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

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Paper 1extensive sediment volume by symbiosis withfungi (Sand-Jensen and Søndergaard 1978,Wigand et al. 1998, Andersen and Andersen2006).Organic enrichment of sedimentsaccompanying higher algal growth byeutrophication or greater terrestrial input,however, has been a serious threat to thepersistence of transparent lake waters andmineral sediments inhabited by isoetids duringthe last 100 years (Sand-Jensen et al. 2000,Smolders et al. 2002). We have recentlyconfirmed the critical consequences of sedimentanoxia for plant performance and survivalfollowing organic enrichment (Møller and Sand-Jensen 2011a,b), but the profound alterations ofsediment chemistry have not been analyzed. Wehere explore changes in sedimentbiogeochemistry by repeated measurements ofpore-water chemistry over ca. 200 days insediments inhabited by the two common isoetidspecies, Lobelia dortmanna and Littorellauniflora including both initial phases ofmarkedly increased organic degradation ratesand later recovery phases after the most labileorganic matter has vanished.O 2 dynamics of sediments is regulatedby O 2 production (photosynthesis), consumption(root and bacterial respiration) and physicalexchange with lake waters. Addition of organicmatter is expected to enhance degradation rates,accelerate O 2 consumption, increase+accumulation of DIC and NH 4 and induceanoxic Fe 3+ -reduction to soluble Fe 2+ . Theaccumulation of DIC should reflect thecombined O 2 respiration and anaerobicrespiration by alternative electron acceptors(NO - 3 , Mn 4+ , Fe 3+ and SO 2- 4 ). NO - 3 respiration isrestricted by low N-content of the sediments andlow nitrification rates once O 2 disappears(Christensen and Sørensen 1986, Risgaard-Petersen and Jensen 1997). Likewise, SO 2- 4 andMn 4+ reduction are constrained by lowconcentrations leaving Fe 3+ as the most potentoxidation agent due to very high sediment pools(Christensen and Sand-Jensen 1998). We hereanalyze the temporal course of sediment porewaterFe 2+ to follow the induction, rise anddecline of anaerobic respiration over time anduse the vertical profiles to estimate Fe 2+ effluxesderiving from anaerobic Fe 3+ reduction. Fe 2+flux estimates are sensitive measures ofanaerobic Fe 3+ respiration in response to organicenrichment and effluxes of Fe 2+ relative to DICprovides a proxy of anaerobic Fe reductionrelative to total aerobic and anaerobicrespiration.Input of organic matter to sedimentsincreases pools and release of organic matter tolake waters. In contrast to inorganic C releasedby organic decomposition, we foresee thatinorganic N and P, in particular, will be moreeffectively retained in the sediment due toincorporation in microbial biomass anddevelopment of higher N:C and P:C ratios inorganic sediment pools. Moreover, NH +4 isbound to organic compounds and sedimentparticles with negative charges, while PO 3- 4 isstrongly adsorbed to all particle surfaces andforms insoluble complexes and minerals with Aland Fe. Thus, when leaf concentrations of N andP and photosynthesis of isoetids dropdramatically upon high organic sedimentenrichment (Møller and Sand-Jensen 2011a,b),despite increasing sediment N and Pconcentrations, the likely reason is poor rootdevelopment and performance (Raun et al.2010, Møller and Sand-Jensen 2011a,b) andimpaired intra-plant translocation of organicsolutes and nutrients as a result of sediment andtissue anoxia (Sorrell 2004).Our objectives here were: (i) todetermine the temporal course and coupling of+O 2 , DIC, Fe and NH 4 and aerobic andanaerobic respiration processes with increasingorganic enrichment of Lobelia and Littorellasediments; (2) to use estimates of Fe 2+ and DICeffluxes as a proxy for the relative changes ofanaerobic respiration to total sedimentrespiration; and (iii) to evaluate C, N and Pretention of added organic matter to sediments.This study present original data for sediment30
Paper 1biogeochemistry, while O 2 penetration depth insediments (Møller and Sand-Jensen 2011b) isincluded to evaluate where and when anoxicFe 3+ reduction should take place and what therelationship is to Fe 3+ reduction rates.Materials and methodsSediment turfs in culture facilitySix intact sediment turfs inhabited by Lobeliadortmanna and six with Littorella uniflora werecollected from homogeneous plant stands inologotrophic, softwater Lake Värsjö, SWSweden as described before (Møller and Sand-Jensen 2011a,b). Turfs were 17 cm long, 15 cmwide and 12-14 cm deep to ensure intact rootsystems of about 20 Lobelia and 150 Littorellaplants with a mean biomass of 47 and 142 g dryweight (DW) m -2 , respectively. Turfs werebrought fully submerged to the laboratory forexperiments. One of the six turfs was used as acontrol, while gradually longer rod-shaped drypellets (5 mm in diameter, 1-15 mm long) ofcommercially available pasture grass (DLG,Copenhagen, Denmark) were added to the otherfive turfs forming a gradient of added organicmatter equivalent to 0 (control), 0.1, 0.2, 0.4, 0.8and 1.6% organic matter of DW. Organic pelletscontained (% of DW) 91% organic matter,46.9% organic carbon, 2.3% total nitrogen (TN)and 0.27% total phosphorus (TP). Pellets wereinserted with pincers at 4 cm sediment depthwith a fixed horizontal distance of 2 cm. Theturfs were incubated at 14-16 o C in 80 l aquariain a 12 : 12 h light : dark cycle exposed to aphotosynthetic active radiation (PAR) of 110µmol photons m -2 s -1 . The water was renewedevery second week to keep nutrients low andavoid algal growth and it was bubbled slowlywith atmospheric air to ensure mixing and airsaturation. Because large water volumes wereneeded we used filtered water from nearby LakeEsrom diluted 20 times with demineralizedwater to obtain a chemical compositionresembling that of Lake Värsjö (details inMøller & Sand-Jensen 2011a).Pore-water chemistry and fluxesPore-water samples for analyzing DIC, pH, Fe 2+and NH + 4 were extracted at intervals during theexperiment from 1 and 4 cm depth and from 1,2, 4, 6 and 8 cm depth at termination of the c.200-days long experiments. Water samples wereanalyzed simultaneously. Sediment sampleswere always taken at two (during theexperiment) or three (at termination)representative sites distributed evenly across theturf area. Pore-water was sampled by insertingthin capillary glass tubes (1 mm in diameter) inthe sediment, keeping the upper end above thewater. Capillary force and pressure differencefilled the capillary tube with water from thedesired sediment depth within a few minutes.Quantities of 50-100 µl of pore-water werewithdrawn with minimum air contact from thecapillary tube and immediately analyzed. DICwas analyzed by injecting a minute volume into3% HNO 3 in a bubble chamber purged with N 2gas carrying evolved CO 2 into an Infrared GasAnalyzer (ADC-225-MK3, Hoddesdon, UK;Vermaat and Sand-Jensen 1987). pH wasmeasured by a flat membrane electrode(LoT403-M8-S7/120, Mettler Toledo,Greifensee, Switzerland) positioned close to aglass surface allowing measurements on smalldroplets injected between the electrodemembrane and the glass surface. Free CO 2 andHCO - 3 were calculated from pH, ionic strengthand temperature (Rebsdorf 1972). Fe 2+ wasanalyzed spectrophotometrically by the+phenanthroline method (Eaton et al 1995). NH 4was measured spectrophotometrically bydiluting 100 µl pore-water with 900 µldemineralized water and adding phenol andhypochlorite reagents according to amicroversion of Solórzano (1996). After theexperiment duplicate cores were analyzed forwet and dry weight in depth strata of 0-1 cm, 1-3 cm, 3-5 cm and 5-8 cm. Dried homogenizedsamples were then analyzed for TN and organicC on a CHN Ea1108-elemental analyzer (CarloErba Instruments, Milan, Italy), TP by the31
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 32 and 33: Paper 1method of Andersen (1976) an
Page 35 and 36: Paper 1Table 3. Retention of added
Page 37 and 38: Paper 1recalcitrant organic pools a
Page 39: Paper 2High sensitivity of Lobelia
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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
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Paper 4Fig. 4. Root density (○) a
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Paper 4hours every night although l
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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
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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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