Recently accepted articles from the lab (May 2013)

Four new papers from the lab have been accepted during the last weeks. These include a paper from Manuel Delgado´s PhD, which presents an experiment on the joint effects of biological soil crusts and the addition of different nutrients on the microbial functional diversity and several variables from the N cycle, the first paper from Juan Gaitán´s PhD, on the use of remote sensing approaches to predict soil functional indices in the Patagonian steppe, a paper from José Luis Quero´s post-doctoral work on multifuntionality in Mediterranean grasslands and shrublands, and a very interesting global meta-analysis led by Pablo García-Palacios on the effects of soil fauna, climate and litter quality on litter decomposition. These articles will be published online early during the next weeks, but here go the abstracts:

García-Palacios, P., F. T. Maestre, J. Kattge & D. H. Wall. 2013. Climate and litter quality differently modulate the effects of soil fauna on litter decomposition across biomes. Ecology Letters

Climate and litter quality have been identified as major drivers of litter decomposition at large spatial scales. However, the role played by soil fauna remains largely unknown, despite its importance for litter fragmentation and microbial activity. We synthesized litterbag studies to quantify the effect sizes of soil fauna on litter decomposition rates at the global and biome scales, and to assess how climate, litter quality and soil fauna interact to determine such rates. Soil fauna consistently enhanced litter decomposition at both global and biome scales (average increment ~27%). However, climate and litter quality differently modulated the effects of soil fauna on decomposition rates between biomes, from climate-driven biomes to those where climate effects were mediated by changes in litter quality. Our results advocate for the inclusion of biome-specific soil fauna effects on litter decomposition as a mean to reduce the unexplained variation in large-scale decomposition models.

Quero, J. L., F. T. Maestre, V. Ochoa, M. García-Gómez & M. Delgado-Baquerizo. 2013. On the importance of shrub encroachment by sprouters, climate, species richness and anthropic factors for ecosystem multifunctionality in semi-arid Mediterranean ecosystems. Ecosystems

One of the most important changes taking place in drylands worldwide is the increase of the cover and dominance of shrubs in areas formerly devoid of them (shrub encroachment). A large body of research has evaluated the causes and consequences of shrub encroachment for both ecosystem structure and functioning. However, there are virtually no studies evaluating how shrub encroachment affects the ability of ecosystems to maintain multiple functions and services simultaneously (multifunctionality). We aimed to do so by gathering data from ten ecosystem functions linked to the maintenance of primary production and nutrient cycling and storage (organic C, activity of β-glucosidase, pentoses, hexoses, total N, total available N, amino acids, proteins, available inorganic P and phosphatase activity), and summarizing them in a multifunctionality index (M). We assessed how climate, species richness, anthropic factors (distance to the nearest town, sandy and asphalted road, and human population in the nearest town at several historical periods) and encroachment by sprouting shrubs impacted M along a regional (ca. 350 km) gradient in Mediterranean grasslands and shrublands dominated by a non-sprouting shrub. Values of M were higher in those grasslands and shrublands containing sprouting shrubs (43% and 62%, respectively). Encroachment was the main driver of changes in M along the regional gradient evaluated, followed by anthropic factors and species richness. Climate had little effects on M in comparison to the other factors studied. Overall, our results showed that M was higher at sites with higher sprouting shrub cover, longer distance to roads and higher perennial plant species richness. Our study is the first documenting that ecosystem multifunctionality in shrublands is enhanced by encroaching shrubs differing in size and leaf attributes. Our findings reinforce the idea that encroachment effects on ecosystem functioning cannot be generalized, and that are largely dependent on the traits of the encroaching shrub relative to those of the species being replaced. 

Gaitán, J. J., D. Bran, G. Oliva, F. T. Maestre, G. Ciari, V. Nakamatsu, J. Salomone, D. Ferrante, G. Buono, G. Humano, D. Celdrán & W. Opazo. 2013. Evaluating the performance of multiple remote sensing indices to predict the spatial variability of ecosystem structure and functioning in Patagonian steppes. Ecological Indicators

Assessing the spatial variability of ecosystem structure and functioning is an important step towards developing monitoring systems to detect changes in ecosystem attributes that could be linked to desertification processes in drylands. Methods based on ground-collected soil and plant indicators are being increasingly used for this aim, but they have limitations regarding the extent of the area that can be measured using them. Approaches based on remote sensing data can successfully assess large areas, but it is largely unknown how the different indices that can be derived from such data relate to groundbased indicators of ecosystem health. We tested whether we can predict ecosystem structure and functioning, as measured with a field methodology based on indicators of ecosystem functioning (the landscape function analysis, LFA), over a large area using spectral vegetation indices (VIs), and evaluated which VIs are the best predictors of these ecosystem  attributes. For doing this, we assessed the relationship between vegetation attributes (cover and species richness), LFA indices (stability, infiltration and nutrient cycling) and nine VIs obtained from satellite images of the MODIS sensor in 194 sites located accross the Patagonian steppe. We found that NDVI was the VI best predictor of ecosystem attributes. This VI showed a significant positive linear relationship with both vegetation basal cover (R² = 0.39) and plant species richness (R² = 0.31). NDVI was also significantly and linearly related to the infiltration and nutrient cycling indices (R² = 0.36 and 0.49, respectively), but the relationship with the stability index was weak (R² = 0.13). Our results indicate that VIs obtained from MODIS, and NDVI in particular, are a suitable tool for estimate the spatial variability of functional and structural ecosystem attributes in the Patagonian steppe at the regional scale.

Delgado-Baquerizo, M., L. Morillas, F. T. Maestre & A. Gallardo. 2013. Biological soil crusts control the N dynamics and microbial functional diversity of semi-arid soils in response to nutrient additions. Plant and Soil.

Aims Human activities are unbalancing nutrient cycles in natural ecosystems. However, our knowledge about how these changes will affect the soil microbial functional diversity and the nitrogen (N) cycle is still scarce in drylands, the biggest biome on Earth. Communities dominated by lichens, mosses and cyanobacteria (biocrusts) influence multiple processes from the N cycle such as N fixation and mineralization rates. We evaluated how biocrusts modulate the effects of different N, carbon (C) and phosphorus (P) additions on theN availability,, the dominance of different available N forms and the microbial functional diversity in dryland soils.

Methods Soil samples from bare ground (BG) and biocrust-dominated areas were gathered from the center of Spain and incubated during seven or 21 days under different combinations of N, C and P additions (N, C, P, N + C, N + P, P + C, and C + N + P).

Results The relative dominance of dissolved organic N (DON) and the microbial functional diversity were higher in biocrust than in BG microsites when C or P was added. Changes in the C to N ratio, more than N availability, seem to modulate N transformation processes in the soils studied. In general, biocrusts increased the resilience to N impacts (N, C+N, N+P, C+N+P) of the total available N, ammonium, nitrate and DON when C was present.

Conclusions Our results suggest that biocrusts may buffer the effects of changes in nutrients ratios on the microbial functional diversity and DON dominance in dryland soils. These organisms may thus have an important role increasing the resilience of the N cycle to unbalances in C, N and P derived from human activities.