soil, while it enhanced CO₂ emissions of the primary forest soil and the secondary forest soil. Reduced precipitation had a significant inhibitory effect on CO₂ emissions of the artificial forest soil and N₂O emissions of the secondary forest (p < 0.01). Reduced precipitation promotes N₂O emissions of the primary forest soil and the artificial forest soil. CH₄ uptake of the primary forest and the secondary forest soil increased significantly with the increase of soil temperature under natural and reduced precipitation. CO₂ and N₂O emission fluxes of the primary forest soil, secondary forest soil and artificial forest soil were positively correlated with soil temperature (p < 0.05). Soil moisture inhibited CH₄ uptake of the secondary forest soil and the artificial forest soil (p < 0.05). CO₂ emissions of the primary forest soil were significantly positively correlated with soil moisture (p < 0.05). N₂O emissions of primary forest soil and secondary forest soil were significantly correlated with the nitrate nitrogen content (p < 0.05). It was implied that reduced precipitation and land use change would have significant effects on greenhouse gas emissions of subtropical forest soils.     

Effects of inoculation with arbuscular mycorrhizal fungi on photosynthetic physiology in females and males of Populus deltoides exposed to cadmium pollution

Aims Populus deltoides is an important plantation tree species in the middle and lower reaches of the Yangtze River and in Huai River Plain. The extensively cultivated varieties are consisted of both females and males of P. deltoides. The objective of this paper was to characterize the difference in cadmium (Cd) tolerance between the sexes and the effects of symbiosis with Rhizophagus intraradices on their Cd tolerance.
Methods The experiment was carried out under semi-controlled conditions in a natural light greenhouse, protected from rain. Rhizophagus intraradices was inoculated on roots of both females and males when transplanting to a sand culture substrate. After one month, half of cuttings were exposed to Cd pollution (10 mg·kg^-1). All cuttings were irrigated with sterile water to avoid infection by other microorganism. About three months later, the gas exchange rate, net photosynthesis rate (P_n)-intercellular CO₂ concentration (C_i) curve, chlorophyll fluorescence, osmotic adjustment and phytohormone content of both females and males of P. deltoides were measured.
Important findings Our main results are as follows: (1) when compared to the controls, decreases in P_n, stomatal conductance, C_i, transpiration rate, maximum photochemical efficiency of photosystem II (PSII), effective quantum yield of PSII, photo-chemical quenching coefficient, maximum rate of carboxylation of Rubisco, photosynthetically active radiation-saturated rate of electron transport and rate of triose phosphate utilization to a different degree in both sexes of P. deltoides under Cd pollution were found, and females exhibited a greater decrease in such parameters than males. Rhizophagus intraradices inoculation mitigated the toxic effect of Cd on such parameters to a different degree in females, not in males. (2) Under Cd pollution, there was an increase in proline content in both sexes when compared to the controls. A further increase in proline content occurred in females, not in males, when inoculated with R. intraradices. (3) When compared to the controls, there was a decrease in indoleacetic acid, but an increase in abscisic acid in leaves of both sexes when exposed to Cd pollution. The amplitude changed in both phytohormones in females was greater than that in males. Rhizophagus intraradices inoculation was helpful for recovery of phytohormone balance in females, which was not observed in males. Therefore, our results indicated that (1) there were a greater negative effect exerted by Cd pollution on gas exchange rate, carbon fixation capacity and phytohormone balance and a more impairment of photosynthetic apparatus in females when compared to males, showing a less tolerance to stress conditions in females; (2) Rhizophagus intraradices inoculation could enhance the osmotic adjustment capacity in females, thus mitigate the negative effect of Cd stress on ability of carbon fixation and phytohormone balance in females. However, such positive effects derived from R. intraradices symbiosis were not observed in males.