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Fernandez-Ugalde O.,Public University of Navarra | Virto I.,Public University of Navarra | Barre P.,CNRS ENS Geology Laboratory | Gartzia-Bengoetxea N.,Neiker Teknalia | And 3 more authors.
Geoderma | Year: 2011

Lithogenic and/or secondary carbonates are present in many semi-arid Mediterranean soils. Their role in aggregation dynamics is not completely known, and can determine the sensitivity of these soils to land-use changes and soil management. The objective of this work was to test the hierarchical model of aggregation, and to determine the relationship between aggregates formation and organic matter decomposition in calcareous soils of semi-arid Mediterranean regions, by comparing macroaggregation in the upper horizon of a calcareous soil (Typic Calcixerept) with a non-calcareous soil (Typic Haploxerept) and a decarbonated terra rosa (Calcic Haploxerept) following fresh straw addition under controlled laboratory conditions during 105. days. We hypothesized that aggregation would work according to the hierarchical model in the non-calcareous soil (NONCALC) and in the decarbonated terra rosa (DECALC), but not in the calcareous soil (CALC). The three soils had similar organic C concentrations and C/N ratio, but differed in their carbonates and clay minerals content: NONCALC had a similar proportion of clay-size silicates than CALC (~. 10%), and the DECALC had a similar proportion of total clay-sized particles than CALC (including carbonates, ~. 20%). An increase in the amount of macroaggregates (> 250 μm) and microaggregates (50-250μm) held within macroaggregates associated to an increase in the fungal activity when maize straw was added, a decline of macroaggregates with time associated to organic matter decomposition, a higher concentration of organic C and maize-derived C in microaggregates within macroaggregates than in free microaggregates, and a transfer of maize-derived C from macroaggregates to free microaggregates with time confirmed that aggregation worked according to the hierarchical model in NONCALC and DECALC. In CALC, however, the hierarchical model worked only partially. Macroaggregates formation was also stimulated by organic residues addition according to the model, but stable macroaggregates showed longer turnover rates and no relationship between straw decomposition and their decline was observed. From this, we postulate that carbonates can help stabilizing macroaggregates formed from fresh organic matter decomposition through abiotic processes, such as dissolution and re-precipitation. These results help to understand field data obtained in semi-arid calcareous agricultural soils, where it has been observed that aggregation is not always directly correlated to organic matter concentration, but that increases in soil organic matter can promote aggregation. They also indicate the need for considering the composition of the mineral fraction when modelling soil structure in semi-arid Mediterranean soils. © 2011 Elsevier B.V.


Martin I.,CSIC - Biological Research Center | Ruiz M.F.,CSIC - Biological Research Center | Sanchez L.,NEIKER TEKNALIA
BMC Developmental Biology | Year: 2011

Background: The gene transformer-2, which is involved in sex determination, has been studied in Drosophila, Musca, Ceratitis, Anastrepha and Lucilia. All these members of Diptera belong to the suborder Brachycera. In this work, it is reported the isolation and characterisation of genes transformer-2 of the dipterans Sciara ocellaris and Bradysia coprophila (formerly Sciara coprophila), which belong to the much less extensively analysed Sciaridae Family of the Suborder Nematocera, which is paraphyletic with respect to Suborder Brachycera. Results: The transformer-2 genes of the studied Sciara species were found to be transcribed in both sexes during development and adult life, in both the soma and germ lines. They produced a single primary transcript, which follows the same alternative splicing in both sexes, giving rise to different mRNAs isoforms. In S. ocellaris the most abundant mRNA isoform encoded a full-length protein of 251 amino acids, while that of B. coprophila encoded a protein of 246 amino acids. Both showed the features of the SR protein family. The less significant mRNA isoforms of both species encoded truncated, presumably non-functional Transformer-2 proteins. The comparison of the functional Sciara Transformer-2 proteins among themselves and those of other insects revealed the greatest degree of conservation in the RRM domain and linker region. In contrast, the RS1 and RS2 domains showed extensive variation with respect to their number of amino acids and their arginine-serine (RS) dipeptide content. The expression of S. ocellaris Transformer-2 protein in Drosophila XX pseudomales lacking the endogenous transformer-2 function caused their partial feminisation. Conclusions: The transformer-2 genes of both Sciaridae species encode a single protein in both sexes that shares the characteristics of the Transformer-2 proteins of other insects. These proteins showed conserved sex-determination function in Drosophila; i.e., they were able to form a complex with the endogenous Drosophila Transformer protein that controls the female-specific splicing of the Drosophila doublesex pre-mRNA. However, it appears that the complex formed between the Drosophila Transformer protein and the Sciara Transformer-2 protein is less effective at inducing the female-specific splicing of the endogenous Drosophila doublesex pre-mRNA than the DrosophilaTransformer-Transformer2 complex. This suggests the existence of species-specific co-evolution of the Transformer and Transformer-2 proteins. © 2011 Martín et al; licensee BioMed Central Ltd.

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