A comparative study of above-ground productivity of dominant U.S. Gulf Coast marsh species

Above-ground productivity of dominant freshwater, brackish, and salt-marsh species from the U.S. Gulf Coast was evaluated using both gas exchange techniques and harvest methods. Both techniques showed significant differences in productivity among the study species which represent major components of their respective communities. Estimates of net aerial primary productivity using the harvest method yielded 3683 g dw (dry weight) m^?2yr^?1 for Spartina alterniflora (tall), 2008 g dw m^?2yr^?1 for S. alterniflora (short), 3677 g dw m^?yr^?1 for S. patens and 1641 g dwm^?yr^?1 for Panicum hemitomon. Carbon balance estimated from gas exchange calculation yielded values approximately equivalent to a biomass accumulation of 6024 g dw m^?2yr^?1 for S. alterniflora (tall), 3047 g dw m^?yr^?1 for S. alterniflora (short), 5702 g dw m^?yr^?1 for S. patens, and 2912 g dm^?yr^?1 for P. hemitomon. The net aerial primary production was estimated to be approximately 61% of total productivity in S. alterniflora (tall-form) and 66%o of total productivity in short-form, 64% in S. patens and 56%) in P. hemitomon. The assimilation data also indicated that Spartina alterniflora and S. patens continue carbon fixation throughout the year while assimilation in Panicum hemitomon is absent due to lack of live leaves during the winter. Various aspects of harvest and gas exchange techniques are discussed.     

Productivity of Chlorella sorokiniana in a short light‐path (SLP) panel photobioreactor under high irradiance

Maximal productivity of a 14 mm light‐path panel photobioreactor under high irradiance was determined. Under continuous illumination of 2,100 µmol photons m^?2 s^?1 with red light emitting diodes (LEDs) the effect of dilution rate on photobioreactor productivity was studied. The light intensity used in this work is similar to the maximal irradiance on a horizontal surface at latitudes lower than 37°. Chlorella sorokiniana, a fast‐growing green microalga, was used as a reference strain in this study. The dilution rate was varied from 0.06 to 0.26 h^?1. The maximal productivity was reached at a dilution rate of 0.24 h^?1, with a value of 7.7 g dw m^?2 h^?1 (m² of illuminated photobioreactor surface) and a volumetric productivity of 0.5 g dw L^?1 h^?1. At this dilution rate the biomass concentration inside the reactor was 2.1 g L^?1 and the photosynthetic efficiency was 1.0 g dw mol photons. This biomass yield on light energy is high but still lower than the theoretical maximal yield of 1.8 g mol photons^?1 which must be related to photosaturation and thermal dissipation of absorbed light energy. Biotechnol. Bioeng. 2009; 104: 352–359 © 2009 Wiley Periodicals, Inc.     

Upper limits of photosynthetic productivity and problems of scaling

Some 1,370 W m^?2 of light energy reaches the outer atmosphere of earth and on average only 240 W m^?2 reaches the earth’s surface. Only a fraction of this is used to fix CO₂ through photosynthesis, and efficiencies ranging from 0.1?8% for total irradiance have been reported. The theoretical maximum quantum efficiency of carbon fixation is 0.125 mol C (mol quanta)^?1 which relates to a maximum productivity of about 12 g C m^?2 day^?1 or 29.8 g(dw) m^?2 day^?1. This could increase to a maximum of 200 g(dw) m^?2 day^?1 in intermittent light of high frequencies, which is on average eight times higher than the average measured under field conditions where rates approaching 25 g(dw) m^?2 day^?1 are considered high. Several possibilities exist for achieving higher yields and photosynthetic efficiencies, such as limiting the antennae sizes and pulsing light at frequencies equivalent to electron turnover in the electron transport chains of photosynthesis. Scaling from laboratory experimental conditions to large commercial photobioreactors is a major stumbling block and may be the single most important factor responsible for the overall low reported areal production rates.     

Phytoplankton and its contribution to primary productivity in two coral reef areas of French Polynesia

A study of phytoplankton productivity and related parameters was carried out in two fringing and barrier reef systems around Moorea island (Tiahura lagoon) and Tahiti (Vairao lagoon), Society Islands, during July–August 1974.In Tiahura lagoon, which is the narrower and the shallower, phytoplankton standing crop and production are extremely low; photosynthetic assimilation, as measured in situ by the ¹⁴C method, ranges from 4 to 27 mg C m^?2 day^?1, presumably less than in the impoverished open ocean, but it is surprisingly high at a station just outside the barrier reef (645 mg C m^?2 day^?1) as the result of some island mass effect. As compared to the latter station, the lagoon shows a ten-times increase in particle content and glucose uptake, and a higher percentage of decomposition products of plant pigments. These data support the concept that, in such environments where benthic primary producers prevail, phytoplankton may have lost its ‘usual’ rôle in the aquatic food web.Vairao lagoon, a deeper and wider one, subjected to a greater extent to land fertilization, is more productive (103–420 mg C m^?2 day^?1). Considering this difference, as well as the considerable range of phytoplankton production in coral reef areas of the world, the need for a trophic classification of such ecosystems is emphasized.     

Terrestrial ecosystems and the carbon cycle

The terrestrial biosphere plays an important role in the global carbon cycle. In the 1994 Intergovernmental Panel Assessment on Climate Change (IPCC), an effort was made to improve the quantification of terrestrial exchanges and potential feedbacks from climate, changing CO₂, and other factors; this paper presents the key results from that assessment, together with expanded discussion. The carbon cycle is the fluxes of carbon among four main reservoirs: fossil carbon, the atmosphere, the oceans, and the terrestrial biosphere. Emissions of fossil carbon during the 1980s averaged 5.5 Gt y^?1. During the same period, the atmosphere gained 3.2 Gt C y^?1 and the oceans are believed to have absorbed 2.0 Gt C y^?1. The regrowing forests of the Northern Hemisphere may have absorbed 0.5 Gt C y^?1 during this period. Meanwhile, tropical deforestation is thought to have released an average 1.6 Gt C y^?1 over the 1980s. While the fluxes among the four pools should balance, the average 198Ds values lead to a ‘missing sink’ of 1.4 Gt C y^?1 Several processes, including forest regrowth, CO₂ fertilization of plant growth (c. 1.0 Gt C y^?1), N deposition (c. 0.6 Gt C y^?1), and their interactions, may account for the budget imbalance. However, it remains difficult to quantify the influences of these separate but interactive processes. Uncertainties in the individual numbers are large, and are themselves poorly quantified. This paper presents detail beyond the IPCC assessment on procedures used to approximate the flux uncertainties. Lack of knowledge about positive and negative feedbacks from the biosphere is a major limiting factor to credible simulations of future atmospheric CO₂ concentrations. Analyses of the atmospheric gradients of CO₂ and ¹³ CO₂ concentrations provide increasingly strong evidence for terrestrial sinks, potentially distributed between Northern Hemisphere and tropical regions, but conclusive detection in direct biomass and soil measurements remains elusive. Current regional-to-global terrestrial ecosystem models with coupled carbon and nitrogen cycles represent the effects of CO₂ fertilization differently, but all suggest longterm responses to CO₂ that are substantially smaller than potential leaf- or laboratory whole plant-level responses. Analyses of emissions and biogeochemical fluxes consistent with eventual stabilization of atmospheric CO₂ concentrations are sensitive to the way in which biospheric feedbacks are modeled by c. 15%. Decisions about land use can have effects of 100s of Gt C over the next few centuries, with similarly significant effects on the atmosphere. Critical areas for future research are continued measurements and analyses of atmospheric data (CO₂ and ¹³CO₂) to serve as large-scale constraints, process studies of the scaling from the photosynthetic response to CO₂ to whole-ecosystem carbon storage, and rigorous quantification of the effects of changing land use on carbon storage.     

Spatial distribution of phytoplankton productivity in the Amundsen Sea, Antarctica

To date, no direct measurements of primary production were taken in the Amundsen Sea, which is one of the highest primary productivity regions in the Antarctic. Phytoplankton carbon and nitrogen uptake experiments were conducted at 16 selected stations using a ¹³C–¹⁵N dual isotope tracer technique. We found no statistically significant depletions of major inorganic nutrients (nitrate?+?nitrite, ammonium, and silicate) although the concentrations of these nutrients were markedly reduced in the surface layer of the polynya stations where large celled phytoplankton (>20?μm) predominated (ca. 64?%). The average chl-a concentration was significantly higher at polynya stations than at non-polynya stations (p?<?0.01). Average daily carbon and nitrogen uptake rates by phytoplankton at polynya stations were 2.2?g?C?m^?2?day^?1 (SD?=?±1.4?g?C?m^?2?day^?1) and 0.9?g?N?m^?2?day^?1 (SD?=?±0.2?g?N?m^?2?day^?1), respectively, about 5–10 times higher than those at non-polynya stations. These ranges are as high as those in the Ross Sea, which has the highest productivity among polynyas in the Antarctic Ocean. The unique productivity patterns in the Amundsen Sea are likely due to differences in iron limitation, phytoplankton productivity, the timing of phytoplankton growing season, or a combination of these factors.     

Production of high ethanol concentrations from glucose using a vertical rotating immobilized cell reactor of the bacterium zymomonas mobilis

Long-term continuous ethanol production of up to 80 g.l¹ with a volumetric ethanol productivity of 63 g. l^?1. h^?1 was maintained for more than 72 days using a Vertical Rotating Immobilized Cell Reactor of the bacterium Z. mobilis. Continuous production of higher ethanol concentration was unsuccessful due to an inhibition of cell growth by long exposure to high ethanol concentrations. However, ethanol concentration as high as 120g. l^?1 and volumetric ethanol productivity of 13g. l^?1. h^?1 were achieved in a repeated-batch fermentation system using the same bioreactor. By a simple washing operation at the end of each run, immobilized biomass could be effectively regenerated and used to carry out more than 10 successive fermentation cycles.     

The large Amazonian peatland carbon sink in the subsiding Pastaza‐Marañón foreland basin,Peru

The carbon (C) dynamics of tropical peatlands can be of global importance, because, particularly in Southeast Asia, they are the source of considerable amounts of C released to the atmosphere as a result of land‐use change and fire. In contrast, the existence of tropical peatlands in Amazonia has been documented only recently. According to a recent study, the 120 000 km² subsiding Pastaza‐Marañón foreland basin in Peruvian Amazonia harbours previously unstudied and up to 7.5 m thick peat deposits. We studied the role of these peat deposits as a C reserve and sink by measuring peat depth, radiocarbon age and peat and C accumulation rates at 5–13 sites. The basal ages varied from 1975 to 8870 cal yr bp , peat accumulation rates from 0.46 to 9.31 mm yr^?1 and C accumulation rates from 28 to 108 g m^?2 yr^?1. The total peatland area and current peat C stock within the area of two studied satellite images were 21 929 km² and 3.116 Gt (with a range of 0.837–9.461 Gt). The C stock is 32% (with a range of 8.7–98%) of the best estimate of the South American tropical peatland C stock and 3.5% (with a range of 0.9–10.7%) of the best estimate of the global tropical peatland C stock. The whole Pastaza‐Marañón basin probably supports about twice this peatland area and peat C stock. In addition to their contemporary geographical extent, these peatlands probably also have a large historical (vertical) extension because of their location in a foreland basin characterized by extensive river sedimentation, peat burial and subsidence for most of the Quaternary period. Burial of peat layers in deposits of up to 1 km thick Quaternary river sediments removes C from the short‐term C cycle between the biosphere and atmosphere, generating a long‐term C sink.     

Asymmetry in above‐ and belowground productivity responses to N addition in a semi‐arid temperate steppe

Nitrogen (N) enrichment often increases aboveground net primary productivity (ANPP) of the ecosystem, but it is unclear if belowground net primary productivity (BNPP) track responses of ANPP. Moreover, the frequency of N inputs may affect primary productivity but is rarely studied. To assess the response patterns of above‐ and belowground productivity to rates of N addition under different addition frequencies, we manipulated the rate (0–50 g N m^?2 year^?1) and frequency (twice vs. monthly additions per year) of NH₄NO₃ inputs for six consecutive years in a temperate grassland in northern China and measured ANPP and BNPP from 2012 to 2014. In the low range of N addition rates, BNPP showed the greatest negative response and ANPP showed the greatest positive responses with increases in N addition (<10 g N m^?2 year^?1). As N addition increased beyond 10 g N m^?2 year^?1, increases in ANPP dampened and decreases in BNPP ceased altogether. The response pattern of net primary productivity (combined above‐ and belowground; NPP) corresponded more closely to ANPP than to BNPP. The N effects on BNPP and BNPP/NPP (f_BNPP) were not dependent on N addition frequency in the range of N additions typically associated with N deposition. BNPP was more sensitive to N addition frequency than ANPP, especially at low rates of N addition. Our findings provide new insights into how plants regulate carbon allocation to different organs with increasing N rates and changing addition frequencies. These root response patterns, if incorporated into Earth system models, may improve the predictive power of C dynamics in dryland ecosystems in the face of global atmospheric N deposition.     

Differential responses of production and respiration to temperature and moisture drive the carbon balance across a climatic gradient in New Mexico

Southwestern North America faces an imminent transition to a warmer, more arid climate, and it is critical to understand how these changes will affect the carbon balance of southwest ecosystems. In order to test our hypothesis that differential responses of production and respiration to temperature and moisture shape the carbon balance across a range of spatio‐temporal scales, we quantified net ecosystem exchange (NEE) of CO₂ and carbon storage across the New Mexico Elevational Gradient, which consists of six eddy‐covariance sites representing biomes ranging from desert to subalpine conifer forest. Within sites, hotter and drier conditions were associated with an increasing advantage of respiration relative to production such that daily carbon uptake peaked at intermediate temperatures – with carbon release often occurring on the hottest days – and increased with soil moisture. Across sites, biotic adaptations modified but did not override the dominant effects of climate. Carbon uptake increased with decreasing temperature and increasing precipitation across the elevational gradient; NEE ranged from a source of ～30 g C m^?2 yr^?1 in the desert grassland to a sink of ～350 g C m^?2 yr^?1 in the subalpine conifer forest. Total aboveground carbon storage increased dramatically with elevation, ranging from 186 g C m^?2 in the desert grassland to 26 600 g C m^?2 in the subalpine conifer forest. These results make sense in the context of global patterns in NEE and biomass storage, and support that increasing temperature and decreasing moisture shift the carbon balance of ecosystems in favor of respiration, such that the potential for ecosystems to sequester and store carbon is reduced under hot and/or dry conditions. This implies that projected climate change will trigger a substantial net release of carbon in these New Mexico ecosystems (～3 Gt CO₂ statewide by the end of the century), thereby acting as a positive feedback to climate change.     

Response of terrestrial carbon uptake to climate interannual variability in China

The interest in national terrestrial ecosystem carbon budgets has been increasing because the Kyoto Protocol has included some terrestrial carbon sinks in a legally binding framework for controlling greenhouse gases emissions. Accurate quantification of the terrestrial carbon sink must account the interannual variations associated with climate variability and change. This study used a process‐based biogeochemical model and a remote sensing‐based production efficiency model to estimate the variations in net primary production (NPP), soil heterotrophic respiration (HR), and net ecosystem production (NEP) caused by climate variability and atmospheric CO₂ increases in China during the period 1981–2000. The results show that China's terrestrial NPP varied between 2.86 and 3.37 Gt C yr^?1 with a growth rate of 0.32% year^?1 and HR varied between 2.89 and 3.21 Gt C yr^?1 with a growth rate of 0.40% year^?1 in the period 1981–1998. Whereas the increases in HR were related mainly to warming, the increases in NPP were attributed to increases in precipitation and atmospheric CO₂. Net ecosystem production (NEP) varied between ?0.32 and 0.25 Gt C yr^?1 with a mean value of 0.07 Gt C yr^?1, leading to carbon accumulation of 0.79 Gt in vegetation and 0.43 Gt in soils during the period. To the interannual variations in NEP changes in NPP contributed more than HR in arid northern China but less in moist southern China. NEP had no a statistically significant trend, but the mean annual NEP for the 1990s was lower than for the 1980s as the increases in NEP in southern China were offset by the decreases in northern China. These estimates indicate that China's terrestrial ecosystems were taking up carbon but the capacity was undermined by the ongoing climate change. The estimated NEP related to climate variation and atmospheric CO₂ increases may account for from 40 to 80% to the total terrestrial carbon sink in China.     

Macrophyte-epiphyte biomass and productivity in an eelgrass (Zostera marina L.) community

The biomass, productivity (¹⁴C), and photosynthetic response to light and temperature of eelgrass, Zostera marina L. and its epiphytes was measured in a shallow estuarine system near Beaufort, North Carolina, during 1974. The maximum of the biomass (above-ground) was measured in March; this was followed by a general decline throughout the rest of the year. The average biomass was 105.0 g dry wt m^?2; 80.3 g dry wt m^?2 was eelgrass and 24.7 g dry wt m^?2 was epiphytes. The productivity of eelgrass averaged 0.88 mg C g^?1 h^?1 which was similar to that of the epiphytes, 0.65 mg C g^?1 h^?1. Eelgrass and epiphyte productivity was low during the spring and early summer, gave a maximum during late summer and fall, and declined during the winter; this progression was probably due to environmental factors associated with tidal heights. On an areal basis, the average annual productivity was 0.9 g C m^?2 day^?1 for eelgrass and 0.2 g C m^?2 day^?1 for the epiphytes. Rates of photosynthesis of both eelgrass and epiphytes increased with increasing temperature to an asymptotic value at which the system was light saturated. Both eelgrass and epiphytes had a temperature optimum of < 29 °C. A negative response to higher temperatures was also reflected in biomass measurements which showed the destruction of eelgrass with increasing summer temperatures. The data suggest that the primary productivity cycles of macrophytes and epiphytes are closely interrelated.     

Secondary production of crustacean zooplankton and biomass of major rotifer species in Lake Bosumtwi/Bosomtwe,Ghana, West Africa

Studies have shown a strong linkage between zooplankton and fisheries' potential in tropical lakes. High zooplankton production provides the basis for fish production, but knowledge of zooplankton production dynamics in African lakes is extremely limited. Crustacean zooplankton production and the biomass of dominant rotifers in Lake Bosumtwi were assessed over a 2‐year period. The crustaceans comprised an endemic and extremely abundant cyclopoid copepod, Mesocyclops bosumtwii and the cladoceran Moina micrura. Mean standing stock of the crustaceans was 429 mg dw m^?3, whilst annual production averaged 2.1 g dw m^?3 y^?1. Production doubled from 1.4 g dw m^?3 y^?1 in 2005 to 2.8 g dw m^?3 y^?1 in 2006. Copepods accounted for 98.5% of crustacean production. The biomass of the dominant rotifers Brachionus calyciflorus and Hexarthra intermedia was less than 1% of total zooplankton biomass. Daily turnover rate and turnover time of the crustaceans was 0.19 day^?1 and 6.2 days respectively. Crustacean production yielded no statistical relationship with phytoplankton biomass. Production was well within the range of tropical lakes. Peak crustacean production synchronized maximum rainfall, lake mixing and phytoplankton production. Most importantly, no one year's set of dynamics can be used to characterize zooplankton production in the lake.     

Net primary productivity allocation and cycling of carbon along a tropical forest elevational transect in the Peruvian Andes

The net primary productivity, carbon (C) stocks and turnover rates (i.e. C dynamics) of tropical forests are an important aspect of the global C cycle. These variables have been investigated in lowland tropical forests, but they have rarely been studied in tropical montane forests (TMFs). This study examines spatial patterns of above‐ and belowground C dynamics along a transect ranging from lowland Amazonia to the high Andes in SE Peru. Fine root biomass values increased from 1.50 Mg C ha^?1 at 194 m to 4.95 ± 0.62 Mg C ha^?1 at 3020 m, reaching a maximum of 6.83 ± 1.13 Mg C ha^?1 at the 2020 m elevation site. Aboveground biomass values decreased from 123.50 Mg C ha^?1 at 194 m to 47.03 Mg C ha^?1 at 3020 m. Mean annual belowground productivity was highest in the most fertile lowland plots (7.40 ± 1.00 Mg C ha^?1 yr^?1) and ranged between 3.43 ± 0.73 and 1.48 ± 0.40 Mg C ha^?1 yr^?1 in the premontane and montane plots. Mean annual aboveground productivity was estimated to vary between 9.50 ± 1.08 Mg C ha^?1 yr^?1 (210 m) and 2.59 ± 0.40 Mg C ha^?1 yr^?1 (2020 m), with consistently lower values observed in the cloud immersion zone of the montane forest. Fine root C residence time increased from 0.31 years in lowland Amazonia to 3.78 ± 0.81 years at 3020 m and stem C residence time remained constant along the elevational transect, with a mean of 54 ± 4 years. The ratio of fine root biomass to stem biomass increased significantly with increasing elevation, whereas the allocation of net primary productivity above‐ and belowground remained approximately constant at all elevations. Although net primary productivity declined in the TMF, the partitioning of productivity between the ecosystem subcomponents remained the same in lowland, premontane and montane forests.     

The contribution of epiphyton to the primary production of tropical floodplain wetlands

Tropical floodplains are one of the most productive ecosystems on earth. Studies on floodplain productivity have primarily focused on trees and macrophytes, rather than algae, due to their greater biomass. However, epiphyton—algae and bacteria attached to the submerged portion of aquatic macrophytes—is a major source of energy in many tropical floodplains. Epiphyton productivity rates are unknown for most tropical floodplain wetlands, and spatial variability is not well understood. In this study, we measured primary productivity of epiphyton in Kakadu National Park in northern Australia. We estimated the relative contribution of epiphyton to aquatic production (epiphyton, + phytoplankton + macrophytes). We sampled sites dominated by different macrophyte structural types: vertical emerging grasses, horizontal emerging grasses, submerged macrophytes, and macrophytes with floating leaves. Epiphyton productivity was highly influenced by the structural type of the macrophyte. Highest potential productivity per weight was measured from epiphyton growing on macrophytes with floating leaves and horizontal grasses (1.52 ± 0.53 and 1.82 ± 0.61 mgC/dw g epiphyton/h, respectively) and lowest in submerged macrophytes and vertical grasses (0.57 ± 0.26 and 0.66 ± 0.47 mgC/dw g epiphyton/h, respectively). When considering the areal biomass of the macrophyte and the amount of epiphyton attached, epiphyton on horizontal grasses and submerged macrophytes had productivity values approximately ten times higher (45–219 mgC/m²/d) compared to those on vertical grasses and macrophytes with floating leaves (2–18 mgC/m²/d). Epiphyton contributed between 2 to 13 percent to the aquatic production of these tropical floodplain wetlands.     

Spatial heterogeneity of ecosystem carbon fluxes in a broadleaved forest in Northern Germany

Carbon fluxes were investigated in a mature deciduous forest, located in Northern Germany (53°47′N–10°36′E), by means of eddy‐covariance technique, stand survey and models. This forest has been managed following a concept of nature‐oriented forestry since the 1980s. One of the goals of the study was to test whether changed management led to increased carbon sequestration. The forest contains several broadleaved tree species. Depending on wind direction, the fetch‐area of the eddy‐covariance data was dominated by different tree species. Three subplots dominated by Oak, Beech or Alder/Ash could be distinguished from the tower data. In each of these subplots, 30 × 30 m² areas were defined to analyse leaf area index, litterfall and the increase of the wood biomass. Eddy‐covariance analysis showed that the gross primary productivity (GPP′) was higher in the Oak subplot (?1794 g C m^?2 yr^?1) in comparison with the Beech plot and the Alder/Ash plot (?1470 and ?1595 g C m^?2 yr^?1, respectively). The total ecosystem respiration (TER) was the highest in the Alder/Ash‐dominated subplot (1401 g C m^?2 yr^?1) followed by the Oak plot and the Beech plot (1235 and 1174 g C m^?2 yr^?1, respectively). The resulting net ecosystem productivity (NEP) was ?559 g C m^?2 yr^?1 for the Oak‐dominated subplot, ?295 g C m^?2 yr^?1 for the Beech plot and ?193 g C m^?2 yr^?1 for the Alder/Ash plot. From Stand survey and modelling, the net primary productivity was estimated as 1103, 702 and 671 g C m^?2 yr^?1 in the Oak, Beech and Alder/Ash plot, respectively. Also carbon flux with litterfall was the highest in the Oak plot 343 g C m^?2 yr^?1 and lowest in Alder/Ash plot (197 g m^?2 yr^?1) with the Beech plot in between (228 g m^?2 yr^?1). The observations indicate an increase of the proportion of litterfall with increasing GPP′ and a different ability of carbon sequestration of the three stands in medium temporary scale. Only in the Oak stand that comprised the oldest trees and the most structured canopy the carbon sequestration was increased compared with conventionally managed forests.     

Variability in iodine in temperate seaweeds and iodine accumulation kinetics of Fucus vesiculosus and Laminaria digitata (Phaeophyceae,Ochrophyta)

The biogeochemistry of iodine in temperate coastal ecosystems is largely mediated by macroalgae, which act as a major biological sink and source of iodine. Their capacity to accumulate, retain and release iodine has been associated with abiotic and biotic stressors, but quantitative information is limited. We evaluated the seasonal iodine retention capacity of eleven macroalgal species belonging to different systematic groups, collected from two sites in Ireland. Iodine accumulation and retention were then further quantified in Fucus vesiculosus and Laminaria digitata in relation to I^? concentrations in seawater and temperature. In general, iodine contents were ~10¹–10² μmol · (g dw)^?1 for Laminariales, 10⁰–10¹ μmol · (g dw)^?1 for Fucales, 10^?1–10⁰ μmol · (g dw)^?1 for Rhodophyta, and 10^?1 μmol · (g dw)^?1 for Chlorophyta. Typically, algal iodine contents were above average in winter and below average in summer. Iodine accumulation in F. vesiculosus and L. digitata depended on I^? availability and followed the Michaelis‐Menten kinetic. The ratio of maximum accumulation rate to half accumulation coefficient (ρ_max: K _t) was 2.4 times higher for F. vesiculosus than for L. digitata , suggesting that F. vesiculosus was more efficient in iodine accumulation. Both species exhibited a temperature‐dependent net loss of iodine, and only an exposure to sufficient external I^? concentrations compensated for this loss. This study revealed that both environmental (e.g., I^? in seawater, temperature) and organismal (e.g., the status of the iodine storage pool) variables determine retention and variability in iodine in temperate seaweeds.     

Phosphorus inputs unmask negative effects of ultraviolet radiation on algae in a high mountain lake

Ultraviolet solar radiation (UVR) and atmospheric nutrient loads to pristine ecosystems are global climate change phenomena that simultaneously affect aquatic organisms in ways not easily predicted by single factor studies. Plankton in a high mountain lake was exposed in situ to increasing phosphorus (P) concentrations (mimicking atmospheric pulses) in absence or presence of UVR in order to identify their interactive effect on functional [primary production, organic carbon (C) release (EOC), and percentage of C released (%EOC)], growth rate, structural–physiological (algal biomass, sestonic C, P content, chlorophyll a (Chl a), and Chl a : C ratio, P cell quota, cell‐specific Chl a), and stoichiometric (autotroph C : P ratio) traits. The availability of P after the pulse determined the intensity of responses by primary producers to UVR stress. All structural–physiological and functional variables significantly increased by up to two orders of magnitude in response to P enrichment. UV radiation, over a long‐term scale, exerted significant deleterious effects on most structural–physiological variables when inorganic P was added at high levels (≥30 μg P L^?1). The subsequent unexpected negative synergistic UVR × P effect on algal development did not support our initial hypothesis that P input might buffer the harmful UVR effect. UVR exerted a weak negative effect on primary production but strongly enhanced the absolute and percentage excretion of C (up to 60%), mechanism responsible of a significant reduction in autotroph C : P ratios. We propose that low sestonic C : P ratios are the outcome of an adaptive strategy of algae in environments with high UVR exposure and extreme nutrient limitation and have important implications for C flux through grazing vs. microbial food webs in oligotrophic systems.     

Productivity of the aquatic macrophyte Pontederia lanceolata Nvtt. (Pontederiaceae) on floodplains of the Pantanal Mato-grossense,Brazil

The Pantanal Mato-grossense is an extensive floodplain system located in the center of South America with important macrophytic primary producers. This study describes the dynamics of net primary production and the biomass of the aquatic macrophyte Pontederia lanceolata, the dominant species in some floodplain fields near Poconé. Productivity was determined from a combination of demographic and growth methods. Biomass was determined using squares of known area, periodically distributed at random. The average productivity during the period was 3.11 g dry weight m^-2 day^-1. The minimum and maximum values (0.04 g dry weight m^-2 day^-1 and 8.59 g dry weight m^-2 day^-1, respectively) occurred during the drought and the flood period, respectively. The standing stock varied between 12.7 and 235.9 g dry weight m^-2, determined at the beginning of the flood and at its peak, respectively. The dynamics of the productivity and the standing stock of the species are associated with the flood patterns of the area and with life cycle of the plant.