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

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Paper 315*15 cm plots homogenously vegetated withboth Lobelia dortmanna and Littorella uniflorawere subjected to organic enrichments withorganic pellets in the sediments as described forthe laboratory experiment over a gradientincluding 0, 0.2 and 0.8 % added organic DW.During the experiment temperature andirradiance were measured every 5 minutes at 0.4m depth at the site by a combined Lux andtemperature logger (Onset ComputerCorporation, Bourne, Massachusetts, USA).Averages for the 90-day long experiment were:20.6 o C (range 12-34), 217 µmol m -2 s -1 (PAR)and a day length of 17.4 hours.At the end of the in situ experiment anintact sediment core was sampled from eachplot in a Perspex tube (5 cm diameter, 30 cmhigh) equipped with rubber stoppers as bottomand lid. The cores were brought back to thelaboratory and stored at 16 o C in a 12-h light: 12-h dark cycle until measurements of pore-waterand sediment characteristics within 1-3 days.All remaining plants from each plot were rinsedand brought to the laboratory in sealed plasticbags holding some water and plenty of air toensure water and O 2 supply. In the laboratory,shoot number of each species, wet weight (WW)and DW of aboveground biomass weredetermined. Leaf samples from each species andplot were then analysed for chlorophyll, TN, TPas described in Møller & Sand-Jensen (2011).Pore-water concentrations of DIC, NH + 3-4 , PO 4and Fe 2+ and sediment content of organicmatter, TN and TP were also determined aspreviously described (Møller & Sand-Jensen2011).O 2 and H 2 O exchange and across leaf surfacesLeaf O 2 exchange for a standard O 2 gradientwas measured as O 2 loss from leaf surfaces tohypoxic water surrounding them with the baseof leaf lacunae exposed to atmospheric air. Sixleaves were cut off and mounted in a PVCcylinder (volume 45.3 ml) through small holesin the lid leaving the most basal 1 mm of theleaf outside the cylinder and leaf surfacesexposed to water in the cylinder. Holes orcracks between leaves, lid and cylinder werecarefully sealed with silicone grease. An O 2electrode (Ox 500, Unisense, Århus, Denmark)connected to a computer for continuouslylogging was introduced to follow O 2concentration in the water of the cylinder. Amagnetic stirrer provided a slow, steady mixing.Measurements were performed undertemperature constant conditions at 5.0 and 15.0o C by submerging the PVC cylinder in water butleaving the exposed leaf bases with air contact.Prior to measurements, the cylinder was flushedwith anoxic water and left for 20 minutes toequilibrate before the linear rate of increase ofO 2 was measured for 10 minutes. Allmeasurements were preformed with a low O 2partial pressure of 1-2 kPa in the watersurrounding the leaves. Similar measurementswithout leaves were used to correct for physicalleakage of O 2 into the PVC cylinder not causedby transport over the leaves. Physical leakagewas very constant (1.45±0.03 and 0.43 ± 0.05nmol O 2 h -1 at 5 and 15 o C respectively). Afterexperiments, leaf dimensions were measured at45 x magnification with a dissectionmicroscope. Three measurements of leaf widthand thickness were made along the length ofevery leaf to calculate surface area. Lobelia hasapproximately rectangular leaves in crosssection while Littorella has cylindrical leaves.Fluxes of O 2 were normalized to leaf surfacesarea and time for a mean gradient of about 19kPa between lacunae at the leaf base and O 258
Paper 3Fig. 1. O 2 penetration depth in sediments inhabited by Lobelia dortmanna (left panel from Møller & Sand-Jensen 2011)and Littorella uniflora (right panel) in laboratory experiments at different time points after addition of different amountsof labile organic matter (0% (○), 0.1% (●), 0.2% (□), 0.4% (■), 0.8% (Δ) and 1.6% (▲) of sediment dry weight).Measurements were made 10-12 hours into the 12 hour light period when O 2 oxygen penetration depth was highest.Values are means ± SD, n = 2 (0-170 days) or n =3 (end of experiment).depleted water surrounding the outer leafsurfaces. The O 2 flux is assumed to be of similarmagnitude but in opposite direction for a reversegradient with air-saturated water around theleaves and anoxia at the base of leaf lacunae.Water loss across surfaces of newlydetached leaves to dry, still air was measured ina desiccator at 20 o C. Each leaf was placedupright with the cut base in a small drop ofsilicone grease in a weighing-boat andrepeatedly weighed on a 5-decimal precisionbalance over time. The initial, constant weightloss by evaporation was normalized to time andleaf surface area measured as described above.Ten replicate leaves of both species were tested.Statistical analysisGraphs and statistical analyses were performedin Graph Pad Prism 5. The laboratoryexperiment was a dose response with sixenrichment levels of organic matter to sedimentsappropriate for correlation or regressionanalysis. The in situ experiment was a blockdesign with three levels of organic addition intriplicate appropriate for ANOVA analysis.Differences in O 2 and H 2 O flux across leafsurfaces were examined by one-way ANOVAfor the influence of temperature and species.Data were square root transformed to meet testrequirements when needed. When transformeddata failed to meet test requirements nonparametrictests were used. Probabilities above95% were considered significant. Data arepresented as mean ± 1 Standard Deviation (SD).ResultsSediment biogeochemistryO 2 penetrated to more than 40-mm depth in unenrichedsediments of both species whenmeasured 10-12 hours into the light period inlaboratory experiment. Addition of labileorganic matter increased O 2 consumption in thesediments and significantly lowered O 2penetration depth (Spearmans r, p
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Oxygen dynamics and plant-sedimenti
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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 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: Paper 3Here, we perform a parallel
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
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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