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

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Paper 4Surveys on aquatic plants report fallingAMF colonization in plants growing insediments of high contents of organic matter andnutrients and low redox potential (Tanner &Calyton 1985; Wigand et al 1998; Beck-Nielsen& Madsen 2001). However, no experiment hasdirectly addressed the response of AMFcolonization of roots to O 2 depletion andchanges in sediment biogeochemistry followingorganic enrichment of aquatic sediments. Herewe tested this aspect by enriching aquaticsediments with labile organic matter andquantifying AMF root colonization, sedimenthyphal density and plant nutrition of the isoetidspecies Lobelia dortmanna and Littorellauniflora.Isoetids are small slow-growing plantsdominating the littoral zones of oligotrophicsoft-water lakes due to their unique adaptationsto take up sediment CO 2 for photosynthesisacross permeable root surfaces and ensure fastintra-plant diffusion through aerenchyma to theleaves (Sand-Jensen et al. 1982; Møller & Sand-Jensen 2008). These features also result in largeproportions of photosynthetic O 2 being releasedfrom the roots and generating an oxygenatedrhizosphere (Sand-Jensen et al. 1982; Pedersenet al. 1995; Møller & Sand-Jensen 2001b) whichis believed to be required by AMF (Le Tacon etal. 1983; Beck-Nielsen & Madsen 2001). Mostisoetids are reported with mycorrhiza(Søndergaard & Laegaard 1977; Wigand et al.1998; Beck-Nielsen & Madsen 2001) and couldbenefit from the symbiosis because they: (i)inhabit the most nutrient-poor aquaticenvironments of low P availability (Christensen& Andersen 1996; Christensen & Wigand 1998;Smolders et al. 2002), (ii) have relatively thickroots and lack roots hairs to provide highsediment contact (Søndergaard & Laegaard721977; Beck-Nielsen & Madsen 2001; Farmer1985), and (iii) have slow root growthincreasing the risk of strong nutrient depletionzones around roots (Sand-Jensen & Søndergaard1978). AMF associations increase both thesurface area and the sediment volume fornutrient uptake and hyphae extend beyond thedepletion zones surrounding the roots (Smith &Read 2008). We report here distribution andextension of the mycorrhizal mycelia in relationto plant density of isoetids in lakes for the firsttime.Most studies on AMF in aquatic plantshave focused on AMF colonization underdifferent natural conditions (Beck-Nielsen &Madsen 2001; Søndergaard & Laegaard 1977;Wigand et al. 1998), and on plant morphologiesassociated with high AMF colonization(Søndergaard & Laegaard 1977; Beck-Nielsen& Madsen 2001). AMF benefits aquatic plantsby increasing P uptake and P content of leaves(Tanner & Clayton 1985; Wigand & Stevenson1997) and plant biomass (Andersen & Andersen2006). Among different populations of Lobeliadortmanna plants with low tissue P content hadhigher AMF colonization (Wigand et al. 1998).Occurrence and extension of hyphae in aquaticsediments are largely unknown in contrast tonumerous terrestrial investigations (Smith &Read 2008). Only Beck-Nielsen and Madsen(2001) reported hyphal densities in aquaticsediments inhabited by Littorella uniflora, butthe lack of measurements of plant densityprevented conversion to densities of hyphae pervolume or surface area of sediments needed forcomparison with terrestrial communities. Herewe made a special effort to measure densities ofhyphae and roots for comparison with terrestrialcommunities.
Paper 4Organic enrichment of lake sedimentscan result from eutrophication and enhancedprimary production and sedimentation oforganic matter (Smolders et al. 2002). A smallorganic increment can stimulate isoetid growthdue to higher sediment concentrations of CO 2and nutrients (Sand-Jensen et al. 2005; Raun etal. 2010; Møller & Sand-Jensen 2011).However, high organic additions lead to anoxiain sediments and root systems during the nightand subsequently reduced nutrient translocationand photosynthesis (Sand-Jensen et al. 2005;Raun et al. 2010; Møller & Sand-Jensen 2011).Nutrient stress in isoetids is ascribed toinefficient transport of inorganic nutrients fromroots and photosynthates from leaves underanaerobic conditions causing root die-off(Sorrell 2004; Møller & Sand-Jensen 2011).Similarly AMF colonization has been found todecrease with increasing organic content ofsediments, but relations has not been evaluatedin regard to plant stress. Hence, lack of AMFassociations could contribute to lower plantnutrition.Two experiments were carried out toaddress the response of plants and AMF toorganic sediment enrichment. In the firstexperiment Littorella uniflora runners with noinitial AMF colonization were grown in naturalsediments without or with addition of organicmatter to determine root colonization rates andplant response. In the second experiment naturalsediment turfs with indigenous arbuscularmycorrhiza fungi inhabited with mono-speciesstands of Lobelia dortmanna or Littorellauniflora were subjected to organic enrichment todetermine the response of AMF in roots andsediments and changes in plant fitness.73Materials and methodsColonization of Littorella unifloraLittorella uniflora without AMF colonizationwas supplied by the aquatic plant manufactureAnubias (France). Prior to the experiment, sixLittorella plants were stained and tested formycorrhizal colonization and none were foundto be colonized (see below). For the experimentnatural sediment with a high density ofLittorella uniflora (ca. 15,000 plants m -2 ) fromoligotrophic, softwater Lake Värsjö, SWSweden was collected. Plants were removed andthe sediment was thoroughly mixed and dividedinto three portions. One portion was used as acontrol, while the other two portions receivedfeeding pellets made of pasture grass equivalentto 0.2% and 0.8% organic matter of sedimentdry weight (DW), respectively. Pellets contained91±1% (n=4) organic matter (47± 0.4% organicC) 2.3 ±0.15% total nitrogen (TN) and 0.27 ±0.01% total phosphorus (TP). Sediments werethen left for two weeks under waterlogging toallow new sediment conditions to establishbefore sediments were transferred to 5 Perspexcylinders (6.5 cm diameter and 15 cm deep) foreach treatment and one AMF-free Littorellauniflora of uniform mean size of 0.23-0.29 gwet weight in the treatments (One-way Anova, p< 0.05) was planted in each cylinder. Cylinderswith plants were placed in 15 separate 9 Laquaria for 135 days in the laboratory at 15 o C ina 12: 12 hour light: dark cycle with aphotosynthetic available radiation (PAR) of 110µmol photons m -2 s -1 . Plants were growncompletely submerged in experimental water ofsimilar composition as water from Lake Värsjö(see Møller & Sand-Jensen 2011a for details)and slowly bubbled with atmospheric air to
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Oxygen dynamics and plant-sedimenti
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PrefaceThe content of this thesis i
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AbstractAbstract● Isoetids occupy
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IntroductionIntroductionOligotrophi
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Introductionwater (Wigand et al. 19
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IntroductionSand-Jensen K, Prahl C,
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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 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 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 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
Page 87 and 88: [Plant Signaling & Behavior 3:10, 8
Page 89: Outstanding Lobelia dortmanna in ir
Page 93 and 94: Planterødders overlevelse ivanddæ
Page 95 and 96: Paper 6Figur 3. Aflejringer af lign
Page 97: Paper 6Vi har sat planterødders ve
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