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

Paper 4ResultsFig 1. O 2 -penetration depth in intact sediment turfsinhabited by Lobelia dortmanna (○) or Littorella uniflora(●) after about 200 days and in sediments from thecolonization experiments with Littorella uniflora (■) after135 days enrichment with labile organic matter. O 2 -penetration deeper that 40 mm could not be measured.Values are mean ± SD (n=3 for turf experiments, n=5 forcolonization experiments).Statistical analysis was performed in GraphPadprism 5 (software info). The colonizationexperiment was a gradient study with threelevels of 5 replicates appropriate for ANOVAanalysis. When data failed to meet testrequirements for variance-homogeneity, datawere square-root transformed prior to analysis.The experiment with intact sediment turfs was agradient study with six levels withoutreplication for Lobelia and Littorella turfs anddifferences were tested by linear regression orSpearmann´s correlation analysis. Differencesbetween Lobelia and Littorella from mixed insitupopulations were investigated by t-test.Probabilities above 0.95 were consideredsignificant. Data are presented as mean ± 1standard deviation (SD) of true replicates for thecolonization experiment and mixed in-situpopulations while SD of pseudo-replicates ispresented for the turf experiment when possible.Sediment biogeochemistryAddition of organic matter caused O 2 depletionand accumulation of DIC, Fe 2+ , NH 4 + and NH 4+in sediments throughout both experiments (Fig1, Fig 2ab & Table 1). O 2 penetrated to morethan 40 mm in control sediments but organicadditions significantly reduced O 2 penetrationdepths (Spearman´s r, p