Evaluating the use of lake sedimentary DNA in palaeolimnology: A comparison with long-term microscopy-based monitoring of the phytoplankton community.

Palaeolimnological records provide valuable information about how phytoplankton respond to long-term drivers of environmental change. Traditional palaeolimnological tools such as microfossils and pigments are restricted to taxa that leave sub-fossil remains, and a method that can be applied to the wider community is required. Sedimentary DNA (sedDNA), extracted from lake sediment cores, shows promise in palaeolimnology, but validation against data from long-term monitoring of lake water is necessary to enable its development as a reliable record of past phytoplankton communities.

The differential ability of two species of seagrass to use carbon dioxide and bicarbonate and their modelled response to rising concentrations of inorganic carbon.

Seagrass meadows are one of the most productive ecosystems on the planet, but their photosynthesis rate may be limited by carbon dioxide but mitigated by exploiting the high concentration of bicarbonate in the ocean using different active processes. Seagrasses are declining worldwide at an accelerating rate because of numerous anthropogenic pressures. However, rising ocean concentrations of dissolved inorganic carbon, caused by increases in atmospheric carbon dioxide, may benefit seagrass photosynthesis.

Seasonal Patterns of Phytoplankton Taxon Richness in Lakes: Effects of Temperature, Turnover and Abundance.

Species richness is a key ecological characteristic that influences numerous ecosystem functions. Here we analyse the patterns and possible causes of phytoplankton taxon richness in seasonal datasets from twenty contrasting lakes in the English Lake District over six years and near-weekly datasets over 33 years from Windermere. Taxon richness was lowest in winter and highest in summer or autumn in all of the lakes.

Lake heatwaves under climate change.

Lake ecosystems, and the organisms that live within them, are vulnerable to temperature change, including the increased occurrence of thermal extremes. However, very little is known about lake heatwaves-periods of extreme warm lake surface water temperature-and how they may change under global warming. Here we use satellite observations and a numerical model to investigate changes in lake heatwaves for hundreds of lakes worldwide from 1901 to 2099.

Regulation of Carbon Metabolism by Environmental Conditions: A Perspective From Diatoms and Other Chromalveolates.

Diatoms belong to a major, diverse and species-rich eukaryotic clade, the Heterokonta, within the polyphyletic chromalveolates. They evolved as a result of secondary endosymbiosis with one or more Plantae ancestors, but their precise evolutionary history is enigmatic. Nevertheless, this has conferred them with unique structural and biochemical properties that have allowed them to flourish in a wide range of different environments and cope with highly variable conditions.

External α-carbonic anhydrase and solute carrier 4 are required for bicarbonate uptake in a freshwater angiosperm.

The freshwater monocot Ottelia alismoides is the only known species to operate three CO2-concentrating mechanisms (CCMs): constitutive bicarbonate (HCO3-) use, C4 photosynthesis, and facultative Crassulacean acid metabolism, but the mechanism of HCO3- use is unknown. We found that the inhibitor of an anion exchange protein, 4,4'-diisothio-cyanatostilbene-2,2'-disulfonate (DIDS), prevented HCO3- use but also had a small effect on CO2 uptake. An inhibitor of external carbonic anhydrase (CA), acetazolamide (AZ), reduced the affinity for CO2 uptake but also prevented HCO3- use via an effect on the anion exchange protein.

Insights on the Functions and Ecophysiological Relevance of the Diverse Carbonic Anhydrases in Microalgae.

Carbonic anhydrases (CAs) exist in all kingdoms of life. They are metalloenzymes, often containing zinc, that catalyze the interconversion of bicarbonate and carbon dioxide-a ubiquitous reaction involved in a variety of cellular processes. So far, eight classes of apparently evolutionary unrelated CAs that are present in a large diversity of living organisms have been described.

Dissolved organic nutrient uptake by riverine phytoplankton varies along a gradient of nutrient enrichment.

The concentration of dissolved organic matter (DOM) in freshwaters is increasing in large areas of the world. In addition to carbon, DOM contains nitrogen and phosphorus and there is growing concern that these organic nutrients may be bioavailable and contribute to eutrophication. However, relatively few studies have assessed the potential for dissolved organic nitrogen (DON) or dissolved organic phosphorus (DOP) compounds to be bioavailable to natural river phytoplankton communities at different locations or times.

Global lake thermal regions shift under climate change.

Water temperature is critical for the ecology of lakes. However, the ability to predict its spatial and seasonal variation is constrained by the lack of a thermal classification system. Here we define lake thermal regions using objective analysis of seasonal surface temperature dynamics from satellite observations.

Hydropower reservoirs on the upper Mekong River modify nutrient bioavailability downstream.

Hydropower development is the key strategy in many developing countries for energy supply, climate-change mitigation and economic development. However, it is commonly assumed that river dams retain nutrients and therefore reduce downstream primary productivity and fishery catches, compromising food security and causing trans-boundary disputes. Contrary to expectation, here we found that a cascade of reservoirs along the upper Mekong River increased downstream bioavailability of nitrogen and phosphorus.

Structural basis for C4 photosynthesis without Kranz anatomy in leaves of the submerged freshwater plant Ottelia alismoides.

Background And Aims: Ottelia alismoides (Hydrocharitaceae) is a freshwater macrophyte that, unusually, possesses three different CO2-concentrating mechanisms. Here we describe its leaf anatomy and chloroplast ultrastructure, how these are altered by CO2 concentration and how they may underlie C4 photosynthesis.

Methods: Light and transmission electron microscopy were used to study the anatomy of mature leaves of O.

Climatic and anthropogenic regulation of carbon transport and transformation in a karst river-reservoir system.

The effect of dams on dissolved inorganic carbon (DIC) transport and riverine ecosystems is unclear in karst cascade reservoirs. Here, we analyzed water samples from a karst river system with seven cascade reservoirs along the Wujiang River, southwestern China, during one hydrological year. From upstream to downstream, the average concentration of DIC increased from 2.

Catchment properties and the photosynthetic trait composition of freshwater plant communities.

Unlike in land plants, photosynthesis in many aquatic plants relies on bicarbonate in addition to carbon dioxide (CO) to compensate for the low diffusivity and potential depletion of CO in water. Concentrations of bicarbonate and CO vary greatly with catchment geology. In this study, we investigate whether there is a link between these concentrations and the frequency of freshwater plants possessing the bicarbonate use trait.

The potential role of sediment organic phosphorus in algal growth in a low nutrient lake.

The role of sediment-bound organic phosphorus (P) as an additional nutrient source is a component of internal P budgets in lake system that is usually neglected. Here we examined the relative importance of sediment P to internal P load and the role of bioavailable P in algal growth in Lake Erhai, China. Lake Erhai sediment extractable P accounted for 11-43% (27% average) of extractable total P, and bioavailable P accounted for 21-66% (40%) of P.

Response of cyanobacteria and phytoplankton abundance to warming, extreme rainfall events and nutrient enrichment.

Cyanobacterial blooms are an increasing threat to water quality and global water security caused by the nutrient enrichment of freshwaters. There is also a broad consensus that blooms are increasing with global warming, but the impacts of other concomitant environmental changes, such as an increase in extreme rainfall events, may affect this response. One of the potential effects of high rainfall events on phytoplankton communities is greater loss of biomass through hydraulic flushing.

Effects of brownification and warming on algal blooms, metabolism and higher trophic levels in productive shallow lake mesocosms.

An increase of dissolved organic carbon (DOC) in inland waters has been reported across the northern temperate region but the effects of this on whole lake ecosystems, often combined with other anthropogenic stressors like nutrient inputs and warming, are poorly known. The effects of these changes on different component of the ecosystem were assessed in an experiment using twenty-four large (3000L) outdoor mesocosms simulating shallow lakes. Two different temperature regimes (ambient and ambient +4 °C) combined with three levels of organic matter (OM, added as filtered peaty water), simulating the DOC increase that is predicted to take place over the next 4 to 21 years were used.

A new widespread subclass of carbonic anhydrase in marine phytoplankton.

Most aquatic photoautotrophs depend on CO-concentrating mechanisms (CCMs) to maintain productivity at ambient concentrations of CO, and carbonic anhydrase (CA) plays a key role in these processes. Here we present different lines of evidence showing that the protein LCIP63, identified in the marine diatom Thalassiosira pseudonana, is a CA. However, sequence analysis showed that it has a low identity with any known CA and therefore belongs to a new subclass that we designate as iota-CA.

Different CO acclimation strategies in juvenile and mature leaves of Ottelia alismoides.

The freshwater macrophyte, Ottelia alismoides, is a bicarbonate user performing C4 photosynthesis in the light, and crassulacean acid metabolism (CAM) when acclimated to low CO. The regulation of the three mechanisms by CO concentration was studied in juvenile and mature leaves. For mature leaves, the ratios of phosphoenolpyruvate carboxylase (PEPC) to ribulose-bisphosphate carboxylase/oxygenase (Rubisco) are in the range of that of C4 plants regardless of CO concentration (1.

Effects of multiple stressors on cyanobacteria abundance vary with lake type.

Blooms of cyanobacteria are a current threat to global water security that is expected to increase in the future because of increasing nutrient enrichment, increasing temperature and extreme precipitation in combination with prolonged drought. However, the responses to multiple stressors, such as those above, are often complex and there is contradictory evidence as to how they may interact. Here we used broad scale data from 494 lakes in central and northern Europe, to assess how cyanobacteria respond to nutrients (phosphorus), temperature and water retention time in different types of lakes.

Adaptive forecasting of phytoplankton communities.

The global proliferation of harmful algal blooms poses an increasing threat to water resources, recreation and ecosystems. Predicting the occurrence of these blooms is therefore needed to assist water managers in making management decisions to mitigate their impact. Evaluation of the potential for forecasting of algal blooms using the phytoplankton community model PROTECH was undertaken in pseudo-real-time.

Physical and chemical impacts of a major storm on a temperate lake: a taste of things to come?

Extreme weather can have a substantial influence on lakes and is expected to become more frequent with climate change. We explored the influence of one particular extreme event, Storm Ophelia, on the physical and chemical environment of England's largest lake, Windermere. We found that the substantial influence of Ophelia on meteorological conditions at Windermere, in particular wind speed, resulted in a 25-fold increase (relative to the study-period average) in the wind energy flux at the lake-air interface.

Regulation of the Calvin-Benson-Bassham cycle in the enigmatic diatoms: biochemical and evolutionary variations on an original theme.

In Plantae, the Calvin-Benson-Bassham (CBB) cycle is highly regulated and most of its enzymes have been thoroughly studied. Since diatoms arose as a result of secondary endosymbiosis with one or more Plantae ancestors, their precise evolutionary history is enigmatic and complex resulting in biochemical variations on the original CBB cycle theme. The Rubisco Michaelis constant for CO is higher in diatoms than land plants and the nuclear-encoded Rubisco activase in Plantae is replaced by an analogous chloroplast-encoded CbbX (Calvin-Benson-Bassham protein X) in diatoms.