Two new papers from the lab have been accepted during the last weeks. They are focused on different aspects of the N cycle in drylands and come from the Ph.D. work of Manu Delgado-Baquerizo. The first presents results from a study aiming to evaluate how different climatic, abiotic, plant- and nutrient- related factors correlate with N availability in semiarid Stipa tenacissima grasslands along a broad aridity gradient from Spain to Tunisia. The second article describes a cool experiment showing how biological soil crusts affect the response of N cycle processes to the addition of dew-like water inputs.
They will be published online during the next weeks, but here go the abstracts:
Delgado-Baquerizo, M., F. T. Maestre, A. Gallardo, J. L. Quero, V. Ochoa, M. García-Gómez, S. Soliveres, C. Escolar, P. García-Palacios, M. Berdugo, E. Valencia, B. Gozalo, Z. Noumi, M. Derak & M. Wallenstein. 2013. Aridity determines N availability in semiarid Mediterranean grasslands. PLoS ONE
While much is known about factors that control each component of the terrestrial nitrogen (N) cycle, it is less clear how these factors affect total N availability, the sum of organic and inorganic forms potentially available to microorganisms and plants. This is particularly true for N-poor ecosystems such as drylands, which are highly sensitive to climate change and desertification processes that can lead to the loss of soil nutrients such as N. We evaluated how different climatic, abiotic, plant- and nutrient- related factors correlate with N availability in semiarid Stipa tenacissima grasslands along a broad aridity gradient from Spain to Tunisia. Aridity had the strongest relationship with N availability, suggesting the importance of abiotic controls of the N cycle in drylands. Aridity appeared to modulate the effects of pH, plant cover and organic C (OC) on N availability. Our results suggest that N transformation rates, which are largely driven by variations in soil moisture, are not the direct drivers of N availability in the studied grasslands. Rather, the strong relationship between aridity and N availability could be driven by indirect effects that operate over long time scales (decades to millennia), including both biotic (e.g. plant cover) and abiotic (e.g. soil OC and pH). If these factors are in fact more important than short-term effects of precipitation on N transformation rates, then we might expect to observe a lagged decrease in N availability in response to increasing aridity. Nevertheless, our results suggest that the increase in the aridity predicted with ongoing climate change will reduce N availability in the Mediterranean basin, impacting plant nutrient uptake and net primary production in semiarid grasslands throughout this region.
Delgado-Baquerizo, M., F. T. Maestre, J. G. P. Rodríguez & A. Gallardo. 2013. Biological soil crusts promote N accumulation in response to dew events in dryland soils. Soil Biology and Biochemistry
Dew is an important source of water in drylands, particularly for biological soil crusts (BSCs), a soil community dominated by lichens, mosses and cyanobacteria that is prevalent in these environments and play important roles in nutrient cycling. While BSCs can retain and use water from dew, the effects of dew events on the cycling of nitrogen (N) and carbon (C) in BSC-dominated ecosystems are largely unknown. We conducted an experiment to evaluate the effects of BSCs and dew on N and C cycling; intact soil cores from either bare ground or BSC-dominated microsites were incubated during 14 days under control and artificial dew addition treatments. A positive increment in the amount of total available N and phenols was observed in response to dew events under BSCs. We also found an increase in the concentration of dissolved organic N, as well as in the pentoses:hexoses ratio, under BSCs, suggesting that dew promoted an increase in the decomposition of organic matter at this microsite. The increase in the amount of available N commonly observed under BSCs has been traditionally associated with the fixation of atmospheric N2 by BSC-forming cyanobacteria and cyanolichens. Our results provide a complementary explanation for such an increase: the stimulation of microbial activity of the microorganisms associated with BSCs by dew inputs. These effects of dew may have important implications for nutrient cycling in drylands, where dew events are common and BSCs cover large areas.