Two new papers from the lab have been accepted during the last weeks. They include a meta-analysis evaluating biogeographical patterns and drivers of bacterial diversity in terrestrial ecosystems at the global scale, led by Manuel Delgado-Baquerizo and resulting from a collaboration with the group of Prof. Brajesh Singh at the Hawkesbury Institute for the Environment on last year, and another paper from the climate change experiments that we are maintaining at the Aranjuez Experimental Station, led by Guadalupe León Sánchez and resulting from a collaboration with the group of José I. Querejeta at CEBAS-CSIC. They will be published online early during the next weeks/months, but here go the abstracts:
Delgado-Baquerizo, M., F. T. Maestre, P. B. Reich, P. Trivedi, Y. Osanai, Y. Liu, K. Hamonts, T. Jeffries & B. K. Singh. Carbon content and climate variability drive global soil bacterial diversity patterns. Ecological Monographs
Despite the vital role of microorganisms for ecosystem functioning and human welfare, our understanding of their global diversity and biogeographical patterns lags significantly behind that of plants and animals. We conducted a meta-analysis including ~600 soil samples from all continents to evaluate the biogeographical patterns and drivers of bacterial diversity in terrestrial ecosystems at the global scale. Similar to what has been found with plants and animals, the diversity of soil bacteria in the Southern Hemisphere decreased from the equator to Antarctica. However, soil bacteria showed similar levels of diversity across the Northern Hemisphere. The composition of bacterial communities followed dissimilar patterns between hemispheres, as the Southern and Northern Hemispheres were dominated by Actinobacteria and Proteobacteria/Acidobacteria, respectively. Moreover, we found a decrease in soil bacterial diversity with altitude. Climatic features (e.g. high diurnal temperature range and low temperature) were correlated with the lower diversity found at high elevations, but geographical gradients in soil total carbon and species turnover were important drivers of the observed latitudinal patterns. We thus found both parallels and differences in the biogeographical patterns of above- versus soil bacterial diversity. Our findings support previous studies that highlighted soil pH, spatial influence and organic matter as important drivers of bacterial diversity and composition. Furthermore, our results provide a novel integrative view of how climate and soil factors influence soil bacterial diversity at the global scale, which is critical to improve ecosystem and earth system simulation models and for formulating sustainable ecosystem management and conservation policies. Our findings contribute to fill important gaps in our understanding of the patterns and drivers of soil microbial diversity at the global scale, and can be of paramount utility for future studies to come
León-Sánchez, L., E. Nicolás, P. A. Nortes, F. T. Maestre & J. I. Querejeta. Photosynthesis and growth reduction under warming are driven by non-stomatal limitations in a Mediterranean semiarid shrub. Ecology and Evolution
Whereas warming enhances plant nutrient status and photosynthesis in most terrestrial ecosystems, dryland vegetation is vulnerable to the likely increases in evapotranspiration and reductions in soil moisture caused by elevated temperatures. Any warming-induced declines in plant primary production and cover in drylands would increase erosion, land degradation and desertification. We conducted a four-year manipulative experiment in a semiarid Mediterranean ecosystem to evaluate the impacts of a ~2ºC warming on the photosynthesis, transpiration, leaf nutrient status, chlorophyll content, isotopic composition, biomass growth and post-summer survival of the native shrub Helianthemum squamatum. We predicted that warmed plants would show reduced photosynthetic activity and growth, primarily due to the greater stomatal limitation imposed by faster and more severe soil drying under warming. On average, warming reduced net photosynthetic rates by 36% across the study period. Despite this strong response, warming did not affect stomatal conductance and transpiration. The reduction of peak photosynthetic rates with warming was more pronounced in a drought year than in years with near-average rainfall (75% and 25-40% reductions relative to controls, respectively), with no indications of photosynthetic acclimation to warming through time. Warmed plants had lower leaf N and P contents, chlorophyll a:b ratios, δ13C and sparser and smaller leaves than control plants. Warming reduced shoot dry mass production by 31%. However, warmed plants were able to cope with large reductions in net photosynthesis, leaf area and biomass production without changes in post-summer survival rates. Our findings highlight the key role of non-stomatal factors (biochemical and/or nutritional) in reducing net carbon assimilation rates and growth under warming, which has important implications for projections of plant carbon balance under the warmer and drier climatic scenario predicted for drylands worldwide. Moderate warming exerted negative effects on the leaf nutrient status, net photosynthetic rate and shoot biomass growth of H. squamatum, especially (but not only) during dry periods. Our findings indicate that projected climate warming could reduce net primary production by about one-third and potentially alter other key ecological processes (through changes in leaf N and P) such as plant-herbivore relationships, litter decomposition and nutrient cycling in semiarid gypsum shrublands dominated by H. squamatum.