Temporal dynamics in epipelic, pelagic and epiphytic algal production in a clear and a turbid shallow lake

SUMMARY 1. Pelagic and epipelic microalgal production were measured over a year in a pre-defined area (depth 0.5 m) in each of two lakes, one turbid and one with clear water. Further estimates of epiphytic production within reed stands were obtained by measuring production of periphyton developed on artificial substrata.
2. Total annual production of phytoplankton and epipelon was 34% greater in the turbid lake (190 g C m⁻² year⁻¹) than in the clearwater lake (141 g C m⁻² year⁻¹). However, the ratio of total production to mean water column TP concentration was two fold greater in the clearwater lake.
3. Phytoplankton accounted for the majority of the annual production (96%) in the turbid lake, while epipelic microalgal production dominated (77%) in the clear lake. The relative contribution of epipelic algae varied over the year, however, and in the turbid lake was higher in winter (11–25%), when the water was relatively clear, than during summer (0.7–1.7%), when the water was more turbid. In the clearwater lake, the relative contribution of epipelon was high both in winter, when the water was most clear, and in mid-summer, when phytoplankton production was constrained either by nutrients or grazing.
4. Compared with pelagic and epipelic primary production, epiphytic production within a reed stand was low and did not vary significantly between the lakes.
5. The study supports the theory of a competitive and compensatory trade-off between primary producers in lakes with contrasting nutrient concentrations, resulting in relatively small differences in overall production between clear and turbid lakes when integrating over the season and over different habitats.     

植物监测大气污染及其抗性

研究了在佛山市不同污染点东村和五星盆栽的30种绿化植物的叶面积、Fv/Fm、叶片细胞膜渗漏率及光合色素含量相对于清洁对照点华南植物园的差异。结果显示,大气污染条件下,绿化植物叶片的生长受到抑制,PSⅡ最大光化学效率下降,光合色素发生降解,细胞膜受到了伤害。各实验点所有植物叶面积、Fv/Fm及光合色素含量平均值均为:植物园>五星>东村,而叶片细胞膜渗漏率平均值为:植物园<五星<东村,与大气污染程度相一致。方差分析表明,上述指标中叶面积对大气污染最敏感,Fv/Fm受种间差异影响最小。受大气污染影响,各生理参数的变化具有不相关性。各项生理参数均表现出抗性的种有白桂木(Artocarpushypargyreus)、环榕(Ficusannulata)、广宁油茶(Camelliasemiserrata);而枫香(Liquidambarformosana)为敏感种。     

Occurrence of cell-associated mucilage and soluble extracellular polysaccharides in Rostherne Mere and their possible significance

The cell-associated mucilage and soluble extracellular polysaccharides (EPS) were investigated in a eutrophic freshwater lake (Rostherne Mere, Cheshire, U.K.) over up to 2 year annual cycles. Five particular lake algae (Anabaena spiroides Klebahn, Anabaena flos-aquae Brébisson ex Bornet & Flahault,Anabaena circinalis Rabenhorst, Microcystis aeruginosa Kützing emend. Elenkin and Eudorina elegans Ehrenberg) were found to be the major contributors to cell-associated mucilage, particularly M. aeruginosa. Calculation of the total amount of cell-associated mucilage in the phytoplankton samples showed that it occupied 0.0001–0.007% (the latter during a bloom of Microcystis) of lake water volume within the epilimnion. Seasonal changes in the total volume of associated mucilage reflected the succession of mucilage-producing algal species in Rostherne Mere, which was closely correlated with the physico-chemical (temperature, oxygen, pH, nutrients) and biological (Secchi depth, phytoplankton) parameters within the lake. High levels of cell-associated mucilage present in the lake may have potential for binding metals or other ions in the aquatic environment. Colourimetric determination of the concentration of soluble EPS revealed concentrations of between 2.5 and 60 mg l^–1, with peak levels during the bacillariophyceaen bloom and late clear water phase. The second phase did not appear to relate directly to changes in algal population, and may result from bacterial activity, algal lysis or zooplankton activity. As soluble EPS forms a major component of the total amount of dissolved carbon in lakes, the study of the soluble EPS is important to understand the carbon cycle in freshwaters. No direct correlation occurred between algal-associated mucilage and soluble EPS over a single annual cycle.     

塔干南缘骆驼刺植被水分关系的研究

对塔克拉玛干沙漠———绿洲过渡带骆驼刺 (AlhagisparsifoliaShap .)水分关系的研究表明 :骆驼刺在夏季保持了正的膨压 ,一直较高较稳定的清晨水势说明植物水分恢复状况良好 ,植物得到了较好的水分供应 ;在 7月 ,干旱胁迫造成的水分亏缺并未影响植株正常的蒸腾作用 ,因而干旱引起的水分胁迫并未威胁到植被的存在。骆驼刺对干旱胁迫的水分生理适应主要体现在叶水平上 ,表现为饱和枝条的渗透势 (Πo)和膨压消失点的渗透势 (Πp)的差值 (ΔΠ)和相对含水量 (RWC)在膨压消失点间更大的变化、渗透调节的产生、较高较稳定的饱和枝条水分与干物质之比 (WCsat)和膨压消失点的相对含水量 (RWCp) ,以及较低的共质体水在总水分中的相对含量 (RWCsym)。但形态学上的特征 ,主要表现为深而发达的根系和蒸腾面积的减少 ,才是骆驼刺适应极端干旱环境的主要途径。非定期的夏季一次性灌溉对地下水位很低地区的骆驼刺植被水分状况的恢复没有帮助。     

Enzyme inhibition by p-cresol and lacticacid in lipase-mediated synthesis of p-cresyl acetate and stearoyl lactic acid: a kinetic study

A detailed kinetic study was carried out to investigate the porcine pancreatic lipase-catalysed esterification reactions of p-cresol–acetic acid and lactic acid–stearic acid. The kinetic data were in agreement with a Ping Pong Bi–Bi mechanism being followed by the enzyme, where inhibition is indicated in the presence of p-cresol and lactic acid in the respective reactions. Mathematical analyses of experimentally observed initial rates yielded various kinetic parameters, K _m(p-cresol) = 0.1, K _{m(acetic acid)} = 0.54, K _{m(lactic acid)} = 0.059 M, K _{m(stearic acid)} = 0.04 M, V _{max(p-cresol–acetic acid)} = 13.2(h^–1), V _{max(lactic acid–stearic acid)} = 0.00163 M/h, K _i(p-cresol) = 0.59 and K _{i(lactic acid)} = 0.079 M. The K _m and K _i values of p-cresol and lactic acid observed in the respective reactions showed both the competitive nature of binding between the substrates p-cresol and acetic acid on the one hand and lactic acid and stearic acid on the other and the inhibitory nature of p-cresol and lactic acid.     

光强对砂仁叶片光合作用光抑制及热耗散的影响

通过测定不同光照条件下砂仁 (AmomumvillosumLour.)叶片气体交换和叶绿素荧光参数 ,探讨了光对其光合机构及其光破坏防御的影响。试验期间 ,上午 11:0 0之前有雾 ,光强较弱。上午砂仁阳生叶净光合速率 (Pn)与下午 (6 .5 3μmol·m-2 ·s-1)相似 ,高于阴生叶 (5 .94μmol·m-2 ·s-1) ,下午阴生叶Pn 高于上午 ,与阳生叶相似。下午砂仁叶片表观量子效率低于上午。其初始荧光 (Fo)、最大荧光 (Fm)、光系统Ⅱ (PSⅡ )最大光能转换效率 (Fv/Fm)、Fm/Fo 及PSⅡ的潜在效率 (Fv/Fo)随日光增强而降低 ,15 :0 0降至最低 ,表明光抑制逐渐加剧。之后随光强减弱这些叶绿素荧光参数升高 ,光抑制得到缓解。与此相反 ,非光化学猝灭系数 (qN)随光强的增加而升高 ,并一直维持在较高水平 ,表明依赖叶黄素循环的保护性反应逐渐增强。阳生叶的光抑制比阴生叶强烈 ,当日遮荫处理使光抑制缓解 ,但各处理间qN 差异不大 ,表明热耗散未受显著影响。结论 :弱光下砂仁叶片即发生光抑制 ,在不同光照下其光抑制的普遍发生 ,是依赖叶黄素循环的保护性反应 ,而非光破坏的结果 ;砂仁叶片叶黄素循环的启动不需过剩光能 ,不同光处理对其影响不大 ;砂仁对光的适应能力较强。     

Deep-sea fishes in Canada’s Atlantic: population declines and predicted recovery times

Because of their slow growth rates, late maturity, low fecundity and long potential lifespans, deep-sea fishes are vulnerable to and theoretically slow to recover from overexploitation and bycatch. As industrial fishing moved into the deep sea, population declines were predicted and five species were shown to meet The World Conservation Union (IUCN) criteria for endangered species in Atlantic Canadian waters and two other deep-living species were listed as threatened by the Committee on the Status of Endangered Wildlife in Canada. We used data from scientific surveys to determine population trends in a 17-year time series for an additional 32 deep-sea fishes from the same geographic region. Eight species exhibited significant population declines, five increased, two were data deficient, and 17 showed no significant trends. Thus approximately 38% of the deep-sea bottom-living fishes in that well-investigated region could be at-risk, but definitive assignment to an IUCN category for most species is hampered by a lack of basic biological information, especially species specific generation times. Lack of biological information also limits efforts to determine possible recovery times, especially with respect to calculating intrinsic rates of population growth (r). For two Atlantic grenadiers (where r could be estimated using life-history parameters and standard life table techniques), the time to recovery with no fishing mortality could range from over a decade to over a century. This broad range results from the general uncertainty on life-history characteristics of these deep-sea species. Given the documented declines, the lack of basic data on life-history parameters, and the conservative assumption that recovery rates are likely to be prolonged, we argue that it is imperative to conduct additional studies pertaining to life history characteristics of deep-sea fishes and implement conservation measures in the deep sea immediately.     

观赏山楂耐热性及其叶片光合与叶绿素荧光特性研究

以引自国内外的15种观赏山楂苗木为材料,于上海夏季自然高温下对其叶片光合气体交换参数及叶绿素荧光参数进行测定,并观察它们的田间耐热性,以揭示其耐热的光合生理机制.结果显示,4种山楂表现出较强耐热性,6种较耐热,而5种耐热性较差;15种山楂叶片净光合速率(P_n)、蒸腾速率(T_r)、气孔导度(G_s)、瞬时水分利用效率(WUE)的种间差异显著(P<0.05),且耐热性强的品种P_n、T_r、G_s、WUE值较高,高温下能够维持较高的光合固碳水平;各品种山楂叶片的PSⅡ最大光能转换效率F_v/F_m、电子传递效率ΦPSⅡ和光能捕获效率F_v'/F_m'差异显著,耐热性强品种F_v/F_m保持在0.8以上,且ΦPSⅡ值与F_v'/F_m'较高.研究表明,观赏山楂主要通过加大气孔蒸腾散热、降低叶表面温度以及维持较高光能电子传递与转化效率来减轻高温对光合机构伤害,以维持植株正常光合作用;山楂叶片PSⅡ原初光能转换效率及潜在活性与其耐热性密切相关,F_v/F_m值可作为山楂耐热性鉴定指标.     

棉花叶片氮含量的空间分布与光合特性

在棉花生长旺季,将冠层按高度分多层测定了田间叶片含氮量和叶片净光合速率对光合有效辐射通量密度的响应(光响应曲线,Pn-PPFD response curve)及相应的生物指标.结果表明,各层叶片氮含量与光合作用关系密切,各层平均值大小依次为上层＞中层＞下层,对应层叶片的最大净光合速率Pmax、表观暗呼吸速率Rd、光补偿点LCP及光饱和点LSP均从上到下依次递减,与氮含量分布一致,而表观光合量子效率AQY则略有不同;氮含量的指数衰减系数 kn =0.762(R2=0.593),根据观测结果,棉田叶片氮含量(N)空间分布可以用相对累积叶面积指数(Lc/Lt)为自变量的指数方程来模拟,从而为建立光合作用机理模型与进行生产力奠定基础.     

小肽营养素对断奶仔猪生产性能及血液生化指标的影响

本试验将40头21 d断奶的三元杂交猪随机分为4组,用4组不同日粮组成及营养水平的饲料(I:基础日粮+2%喷雾干燥血浆蛋白粉(SDPP);Ⅱ、Ⅲ和Ⅳ组分别在基础日粮中添加1%,2%和3%小肽营养素)饲养21 d后称重、测定血液生化指标并进行统计分析.结果表明:添加小肽营养素对断奶仔猪的生产性能无显著影响;各处理组的血清总蛋白、血糖和血清尿素差异不显著,2%小肽组的球蛋白、免疫球蛋白含量显著高于其它组;小肽产品可以部分等蛋白取代断奶仔猪日粮中的血浆蛋白粉.通过了解小肽营养素替代喷雾干燥血浆蛋白粉对21 d断奶仔猪的生产性能和血液生化指标的影响,为肽类产品在断奶仔猪日粮中的应用提供了依据.