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

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Thesis summaryexperiment (15 o C), speeding up decompositionprocesses and respiration in both plants andsediment, hence, increased temperature isprobably an extra stress factor. The ability tomaintain oxic conditions in plant tissue canexplain the broader occurrence of Littorella inlakes undergoing eutrophication. Hence,Littorella only needs sufficient light to sustaincarbon production to cover aerobic respirationof the plant tissue. In eutrophic lakes Lobeliawill suffer from both decreased production andlow energy output under anaerobic respirationwhich could be the main reason for loss ofLobelia from many former growth sites.Although widespread anoxia occurred inLobelia at summer temperatures, O 2 diffusionacross leaves may be sufficient to satisfy therespiratory demand during winter when snowcovered ice prevents photosynthesis and lowtemperature slow down respiration.Paper 4 focus on occurrence of arbuscularmycorrhizal fungi associations in isoetids andsediments and the responses to organicenrichment. Mixed field populations were usedto compare AMF colonization of both specieswhile experiments with intact sediment turfs ofLobelia or Littorella with indigenous AMFassociations were used to investigate responseof AMF colonization and hyphal density insediment to organic enrichment. Furthermore,experiments with non-colonized Littorellaintroduced to sediments with AMF and differentorganic additions were performed to investigatecolonization under more eutrophic conditions.In nutrient poor sediments Littorellahave higher AMF colonization than Lobeliawhen growing in mixed populations undernatural conditions. This result is consistent withthe two times higher growth rate of LittorellaFig 5. Root length colonized by AM fungi (%) in rootsof Lobelia dortmanna (upper panel) and Littorellauniflora (lower panel) after experimentation withaddition of labile organic matter to sediments.Colonization frequencies of roots produced during theexperiment (○) and roots most likely established priorexperimentation (●) are presented. Values are means ±SD.than Lobelia. i.e., more nutrients are required tosustain higher growth. The investigation alsoshowed that hyphal density in the aquaticsediments were high and comparable withterrestrial systems, with hyphal surfacesexceeding the area of roots several times andscavenging a much larger sediment volume.Hyphal density was well correlated to colonizedroot length in the sediments.Addition of organic matter to sedimentsdecreased colonization of roots of plants alreadycolonized by AMF and was mainly caused bydecreased colonization of roots produced whilegrowing in more reduced sediments (Fig 5).Almost no colonization occurred in initiallynon-colonized Littorella at low additions whileAMF colonized roots in low-organic controlsediments. The stress of Lobelia and Littorellaobserved at high organic additions could not be22
Thesis summaryascribed to lack of AMF and AMF should beseen as an advantage under the extremelynutrient poor conditions that characterize thegrowth habitat of isoetids.Paper 5 is a short communication (addendum)addressing effects of organic enrichment ofsediments on O 2 dynamics and survival ofisoetid species. Radial O 2 loss (ROL) from rootsof isoetids was compared to other rootedmacrophytes and effects of Fe-plaques on rootsurfaces was discussed.Species that normally grow in reducedsediments form barriers to prevent O 2 loss fromroots whereas isoetids are believed to lack thisability. However, Fe-plaques form when Fe 2+from anoxic pore-water enters an oxygenatedroot rhizosphere where it precipitates as varioushighly insoluble crystalline oxidized ironcompounds. An investigation of ROL fromroots of Lobelia has shown that Fe-plaquesconstitute a barrier to ROL (Fig 6) resulting inhigher downward O 2 supply to root meristems.This could improve internal oxygenation ofisoetids when eutrophication leads to increasedO 2 demand of sediments. However, uponenrichment roots of isoetids are dramaticallyshortened and offer week anchorage.Furthermore, a recent investigation showed thatLobelia is depleted of O 2 when grown insediments added labile organic matter eventhough Fe-plaques occurred on roots (Paper 2).Whether Fe-plaques benefit isoetids growing inorganically enriched sediments is still to beshown.Fig 6. Radial oxygen loss measured with platinum sleeveelectrodes along the length of roots in an anoxic medium.The basal part of the roots was in contact withatmospheric air. Lobelia dortmanna had either none orthick iron coatings of the root surface (0.09 ± 0.05 and 30± 3 mmol Fe m-2 root surface respectively), whilePhragmites australis (from Armstrong & Armstrong2001) and the seagrass, Zostera marina (Unpublished)were without iron coatings.scientific language to communicate findings ofseveral investigations to a broader audience. O 2supply to root systems via rapid diffusionthrough aerenchyma or pressurized convectivegas-flow in stems and gas impermeable rootbarriers preventing excessive O 2 loss from rootsto sediment are discussed in regard to sedimentO 2 demand.Paper 6 is a Danish article addressingmorphological adaptations of aquatic andemergent plants to life in waterloggedsediments. The article is written in a popular23
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: Thesis summaryFig. 4. Chlorophyll c
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
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
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Paper 4Surveys on aquatic plants re
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Paper 4ensure mixing and air satura
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Paper 4ResultsFig 1. O 2 -penetrati
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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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