不同藻密度下Zn2+ 浓度对萼花臂尾轮虫实验种群增长参数的影响

为了比较不同食物密度下污染物浓度对受试生物的慢性毒性,筛选出以轮虫为受试生物对水环境中Zn2+污染进行监测的敏感指标,在不同斜生栅藻(Scenedesmus obliquus)密度(1.0×106、2.0×106和4.0×106个/m L)下不同浓度(0、0.1、0.3、0.5、0.7、0.9 mg/L)的Zn2+对萼花臂尾轮虫(Brachionus calyciflorus)实验种群增长参数的影响。结果表明,25℃以及1.0×106、2.0×106和4.0×106个/m L藻密度下Zn2+对萼花臂尾轮虫的24 h LC50值分别是6.647、8.102和5.873 mg/L。与各食物密度下的对照组相比,当食物密度为1.0×106个/m L时,各浓度的Zn2+对萼花臂尾轮虫的各种群增长参数均无显著性影响(P0.05)。当食物密度为2.0×106个/m L时,各浓度的Zn2+均显著延长了轮虫的生命期望、世代时间和平均寿命,提高了轮虫的净生殖率;除0.3 mg/L外,其他浓度的Zn2+显著提高了轮虫的种群内禀增长率。当食物密度为4.0×106个/m L时,0.1、0.3和0.7mg/L的Zn2+显著提高了轮虫的种群内禀增长率,0.7和0.9 mg/L的Zn2+显著提高了轮虫的后代混交率。藻密度对轮虫的生命期望、世代时间、净生殖率、种群内禀增长率、平均寿命和后代混交率均有极显著性影响(P0.01),Zn2+浓度对轮虫的生命期望、世代时间、净生殖率、种群内禀增长率和后代混交率均有极显著性影响(P0.01),藻密度和Zn2+浓度之间的交互作用对轮虫的生命期望、种群内禀增长率和后代混交率均有显著性影响(P0.05)。2.0×106个/m L食物密度下,Zn2+浓度与轮虫的生命期望、世代时间、净生殖率和平均寿命之间具有显著的剂量-效应关系;4.0×106个/m L食物密度下,Zn2+浓度与轮虫的后代混交率间也具有显著的剂量-效应关系。     

斜生栅藻对不同形态锑胁迫的响应及抗性研究

该研究以斜生栅藻(Scenedesmus obliquus)为研究对象,研究不同浓度的Sb(Ⅲ)、Sb(Ⅴ)胁迫下对斜生栅藻生长速率、叶绿素a、抗氧化酶活性和细胞表面结构的影响,以探讨重金属胁迫下斜生栅藻的抗性机理。结果表明:(1)在高浓度Sb(Ⅲ)、Sb(Ⅴ)胁迫处理中,斜生栅藻生长对Sb(Ⅲ)胁迫的响应更加迅速;随着Sb(Ⅲ)、Sb(Ⅴ)胁迫浓度增加,斜生栅藻体内叶绿素a含量呈下降趋势,且对Sb(Ⅲ)胁迫浓度的变化反应更为敏感。(2)在800μmol/L Sb(Ⅲ)和Sb(Ⅴ)胁迫下,斜生栅藻体内丙二醛(MDA)含量及超氧化物歧化酶(SOD)活性分别在胁迫第7~8天和第6~7天时变化更为明显;过氧化氢酶(CAT)活性在胁迫处理的第4~5天就迅速增加,对Sb胁迫响应比SOD更为迅速。(3)在高浓度Sb(Ⅲ)、Sb(Ⅴ)胁迫下,斜生栅藻细胞结构受到严重损伤,而且Sb(Ⅲ)对斜生栅藻细胞的损伤更加明显。研究发现,Sb(Ⅲ)、Sb(Ⅴ)对斜生栅藻生长、叶绿素a及细胞结构表现出不同程度的抑制和破坏作用,其细胞受到的影响程度与Sb(Ⅲ)、Sb(Ⅴ)的处理浓度及处理时间均密切相关,但斜生栅藻依靠自身抗氧化酶系统在一定程度上能够缓解Sb胁迫的不利影响。     

Cadmium effect on the growth, photosynthesis, ultrastructure and phytochelatin content of green microalga Scenedesmus armatus: A study at low and elevated CO2 concentration

Short-term experiments were carried out to examine the toxicity of cadmium chloride (CdCl₂) at a concentration of 93 μM (EC_50/24) to green microalga Scenedesmus armatus, cultured at low (0.1%) and elevated (2%) concentration of CO₂. Cadmium did not affect the viability of cells cultured for 24 h in both CO₂ variants but markedly inhibited the growth of algae. This inhibition was more pronounced in cultures aerated with 0.1% (about 50% of control) than with 2% CO₂ (about 75% of control) and did not change during 72 h of culture. Cadmium inhibited the rate of oxygen evolution (P_oxy.) (70% of control) of cells cultured at 0.1% CO₂ and had no effect on P_oxy. of cells cultured at 2% CO₂. The values of the chlorophyll fluorescence parameters, i.e. F_M (maximum fluorescence yield), F_V (variable fluorescence), F_V/F_M (maximum quantum yield of PSII), Φ_PSII (effective quantum yield of PSII) and qP (photochemical quenching) were reduced by cadmium treatment in algae grown at 0.1% CO₂ concentration, whereas F₀ (initial fluorescence yield) remained unaffected. In high-CO₂ grown cells only F_V was significantly reduced. Cd-treated cells synthesized several thiol-containing peptides identified by HPLC as a dimer (PC₂), a trimer (PC₃) and a tetramer (PC₄) of phytochelatins (PC_S). High-CO₂ grown cells produced significantly more PCs than low-CO₂ grown cells and their individual appearance depended on the time of exposure and CO₂ level. The ultrastructural analysis of low-CO₂ grown cells showed in chloroplasts an increased number of small starch grains visible around the pyrenoid. In the enhanced vacuome compartment, various types of vacuoles were clearly seen in Cd-treated cells. Vacuoles containing non-membranous, electron-opaque deposits of an undefined structure and myelin-like figures were especially observed. The results suggest that algae living in conditions of elevated CO₂ are better protected against cadmium than those at ordinary CO₂ level, and productive processes are less affected than the growth ones.     

青霉素钠对萼花臂尾轮虫适合度的促进作用及其与藻密度的关系

以萼花臂尾轮虫（Brachionus calyciflorus）为受试动物,在1.0×10⁶（较低）、2.0×10⁶（中等）和4.0×10⁶个细胞/mL （较高）的斜生栅藻（Scenedesmus obliquus）密度下,研究了不同浓度（0、200、400、600、800和1000 μg/L）的青霉素钠对轮虫各生命表统计学参数的影响。结果表明,与各藻密度下的对照组相比,当藻密度为2.0×10⁶个细胞/mL时,200-1000 μg/L的青霉素钠处理组中轮虫的生命期望和世代时间分别延长了40.67%-70.67%和34.04%-50.23%（P<0.05）,净生殖率和内禀增长率分别提高了204.35%-358.70%和36.26%-62.09%（P<0.05）;藻密度的降低或升高均显著降低青霉素钠对轮虫存活、生殖和种群增长的促进幅度。1.0×10⁶ 个细胞/mL的斜生栅藻密度下,400 μg/L的青霉素钠处理组中轮虫的生命期望延长了21%（P<0.05）,200-400μg/L的青霉素钠处理组中轮虫的世代时间延长了23.15%-33.13%（P<0.05）,200-600和1000 μg/L的青霉素钠处理组中轮虫的净生殖率分别升高了40%-81.05%和41.05%（P<0.05）;但4.0×10⁶个细胞/mL的斜生栅藻密度下,各青霉素钠处理组中轮虫的所有生命表统计学参数均与对照组之间无显著性差异（P>0.05）。藻密度对轮虫的生命期望、净生殖率、内禀增长率和后代混交率均具有显著性影响（P<0.01）,青霉素钠浓度对轮虫的世代时间、净生殖率和内禀增长率均具有显著性影响（P<0.05）,藻密度和青霉素钠浓度的交互作用对轮虫的生命期望、净生殖率和内禀增长率也具有显著性影响（P<0.05）。在实验设置的青霉素钠浓度范围内,1.0×10⁶个细胞/mL藻密度下轮虫的生命期望、世代时间和净生殖率与青霉素钠浓度之间均具有显著的剂量-效应关系（P<0.05）;2.0×10⁶个细胞/mL藻密度下,轮虫的生命期望、世代时间和内禀增长率与青霉素钠浓度之间均具有显著的剂量-效应关系（P<0.05）。本研究结果提示,环境相关浓度的青霉素钠不会对萼花臂尾轮虫的存活、生殖和种群增长产生显著性影响。     

氮磷施肥对拟南芥叶片碳氮磷化学计量特征的影响

研究植物碳(C)氮(N)磷(P)化学计量特征, 有助于了解C、N、P元素的分配规律和确定限制植物生长的元素类型, 理解生长速率调控的内在机制。该研究基于盆栽施肥试验, 测定不同N、P供应水平下拟南芥(Arabidopsis thaliana)叶片的生物量和C、N、P含量, 分析拟南芥的限制元素类型、验证生长速率假说、探讨N、P的内稳性差异和C、N、P元素间的异速生长关系。主要结果如下: 盆栽试验基质中限制元素是P, 施N过多可能引起毒害作用; 拟南芥的生长符合生长速率假说, 即随着叶片N:P和C:P的增加, 比生长速率显著减小; 叶片P含量存在显著的调整系数(3.5), 但叶片N含量与基质N含量之间无显著相关; 叶片N和P含量具有显著的异速生长关系, 但不符合N-P^3/4关系, 施P肥导致表征N、P异速生长关系的幂指数(0.209)显著低于施N肥处理(0.466)。该研究首次基于温室培养实验分析了拟南芥C、N、P的化学计量特征及其对N、P添加的响应, 研究结果将为野外研究不同物种、群落或生态系统的化学计量特征提供参考。     

Effects of different nitrogen:phosphorus levels on the growth and ecological stoichiometry of Glycyrrhiza uralensis

Aims The increase in atmospheric nitrogen (N) deposition has accelerated N cycling of ecosystems, probably resulting in increases in phosphorus (P) demand of ecosystems. Studies on the effects of artificial N:P treatment on the growth and carbon (C), N, P ecological stoichiometry of desert steppe species could provide not only a new insight into the forecasting of how the interaction between soils and plants responses to long-term atmospheric N deposition increase, but also a scientific guidance for sustainable management of grassland in northern China under global climate change. Methods Based on a pot-cultured experiment conducted for Glycyrrhiza uralensis (an N-fixing species) during 2013 to 2014, we studied the effects of different N:P supply ratios (all pots were treated with the same amount of N but with different amounts of P) on aboveground biomass, root biomass, root/shoot ratio, and C:N:P ecological stoichiometry both in G. uralensis (leaves and roots) and in soils. Additionally, through the correlation analyses between biomass and C:N:P ecological stoichiometry in leaves, roots, and soils, we compared the differences among the C:N:P ecological stoichiometry of the three pools, and discussed the indication of C:N:P ecological stoichiometry in soils for the growth and nutrient uptake of G. uralensis. Important findings The results showed that, reducing N:P decreased C:P and N:P ratios both in G. uralensis (leaves and roots) and in soils but increased aboveground biomass and root biomass of G. uralensis, indicating that low to moderate P addition increased P availability of soils and P uptake of G. uralensis. However, excessive low N:P (high P addition) led to great decreases in soil C:P and N:P ratios, thus hindering N uptake and the growth of G. uralensis. C:N:P ratios in the two pools of G. uralensis (especially in leaves) had close correlations with soil C:N:P ratio, indicating that the change in soil C:N:P ratio would have a direct influence on plants. Our results suggest that, through regulating C:N:P ratio in leaves and soils, appropriate amounts of P addition could balance soil P supply and plant P demand and compensate the opposite influences of long-term atmospheric N deposition increase on the structure of desert steppe.     

Substrate stoichiometry determines nitrogen fixation throughout succession in southern Chinese forests

The traditional view holds that biological nitrogen (N) fixation often peaks in early‐ or mid‐successional ecosystems and declines throughout succession based on the hypothesis that soil N richness and/or phosphorus (P) depletion become disadvantageous to N fixers. This view, however, fails to support the observation that N fixers can remain active in many old‐growth forests despite the presence of N‐rich and/or P‐limiting soils. Here, we found unexpected increases in N fixation rates in the soil, forest floor, and moss throughout three successional forests and along six age‐gradient forests in southern China. We further found that the variation in N fixation was controlled by substrate carbon(C) : N and C : (N : P) stoichiometry rather than by substrate N or P. Our findings highlight the utility of ecological stoichiometry in illuminating the mechanisms that couple forest succession and N cycling.     

5 氨基乙酰丙酸对不同温度下斜生栅藻叶绿素荧光诱导动力学的影响

为探究外源5-氨基乙酰丙酸(ALA)对不同温度下斜生栅藻(Scenedesmus obliquus)生长及叶绿素荧光诱导动力学的影响,设置1次添加ALA(ALA组)、每隔3d添加ALA(C-ALA组)和对照(CK组)3个处理,分别置于5℃、15℃和25℃条件下培养,并于对数生长期测定斜生栅藻叶绿素荧光参数。结果表明:(1)在5℃和15℃时,斜生栅藻的最大比生长速率(μmax)表现为ALAC-ALACK,其中ALA组的μmax分别达到各自CK组的122.7%和126.8%。(2)在5℃低温时,一次添加ALA后斜生栅藻PSⅡ最大光化学效率(F_v/F_m)和以吸收光能为基础的性能指数(PIABS)下降幅度显著低于CK组(P0.05),放氧复合体(OEC)活性状态(Fo-k)、QA被还原能力(F_(k-J))、QB(含快还原PQ库)被还原能力(F_(j-i))和慢还原PQ库被还原的能力(F_(i-p))均显著升高(P0.05)。(3)JIP-test参数显示,ALA处理使得斜生栅藻单位反应中心吸收的光能降低,热耗散也减少,更多的能量通过电子传递链传递并参与光化学反应。研究表明,外源ALA能在一定程度上促进斜生栅藻的生长,且在5℃低温下促进作用更加明显;外源ALA使得斜生栅藻光合效率提高,QA、QB被还原的能力以及PQ库被慢还原的能力获得显著提升;在一定温度范围内,环境温度越低,ALA对斜生栅藻PSⅡ保护作用越显著。     

Efficiency of ammonia and phosphorus removal from a colombian agroindustrial wastewater by the microalgae Chlorella vulgaris and Scenedesmus dimorphus

The ammonia and phosphorus removal efficiencies of the microalgae Chlorella vulgaris and Scenedesmus dimorphus, during biotreatment of secondary effluent from an agroindustrial wastewater of a dairy industry and pig farming, were evaluated. The microalgae were isolated from a wastewater stabilization pond near Santafé de Bogotá, Colombia. Batch cultures were made using both species in 4-1 cylindrical glass bioreactors each containing 2l of culture. Chlorella vulgaris was also cultivated on wastewater in a triangular bioreactor. Three 216-h experimental cycles were run for each microalga and in each bioreactor. In the cylindrical bioreactor, S. dimorphus was more efficient in removing ammonia than C. vulgaris. However, the final efficiency of both microalgae at the end of each cycle was similar. Both microalgae removed phosphorus from the wastewater to the same extent in a cylindrical bioreactor. Using C. vulgaris, the triangular bioreactor was superior for removing ammonia and the cylindrical bioreactor was superior for removing phosphorus. This study shows the potential of using these microalgae to reduce the environmental pollution of heavily contaminated agroindustrial waters currently disposed of untreated into the waterways and streams of tropical Colombia.     

Effects of CO2 concentrations on the freshwater microalgae, Chlamydomonas reinhardtii, Chlorella pyrenoidosa and Scenedesmus obliquus (Chlorophyta)

In order to investigate the possible impacts of increased atmospheric CO₂ levels on algal growth and photosynthesis, the influence of CO₂ concentration was tested on three planktonic algae (Chlamydomonas reinhardtii, Chlorella pyrenoidosa, and Scenedesmus obliquus). Increased CO₂ concentration enhanced significantly the growth rate of all three species. Specific growth rates reached maximal values at 30, 100, and 60 M CO₂ in C. reinhardtii, C. pyrenoidosa, and S. obliquus, respectively. Such significant enhancement of growth rate with enriched CO₂ was also confirmed at different levels of inorganic N and P, being more profound at limiting levels of N inC. pyrenoidosa and P in S. obliquus. The maximal rates of net photosynthesis, photosynthetic efficiency and light-saturating point increased significantly (p < 0.05) in high-CO₂-grown cells. Elevation of the CO₂ levels in cultures enhanced the photoinhibition of C. reinhardtii, but reduced that of C. pyrenoidosa and S. obliquus when exposed to high photon flux density. The photoinhibited cells recovered to some extent (from 71% to 99%) when placed under dim light or in darkness, with better recovery in high-CO₂-grownC. pyrenoidosa and S. obliquus. Although pH and pCO₂ effects cannot be distinguished from this study, it can be concluded that increased CO₂ concentrations with decreased pH could affect the growth rate and photosynthetic physiology of C. reinhardtii, C. pyrenoidosa, and S. obliquus.     

不同林龄油茶人工林土壤-叶片碳氮磷生态化学计量特征

油茶是世界四大木本油料植物之一,在我国有着2000多年的栽培和利用历史。碳(C)、氮(N)、磷(P)化学计量元素是近年来研究的热点,通过C、N、P化学计量我们可以深入了解植物-土壤间元素相互关系,并能揭示土壤养分限制状况。为了解油茶人工林生态系统C、N、P化学计量特征及油茶人工林养分元素限制因素,以长江中下游油茶适宜栽培区湖南、江西和湖北三省油茶林为研究对象,采用空间代替时间的研究方法,在区域尺度上随机选择32个典型油茶人工林并分为4个林龄组(9年低龄林;9—20年高产林;21—60年低产林; 60年生产退化林)。测定油茶人工林土壤与油茶叶片中的C、N、P含量并分析其化学计量特征。研究结果表明:(1)随林龄增加,油茶人工林土壤有机碳(SOC)和全氮(TN)含量增大,而土壤全磷(TP)和速效/kg和5.43 mg P在一定的林龄(60 a)内具有增加的趋势。(2)随林龄增加,油茶人工林叶片C含量无显著变化,N、P含量降低,叶片的C、/kg、11.66—15.46 g增大。此外,叶片N∶P阈值分析发现,叶片N∶P比在四个林龄段均16。(3)相关分析结果表明,油茶人工林土壤SOC和TN具有显著正相关,油茶叶片N和P具有显著正相关。同时,叶片N含量与土壤TN无相关性,而油茶叶片P含量与土壤Olsen-P显著正相关。油茶人工林土壤化学计量C∶N、C∶P和N∶P与叶片C∶N、C∶P呈显著正相关,以及叶片N∶P与土壤C∶P、N∶P呈显著正相关(P0.05)。由以上可见,油茶人工林土壤主要受P养分限制,且随林龄增加,P限制增加。此外油茶叶片N、P吸收具有协同效应,且油茶叶片与土壤元素存在广泛的计量耦合关系。本研究综合分析油茶林叶片与土壤的C、N、P计量特征及其关系,有助于全面系统的揭示油茶人工林生态系统的养分状况,对油茶林高效培育、养分补充或退化林诊断等具有指导意义。     

Effects of phosphorus enrichment and grazing snails on modern stromatolitic microbial communities

1. The effects of phosphorus enrichment and grazing snails on a benthic microbial community that builds stromatolic oncolites were examined in an experiment at Rio Mesquites, Cuatro Ciénegas, Mexico. Chemical analyses of stream water samples indicated that overall atomic ratios of total nitrogen (N) to total phosphorus (P) were approximately 110, indicating a strong potential for P‐limitation of microbial growth. 2. Phosphorus enrichment involved addition of 5 μmol Na₂HPO₄ L^?1 to streamside microcosms receiving intermittent inputs of stream water while grazer manipulation involved removal of the dominant grazer, the snail Mexithauma quadripaludium. After 7 weeks, we examined responses in organic matter content, C : N : P ratios, metabolism (P removal, primary production, dark respiration, and calcification), and microbial community structure using molecular fingerprinting of 16S rRNA genes. 3. Manipulation of snails did not affect response variables measured in these treatments (organic matter, C : P ratio, P removal rate). However, P enrichment significantly decreased the C : P and N : P ratios of surficial materials in the oncolites (organic matter content was unchanged), increased net and gross photosynthesis (oxygen consumption in the dark was unchanged), increased rates of calcification, and increased diatoms relative to cyanobacteria. Heterotrophic Eubacteria and Archaea were only modestly affected. Thus, our results indicate weak grazing effects but strong impacts of P in this benthic system. 4. We hypothesise that a state of severe P‐limitation is imposed on autotrophic production in this food web due, at least in part, to co‐precipitation of phosphate during calcite deposition. This produces severe P‐limitation of the benthic algae and cyanobacteria, resulting in high C : P ratio of microbial mats relative to the biomass of photoautotrophs (phytoplankton, terrestrial foliage) in other ecosystems. In turn, this high C : P ratio is likely to generate severe stoichiometric constraints on the herbivores, thus limiting their populations and resulting in weak overall grazing impacts.     

Atmospheric nitrogen deposition is associated with elevated phosphorus limitation of lake zooplankton

Here, we present data that for the first time suggests that the effects of atmospheric nitrogen (N) deposition on nutrient limitation extend into the food web. We used a novel and sensitive assay for an enzyme that is over‐expressed in animals growing under dietary phosphorus (P) deficiency (alkaline phosphatase activity, APA) to assess the nutritional status of major crustacean zooplankton taxa in lakes across a gradient of atmospheric N deposition in Norway. Lakes receiving high N deposition had suspended organic matter (seston) with significantly elevated carbon:P and N:P ratios, indicative of amplified phytoplankton P limitation. This P limitation appeared to be transferred up the food chain, as the cosmopolitan seston‐feeding zooplankton taxa Daphnia and Holopedium had significantly increased APA. These results indicate that N deposition can impair the efficiency of trophic interactions by accentuating stoichiometric food quality constraints in lake food webs.     

C-nuclear magnetic resonance studies of the biosynthesis of 5-aminolevulinic acid destined for chlorophyll formation in dark-grown Scenedesmus obliquus

The ¹³C-nuclear magnetic resonance (NMR) spectra of chlorophyll a formed in dark-grown Scenedesmus obliquus (Turp.) Kützing in the presence of [1-¹³C]glutamate, [2-¹³C]- and [1-¹³C]glycineshowed that the ¹³C of glutamate was specifically incorporated into the eight-carbon atoms in the tetrapyrrole macrocycles derived from C-5 of 5-aminolevulinic acid (ALA), while the C-2 of glycine was only incorporated into the methyl carbon of the methoxycarbonyl group attached to the isocyclic ring of chlorophyll a. No specific enrichment of these nine carbon atoms was observed in the spectrum of chlorophyll a formed in the presence of [1-¹³C]-glycine. These labeling patterns provide evidence for the operation of the C₅-pathway and against the operation of the ALA synthase pathway for chlorophyll formation in darkness.     

不同藻密度下布洛芬浓度对萼花臂尾轮虫生命表统计学参数的影响

在不同斜生栅藻(Scenedesmus obliquus)密度(1.0×10~6、2.0×10~6个细胞/m L和4.0×10~6个细胞/m L)下,研究了不同浓度的(0、1、10、100、1000μg/L和5000μg/L)布洛芬对萼花臂尾轮虫(Brachionus calyciflorus)生命表统计学参数的影响。结果表明,与各藻密度下的对照组相比,当藻密度为1.0×106个细胞/m L时,100—5000μg/L布洛芬处理组中轮虫的生命期望和平均寿命显著缩短,100μg/L布洛芬处理组中轮虫的世代时间显著缩短,1.0μg/L布洛芬处理组中轮虫的净生殖率显著提高,10—5000μg/L布洛芬处理组中轮虫的后代混交率显著提高。当藻密度为2.0×10~6个细胞/mL时,10—5000μg/L布洛芬处理组中轮虫的生命期望和平均寿命显著缩短,1000μg/L和5000μg/L布洛芬处理组中轮虫的世代时间显著缩短,1、10、1000μg/L和5000μg/L布洛芬处理组中轮虫的种群内禀增长率显著提高,1μg/L和1000μg/L布洛芬处理组中轮虫的后代混交率显著提高。当藻密度为4.0×10~6个细胞/mL时,10—5000μg/L布洛芬处理组中轮虫的生命期望、平均寿命和世代时间显著缩短。藻密度对轮虫的世代时间、净生殖率和种群内禀增长率有显著性影响(P0.05),布洛芬浓度对轮虫的生命期望、平均寿命、世代时间、净生殖率和种群内禀增长率有显著性影响(P0.05),藻密度和布洛芬浓度的交互作用对轮虫的生命期望、平均寿命和后代混交率有显著性影响(P0.05)。在实验设置的布洛芬浓度范围内,2.0×10~6个细胞/m L藻密度下,轮虫的生命期望、平均寿命和世代时间与布洛芬浓度之间均具有显著的剂量—效应关系(P0.05); 4.0×10~6个细胞/m L藻密度下,轮虫的生命期望、平均寿命和净生殖率与布洛芬浓度之间均具有显著的剂量—效应关系(P0.05)。     

三峡库区消落带水位变化对落羽杉C、N、P 生态化学计量特征的影响

为了解落羽杉C、N、P生态化学计量特征对三峡库区消落带水位变化的响应,2016年9月测定重庆市忠县汝溪河消落带植被修复示范基地内种植于海拔165 m(重度水淹组)、170 m(中度水淹组)、175 m(对照组)的落羽杉根、枝条、叶片中碳(C)、氮(N)、磷(P)元素含量以及植株生长指标,分析水位变化对其生长和C、N、P生态化学计量特征的影响。结果表明:(1)三峡库区消落带落羽杉通过降低生长速率来适应水位变化,植株整体生长状态良好;(2)落羽杉各器官C含量分配比较均衡,N集中在叶片中,P主要贮存在根中,未见严重缺素现象;(3)重度水淹组植株叶片C含量受到水位变化显著提高;水位变化显著降低了中度水淹组植株根P含量却显著提高了其叶片P含量,导致中度水淹组植株叶片C∶P和N∶P显著降低,根C∶P显著升高。研究结果表明,三峡库区消落带落羽杉能保持器官之间合理的元素分配来保障其生长所需,表现出对三峡库区消落带水位变化的良好适应性。     

Photosynthetic and growth responses of three freshwater algae to phosphorus limitation and daylength

1. Three common species of freshwater phytoplankton, the diatom Nitzschia sp., green alga Sphaerocystis schroeteri and cyanobacterium Phormidium luridum, were grown under contrasting daylengths [18 : 6 h light : dark cycles (LD) versus 6 : 18 h LD] and phosphorus (P) regimes (P‐sufficient versus 1 μm P). The rates of growth and photosynthesis, as well as growth efficiencies and pigment concentrations, were compared among treatments. 2. The growth and photosynthetic parameters of the three species depended on both P status and daylength in a species‐specific way. The responses to P limitation depended on daylength and, conversely, the responses to daylength depended on P status. 3. Growth rates and the maximum rates of photosynthesis (P_max) of all species decreased under P limitation under both light regimes. However, the decrease of P_max because of P limitation was greater under long daylength. The P_max of the green alga S. schroeteri decreased the most (ca. sixfold) under P limitation compared with the other two species. The photosynthesis saturation parameter I_k also decreased under P limitation; the decline was significant in Nitzschia and Sphaerocystis. P‐limitation significantly increased photoinhibition (β) in Nitzschia and Sphaerocystis, but not in Phormidium. The excess photochemical capacity (the ratio of the maximum photosynthesis rate to the photosynthesis rate at the growth irradiance), characterising the ability to utilise fluctuating light, was significantly lower under P limitation. 4. The growth efficiency (growth rate normalised to daylength) declined with increasing daylength in all species. Under short daylength the cyanobacterium Phormidium had the lowest growth efficiency of the three species. 5. The cellular chlorophyll a concentration in both Nitzschia and Sphaerocystis was significantly higher under short daylength, but only under P‐sufficient conditions. In Nitzschia, under short daylength, P‐limitation significantly decreased cellular chlorophyll concentration. In contrast, P‐limitation increased cellular chlorophyll concentration in Sphaerocystis, but under long daylength only. The ratio of chlorophyll a to b in the green alga also declined under short daylength and under P‐limited conditions.