Functional diversification within bacterial lineages promotes wide functional overlapping between taxonomic groups in a Mediterranean forest soil

Curiel Yuste J., Fernandez-Gonzalez A.J., Fernandez-Lopez M., Ogaya R., Penuelas J., Lloret F. (2014) Functional diversification within bacterial lineages promotes wide functional overlapping between taxonomic groups in a Mediterranean forest soil. FEMS Microbiology Ecology. : 0-0.
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Doi: 10.1111/1574-6941.12373

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We investigated the relationship between taxonomy and functioning of soil bacterial communities in soils from a Mediterranean holm oak forest using a high-throughput DNA pyrosequencing technique. We used nonparametric tests (Mann-Whitney U-test) to evaluate the sensitivity of each single bacterial genus within the community to the fluctuations of plant physiological and environmental abiotic variables, as well as to fluctuations in soil microbial respiration. Within-lineage (phylum/class) functional similarities were evaluated by the distribution of the Mann-Whitney U-test standardized coefficients (z) obtained for all genera within a given lineage. We further defined different ecological niches and within-lineage degree of functional diversification based on multivariate analyses (principal component analyses, PCA). Our results indicate that strong within-lineage functional diversification causes extensive functional overlapping between lineages, which hinders the translation of taxonomic diversity into a meaningful functional classification of bacteria. Our results further suggest a widespread colonization of possible ecological niches as taxonomic diversity increases. While no strong functional differentiation could be drawn from the analyses at the phylum/class level, our results suggest a strong ecological niche differentiation of bacteria based mainly on the distinct response of Gram-positive and Gram-negative bacteria to fluctuations in soil moisture. We investigated the relation between taxonomy and functioning of soil bacterial communities in soils from a Mediterranean Holm-oak forest using a high throughput DNA pyrosequencing technique. © 2014 Federation of European Microbiological Societies.

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Strong functional stability of soil microbial communities under semiarid Mediterranean conditions and subjected to long-term shifts in baseline precipitation

Curiel Yuste J., Fernandez-Gonzalez A.J., Fernandez-Lopez M., Ogaya R., Penuelas J., Sardans J., Lloret F. (2014) Strong functional stability of soil microbial communities under semiarid Mediterranean conditions and subjected to long-term shifts in baseline precipitation. Soil Biology and Biochemistry. 69: 223-233.
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Doi: 10.1016/j.soilbio.2013.10.045

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We investigated the effect of soil microclimate on the structure and functioning of soil microbial communities in a Mediterranean Holm-oak forest subjected to 10 years of partial rain exclusion manipulations, simulating average drought conditions expected in Mediterranean areas for the following decades. We applied a high throughput DNA pyrosequencing technique coupled to parallel measurements of microbial respiration (RH) and temperature sensitivity of microbial respiration (Q10). Some consistent changes in the structure of bacterial communities suggest a slow process of community shifts parallel to the trend towards oligotrophy in response to long-term droughts. However, the structure of bacterial communities was mainly determined by short-term environmental fluctuations associated with sampling date (winter, spring and summer) rather than long-term (10 years) shifts in baseline precipitation. Moreover, long-term drought did not exert any chronic effect on the functioning of soil microbial communities (RH and Q10), emphasizing the functional stability of these communities to this long-term but mild shifts in water availability. We hypothesize that the particular conditions of the Mediterranean climate with strong seasonal shifts in both temperature and soil water availability but also characterized by very extreme environmental conditions during summer, was acting as a strong force in community assembling, selecting phenotypes adapted to the semiarid conditions characterizing Mediterranean ecosystems. Relations of climate with the phylogenetic structure and overall diversity of the communities as well as the distribution of the individual responses of different lineages (genera) to climate confirmed our hypotheses, evidencing communities dominated by thermotolerant and drought-tolerant phenotypes. © 2013 Elsevier Ltd.

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Two thresholds determine climatic control of forest fire size in Europe and northern Africa

Loepfe L., Rodrigo A., Lloret F. (2014) Two thresholds determine climatic control of forest fire size in Europe and northern Africa. Regional Environmental Change. 14: 1395-1404.
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Doi: 10.1007/s10113-013-0583-7

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Fire weather indices predict fire extent from meteorological conditions assuming a monotonic function; this approach is frequently used to predict future fire patterns under climate change scenarios using linear extrapolation. However, the relationship between weather and fire extent may potentially depend on the existence of fuel moisture content thresholds above which this relationship changes dramatically, challenging this statistical approach. Here, we combine the continuous and the threshold approaches to analyze satellite-detected fires in Europe during 2001-2010 in relation to meteorological conditions, showing that fire size response to decreasing fuel moisture content follows a ramp function, i.e., with two plateaus separated by a phase of monotonic increase. This study confirms that at continental and high-resolution temporal scales, large fires are very unlikely to occur under moist conditions, but it also reveals that fire size stops to be controlled by fuel moisture content above a given threshold of dryness. Thus, fuel moisture content control only applies when fire is not limited by other factors such as fuel load, as large fires were virtually absent during the considered period in dry regions with less than 500 mm of average annual precipitation, i.e., low-productive areas where fuel amount would be scarce and discontinuous. In regions with sufficient fuel, other factors such as fire suppression or fuel discontinuity can impede large fires even under very dry weather conditions. These findings are relevant under current climatic trends in which the fire season length, in terms of number of days with drought code values above the observed thresholds (break points), is increasing in many parts of the Mediterranean, while it is decreasing in eastern Europe and remains unchanged in central Europe. © 2014 Springer-Verlag Berlin Heidelberg.

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Plant community response to drought-induced canopy defoliation in a Mediterranean Quercus ilex forest

Saura-Mas S., Bonas A., Lloret F. (2014) Plant community response to drought-induced canopy defoliation in a Mediterranean Quercus ilex forest. European Journal of Forest Research. : 0-0.
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Doi: 10.1007/s10342-014-0848-9

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Climate change has increased drought-induced tree die-off in many parts of the world, and future climate models expect a higher recurrence of these perturbations. However, few studies have addressed plant community recovery after drought events, particularly in Mediterranean forests. This study evaluates the consequences of drought-induced die-off of the dominant holm-oak (Quercus ilex) trees on composition, structure and recruitment of the plant community, 6 years after a severe drought episode in Montserrat mountain (Catalonia, NE Spain). We evaluated the relationship of the vegetation response variables to two parameters related to the die-off consequences: canopy openness, as a measure of radiation arriving to ground, and canopy defoliation weighed by plant size, as a measure of drought impact on dominant neighbor plants. We also included in our analyses topographic situation to account for the proximity to ridge summits. Six years after the drought episode, the main findings were as follows: (1) There was a general loss of canopy cover, but Q. ilex still remained as dominant; nevertheless, the small tree Phyllirea latifolia and the shrub Buxus sempervirens tended to increase its relative abundance in the upper vegetation canopy; (2) overall, in open canopy conditions, species richness was higher mostly due to the presence of shade-intolerant herbaceous plants and early successional shrubs, such as Cistus albidus; (3) die-off did not result in increasing recruitment of the dominant species but preexisting Q. ilex sprouts were taller in sites with more open canopy; (4) there was a negative relationship between weighed defoliation and understory height, including Q. ilex sprouts, that can be attributed to large drought impact to both understory and canopy holm-oaks in some microhabitats, such as sites with abundant outcrops. This study highlights the ways in which Q. ilex Mediterranean forests regenerate after drought-induced events of canopy die-off. This regeneration involves changes in community structure and composition involving the increase in species, mostly small shrubs and herbaceous plants, which are able to grow in habitats created by canopy openness, likely becoming dominant in the landscape, as well as the arrival of non-dominant shrubs and short trees to the canopy. Potential shift in vegetation may be facilitated by the lack of increasing recruitment of Q. ilex, but this may be counterbalanced by the ability of holm-oak canopy to resprout and because pre-established saplings grown more with canopy openness. Thus, if tree canopies do not recover in a certain amount of time after the drought episode, then defoliation could lead to permanent changes in diversity and composition of the community.

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Adult root structure of mediterranean shrubs: Relationship with post-fire regenerative syndrome

Saura-Mas S., Lloret F. (2014) Adult root structure of mediterranean shrubs: Relationship with post-fire regenerative syndrome. Plant Biology. 16: 147-154.
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Doi: 10.1111/plb.12043

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Life-history attributes can impose differences on root system structures and properties related to nutrient and water uptake. Here, we assess whether plants with different post-fire regenerative strategies (resprouters, seeders and seeder-resprouters) differ in the topological and morphological properties of their root systems (external path, altitude, magnitude, topological index, specific root length, root length, root-to-shoot biomass ratio, length of the main axis of the root system and link length). To achieve these objectives, we sampled individuals from eight woody species in a shrubland located in the western Mediterranean Basin. We sampled the adult root systems using manual field excavation with the aid of an air compressor. The results indicate that resprouters have a higher root-to-shoot ratio, confirming their higher ability to store water, starch and nutrients and to invest in the belowground biomass. Moreover, this pattern would allow them to explore deeper parts of the soil layers. Seeder species would benefit from a higher specific root length, pointing to increased relative root growth and water uptake rates. This study confirms that seeders and resprouters may differ in nutrient and water uptake ability according to the characteristics of their root system. Species that can both resprout and establish seedlings after fire had different patterns of root system structure; in particular, root:shoot ratio was more similar to resprouters and specific root length was closer to seeders, supporting the distinct functional performance of this type of species. © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.

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