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1. Immobilized phosphate‐binding protein can effectively discriminate against arsenate during phosphate adsorption and recovery

   https://doi.org/10.1002/wer.1498  

   Venkiteshwaran, Kaushik ; Wells, Erin ; Mayer, Brooke K. ( December 2020 , Water Environment Research)

   There is a strong impetus to establish a circular phosphorus economy by securing internally renewable phosphate (P_i) resources for use as agricultural fertilizers. Reversible P_iadsorption technologies such as ion exchange can remove and recover P_ifrom water/wastewater for reuse. However, existing reversible adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity between As(V) and P_ichemical structure. If As(V) is co‐recovered with P_i, the value of the recovered products for agricultural reuse is low. The objective of this study was to construct an immobilized phosphate‐binding protein (PBP)‐based P_iremoval and recovery system and analyze its selectivity for P_iadsorption in the presence of As(V). A range of conditions was tested, including independent, sequential, and simultaneous exposure of the two oxyanions to immobilized PBP (PBP resin). The purity of the recovered P_iproduct was assessed after inducing controlled desorption of the adsorbed oxyanions at high pH (pH 12.5). P_iconstituted more than 97% of the adsorbed oxyanions in the recovered product, even when As(V) was initially present at twofold higher concentrations than P_i. Therefore, PBP resin has potential to selectively remove P_i, as well as release high‐purity P_ifree of As(V) contamination suitable for subsequent agricultural reuse.

   Existing reversible phosphate (P_i) adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity in their chemical structure.

   Co‐recovery of As(V) with P_ican reduce the recovered product's reuse as a fertilizer.

   An immobilized phosphate‐binding protein (PBP)‐based system can be highly selective for P_ieven in the presence of As(V).

   P_iconstituted more than 97% of the recovered product, even when As(V) was present at 2‐fold higher concentrations than P_i.

   Immobilized PBP offers advantages over existing P_iadsorbents by providing high‐purity P_iproducts free of As(V) contamination for reuse.

    

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2. Carnivore identity mediates the effects of light and nutrients on aquatic food‐chain efficiency

   https://doi.org/10.1111/fwb.12790  

   Rock, Amber M. ; Hall, Mia R. ; Vanni, Michael J. ; González, María J. ( June 2016 , Freshwater Biology)

   Food chain efficiency (FCE), the proportion of primary production converted to production of the top trophic level, can influence several ecosystem services as well as the biodiversity and productivity of each trophic level. AquaticFCEis affected by light and nutrient supply, largely via effects on primary producer stoichiometry that propagate to herbivores and then carnivores. Here, we test the hypothesis that the identity of the top carnivore mediatesFCEresponses to changes in light and nutrient supply.

   We conducted a large‐scale, 6‐week mesocosm experiment in which we manipulated light and nutrient (nitrogen and phosphorus) supply and the identity of the carnivore in a 2 × 2 × 2 factorial design. We quantified the response ofFCEand the biomass and productivity of each trophic level (phytoplankton, zooplankton, and carnivore). We used an invertebrate,Chaoborus americanus, and a vertebrate, bluegill sunfish (Lepomis macrochirus), as the two carnivores in this study because of the large difference in phosphorus requirements between these taxa.

   We predicted that bluegill would be more likely to experience P‐limitation due to higher P requirements, and hence thatFCEwould be lower in the bluegill treatments than in theChaoborustreatments. We also expected the interactive effect of light and nutrients to be stronger in the bluegill treatments. Within a carnivore treatment, we predicted highestFCEunder low light and high nutrient supply, as these conditions would produce high‐quality (low C:nutrient) algal resources. In contrast, if food quantity had a stronger effect on carnivore production than food quality, carnivore production would increase proportionally with primary production, thusFCEwould be similar across light and nutrient treatments.

   Carnivore identity mediated the effects of light and nutrients onFCE, and as predictedFCEwas higher in food chains withChaoborusthan with bluegill. Also as predicted,FCEinChaoborustreatments was higher under low light. However,FCEin bluegill treatments was higher at high light supply, opposite to our predictions. In addition, bluegill production increased proportionally with primary production, whileChaoborusproduction was not correlated with primary production, suggesting that bluegill responded more strongly to food quantity than to food quality. These carnivore taxa differ in traits other than body stoichiometry, for example, feeding selectivity, which may have contributed to the observed differences inFCEbetween carnivores.

   Comparison of our results with those from previous experiments showed thatFCEresponds similarly to light and nutrients in food chains withChaoborusand larval fish (gizzard shad: Clupeidae), but very differently in food chains with bluegill. These findings warrant further investigation into the mechanisms related to carnivore identity (e.g., developmental stage, feeding selectivity) underlying these responses, and highlight the importance of considering both top‐down and bottom‐up effects when evaluating food chain responses to changing light and nutrient conditions.

    

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3. Molecular and electrophysiological characterization of anion transport in Arabidopsis thaliana pollen reveals regulatory roles for pH , Ca 2+ and GABA

   https://doi.org/10.1111/nph.15863  

   Domingos, Patrícia ; Dias, Pedro N. ; Tavares, Bárbara ; Portes, Maria Teresa ; Wudick, Michael M. ; Konrad, Kai R. ; Gilliham, Matthew ; Bicho, Ana ; Feijó, José A. ( May 2019 , New Phytologist)

   We investigated the molecular basis and physiological implications of anion transport during pollen tube (PT) growth inArabidopsis thaliana(Col‐0).

   Patch‐clamp whole‐cell configuration analysis of pollen grain protoplasts revealed three subpopulations of anionic currents differentially regulated by cytoplasmic calcium ([Ca²⁺]_cyt). We investigated the pollen‐expressed proteinsAtSLAH3,AtALMT12,AtTMEM16 andAtCCCas the putative anion transporters responsible for these currents.

   AtCCC‐GFPwas observed at the shank andAtSLAH3‐GFPat the tip and shank of thePTplasma membrane. Both are likely to carry the majority of anion current at negative potentials, as extracellular anionic fluxes measured at the tip ofPTs with an anion vibrating probe were significantly lower inslah3^−/−andccc^−/−mutants, but unaffected inalmt12^−/−andtmem16^−/−. We further characterised the effect ofpHandGABAby patch clamp. Strong regulation by extracellularpHwas observed in the wild‐type, but not intmem16^−/−. Our results are compatible withAtTMEM16 functioning as an anion/H⁺cotransporter and therefore, as a putativepHsensor.GABApresence: (1) inhibited the overall currents, an effect that is abrogated in thealmt12^−/−and (2) reduced the current inAtALMT12 transfectedCOS‐7 cells, strongly suggesting the direct interaction ofGABAwithAtALMT12.

   Our data show thatAtSLAH3 andAtCCCactivity is sufficient to explain the major component of extracellular anion fluxes, and unveils a possible regulatory system linkingPTgrowth modulation bypH,GABA, and [Ca²⁺]_cytthrough anionic transporters.

    

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4. Ectomycorrhizal fungi and soil enzymes exhibit contrasting patterns along elevation gradients in southern Patagonia

   https://doi.org/10.1111/nph.15714  

   Truong, Camille ; Gabbarini, Luciano A. ; Corrales, Adriana ; Mujic, Alija B. ; Escobar, Julio M. ; Moretto, Alicia ; Smith, Matthew E. ( March 2019 , New Phytologist)

   The biological and functional diversity of ectomycorrhizal (ECM) associations remain largely unknown in South America. In Patagonia, theECMtreeNothofagus pumilioforms monospecific forests along mountain slopes without confounding effects of vegetation on plant–fungi interactions.

   To determine how fungal diversity and function are linked to elevation, we characterized fungal communities, edaphic variables, and eight extracellular enzyme activities along six elevation transects in Tierra del Fuego (Argentina and Chile). We also tested whether pairingITS1rDNAIllumina sequences generated taxonomic biases related to sequence length.

   Fungal community shifts across elevations were mediated primarily by soilpHwith the most species‐rich fungal families occurring mostly within a narrowpHrange. By contrast, enzyme activities were minimally influenced by elevation but correlated with soil factors, especially total soil carbon. The activity of leucine aminopeptidase was positively correlated withECMfungal richness and abundance, and acid phosphatase was correlated with nonECM fungal abundance. Several fungal lineages were undetected when using exclusively paired or unpaired forwardITS1 sequences, and these taxonomic biases need reconsideration for future studies.

   Our results suggest that soil fungi inN. pumilioforests are functionally similar across elevations and that these diverse communities help to maintain nutrient mobilization across the elevation gradient.

    

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5. Responses of benthic algae to nutrient enrichment in a shallow lake: Linking community production, biomass, and composition

   https://doi.org/10.1111/fwb.13375  

   McCormick, Amanda R. ; Phillips, Joseph S. ; Ives, Anthony R. ( July 2019 , Freshwater Biology)

   Understanding how nutrient limitation affects algal biomass and production is a long‐standing interest in aquatic ecology. Nutrients can influence these whole‐community characteristics through several mechanisms, including shifting community composition. Therefore, incorporating the joint responses of biomass, taxonomic composition, and production of algal communities, and relationships among them, is important for understanding effects of nutrient enrichment.

   In shallow subarctic Lake Mývatn, Iceland, benthic algae compose a majority of whole‐lake primary production, support high secondary production, and influence nutrient cycling. Given the importance of these ecosystem processes, the factors that limit benthic algae have a large effect on the function and dynamics of the Mývatn system.

   In a 33‐day nutrient enrichment experiment conducted in Lake Mývatn, we measured the joint responses of benthic algal biomass, primary production, and composition to nitrogen (N) and phosphorus (P) supplementation. We enriched N and P using nutrient‐diffusing agar overlain by sediment, with three levels of N and P that were crossed in a factorial design.

   We found little evidence of community‐wide nutrient limitation, as chlorophyll‐aconcentrations showed a negligible response to nutrients. Gross primary production (GPP) was unaffected by P and inhibited by N enrichment after 10 days, although the inhibitory effect of N diminished by day 33.

   In contrast to biomass and primary production, community composition was strongly affected by N and marginally affected by P, with some algal groups increasing and others decreasing with enrichment. The taxa with the most negative and positive responses to N enrichment were Fragilariaceae andScenedesmus, respectively.

   The abundances of particular algal groups, based on standardised cell counts, were related toGPPmeasured at the end of the experiment.Oocystiswas negatively associated withGPPbut was unaffected by N or P, while Fragilariaceae andScenedesmuswere positively associated withGPPbut had opposite responses to N. As a result, nutrient‐induced compositional shifts did not alterGPP.

   Overall, our results show that nutrient enrichment can have large effects on algal community composition while having little effect on total biomass and primary production. Our study suggests that nutrient‐driven compositional shifts may not alter the overall ecological function of algal communities if (1) taxa have contrasting responses to nutrient enrichment but have similar effects on ecological processes, and/or (2) taxa that have strong influences on ecological function are not strongly affected by nutrients.

    

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