Recently accepted articles from the lab

Two new papers from the lab have been accepted during the last weeks. They will be published online early during the next weeks/months, but here go the abstracts:

Ochoa-Hueso, C. R.,  F. T. Maestre, A. de los Ríos, S. Valea, M. R. Theobald, M. G. Vivanco, E. Manrique & M. A. Bowker. Nitrogen deposition gradients reduce N-fixation and carbon stocks in semiarid Mediterranean Spain. Environmental Pollution

Nitrogen (N) deposition is a threat to European Mediterranean ecosystems, but the evidence of real ecological impacts is still scarce. We combined data from a real N deposition gradient (4.3-7.3 kg N ha^-1 yr^-1) from semiarid portions of Spain with data from a field experiment in central Spain to evaluate N deposition effects on soil fertility, function and cyanobacteria community structure. Soil organic N did not increase along the extant deposition gradient, whereas C:N ratios decreased in most locations. Nitrogen fixation decreased along existing and experimental N deposition gradients, a result possibly related to compositional shifts in soil cyanobacteria community. Nitrogen mineralization rates were reduced by N fertilization, suggesting ecosystem N saturation. Soil organic C content and the activity of β-glucosidase decreased along the extant gradient. Our results suggest that semiarid soils in low-productivity sites are unable to store additional N inputs, and that are also unable to mitigate increasing C emissions to the atmosphere when experiencing increased N deposition.

Delgado-Baquerizo, M., A. Gallardo, M. Wallenstein & F. T. Maestre. 2013. Vascular plants mediate the effects of aridity and soil properties on ammonia-oxidizing bacteria and archaea. FEMS Microbiology Ecology

An integrated perspective of the most important factors driving the abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in natural ecosystems is lacking, especially in drylands.  We evaluated how different climatic, abiotic, and nutrient-related factors determine AOA and AOB abundance in bare and vegetated microsites from grasslands throughout the Mediterranean Basin. We found a strong negative relationship between the abundance of AOA  genes and soil fertility (availability of C, N and P). Aridity and other abiotic factors (pH, sand content and electrical conductivity) were more important than soil fertility in modulating the AOA:AOB ratio. AOB were more abundant under vegetated microsites, while AOA, highly resistant to stressful conditions, were more abundant in bare ground areas.  These results suggest that AOA may carry out nitrification in less fertile microsites, while AOB predominate under more fertile conditions. Our results indicate that the influence of aridity and pH on the relative dominance of AOA and AOB genes is ultimately determined by local-scale environmental changes promoted by perennial vegetation. Thus, in spatially heterogeneous ecosystems such as drylands, there is a mutual exclusion and niche division between these microorganisms, suggesting that they may be functionally complementary.