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BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Question Biological soil crust (BSC) communities can be used in the identification and monitoring of degradation. A key question is how landscape‐scale livestock disturbance and other local‐scale factors influence BSC communities. We hypothesize that at the landscape scale, increased grazing pressure would lead to decreasing cover of BSC, but at the local scale biotic interactions between BSC and vascular plants would modulate the influence of grazing on BSC. Methods Spatially explicit sampling of vegetation composition and cover was conducted using point‐sampling methods in digital images along two disturbance gradients in the central Monte Desert in Argentina. Results The grazing gradient is the major determinant of changes in the structure of plant communities at the landscape scale. Approximately 1500 to 2000 m from a watering point, there is a threshold in vegetation structure associated with a nonlinear trend of the BSC, herb, grass and shrub cover. Bivariate spatial patterns show attraction between BSC and shrubs in the vicinity of settlements, and repulsion between BSC and both grasses and litter in less disturbed sites. Conclusion Grazing affects BSC directly through trampling and indirectly by altering vascular plant communities that interact with the BSC communities. Both these effects vary according to the spatial scale being considered. The results evidence that understanding of livestock impact in structuring arid ecosystems requires an integrated analysis of BSC and vascular plant communities at different spatial scales.

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Desert evergreen shrubs, which are adapted to low-fertility ecosystems, generally exhibit limited responses to increased nutrient availability and tend to absorb and store nutrients rather than synthesize new tissues. The objective of this work was to analyze the effect of nitrogen fertilization combined with soil water availability on growth, nitrogen content, and nitrogen use efficiency on four shrubs (Atriplex lampa, Capparis atamisquea, Larrea cuneifolia, and Senecio subulatus) from the Monte Desert. In a 120-day glasshouse experiment in Mendoza, Argentina, we compared the effects of three levels of nitrogen fertilization combined with two levels of water availability on seedling biomass, nitrogen content, water potential, and nitrogen use efficiency. Fertilization induced a higher biomass on A. lampa under high water availability and on C. atamisquea regardless of water level. Shoot:root ratios of these two species were lower under water stress without fertilization. On the other hand, L. cuneifolia presented lower root biomass and lower water potential with N fertilization. All species when fertilized exhibited higher nitrogen content and lower nitrogen use efficiency. Also, A. lampa and L. cuneifolia presented higher nitrogen content under water stress conditions. In conclusion, some desert shrubs (A. lampa and C. atamisquea) were able to take advantage of increased nitrogen availability producing more biomass. Understanding seedlings response to nitrogen and water availability on arid lands is critically important to develop adequate revegetation techniques of degraded areas.Communicated by Katinka Ruthrof.