Recently accepted articles from the lab

Three new papers from the lab have been accepted during the last weeks. These include the first paper derived from the collaboration between our lab and that of Nicolas Gross in France, which we are enjoying a lot, a paper on plant-plant interactions from Santiago Soliveres´ Ph.D. work and an interesting article from Matt Bowker´s work on multifunctionality using biological soil crusts as a model system.

They will be published online early during the next weeks/months, but as a sneak preview here are the abstracts:

Bowker, M. A., F. T. Maestre & R. L. Mau. Diversity and patch-size distributions of biological soil crusts regulate dryland ecosystem multifunctionality. Ecosystems

Recent studies report that multifunctionality - the simultaneous provision of multiple ecosystem functions - in drylands depends on biodiversity.  Others report that specific size distributions of vegetation patches indicate overall ecosystem health and function. Using a biocrust (micro-vegetation of mosses, lichens and cyanobacteria) model system, and multivariate modeling, we determined the relative importance of biodiversity, patch-size distribution and total abundance to nutrient cycling and multifunctionality.  In most cases we explained at least 20%, and up to 65%, of the variation in ecosystem functions, and 42% of the variation in multifunctionality.  Species richness was the most important determinant of C cycling, constituting an uncommonly clear link between diversity and function in a non-experimental field setting. Regarding C cycling in gypsiferous soils, we found that patch size distributions with a greater frequency of small to medium patches, as opposed to very small patches, were more highly functional. Nitrogen cycling was largely a function of biocrust cover in two soil types, whereas in gypsiferous soils, more central-tending patch size distributions were less functional with regards to N cycling. All three community properties were about equally important to multifunctionality. Our results highlight the functional role of biotic attributes other than biodiversity, and indicate that high cover and diversity, together with a particular patch-size distribution, must be attained simultaneously to maximize multifunctionality. The results also agree with trends observed with other terrestrial and aquatic communities that more biodiversity is needed to sustain multifunctionality compared to single functions considered independently

Gross, N., L. Börger, M. S. Soriano, Y. Le Bagousse-Pinguet, J. L. Quero, M. García-Gómez, E. Valencia-Gómez & F. T. Maestre. Uncovering multi-scale effects of aridity and biotic interactions on the functional structure of Mediterranean shrublands. Journal of Ecology

1. Habitat filtering (HF, trait convergence) and niche differentiation (ND, trait divergence) are known to impact plant community structure. Both processes integrate individual responses to the abiotic environment and biotic interactions. Thus, it is difficult to clearly identify the underlying abiotic and biotic factors that ultimately impact community structure by looking at community-level patterns of trait divergence or convergence alone.

2. We used a functional trait-based and multi-scale approach to assess how biotic interactions and aridity determine the functional structure of semi-arid shrublands sampled along a large aridity gradient in Spain. At the regional scale, we investigated functional differences among species (axes of specialization) to identify important traits for community assembly. At the community scale, we evaluated the relative impact of HF and ND on community structure using a null model approach. Finally, at the plant neighbourhood scale, we evaluated the impact of biotic interactions on community structure by investigating the spatial patterns of trait aggregation.

3. The shrub species surveyed can be separated along four axes of specialization based on their aboveground architecture and leaf morphology. Our community-scale analysis suggested that the functional structure of semi-arid communities was clearly non-random, HF and ND acting independently on different traits to determine community structure along the aridity gradient. At the plant neighborhood scale, the spatial distribution of species was also clearly not random, suggesting that competition and facilitation impacted the observed changes in the functional diversity of shrubland communities along the aridity gradient.

4. Synthesis: Our results demonstrated that HF and ND acted simultaneously on independent traits to jointly determine community structure. Most importantly, our multi-scale approach suggested that competition and facilitation interplayed with aridity to determine this structure. Competition appeared to be constant along the aridity gradient, and explained the high functional diversity observed in semi-arid shrublands. Facilitation affected subordinate and rare species and thus may act to enhance the biodiversity of these ecosystems. Finally, the framework employed in our study allows moving forward from the examination of patterns to the development of mechanistic trait-based approaches to study plant community assembly.

Soliveres, S., F. T. Maestre, A. Escudero, P. García-Palacios, F. Valladares & A. P. Castillo-Monroy. Changes in rainfall amount and frequency do not affect the outcome of the interaction between the shrub Retama sphaerocarpa (L.) neighbour grasses in two contrasted semiarid communities. Journal of Arid Environments

We evaluated the net outcome of the interaction between the shrub Retama sphaerocarpa, our target plant, and different herbaceous neighbours in response to changes in the magnitude and frequency of rainfall events during three years. The experiment was conducted in natural and anthropogenic grasslands dominated by a perennial stress-tolerator and ruderal annual species, respectively. In spite of the neutral or positive effects of neighbours on water availability, neighbouring plants reduced the performance of Retama juveniles, suggesting competition for resources other than water. The negative effects of grasses on the photochemical efficiency of Retama juveniles decreased with higher water availabilities or heavier irrigation pulses, depending on the grassland studied; however, these effects did not extent to the survival and growth of Retama juveniles. Our findings show the prevalence of competitive interactions among the studied plants, regardless of the water availability and its temporal pattern. These results suggest that positive interactions may not prevail under harsher conditions when shade-intolerant species are involved. This study could be used to further refine our predictions of how plant-plant interactions will respond to changes in rainfall, either natural or increased by the ongoing climatic change, in ecosystems where grass-shrubs interactions are prevalent.