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

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Aim of thesisAim of thesisThe aim of this thesis was 1) to investigate response of isoetids to sediments undergoing organic enrichment2) to establish thresholds for sediment conditions where isoetid species can grow and 3) improve ourunderstanding of the complex interactions between isoetids and sediment under both oligotrophic andeutrophic conditions. Sediment conditions were investigated by measuring O 2 availability in sediments and byanalyzing pore-water for potential phytotoxins and reduced compounds to clarify main biogeochemicalprocesses. Plant response and interactions with sediments were investigated by measuring O 2 dynamics withmicro O 2 electrodes and analyzing plant content and morphology after exposure to hostile sediment conditions.18
Thesis summaryThesis summaryAddition of labile organic matter dramaticallychanged biogeochemistry of sedimentsinhabited by Lobelia dortmanna and Littorellauniflora and affected growth and survival of theplants. In paper 1 changes in sedimentbiogeochemistry, fluxes from sediments andretention of carbon and nutrients was followedin intact sediment turfs subjected to addition ofdifferent amounts of labile organic matter in thelaboratory. Sediment biogeochemistry wasmonitored by frequent extraction of pore-watersamples and O 2 availability in sediments wasmeasured by O 2 mini-electrodes.Organic enrichment caused decreased O 2availability since O 2 consumption fordegradation of added organic matter exceededthe oxygenation capacity of the plants and O 2flux from the water (Fig 1). The lack of O 2resulted in accumulation of NH +4 and use ofalternative electron acceptors causingaccumulation of Fe 2+ in the pore-water lastingFig. 1. Depth of O 2 penetration in Lobelia sediments as afunction of time after addition of different amounts oflabile organic matter (per sediment DW) (○=control;●=0.1%; □=0.2%; ■=0.4%; ◊= 0.8%; ♦=1.6%).Measurements were made 10–12 h into the 12 h lightperiod. Measurements could not extend deeper than 40mm into the sediment, when O 2 penetration in controlsediments was described as > 40 mm. Values are mean oftwo (0–170 d) and three (194 d) measurements ± SD.From Møller & Sand-Jensen 2011.Fig 2. Pore-water concentrations of Fe 2+ and NH 4 + insediments inhabited by Lobelia dortmanna (a & b) orLittorella uniflora(c & d) following enrichment withdifferent amounts of labile organic matter (% ofsediment dry weight; ○=control; ●=0.1%; □=0.2%;■=0.4%; ◊= 0.8%; ♦=1.6%).throughout the experiments and being morepronounced with increasing organic additions(Fig 2). Therefore, addition of even smallamounts of labile organic matter has longlasting effects on sediment biogeochemistry inisoetid sediments. In anoxic sediments oxidizediron becomes increasingly important fordecomposition processes; hence, iron reductionconstituted a larger fraction of DIC formation athigh organic additions than at lower additionsbut although sediments at high additionsremained anoxic for 200 days only 14% of the+iron pool was reduced. Accumulation of NH 4can be explained by nitrification and the lack ofshifts from oxic to anoxic conditions leading tolittle denitrification. In the anoxic sedimentsnitrogen released from degradation thereforeexceeds denitrification rates and loss to the-overlying water. Since isoetids prefers NO 3over NH + 4 as a source of N and that other fastergrowing plants and algae prefers NH + 4 this is apotential problem for preserving isoetidcommunities. Phosphorus (P) was opposite+NH 4 efficiently retained in the sediments19
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: IntroductionSand-Jensen K, Prahl C,
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
Page 42 and 43: NewPaper 2Phytologist Research 321w
Page 44 and 45: NewPaper 2Phytologist Research 323V
Page 46 and 47: NewPaper 2Phytologist Research 325T
Page 48 and 49: NewPaper 2Phytologist Research 327(
Page 50 and 51: NewPaper 2Phytologist Research 329o
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
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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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