The role of large benthic sulfur bacteria in biogeochemical cycles - a model approach.

<p>On the seabed of oxygen minimum zones (OMZ), embedded in organic-rich sediments, large sulfur bacteria (LSB) fulfil an important ecological role by detoxifying the overlying bottom waters. <em>Thiomargarita Namibiensis</em> and <em>Beggiatoa</em> spp. are chemoautotrophic microorganisms that reduce sulfur compounds to create biomass and link by doing so the carbon, sulfur, oxygen and nitrate cycle very efficiently. This particular ability make life in suboxic and hypoxic coastal waters feasible. Nevertheless, due to the complexity of sulfur oxidation and its various pathways the quantification of such activity is of great complexity. Hereby, we describe a model framework of LSB activity to implement intrinsic properties of the bacteria based on field observations and numerical modelling validations, linking the stoichiometry and energy conservation efficiency of LSB while counting for the reduced sulfur pools and its partitioning sub-products.</p>

Conservation efficiency and nutritive value of silages made from grass-red clover and multi-species swards compared with grass monocultures

Binary grass-clover and multi-species swards can increase herbage yields or facilitate reduced inputs of inorganic fertiliser nitrogen (N) compared with perennial ryegrass monocultures. However, the efficiency of the ensilage process and the nutritive value of silage produced from multi-species swards has not been documented. Replicate samples from grass-red clover binary mixture and multi-species mixture swards were ensiled in laboratory silos to assess the ensilability, fermentation characteristics, conservation losses and silage nutritive value compared with grass monocultures produced using inorganic N fertiliser. The results suggest that assessment of the ensilability and subsequent ensilage characteristics of binary and multi-species mixtures should be based on direct sampling from such mixtures rather than being predicted from values obtained from monocultures of constituent species. Under favourable ensiling conditions, unwilted binary mixtures and multi-species mixtures are satisfactorily preserved as silage, comparable to a perennial ryegrass monoculture receiving inorganic N fertiliser. However, when ensiled under more challenging crop conditions the mixtures exhibited a greater requirement for their preservation to be aided, compared with the perennial ryegrass monoculture. Despite the application of inorganic N reducing the legume content of multi-species mixture swards, it had relatively little effect on herbage ensilability or silage preservation. For all species treatments, silage nutritive values were primarily dependent on the pre-ensiling values, although herbage digestibility values declined during ensilage where the ensilage process was inefficient. The current study suggests that in order to be satisfactorily preserved as silage, binary grass-clover and multi-species swards have a greater requirement for an adequate rapid field wilt and/or effective preservative application compared with perennial ryegrass produced using inorganic fertiliser N.

Developing a Modified Umbrella Index for Conservation of Macroinvertebrate Diversity in Taizi River Basin, China

Conservation strategies for a reliable set of umbrella species should benefit many co-occurring species and will improve conservation efficiency. The umbrella index (UI) is increasingly applied for umbrella species selection in different ecosystems. We developed a modified river UI to select potential macroinvertebrate umbrella species with a combination of 69 sites in the Taizi River Basin of northeast China. Calculation of UI and comparison of biotic indices between sites of presence and absence of umbrella species were performed to make the final umbrella species list. The umbrella scheme, based on the proportion and composition of sites supporting the confirmed umbrella species, was introduced to illustrate the conservation effectiveness. A total of eight umbrella species were obtained and all of them were aquatic insects, such as caddisfly and mayfly larva. Umbrella schemes supporting the top umbrella species, hosted the majority of co-occurring species and only 7% of beneficiary species were missed by the umbrella schemes of 70% effort. The positive relationship between abundance of co-occurring species and umbrella species, validated the ability of umbrella species to confer protection and co-existence of co-occurring species, and thus indicated the effectiveness of umbrella species conservation. Co-occurring species were located close to umbrella species in ordinations, suggesting they respond to similar environmental variables characterized by high flow velocity, dissolved oxygen and pebble-covered substrate. On account of good performance of umbrella schemes in our study, UI with further improving methods should be promoted for selection of umbrella species and decision for optimizing of conservation sites in the future.