Carbon flow in the littoral food web of an oligotrophic lake

Benthic food web dynamics and carbon flow were examined in the littoral zone of Lake Coleridge, a large deep oligotrophic lake, using radioactive and stable isotope techniques in conjunction with analyses of stomach contents of the fauna. We specifically address two hypotheses: (1) that macrophytes only contribute to the carbon flow to higher trophic levels when they have decayed; and (2) that epiphytic algae is the major source of carbon for macroinvertebrates, and thus fish, with only minor contributions from phytoplankton or terrestrial sources. Epiphytic diatoms were a major component of the stomach contents of the gastropod snail Potamopyrgus antipodarum, and of chironomids. Animal remains were also common in the diet of some chironomids, while amorphous organic matter predominated in the stomachs of oligochaetes. A variety of epiphytic algal taxa was found in trichopteran larvae. Feeding rate of P. antipodarum measured with radioactive tracers increased by 10× on decayed macrophytes (Elodea) compared with live material, while feeding rates on characean algae increased by a factor of 3 when decayed material was presented. However, assimilation rates were less than 20% on decayed material compared with 48–52% on live material. Potential carbon sources were easily distinguished based on their ¹³C values, although isotopic ratios showed significant variation among sites. Epiphytic algae showed less variation among sites than macrophytes and were depleted by 4–5 compared with macrophytes. Detrital material, organic matter in the sediments and plankton were significantly depleted in ¹³C relative to macrophytes and slightly depleted relative to epiphytic algae. Most macroinvertebrate taxa showed a similar pattern among sites to macrophytes and epiphytic algae. P. antipodarum and chironomids were slightly enriched compared with epiphytic algae. Ratios for the common bully (Gobiomorphus cotidianus) were generally consistent with a diet dominated by chironomids, while there was some evidence for terrestrial inputs for koaro (Galaxias brevipinnis) and juvenile brown trout. Epiphytic algae appear to underpin much of the production in the littoral zone of this oligotrophic lake, with trichopteran and chironomid larvae mediating carbon flows from algae to fish. Macrophytes do not make a major contribution directly to carbon flow to higher trophic levels even when decayed. The lack of a direct link between macrophytes and higher trophic levels is due to the faunal composition, including a lack of large herbivores.     

Evidence for iron‐regulated cyanobacterial predominance in oligotrophic lakes

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Microbial metabolism in surface sediments and its role in the immobilization of phosphorus in oligotrophic lake sediments

Rapid microbial metabolism and a large phosphorus uptake potential were observed in surface sediments of Lake George, New York. This sediment (termed the flocculent layer) also exhibited a phosphorus limited condition and a large reservoir of inorganic phosphorus associated with humic substances. These observations suggest that the empirically observed phosphorus retention in oligotrophic lake sediments may be promoted by a rapid cycling of phosphorus between microflora and its associated organic matter.     

Heterotrophic nitrogen fixation in oligotrophic tropical marshes: changes after phosphorus addition

In order to determine the impact of nutrient enrichment on phosphorus (P) limited wetlands, we established experimental P additions in marshes throughout northern Belize. P significantly increased macrophyte primary production, which led to the rapid elimination of cyanobacterial mats. The replacement of cyanobacterial mats by macrophytes constrained autotrophic nitrogen (N) fixation, increased the quantity, and changed the quality of organic matter input to the sediments. We predicted that the activity of sediment heterotrophic N fixers will be impacted by these alterations in carbon input. We used the acetylene reduction technique to measure potential (glucose amended) nitrogenase activity (NA) in sediments from controls and treatment plots that have been P enriched for four years and dominated either by Eleocharis cellulosa, or Typha domingensis for two years. NA in P-enriched plots was 2–3 orders of magnitude higher than NA in controls. NA was positively correlated with the soil reactive P, both total organic and microbial carbon, live root biomass, and total phospholipid fatty acids (PLFA) as an indicator of active microbial biomass. It was negatively correlated with the concentration of ammonium-N. Path analysis revealed that the indirect effect of P on NA through the root biomass was more important than the direct effect of P. NA of the upper sediment layer was consistently higher in Eleocharis than in Typha dominated plots, despite the higher litter input by Typha. We feel that the higher levels of lignin and phenolics occurring in Typha litter, relative to Eleocharis, constrained NA in Typha plots. Handling editor: Luis Mauricio Bini     

三峡库区消落带落羽杉与立柳林土壤微生物生物量碳氮磷动态变化

为探究库区消落带人工乔木植被恢复重建后土壤质量及肥力的变化特征,于2016年6月(T_1)、2016年9月(T_2)、2017年6月(T_3)及2017年9月(T_4)选择165—175 m高程落羽杉与立柳土壤为研究对象,并以裸地作为对照,测定土壤微生物生物量碳、氮、磷和相关理化性质。结果表明:(1)经历水淹(T_2—T_3)会使土壤微生物生物量处于较低水平,落干期(T_1—T_2、T_3—T_4)落羽杉与立柳人工植被恢复生长能显著提高土壤微生物生物量,对土壤微生物恢复具有重要意义。(2)落羽杉与立柳土壤微生物生物量碳、氮占土壤有机碳、全氮百分比在4个时期均显著高于裸地,表明落羽杉与立柳土壤微生物对土壤碳、氮库的贡献大于裸地;落羽杉土壤微生物生物量磷及其占全磷百分比在T_1和T_3处于极低水平,T_2和T_4处于较高水平,应注意磷元素的迁移。(3)土壤微生物生物量碳、氮、磷与土壤有机碳和全氮有极显著相关性,与土壤pH值呈不同程度的负相关。在三峡库区消落带进行落羽杉与立柳乔木植被恢复重建能显著提高土壤微生物生物量及土壤肥力,进一步证实开展科学的植被修复与重建值得提倡和肯定。     

Zooplankton induced decrease in inorganic phosphorus uptake by plankton in an oligotrophic lake

Experiments conducted on samples collected from a large oligotrophic lake revealed the following: (1) excretion rates of PO _inf4 ^sup3– by single Daphnia thorata were below detection (5 pmol animal^–1 min^–1) in 20 ml of oligotrophic lake water over a period of 10 min, (2) experimental addition of D. thorata to 20 ml aliquots of lake water decreased community-wide microbial uptake of PO _inf4 ^sup3– on two occasions (as measured by ³²PO _inf4 ^sup3– incorporation), and (3) the presence of D. thorata increased uptake by organisms smaller than 1µm, and decreased uptake by large phytoplankton. The specific mechanism for these responses remains unclear, but the results imply that when phytoplankton larger than 1µm encounter cm scale patches of water recently occupied by Daphnia they may experience decreased PO _inf4 ^sup3– availability rather than elevated concentrations of PO _inf4 ^sup3– caused by excretion. We show that ³²P uptake experiments using natural plankton assemblages can be influenced by the presence or absence of large zooplankton, and that neither grazing, turbulence, nor PO _inf4 ^sup3– excretion can account for this influence.     

Effects of nitrogen,phosphorus and carbon enrichment on planktonic and periphytic algae in a softwater,oligotrophic lake in Florida,USA

The objective of this study was to investigate nutrient limitation of algal abundance in Anderson-Cue Lake, a softwater clear oligotrophic lake in north-central Florida. Nutrient diffusing clay pots and cylindrical enclosures were used in the field to test effects of different combinations of nitrogen, phosphorus, silica, and carbon on algal standing crop and composition of periphytic and planktonic algae, respectively. Effects of nutrient enrichment on periphytic algae were examined in two studies conducted 31 May – 8 July and 10 June – 15 July 1991. Nutrient effects on planktonic algae were examined in one study from 13 June – 1 July 1991. Planktonic and periphytic algal biovolume was significantly higher (p<0.05) when nitrogen and carbon were added in combination than with treatments without nitrogen, carbon, or nitrogen and carbon. Treatments with nitrogen and carbon combined resulted in lower algal diversity and dominance by coccoid green algae andScenedesmus. Results indicate that carbon and nitrogen can be limiting factors to algal growth in Anderson-Cue Lake and possibly other lakes of similar water quality.     

Leaf litter colonization by invertebrates in the littoral zone of a small oligotrophic lake

The colonization of deciduous leaf litter by aquatic invertebrates was studied at Scott Lake in Algonquin Park, Ontario, Canada. Deciduous leaf packs were colonized after only 2 days submergence. The invertebrate community was dominated by chironomids (25–94% depending on sampling period), and to a lesser extent by oligochaetes, turbellarians, and mayflies. Collectors, such as the chironomids Dicrotendipes, Pseudochironomus, Paratanytarsus and Parakiefferiella were the dominant functional-feeding group suggesting that leaf litter is being used as habitat rather than a direct food source. Deciduous leaf litter lost a substantial amount of weight, due to leaching, after only 48 h submergence. Fall-shed beech (Fagus grandifolia) leaves decomposed more rapidly than fall-shed sugar maple (Acer saccharum) leaves with daily processing coefficients (k), determined using an exponential decay model, of 0.0058 and 0.0039, respectively. Conversely, conditioned maple leaves, defined as leaves remaining on the ground over winter, were processed faster than conditioned beech leaves, with coefficients of 0.0042 and 0.0014, respectively. It is speculated that inhibitory compounds have been leached from the maple leaves, allowing for faster leaf processing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrogen-fixation in the littoral benthos of an oligotrophic lake

Blue-green algae are common in the benthos of Mirror Lake, New Hampshire (U. S. A.) — on macrophytes and on the lake bottom-and are probably responsible for the variable, sometimes high rates of N-fixation that detected by a series of acetylene-reduction assays during September and October.     

Carbon, nitrogen and phosphorus cycling in rivermarginal wetlands; a model examination of landscapegeochemical flows

The importance of landscape geochemical flows wasinvestigated using a dynamic model simulating carbon,nitrogen and phosphorus cycling in riverine wetlands,which has been described in a previous paper. Thehydro-geomorphic unit (HGMU) concept was incorporatedin the model by defining a separate, completeunit-model for each unit (HGMU) within the wetland.These unit-models were connected by defining the flowsof nitrogen and phosphorus between them. These flows,also called landscape geochemical flows, usuallyconsist of flows of water containing N and P.The model was applied to a site at Kismeldon Meadows,in south-western England. This site consists of twounits, a slope and a floodplain, separated by a ditch,which catches most of the run off and shallowgroundwater flows from the slope. Only an estimated1% of the N and P that leaves the slope unit in thewater outflow reaches the floodplain unit; the rest iscaught in the system of ditches, which prevent thegeochemical flows taking their natural course. Toexamine the influence of this system of ditches, themodel was run for the same site, but without theditches. This is comparable to a situation of arestored site, where run off and shallow groundwaterflows containing nutrients, can freely get from theslope to the floodplain.The computer simulation experiment reconnecting theslope and floodplain showed that this (1) increasedthe nutrient input into the floodplain, causing ahigher biomass production, and (2) increased thewetness of the floodplain, causing slowerdecomposition, which together (3) led to a faster soilorganic matter accumulation in the floodplain.Nutrient inflows became relatively more importantcompared to atmospheric deposition, especially forphosphorus. By connecting the slope and the floodplainmore nitrogen and less phosphorus flowed into theriver.     

Plasma-membrane rosettes in root hairs of Equisetum hyemale

Particle arrangement in the plasma membrane during cell wall formation was investigated by means of the double-replica technique in root hairs of Equisetum hyemale. Particle density in the protoplasmic fracture face of the plasma membrane was higher than in the extraplasmic fracture face. Apart from randomly distributed particles, particle rosettes were visible in the PF face of the plasma membrane. The rosettes consisted of six particles arranged in a circle and had an outer diameter of approx. 26 nm. No gradient in the number of rosettes was found, which agrees with micrifibril deposition taking place over the whole hair. The particle rosettes were found individually, which might indicate that they spin out thin microfibrils as found in higher-plant cell walls. Indeed microfibril width in these walls, measured in shadowed preparations, is 8.5±1.5 nm. It is suggested that the rosettes are involved in microfibril synthesis. Non-turgid cells lacked microfibril imprints in the plasma membrane and no particle rosettes were present on their PF face. Fixation with glutaraldehyde caused, probably as a result of plasmolysis, the microfibril imprints to disappear together with the particle rosettes. The PF face of the plasma membrane of non-turgid hairs sometimes showed domains in which the intramembrane particles were aggregated in a hexagonal pattern. Microfibril orientation during deposition will be discussed.Abbreviations EF extraplasmic fracture face - PF protoplasmic fracture face     

Physical control of Eurasian watermilfoil in an oligotrophic lake

The introduction of Eurasian watermilfoil (Myriophyllum spicatum) into oligotrophic waters of high water clarity in temperate zones of North America has produced growth in excess of 6 m depth and yearly biomass approaching 1000 g m^–2 dry weight. From its initial observation in Lake George, New York, USA in 1985, by 1993 milfoil had spread to 106 discrete locations within the lake. A 7-year study of one site having no management showed milfoil to grow expansively, suppressing native plant species from 20 in 1987 to 6 in 1993 with the average number of species m^–2 quadrat declining from 5.5 in 1987 to less than 2 in 1993. Management of milfoil by means of hand harvesting, suction harvesting and benthic barrier has reduced the number of unmanaged sites from 106 in 1993 to 11. One year post-treatment at sites utilizing suction harvesting, showed a greater number of native species at all sites than pretreatment with a substantial reduction in milfoil biomass. At sites where benthic barrier was removed 1–2 years after installation, milfoil had recolonized 44% of grid squares within 30 days. Ninety days after barrier removal 74% of grid squares contained milfoil and one year later 71% of the grids supported milfoil. During the first year following mat removal, the average number of species m^–2 peaked at 4.7 and stabilized at 4.5 during the second year. Hand harvesting by SCUBA in areas of limited milfoil growth (new sites of infestation and sites of former treatment) was found to reduce the number of milfoil plants present in subsequent years. Hand harvesting did not eliminate milfoil at any of the sites and regrowth/colonization necessitated reharvesting every 3 or more years. Results of evaluations of physical plant management techniques indicate that (1) an integrated program utilizing different techniques based on plant density reduced the growth of milfoil and (2) long term commitment to aquatic plant management is necessary since none of the techniques employed singly were found to eliminate milfoil.     

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。     

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。     

Carbon assimilation, nitrogen, and photochemical efficiency of different Himalayan tree species along an altitudinal gradient

In the area of Jumla region in Western Nepal, measurements of saturated leaf net photosynthetic rate (P_sat), nitrogen content, leaf fluorescence, carbon isotopic composition, and water status were performed on woody coniferous (Pinus wallichiana, Picea smithiana, Abies spectabilis, Juniperus wallichiana, Taxus baccata), evergreen (Quercus semecarpifolia, Rhododendron campanulatum), and deciduous broadleaved species (Betula utilis, Populus ciliata, Sorbus cuspidata) spreading from 2 400 m up to the treeline at 4 200 m a.s.l. With the exception of J. wallichiana, P_sat values were lower in coniferous than broadleaved species. Q. semecarpifolia, that in this area grows above the coniferous belt between 3 000 and 4 000 m, showed the highest P_sat at saturating irradiance and the highest leaf N content. This N content was higher and P_sat lower than those of evergreen oak species of tempe forests at middle and low altitudes. For all species, P_sat and N content were linearly correlated, but instantaneous nitrogen use efficiency was lower than values measured in lowland and temperate plant communities. The values of carbon isotopic composition, estimated by ₁₃C, showed the same range reported for temperate tree species. The ranking of ₁₃C values for the different tree types was conifers < evergreen broadleaved13C were found along the altitudinal gradient. Quantum yield of photochemistry at saturating irradiance, measured by leaf fluorescence (F/F_m), was highest in J. wallichiana and lowest in T. baccata. Overall, photochemical efficiency was more strongly related to species than to altitude. Interestingly, changes of .F/F_m along the altitudinal gradient correlated well with the reported altitudinal distribution of the species.This revised version was published online in March 2005 with corrections to the page numbers.     

岷江上游高山森林溪流木质残体碳、氮和磷贮量特征

森林溪流木质残体是森林生态系统与水域之间物质循环和能量流动的主要联结之一,其碳、氮和磷贮量不仅可影响森林与溪流生态系统的结构和功能,而且与下游水体环境密切相关。因此,于2013年8月雨季以岷江上游典型高山森林为研究对象,调查了12条森林溪流木质残体的碳、氮和磷贮量分配特征,并汇算了研究区域内碳、氮和磷在溪流中单位面积的总贮量。结果表明,高山森林溪流木质残体碳、氮和磷的溪流单位面积总贮量分别为312.1 g/m2、809.5 mg/m2和110.9 mg/m2;在溪流中,木质残体碳、氮和磷贮量以径级为1—2.5 cm和2.5—5 cm的木质残体分布居多,分别共占碳、氮和磷总贮量的86.71%、87.20%和84.55%;木质残体碳、氮和磷贮量以Ⅴ腐烂级分配最多,分别共占碳、氮和磷总贮量的65.86%、67.86%和60.31%;尽管溪流各项特征与碳、氮和磷元素贮量的相关性不显著,但基本达到中度相关关系。这些结果为认识森林生态系统中以木质残体为载体的碳、氮和磷输出潜力提供了基础数据。     

Regeneration of inorganic phosphorus and nitrogen from decomposition of seston in a freshwater sediment

The mineralization of phosphorus and nitrogen from seston was studied in consolidated sediment from the shallow Lake Arreskov (July and November) and in suspensions without sediment (July). In the suspension experiment, phosphorus and nitrogen were mineralized in the same proportions as they occurred in the seston. During the 30 days suspension experiment, 47 and 43% of the particulate phosphorus and nitrogen, respectively, was mineralized with constant rates.Addition of seston to the sediment had an immediate enhancing effect on oxygen uptake, phosphate and ammonia release, whereas nitrate release decreased due to denitrification. The enhanced rates lasted for 2–5 weeks, while the decrease in nitrate release persisted throughout the experiment. The increase in oxygen uptake (equivalent to 21% of the seston carbon) was, however, only observed in the July experiment. The release of phosphorus and nitrogen from seston decomposing on the sediment surface differed from the suspension experiments. Thus, between 91 and 111% of the phosphorus in the seston was released during the experiments. Due to opposite directed effects on ammonium and nitrate release, the resulting net release of nitrogen was relatively low.A comparison of C/N/P ratios in seston, sediment and flux rates indicated that nitrogen was mineralized faster than phosphorus and carbon. Some of this nitrogen was lost through denitrification and therefore not measurable in the flux of inorganic nitrogen ions. This investigation also suggests that decomposition of newly settled organic matter in sediments have indirect effects on sediment-water exchanges (e.g. by changing of redox potentials and stimulation of denitrification) that modifies the release of mineralized phosphate and nitrogen from the sediment.     

氮磷肥对茶树锌硒等中微量元素吸收与分配的影响

锌（Zn）和硒（Se）及其他中微量元素（铝Al,钙Ca,铁Fe,铜Cu,锰Mn）是茶叶品质的重要指标,但茶树吸收Zn、Se能力及氮（N）磷（P）肥影响中微量元素吸收与分配的过程尚不清楚。以红壤丘陵区福鼎大白茶树为研究对象,开展Zn+Se、Zn+Se+N、Zn+Se+P、Zn+Se+N+P和对照共5种处理3次重复随机化区组试验,处理第3年春季分茶叶、成熟叶、吸收根、运输根和储藏根采集植物样品,测定其元素含量。结果表明,茶树地上和地下器官Zn和Se及其他中微量元素对N、P、Zn、Se添加的响应具分异性。与对照相比,茶树地上和地下器官Zn和Se含量均显著增加,与Zn+Se相比,施N和/或P肥仅显著提高茶叶和成熟叶Se含量（P<0.05）;与对照相比,施肥处理均显著提高吸收根和运输根Al、Fe含量以及储藏根Cu含量;运输根Mn含量表现为Zn+Se+N、Zn+Se+P、Zn+Se+N+P显著高于对照,储藏根Mn含量为Zn+Se+N+P显著高于其他处理;茶树各器官Ca含量对施肥处理无显著响应。此外,茶叶和成熟叶的Zn含量与吸收根显著正相关,而Se含量则与储藏根显著正相关。茶树具有吸收和积累Zn和Se的能力,而施N、P肥有助于提高茶叶Se含量,研究结果为红壤丘陵区培育高品质锌硒茶及营建生态高值茶园提供了依据。     

Effects of arbuscular mycorrhizae on biomass and nutrients in the aquatic plant Littorella uniflora

1. It has been hypothesised that the symbiosis with arbuscular mycorrhizal fungi (AMF) leads to a higher uptake of phosphorus (P) and nitrogen (N) in aquatic plants, but it has never been shown experimentally without the use of fungicides. In particular, the symbiosis may be important for nutrient uptake by isoetids in oligotrophic lakes, where low concentrations of inorganic N and P both in the water and in the sediment limit the growth of plants and where symbiosis facilitates the uptake of nutrients from the sediment. 2. Plants of the isoetid Littorella uniflora were propagated under the sterile conditions without an AMF infection. The plants were then grown for 60 days with and without re‐infection by AMF, and with either high (150 μm ) or low (ambient concentration approximately 15 μm ) CO₂ concentration. 3. The study proved that the symbiosis between AMF and L. uniflora had a positive impact on the retention of N and P in the plants at very low nutrient concentrations in the water and on biomass development. Shoot biomass and standing stocks of both P and N were significantly higher in re‐infected plants. 4. Raised CO₂ concentration resulted in a fivefold increase in hyphal infection, but had no impact on the number of arbuscules and vesicles in the cross sections. There were significantly higher biomass and lower tissue P and N concentrations in the plants from high CO₂ treatments. This resulted in similar standing stocks of P and N in plants from low and high CO₂ treatments. 5. The results from this study showed that the symbiosis between AMF and L. uniflora is an important adaptation enabling isoetids to grow on nutrient‐poor sediments in oligotrophic lakes.     

茯苓碳氮磷化学计量学特征

为探明茯苓的碳、氮、磷生态化学计量学特征,采集了云南省11个州、市42个居群的茯苓样本,分析了其菌核与表皮中碳(C)、氮(N)、磷(P)的化学计量特征.结果 表明:茯苓菌核中C、N、P的含量分别为40.24％-43.58％、0.176％-0.532％和0.020％-0.077％;C∶N、C∶P和N∶P的范围分别为93....