Mineralization, pore water chemistry and phosphorus release from peaty sediments in the eutrophic Loosdrecht lakes, The Netherlands

SUMMARY. 1. Pore water chemistry in peaty sediment was monitored for a year at two representative locations of the eutrophic shallow Loosdrecht lakes. The Netherlands. Phosphorus fluxes over the sediment-water interface were calculated using measured concentration gradients in the pore water and compared to fluxes measured under laboratory conditions. Results were analysed with Redundancy Analysis to detect patterns of variation in pore water chemistry and in measured and calculated fluxes, that could be ascribed to environmental variables.
2. It was demonstrated that phosphorus fluxes measured in long-term laboratory incubations were not correlated to any of the pore water characteristics.
3. Initial phosphorus fluxes measured in sediment columns, which varied between −7.7 and 1330 μmol m⁻²: day⁻¹, were correlated significantly to the calculated phosphorus flux over the sediment-water interface.
4. The high correlation between calculated fluxes of ammonia, phosphorus and methane and measured initial flux of phosphorus, conclusively pointed to mineralization of organic matter as the driving force for phosphorus release from the sediment.
5. Redundancy Analysis demonstrated that the rates of mineralization and phosphorus release were only weakly related to temperature. They appeared to be especially stimulated by the autumnal decrease in temperature which was probably related to an extra input of organic matter.     

The alternative oxidase from Euglena gracilis

We still have a rudimentary understanding about the mechanism by which plant roots may stimulate soil microbial interactions. A biochemical model involving plant-derived biochemical fractions, such as exudates, has been used to explain this "rhizosphere effect" on bacteria. However, the variable response of other soil microbial groups, such as protozoa, to the rhizosphere suggests that other factors could be involved in shaping their communities. Thus, two experiments were designed to (a) obtain a better understanding of the mechanism by which ciliate species richness and abundance differ among plant species and (b) to determine whether this mechanism is maintained via stimulatory and/or inhibiting factors associated with particular plant species. Bacterial and chemical slurries were reciprocally exchanged between two plant species known to differ in terms of ciliate species richness and abundance (i.e., Canella winterana and plantation Tectona grandis ). The ANOVA showed that the bacteria plus nutrients, and the nutrients-only treatment have no significant effect on the overall ciliate species richness and abundance when compared to the control treatment. However, the use of only colpodean species to increase the taxonomic resolution of treatment effects showed that bacterial slurries have a significant effect on colpodean ciliate species richness. These results suggest that for particular rhizosphere ciliates, biological properties, such as bacterial diversity or abundance, may have a strong influence on their diversity and possibly abundance. These results are consistent with a model of soil bacteria-mediated mutualism between plants and protozoa.     

Metazoan Relationships on the Basis of 18S rRNA Sequences: A Few Years Later...

SYNOPSIS. The 18S rRNA database is continuously growing andnew tree construction methods are being developed. The presentstudy aims at assessing what effect the addition of recentlydetermined animal 18S rRNA sequences and the use of a recentlydeveloped distance matrix calculation method have on the resultsof some previously published case studies on metazoan phytogeny.When re-assessing three case studies, part of their conclusionswas confirmed on the basis of the present 18S rRNA data set:1) the monophyly of Arthropoda; 2) the monophyly of the Vestimentifera-Pogonophoraand their protostome character; 3) the doubt about the monophyleticorigin of Echiura-Sipuncula and 4) the coelomate characterofNemertea. Yet, it is also demonstrated that some of the previousresults are no longer warranted when updating the analyses:1) the monophyly of both the Annelida and the Eutrochozoa; 2)the sister-group relationship of Echiura to Vestimentifera-Pogonophoraand 3) the polyphyly of the Mesozoa and their close relationshipto Myxozoa and Nematodes. In addition, some new very preliminaryevidence is provided for: 1) a common ancestry of Platyhelminthesand Mesozoa and the monophyly of the latter group and 2) themonophyly of Clitellata, Hirudinida and Oligochaeta. Finally,doubt is casted on the monophyly of the Polychaeta and the polychaeteorders Spionida, Phyllodocida, and Sabellidae. Of course, thesehypotheses also need further testing.