长期施肥下农田土壤-有机质-微生物的碳氮磷化学计量学特征

探讨外源养分的输入对土壤系统内碳、氮、磷化学计量特征的影响,对于深刻认识农田土壤有机碳(C)和养分循环及其相互作用过程具有重要意义。以26年的农田长期定位施肥试验为平台,分析长期不同施肥条件下土壤、有机态及微生物生物量碳、氮、磷含量及其化学计量学特征,并根据内稳性模型y=c x~(1/H)计算其化学计量内稳性指数H。结果表明:与长期撂荒处理(CK_0)相比,种植作物条件下26年化肥配施有机肥处理(MNPK和1.5MNPK)显著降低微生物生物量氮含量,但显著提高了微生物生物量磷的含量。相对于撂荒处理,即使长期配施化肥磷处理(NP、PK、NPK),其土壤有机磷降低显著。对于C∶N比而言,化肥配施有机物料处理(秸秆或有机肥)的土壤C∶N比、有机质C∶N及微生物生物量C∶N比均显著低于化肥处理(N、NP、PK和NPK)。对于C∶P比而言,相对于撂荒处理,26年施用磷肥(化肥磷或有机磷)显著降低了土壤C∶P比和微生物生物量C∶P比,而CK和偏施化肥处理(N、NP和PK)显著降低了土壤有机质C∶P比。对于土壤N∶P比而言,撂荒处理土壤N∶P比显著高于其他处理,而撂荒处理土壤有机质N∶P比显著高于CK和化肥处理,表明不施肥或化肥条件下作物种植加剧了土壤有机质中氮素的消耗。微生物生物量C∶N、C∶P、N∶P比的内稳性指数H分别为0.24、0.75、0.64,不具有内稳性特征。微生物生物量C∶N、C∶P、N∶P比分别与土壤C∶N、C∶P、N∶P比呈显著正相关关系,但与土壤有机质碳氮磷化学计量比之间无显著相关性。表明土壤碳、氮、磷元素的改变会直接导致微生物生物量碳、氮、磷化学计量比的改变,但微生物生物量碳氮磷化学计量比对土壤有机质碳氮磷化学计量比无显著影响,土壤有机质的碳氮磷计量比可能更多是受到作物和施肥等养分管理措施的影响。     

不同植茶年限土壤-微生物生物量碳氮磷化学计量特征

退耕还林(草)等生态建设工程的实施引起土壤碳(C)、氮(N)、磷(P)循环及其化学计量特征发生变化,继而对土壤微生物生物量的化学计量造成潜在影响,然而,土壤-微生物C∶N∶P化学计量的时间动态及协调关系仍不明确。本试验选取三峡库区小流域退耕地——茶园为研究对象,以玉米地为对照,探索土壤-微生物生物量C、N、P随植茶年限(<5 a、5～10 a、10～20 a、20～30 a和>30 a)的变化特征,分析其化学计量比、微生物熵(qMBC、qMBN、qMBP)、化学计量不平衡性(土壤C、N、P计量比与微生物生物量C、N、P计量比的比值)之间的关系。结果表明：随着植茶年限增加,土壤和微生物生物量C、N、P、土壤C∶N和C∶P均显著升高,而土壤N∶P整体下降,微生物生物量C∶P和N∶P呈先升后降的变化趋势,微生物生物量C∶N变化不显著。此外,茶树种植年限对土壤、微生物间的化学计量不平衡性以及微生物熵均存在显著影响,随着植茶年限增加,qMBC先降低后升高,qMBN和qMBP呈波动上升;碳氮化学计量不平衡性(C∶N_imb)和碳磷化学计量不平衡性(C∶P_i...     

生态系统碳氮磷元素的生态化学计量学特征

生态系统元素平衡是当前全球变化生态学和生物地球化学循环的研究热点和焦点.在系统介绍生态化学计量学与碳氮磷元素循环研究进展的基础上,重点从土壤C:N:P化学计量比的分布特征、指示作用、对碳固定的影响,以及人类活动对C:N:P比的影响等方面探讨了C:N:P比在养分限制、生物地球化学循环、森林演替与退化等领域中的应用等问题,并展望了生态系统碳氮磷平衡的元素化学计量学未来研究的发展方向.通过对生态化学计量学理论和方法的研究,可以深入认识植物-凋落物-土壤相互作用的养分调控因素,对于揭示碳氮磷元素之间的相互作用及平衡制约关系,为减缓温室效应提供新思路和理论依据,具有重要的现实意义.     

土地利用变化对东北温带幼龄林土壤碳氮磷含量及其化学计量特征的影响

土地利用方式的改变打破森林生态系统原有的碳氮磷平衡,从而显著地影响森林生态系统的生物地球化学循环过程。以地段相邻、林龄相同(10年生)、原始植被一致但土地利用方式不同(无土壤翻动的天然次生林[NS]、间作大豆而土壤翻动中等的人工林[MS]、间作人参而土壤翻动严重的次生林[SS])的温带幼龄林为对象,探索土地利用变化对土壤碳、氮、磷含量及相互关系的影响。结果显示:(1)土地利用方式显著改变表层和深层土壤碳含量,各土壤层次碳含量均呈现NSMSSS;而氮含量仅在0—20 cm具有显著性差异(P0.05);不同土地利用类型之间磷含量无显著差异(P0.05);表明碳氮磷对土地利用变化敏感程度不同。(2)SS土壤碳氮比(C/N)和碳磷比(C/P)低于NS和MS,而NS和MS之间C/N和C/P因土壤层次而异。不同土壤层次氮磷比(N/P)均随土壤翻动强度的增加而显著减小(NSMSSS,P0.05),且随土层加深而降低;表明N/P相对于C/N和C/P可能对土地利用变化具有更优生态指示功能。(3)土地利用变化显著改变土壤碳-氮、碳-磷、氮-磷的耦合关系。土壤碳-氮(C-N)之间存在极显著(P0.001)的线性关系,其中3种土地利用方式的土壤C-N关系的斜率差异不显著(P=0.458,共同斜率为11.1),但截距差异显著(P0.001)。结合本地区和全球文献数据分析指出,森林土壤碳氮关系既有大尺度上的普适性,又有小尺度上对土地利用方式响应的局域分异性。     

中国南亚热带不同造林模式碳汇林土壤碳、氮、磷的积累及化学计量特征

碳汇林的固碳效益十分显著，是实现“碳中和”的主要碳增汇途径之一，在研究南亚热带地区不同造林模式碳汇林土壤碳汇的同时，研究碳汇林土壤氮、磷储量及土壤碳、氮、磷的生态化学计量特征，能够为不同造林模式碳汇林的土壤碳、氮、磷储量的评估提供科学依据。采取单因素随机区组设计，选择立地条件基本一致的研究区和4种造林模式(新造林、封山育林、补植套种、更新改造)的碳汇林，分析了不同造林模式土壤有机碳(SOC)、全氮(TN)、全磷(TP)的含量、储量、生态化学计量比，以及微生物生物量碳(MBC)的变化特征。结果表明，不同造林模式碳汇林的土壤理化性质，碳氮磷储量、化学计量比及微生物生物量碳含量差异显著，且土壤碳氮磷储量随土壤深度增加而减少，表现出明显的垂直变化特征。4种造林模式下碳氮比(C/N)介于11.11—17.86,碳磷比(C/P)介于17.00—242.59,氮磷比(N/P)介于1.18—15.99之间，在0—60 cm土层上均以更新改造模式林最低，封山育林模式下C/P和N/P均显著高于其他造林模式。土壤SOC与TN、N/P呈极显著正相关关系，土壤TN与C/P呈极显著正相关关系。综合来看，封山育林模...     

中华哲水蚤(Calanus sinicus)对浮游植物和微型浮游动物的摄食速率估算

2005年4月27日至5月30日在东海有害藻华高发区的6个典型站位采样,结合稀释法实验和Frost的直接计量法研究了中型浮游动物对浮游植物和微型浮游动物群落的现场摄食速率,并对中华哲水蚤(Calanus sinicus)的食物组成、中型浮游动物和微型浮游动物对浮游植物群落的摄食压力进行了估算。研究结果表明春季调查区:中华哲水蚤对浮游植物的物种比摄食率介于0.01~8.43d-1,平均值为(2.72±2.14)d-1。中华哲水蚤对浮游植物的物种摄食速率介于0.05~838.23cells ind.-1d-1,平均值为(52.72±154.21)cells ind.-1d-1,对几种有害藻华原因生物的摄食速率较高。中华哲水蚤对浮游植物物种摄食速率具有食物密度依赖性,在低浮游植物丰度下,其摄食速率会随着浮游植物丰度的增加而增加,达到一定阈值后随着浮游植物丰度增加而逐渐降低。中型浮游动物群落对浮游植物群落碳摄食速率介于0.53~4.97ngC L-1d-1,平均值为(2.16±1.63)ngC L-1d-1。微型浮游动物对浮游植物群落物种平均碳摄食速率介于0.04~13.20ngC ind.-1d-1,平均值为(2.91±5.22)ngCind.-1d-1。微型浮游动物群落对浮游植物群落碳摄食速率介于61.07~8632.85ngC L-1d-1,平均值为(2801.01±4198.46)ngC L-1d-1。分析比较中型浮游动物和微型浮游动物对浮游植物现存量摄食压力表明,海区中微型浮游动物的摄食压力要远高于中型浮游动物,介于95.59%~99.98%,平均值为97.88%±2.33%。调查海区中型浮游动物还通过对微型浮游动物的摄食影响浮游植物生长。     

盐碱地柽柳“盐岛”和“肥岛”效应及其碳氮磷生态化学计量学特征

为了探讨“盐岛”和“肥岛”效应影响下盐碱土的养分特征,对黄河三角洲盐碱地柽柳植株周围不同土层的pH值、电导率和碳氮磷含量及其生态化学计量学特征进行了研究.结果表明: 土壤pH和电导率均随土层的加深而升高,0～20 cm土层土壤电导率随离植株距离的增加而降低,全磷含量则升高.20～40 cm土层土壤有机碳、全氮、N/P和C/P随离柽柳植株距离的增加而降低,C/N则升高.随着土层的加深,有机碳和全氮均呈降低趋势,而全磷则先降低后升高.土壤pH与电导率呈显著正相关,且二者与土壤碳氮磷及其生态化学计量比之间均呈显著负相关.     

盐碱地柽柳“盐岛”和“肥岛”效应及其碳氮磷生态化学计量学特征

为了探讨"盐岛"和"肥岛"效应影响下盐碱土的养分特征,对黄河三角洲盐碱地柽柳植株周围不同土层的pH值、电导率和碳氮磷含量及其生态化学计量学特征进行了研究.结果表明:土壤pH和电导率均随土层的加深而升高,0~20 cm土层土壤电导率随离植株距离的增加而降低,全磷含量则升高.20~40 cm土层土壤有机碳、全氮、N/P和C/P随离柽柳植株距离的增加而降低,C/N则升高.随着土层的加深,有机碳和全氮均呈降低趋势,而全磷则先降低后升高.土壤pH与电导率呈显著正相关,且二者与土壤碳氮磷及其生态化学计量比之间均呈显著负相关.     

川西亚高山三种优势树种不同根序碳氮磷化学计量特征

采用Pregitzer的方法对细根进行分级,测定川西亚高山红桦、岷江冷杉和粗枝云杉3种优势树种1~5级细根(直径<2 mm)碳(C)、氮(N)和磷(P)浓度,并计算它们之间的化学计量比.结果表明:3种优势树种的细根的C浓度、C/N和C/P随根序的升高而升高,N和P浓度随根序的升高而降低,而N/P在不同根序间变化不显著.细根C、N和P浓度及其化学计量比在3个物种之间差异显著,且这种差异随细根根序的不同而变化.3种树种的细根C、N、P浓度及其化学计量比之间存在显著相关关系.     

中温-暖温带表土碳氮磷生态化学计量特征的空间变异性——以河北省为例

解析区域土壤碳氮磷元素的生态化学计量特征的空间分异格局有助于土壤养分的综合管理与利用。运用传统统计学和地统计学分析方法,以河北省为例分析了中温-暖温带表土(0—30cm)碳氮磷元素的生态化学计量特征的空间变异性及影响因素。结果显示:(1)土壤有机碳(SOC)、全氮(TSN)、全磷(TSP)其摩尔比率的变异系数均介于0.1—1之间,表明其在空间上存在中等程度的变异性。此外,C∶N的变异系数较小,表明C∶N较稳定。(2)表土TSP和C∶N具有小范围、强烈的空间自相关性,SOC、TSN、C∶P和N∶P具有较大范围、中等程度的空间自相关性,结构性因素是土壤碳氮磷含量及其摩尔比率空间变异的主要影响因素。从空间分布规律来看,表土碳氮磷含量及其摩尔比率均没有呈现明显的递增或递减的变化规律,SOC、TSN、C∶P和N∶P具有相同的空间分布趋势,高值区主要分布在冀北地区,分布面积较小,低值区分布范围较广;C∶N的高值区零星分布在冀北地区,TSP的高值区和低值区呈现斑块状分布。(3)土壤C∶N、C∶P和N∶P受到土壤理化性状、土地利用方式、人类扰动、气候及地形等因素的调控。此外,不同气候带的C∶N、C∶P和N∶P也存在一定的差异,研究区土壤C∶N与高寒带较接近,同时与其他气候带没有显著的差异;C∶P和N∶P与温带沙漠区较接近,与其余气候带存在显著的差异性,说明不同气候带之间的C∶N较C∶P和N∶P稳定。     

Inter- and intra-annual variability in the phytoplankton community of a high mountain lake: the influence of external (atmospheric) and internal (recycled) sources of phosphorus

1. The inter‐ and intra‐annual changes in the biomass, elemental (carbon (C), nitrogen (N) and phosphorus (P)) and taxonomical composition of the phytoplankton in a high mountain lake in Spain were studied during 3 years with different physical (fluctuating hydrological regime) and chemical conditions. The importance of internal and external sources of P to the phytoplankton was estimated as the amount of P supplied via zooplankton recycling (internal) or through ice‐melting and atmospheric deposition (external). 2. Inter‐annual differences in phytoplankton biomass were associated with temperature and total dissolved phosphorus. In 1995, phytoplankton biomass was positively correlated with total dissolved phosphorus. In contrast, the negative relationship between zooplankton and seston biomass (direct predatory effects) and the positive relationship between zooplankton P excretion and phytoplankton biomass in 1997 (indirect P‐recycling effects), reinforces the primary role of zooplankton in regulating the total biomass of phytoplankton but, at the same time, encouraging its growth via P‐recycling. 3. Year‐to‐year variations in seston C : P and N : P ratios exceeded intra‐annual variations. The C : P and N : P ratios were high in 1995, indicating strong P limitation. In contrast, in 1996 and 1997, these ratios were low during ice‐out (C : P < 100 and N : P < 10) and increased markedly as the season progressed. Atmospheric P load to the lake was responsible for the decline in C : P and N : P ratios. 4. Intra‐annual variations in zooplankton stoichiometry were more pronounced than the overall differences between 1995 and 1996. Thus, the zooplankton N : P ratio ranged from 6.9 to 40.1 (mean 21.4) in 1995, and from 10.4 to 42.2 (mean 24.9) in 1996. The zooplankton N : P ratio tended to be low after ice‐out, when the zooplankton community was dominated by copepod nauplii, and high towards mid‐ and late‐season, when these were replaced by copepodites and adults. 5. In 1995, the minimum demands for P of phytoplankton were satisfied by ice‐melting, atmospheric loading and zooplankton recycling over 100%. In order of importance, atmospheric inputs (> 1000%), zooplankton recycling (9–542%), and ice‐melting processes (0.37–5.16%) satisfied the minimum demand for P of phytoplankton during 1996 and 1997. Although the effect of external forces was rather sporadic and unpredictable in comparison with biologically driven recycle processes, both may affect phytoplankton structure and elemental composition. 6. We identified three conceptual models representing the seasonal phosphorus flux among the major compartments of the pelagic zone. While ice‐melting processes dominated the nutrient flow at the thaw, biologically driven processes such as zooplankton recycling became relevant as the season and zooplankton ontogeny progressed. The stochastic nature of P inputs associated with atmospheric events can promote rapid transitional changes between a community limited by internal recycling and one regulated by external load. 7. The elemental composition of the zooplankton explains changes in phytoplankton taxonomic and elemental composition. The elemental negative balance (seston N : P < zooplankton N : P, low N : P recycled) during the thaw, would promote a community dominated by species with a high demand for P (Cryptophyceae). The shift to an elemental positive balance (seston N : P > zooplankton N : P, high N : P recycled) in mid‐season would skew the N : P ratio of the recycled nutrients, favouring dominance by chrysophytes. The return to negative balance, as a consequence of the ontogenetic increase in zooplankton N : P ratio and the external P inputs towards the end of the ice‐free season, could alleviate the limitation of P and account for the appearance of other phytoplankton classes (Chlorophyceae or Dinophyceae).     

Seasonal correlations of elemental and ω3 PUFA composition of seston and dominant phytoplankton species in a eutrophic Siberian Reservoir

The elemental and fatty acid composition of seston was studied for 3 years, from May to October, in a small Reservoir. Under comparatively low C:P ratio, multivariate canonical analysis revealed no straightforward simple correlations between phosphorus and single ω3 PUFA species, but complex significant interaction between elemental composition (stoichiometry) of seston and total sestonic ω3 PUFA as a whole. Since sestonic C, P and N were found to originate mostly from phytoplankton, the contents of particulate elements and PUFA were attributed to single species in periods of their pronounced dominance. Phytoplankton species of genera of Stephanodiscus, Peridinium, Gomphosphaeria, Planktothrix and Anabaena in periods of their pronounced dominance had relatively constant species-specific elemental and PUFA composition. Phytoplankton species significantly differed in their elemental and PUFA composition, as well as in ratios of C:N, N:P, PUFA:P and partly C:P that indicate food quality for zooplankton. Hence, there were no phytoplankton species of clearly high or low nutritional value. All of phytoplankters, or at least detritus, that originated from them, may meet specific elemental and biochemical requirements of specific groups of zooplankton. Dividing phytoplankton on basis of their elemental and biochemical composition, i.e., nutrition quality, into large taxa (cyanobacteria, diatoms, etc.) appeared to be too coarse for assessing nutritional value for zooplankton.     

Elemental stoichiometry of lower food web components in arctic and temperate lakes

Lakes were surveyed to assess the potential patterns of latitudinalvariation in carbon:nitrogen:phosphorus (C:N:P) stoichiometryof lower food web components. Thirty-four lakes were surveyedat an arctic latitude (68°38'N, 149°38'W) and 10 lakesat a temperate latitude (46°13'N, 89°32'W) during 1997.The temperate data set was augmented with earlier survey resultsemploying similar methods. It was hypothesized that differencesin environmental variables across latitude would cause differencesin community C:N:P ratios, leading to differences in trophicinteractions. Physical measurements (light, temperature), sestonand zooplankton were collected from each lake. Seston and zooplanktonwere analyzed for C, N and P content, and zooplankton were countedand measured for biomass estimates. The degree of trophic interactionbetween seston and zooplankton was assessed by (i) measuringelemental imbalances between seston and zooplankton and (ii)calculating the potential recycling ratio by the zooplanktoncommunity available for seston. Seston C:nutrient, but not N:P,ratios were higher in temperate than arctic lakes. Conversely,arctic zooplankton had higher C:nutrient, but not N:P, ratiosthan zooplankton in temperate lakes. Elemental imbalances weregreater in temperate than in arctic lakes, but N:P stoichiometryof potential zooplankton recycling was nearly identical betweenthe two latitudes. Zooplankton community C:N:P ratios were notrelated to either latitude or seston C:N:P. In accordance withstoichiometric theory, relative abundances of calanoid copepodswere positively correlated with seston C:N in temperate lakes.Additionally, relative abundances of Daphnia were negativelycorrelated with seston C:N ratios in temperate and arctic lakes,and positively correlated with N:P ratios in the arctic. Ingeneral, these results suggest that seston and zooplankton communitystoichiometry differ across latitude, and these differenceshave the potential to affect trophic interactions.     

The stoichiometry of N and P in the pelagic zone of Castle Lake, California

We measured the concentrations, as well as lake-wide amounts,of nitrogen (N) and phosphorus (P) in dissolved, seston andzooplankton pools throughout the water column of Castle Lake,California, during summer, 1991. This allowed us to determinethe stoichiometric ratios of important elements in each pool(C:N, C:P, N:P) as well as for the entire lake. Dissolved andseston pools were the predominant storage compartments for bothN and P; zooplankton never contained >5% of N or 10% of Plake wide. However, by late summer, the concentrations of Pin seston and in zooplankton were similar in the upper portionsof the water column, suggesting that changes in food web structurethat alter zooplankton biomass and community composition (andhence elemental storage in the zooplankton) may produce significantshifts in nutrient storage among pelagic pools. Lake-wide levelsof dissolved N were largely constant over the study period;however, lake-wide dissolved P increased. These dynamics suggestedthat the majority of nutrients stored in dissolved pools wereunavailable for phytoplankton growth. N:P and C:P ratios indicatedthat Castle Lake phytoplankton became severely deficient inP during the course of our observations. These ratios also greatlyexceeded recently reported threshold values for elemental constraintson growth and reproduction for several species of zooplankton.The ratio of N to P in the zooplankton pool was relatively constantand consistently lower than that in the sestion. As a result,the predicted N:P ratio of zooplankton-regenerated nutrientsexceeded the N:P ratio of the seston, implying that zooplanktonnutrient regeneration further skewed N and P supply ratios,and potentially enhanced P limitation of phytoplankton in CastleLake. ¹Present address: Department of Biology, Box 19498, Universityof Texas at Arlington, Arlington, TX 76019, USA     

Stoichiometric relationships among producers,consumers and nutrient cycling in pelagic ecosystems

Most ecosystem models consolidate members of food-webs, e.g. species, into a small number of functional components. Each of these is then described by a single state variable such as biomass. When a multivariate approach incorporating multiple substances within components is substituted for this univariate one, a stoichiometric model is formed. Here we show that the Nitrogen:Phosphorus ratio within zooplankton herbivores varies substantially intraspecifically but not intraspecifically. By using stoichiometric theory and recent measurements of the N:P ratio within different zooplankton taxa, we calculate large differences in ratios of nutrients recycled by different zooplankton species. Finally, we demonstrate that N:P stoichiometry can successfully account for shifts in N- and P-limitation previously observed in whole-lake experiments. Species stoichiometry merges food-web dynamics with biogeochemical cycles to yield new insights.Abbreviations b N:P in zooplankton biomass - f N:P in algal biomass - L maximum accumulation eficiency - N:P ratio of nitrogen to phosphorus (moles:moles) - s N:P supply ratio from grazers - TN Total nitrogen = seston N + dissolved N (µmoles/liter) - TP Total phosphorus = seston P + dissolved P (µmoles/liter)     

Examination of the role of detritus food quality,phytoplankton intracellular storage capacity,and zooplankton stoichiometry on planktonic dynamics

Nutrient stoichiometric ratios are primary driving factors of planktonic food web dynamics. Ecological stoichiometry theory postulates the elemental ratios of consumer species to be homeostatic, while primary-producer stoichiometry may vary with ambient nutrient availability. The notion of phytoplankton intracellular storage is far from novel, but remains largely unexplored in modeling studies of population dynamics. We constructed a seasonally-unforced, zero-dimensional, nutrient–phytoplankton–zooplankton–detritus (NPZD) model that considers dynamic phytoplankton phosphorus reserves and quasi-dynamic zooplankton stoichiometry. A generic food quality term is used to express seston biochemical composition, ingestibility, and digestibility. We examined the sensitivity of the planktonic food web patterns to light and nutrient availability, zooplankton mortality, and detritus food quality as well as to phytoplankton intracellular storage and zooplankton stoichiometry. Our results reinforce earlier findings that high quality seston exerts a stabilizing effect on food web dynamics. However, we also found that the combination of low algal and high detritus food quality with high zooplankton mortality yielded limit cycles and multiple steady states, suggesting that the heterogeneity characterizing seston nutritional quality may have more complicated ecological ramifications. Our numerical experiments identify resource competition strategies related to nutrient transport rates and internal nutrient quotas that may be beneficial for phytoplankton to persevere in resource-limiting habitats. We also highlight the importance of the interplay between optimal stoichiometry and the factors controlling homeostatic rigidity in zooplankton. In particular, our predictions show that the predominance of phosphorus-rich and tightly-homeostatic herbivores in nutrient-enriched environments with low seston food quality can potentially result in high phytoplankton abundance, high phytoplankton-to-zooplankton ratios, and acceleration of oscillatory dynamics. Generally, our modeling study emphasizes the impact of both intracellular/somatic storage and food quality on prey–predator interactions, pinpointing an important aspect of food web dynamics usually neglected by the contemporary modeling studies.     

Effects of zooplankton on nutrient availability and seston C : N : P stoichiometry in inshore waters of Lake Biwa, Japan

Forty-eight-hour experimental manipulations of zooplankton biomass were performed to examine the potential effects of zooplankton on nutrient availability and phytoplankton biomass (as measured by seston concentration) and C : N : P stoichiometry in eutrophic nearshore waters of Lake Biwa, Japan. Increasing zooplankton, both mixed-species communities and Daphnia alone, consistently reduced seston concentration, indicating that nearshore phytoplankton were generally edible. The zooplankton clearance rates of inshore phytoplankton were similar to rates measured previously for offshore phytoplankton. Increased zooplankton biomass led to increased concentrations of nutrients (NH₄-N, soluble reactive phosphorus [SRP]). Net release rates were higher than those found in previous measurements made offshore, reflecting the nutrient-rich nature of inshore seston. Zooplankton nutrient recycling consistently decreased TIN : SRP ratios (TIN = NH₄ + NO₃ + NO₂). This effect probably resulted from the low N : P ratios of nearshore seston, which were lower than those commonly found in crustacean zooplankton and thus resulted in low retention efficiency of P (relative to N) by the zooplankton. Thus, zooplankton grazing inshore may ameliorate algal blooms due to direct consumption but tends to create nutrient supply conditions with low N : P, potentially favoring cyanobacteria. In comparison with previous findings for offshore, it appears that potential zooplankton effects on phytoplankton and nutrient dynamics differ qualitatively in inshore and offshore regions of Lake Biwa. Received: September 4, 2000 / Accepted: January 23, 2001     

Effects of nitrogen enrichment on zooplankton biomass and N:P recycling ratios across a DOC gradient in northern-latitude lakes

We used data from whole-lake studies to assess how changes in food quantity (phytoplankton biomass) and quality (phytoplankton community composition, seston C:P and N:P) with N fertilization affect zooplankton biomass, community composition and C:N:P stoichiometry, and their N:P recycling ratio along a gradient in lake DOC concentrations. We found that despite major differences in phytoplankton biomass with DOC (unimodal distributions, especially with N fertilization), no major differences in zooplankton biomass were detectable. Instead, phytoplankton to zooplankton biomass ratios were high, especially at intermediate DOC and after N fertilization, implying low trophic transfer efficiencies. An explanation for the observed low phytoplankton resource use, and biomass responses in zooplankton, was dominance of colony forming chlorophytes of reduced edibility at intermediate lake DOC, combined with reduced phytoplankton mineral quality (enhanced seston N:P) with N fertilization. N fertilization, however, increased zooplankton N:P recycling ratios, with largest impact at low DOC where phytoplankton benefitted from light sufficiently to cause enhanced seston N:P. Our results suggest that although N enrichment and increased phytoplankton biomass do not necessarily increase zooplankton biomass, bottom-up effects may still impact zooplankton and their N:P recycling ratio through promotion of phytoplankton species of low edibility and altered mineral quality.

     

Ontogenetic diet shifts produce trade‐offs in elemental imbalance in bluegill sunfish

相似文献   

Parasite and host elemental content and parasite effects on host nutrient excretion and metabolic rate

Ecological stoichiometry uses the mass balance of elements to predict energy and elemental fluxes across different levels of ecological organization. A specific prediction of ecological stoichiometry is the growth rate hypothesis (GRH), which states that organisms with faster growth or reproductive rates will require higher phosphorus content for nucleic acid and protein synthesis. Although parasites are found ubiquitously throughout ecosystems, little is understood about how they affect nutrient imbalances in ecosystems. We (1) tested the GRH by determining the carbon (C), nitrogen (N), and phosphorus (P) content of parasitic trematodes and their intermediate host, the freshwater snail Elimia livescens, and (2) used this framework to determine the trematode effects on host nutrient excretion and metabolism. Snail and parasite tissues were analyzed for elemental content using a CHN analyzer and soluble reactive phosphorus (SRP) methods. Ammonium and SRP assays were used to estimate N and P excretion rates. A respirometer was used to calculate individual snail metabolism. Trematode tissues contained lower C:P and N:P (more P per unit C and N) than the snail tissues. Snail gonadal tissues more closely resembled the elemental content of parasite tissues, although P content was 13% higher in the gonad than the trematode tissues. Despite differences in elemental content, N and P excretion rates of snails were not affected by the presence of parasites. Parasitized snails maintained faster metabolic rates than nonparasitized snails. However, the species of parasite did not affect metabolic rate. Together, this elemental imbalance between parasite and host, and the altered metabolic rate of infected snails may lead to broader parasite effects in stream ecosystems.