Oxygen dynamics and plant-sediment interactions in isoetid ...

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Paper 1denitrification in the lower anoxic zone(Risgaard-Petersen and Jensen 1997). Thisstimulation of nitrification and denitrificationcan also develop in cylindrical zones withincreasing distance from individual roots.It may seem paradoxical that Lobelia byrelease of O 2 introduces bacterial competitorsfor inorganic nitrogen in the rhizosphere.However, the special anatomy and morphologyof Lobelia has evolved as an adaptation toutilize CO 2 from the rhizosphere and the rootrelease of O 2 stimulating N loss bydenitrification is simply a side effect of havinghighly gas permeable roots. We can argue thatLobelia due to its highly stress-selected traitscan better tolerate N loss than possible plantcompetitors and that it by depriving thesediments of N and reducing the availability ofP due to strong binding to oxidized Fecompounds generate nutrient-poor sedimentconditions that it can better tolerate than anyother species. Although the isoetid sedimentswere strongly enriched by addition of organicmatter, they maintained the ability to retain most(avg. 91%) of the added P and dissolved ortho-Pcould not be detected in the pore-water except inthe most enriched sediments (Møller and Sand-Jensen 2011a,b).Estimated Fe 3+ -reduction is negligible (c.9-18 µmol m -2 d -1 ) in low-organic controlsediments of both species relative todenitrification rates, but high Fe 3+ reductionrates (1050-3500 µmol m -2 d -1 ) develop insediments of 0.4-1.6% organic enrichment forLobelia and 0.8-1.6 % for Littorella, whereasdenitrification should be strongly inhibited by-the decline of NO 3 following reduction ofsediment O 2 penetration to just a few mm thicksurface layer and loss of the deep denitrificationzone.Oxidized Mn is more soluble thanoxidized Fe and although Mn pools in thesediments are 10 times smaller than Fe pools,Mn exceeds Fe concentrations in root plaques incontrol and low-organic sediments (Christensenand Sand-Jensen 1998). In contrast, Feconcentrations are 10-fold higher in the thickroot plaques formed in high-organic sedimentsof intense anaerobic degradation (Christensenand Sand-Jensen 1998). These results suggestthat oxidized Mn contributes significantly toanaerobic respiration at low organic enrichmentand in the early phases following higher organicenrichment, while oxidized Fe takes over withtime at high organic enrichment because thesmaller Mn pools are exhausted. Oxidized Feforms such large pools in the oligotrophicisoetid sediments that even high Fe reductionover 200 days at 1.6% organic enrichmentconsumes less than 11% of the total Fe pool.Bulk measurements of inorganicelements and redox potential are often used infreshwater sediments as relatively unspecificmeasures of the characteristics and the processesoccurring there. We demonstrate here thatspecific pore-water measurements ofconcentrations at high depth resolution by theaid of microelectrodes and capillary samplesand estimates of fluxes of O 2 , DIC, Fe 2+ and+NH 4 can be made over extended periodswithout disturbing the sediment. Thus, O 2microelectode measurements are extremelyprecise descriptors of the spatial and temporalvariation of oxic and anoxic zones that can evenbe applied in the field and Fe 2+ is a highlysensitive measure of whether strictly anoxicconditions have existed for some time at thespecific sampling depth. DIC concentrations andefflux estimates are suitable quantifications ofthe combined CO 2 formation by aerobic andanaerobic respiration over time. In the isoetidsediments, it is evident that Fe reduction is agradually increasing contributor to microbialrespiration following higher organic enrichmentbut that its molar magnitude relative to theformation and efflux of DIC remains relativelymodest (< 15%). The biphasic temporal patternof DIC concentrations suggests that a pool ofhighly labile organic matter (e.g. simplecarbohydrates, organic acids and amino acids inthe organic pellets) is rapidly degraded duringthe first one-two weeks whereas more36
Paper 1recalcitrant organic pools are later degradedleading to secondary peaks after more than 100days when the sufficient microbial biomasseshave been established. The late peak of Fe 3+reduction rates after about 60 days suggests thatit takes a while before Mn pools have beenexhausted and populations of Fe-reducingbacteria have been fully established. The timecourse of DIC release and Fe reduction is highlytemperature sensitive because it is markedlyshortened by higher temperatures (28 o C) andprolonged by lower temperatures (8o C,Hammer 2010). If pulses of organic matter arereceived by the sediments, isoetid plants may,therefore, be more capable of coping with thisimpact at low temperatures because anoxicstress is less severe and concentrations ofreduced compounds are lower though of moreprolonged duration because degradation ratesare impeded.AcknowledgementsWe thank the Center for Lake Restoration(CLEAR) a Willum Kann Rasmussen center ofexcellence for funding.ReferencesAndersen JM 1976. An ignition method fordetermination of total phosphorus in lake sediments.Water Research 10: 329-331.Andersen FØ, Andersen T 2006. Effects of arbuscularmycorrhizae on biomass and nutrients in the aquatic plantLittorella uniflora. Freshwater Biology 51: 1623-1633.Christensen KK, Sand-Jensen K 1998. Precipitated ironand manganese plaques restrict root uptake of phosphorusin Lobelia dortmanna. Canadian Journal of Botany 76:2158-2163.Christensen PB, Sørensen J 1986. Temporal variation ofdenitrification in plant-covered, littoral sedimentfromLake Hampen, Denmark. Applied and EnvironmentalMicrobiology 51: 1174-1179.Christensen PB, Revsbech NP, Sand-Jensen K 1994.Microsensor analysis of oxygen in the rhizosphere of theaquatic macrophyte Littorella uniflora (L.) Aschers. PlantPhysiology 105: 1174-1179.Eaton AD, Clesceri LS, Greenberg AE 1995. Standardmethods for the examination of water and wastewater.Washington DC, USA: American Public HealthAssociation.Farmer AM, Spence DHN 1986. The growth strategiesand distribution of isoetids in Scottish freshwater lochs.Aquatic Botany 26: 247-258.Geurts JJM, Smolders AJP, Verhoeven JTA, RoelofsJGM, Lamers LPM 2008. Sediment Fe:PO 3 ratio as adiagnostic and prognostic tool for the restoration ofmacrophyte biodiversity in fen waters. FreshwaterBiology 53: 2101-2116.Grime JP 1977. Plant Strategies and VegetationProcesses. John Wileys and Sons, New York.Hammer KH 2010. Plante-sediment samspil hos Lobeliadortmanna ved stigende temperaturer. BC-Thesis,University of Copenhagen, Denmark.Li Y-H, Gregory S 1974. Diffusion of ions in sea waterand in deep-sea sediments. Geochimica et CosmochimicaActa 38: 703-714.Møller CL, Sand-Jensen K 2008. Iron plaques improvethe oxygen supply to root meristems of the freshwaterplant, Lobelia dortmanna. New Phytologist 179: 848-856.Møller CL, Sand-Jensen K 2011a. High sensitivity ofLobelia dortmanna to sediment oxygen depletionfollowing organic enrichment. New Phytologist 190:320-331.Møller CL, Sand-Jensen K 2011b. Higher gaspermeability of leaves provides greater tolerance ofLittorella uniflora than Lobelia dortmanna to sedimentorganic enrichment. (Paper 3).Pedersen O, Sand-Jensen K, Revsbech NP 1995. Dielpulses of O 2 and CO 2 in sandy sediments inhabited byLobelia dortmanna. Ecology 76: 1536-1545.Raun AL, Borum J, Sand-Jensen K 2010. Influence ofsediment organic enrichment and water alkalinity ongrowth of aquatic isoetid and elodeid plants. FreshwaterBiology 55: 1891-1904.Rebsdorf A 1972. The carbon dioxide system infreshwater. Freshwater Biological Laboratory,Copenhagen.Risgaard-Petersen N, Jensen K 1997. Nitrification anddenitrification in the rhizosphere of the aquaticmacrophyte Lobelia dortmanna L. Limnology andOceanography 42: 520-537.Sand-Jensen K, Borum J, Binzer T. 2005. Oxygenstress and reduced growth of Lobelia dortmanna in sandylake sediments subject to organic enrichment. FreshwaterBiology 50: 1034-1048.Sand-Jensen K, Prahl C 1982. Oxygen exchange withthe lacunae and across leaves and roots of the submerged37
Page 1: Oxygen dynamics and plant-sedimenti
Page 5: PrefaceThe content of this thesis i
Page 9: AbstractAbstract● Isoetids occupy
Page 13 and 14: IntroductionIntroductionOligotrophi
Page 15 and 16: Introductionwater (Wigand et al. 19
Page 17 and 18: IntroductionSand-Jensen K, Prahl C,
Page 19 and 20: Thesis summaryThesis summaryAdditio
Page 21 and 22: Thesis summaryFig. 4. Chlorophyll c
Page 23: Thesis summaryascribed to lack of A
Page 27: Paper 1Oxygen, carbon and iron dyna
Page 30 and 31: Paper 1extensive sediment volume by
Page 32 and 33: Paper 1method of Andersen (1976) an
Page 35: Paper 1Table 3. Retention of added
Page 39: Paper 2High sensitivity of Lobelia
Page 42 and 43: NewPaper 2Phytologist Research 321w
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Page 48 and 49: NewPaper 2Phytologist Research 327(
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Page 52 and 53: NewPaper 2Phytologist Research 331c
Page 55 and 56: Paper 3Higher gas permeability of l
Page 57 and 58: Paper 3Here, we perform a parallel
Page 59 and 60: Paper 3Fig. 1. O 2 penetration dept
Page 61 and 62: Paper 3Table 2. O 2 flux across lea
Page 63 and 64: Paper 3Fig. 4. Leaf chlorophyll of
Page 65 and 66: Paper 3high internal concentrations
Page 67 and 68: Paper 3Colmer TD 2003. Long-distanc
Page 69: Paper 4Organic enrichment of sedime
Page 72 and 73: Paper 4Surveys on aquatic plants re
Page 74 and 75: Paper 4ensure mixing and air satura
Page 76 and 77: Paper 4ResultsFig 1. O 2 -penetrati
Page 78 and 79: Paper 4Table 2. Individual leaf bio
Page 80 and 81: Paper 4Fig. 4. Root density (○) a
Page 82 and 83: Paper 4hours every night although l
Page 84 and 85: Paper 4Møller CL, Sand-Jensen K. 2
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[Plant Signaling & Behavior 3:10, 8
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Outstanding Lobelia dortmanna in ir
Page 93 and 94:
Planterødders overlevelse ivanddæ
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Paper 6Figur 3. Aflejringer af lign
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Paper 6Vi har sat planterødders ve
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