Soil enzymes associated with carbon and nitrogen cycling in invaded and native secondary forests of northwestern Argentina

Aragon R., Sardans J., Penuelas J. (2014) Soil enzymes associated with carbon and nitrogen cycling in invaded and native secondary forests of northwestern Argentina. Plant and Soil. : 0-0.
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Doi: 10.1007/s11104-014-2192-8

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Background and aims Alien success has frequently been associated with changes in the concentrations of soil nutrients. We aim to investigate the effects of plant invasion on soil nutrients, potential enzyme activity and litter elemental composition and stoichiometry. Methods We compared stands of secondary forest invaded by Ligustrum lucidum and those dominated by natives, and performed litter chemical analyses on 3 native and 2 exotic tree species. Results Soils of invaded sites had 20 and 30 % increase in β-glucosidase and alkaline phosphatase activity, higher Olsen-phosphorus (P) and potassium (K) concentrations and lower nitrogen (N) concentration and N:P, N:K and ammonium:Olsen-P ratios. Invaded and non-invaded sites differed in their overall nutrient composition and enzyme activity. Natives and exotics differed in nine of the 16 litter elemental composition and stoichiometry variables analyzed. Conclusions The low N:P ratio in litter, the decrease in soil N in invaded stands and the low N concentration of exotics suggest that N is the limiting nutrient and that exotic success is related to higher N uptake and use efficiency. The higher investment in the acquisition of soil resources, higher nutrient uptake and use efficiency of limiting nutrients contribute to the success of exotics in this subtropical forest. © 2014 Springer International Publishing Switzerland.

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Global biodiversity, stoichiometry and ecosystem function responses to human-induced C-N-P imbalances

Carnicer J., Sardans J., Stefanescu C., Ubach A., Bartons M., Asensio D., Penuelas J. (2014) Global biodiversity, stoichiometry and ecosystem function responses to human-induced C-N-P imbalances. Journal of Plant Physiology. : 0-0.
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Doi: 10.1016/j.jplph.2014.07.022

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Global change analyses usually consider biodiversity as a global asset that needs to be preserved. Biodiversity is frequently analysed mainly as a response variable affected by diverse environmental drivers. However, recent studies highlight that gradients of biodiversity are associated with gradual changes in the distribution of key dominant functional groups characterized by distinctive traits and stoichiometry, which in turn often define the rates of ecosystem processes and nutrient cycling. Moreover, pervasive links have been reported between biodiversity, food web structure, ecosystem function and species stoichiometry. Here we review current global stoichiometric gradients and how future distributional shifts in key functional groups may in turn influence basic ecosystem functions (production, nutrient cycling, decomposition) and therefore could exert a feedback effect on stoichiometric gradients. The C-N-P stoichiometry of most primary producers (phytoplankton, algae, plants) has been linked to functional trait continua (i.e. to major axes of phenotypic variation observed in inter-specific analyses of multiple traits). In contrast, the C-N-P stoichiometry of higher-level consumers remains less precisely quantified in many taxonomic groups. We show that significant links are observed between trait continua across trophic levels. In spite of recent advances, the future reciprocal feedbacks between key functional groups, biodiversity and ecosystem functions remain largely uncertain. The reported evidence, however, highlights the key role of stoichiometric traits and suggests the need of a progressive shift towards an ecosystemic and stoichiometric perspective in global biodiversity analyses.

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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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Spatial variability and controls over biomass stocks, carbon fluxes, and resource-use efficiencies across forest ecosystems

Fernandez-Martinez M., Vicca S., Janssens I.A., Luyssaert S., Campioli M., Sardans J., Estiarte M., Penuelas J. (2014) Spatial variability and controls over biomass stocks, carbon fluxes, and resource-use efficiencies across forest ecosystems. Trees - Structure and Function. 28: 597-611.
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Doi: 10.1007/s00468-013-0975-9

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Key message: Stand age, water availability, and the length of the warm period are the most influencing controls of forest structure, functioning, and efficiency. We aimed to discern the distribution and controls of plant biomass, carbon fluxes, and resource-use efficiencies of forest ecosystems ranging from boreal to tropical forests. We analysed a global forest database containing estimates of stand biomass and carbon fluxes (400 and 111 sites, respectively) from which we calculated resource-use efficiencies (biomass production, carbon sequestration, light, and water-use efficiencies). We used the WorldClim climatic database and remote-sensing data derived from the Moderate Resolution Imaging Spectroradiometer to analyse climatic controls of ecosystem functioning. The influences of forest type, stand age, management, and nitrogen deposition were also explored. Tropical forests exhibited the largest gross carbon fluxes (photosynthesis and ecosystem respiration), but rather low net ecosystem production, which peaks in temperate forests. Stand age, water availability, and length of the warm period were the main factors controlling forest structure (biomass) and functionality (carbon fluxes and efficiencies). The interaction between temperature and precipitation was the main climatic driver of gross primary production and ecosystem respiration. The mean resource-use efficiency varied little among biomes. The spatial variability of biomass stocks and their distribution among ecosystem compartments were strongly correlated with the variability in carbon fluxes, and both were strongly controlled by climate (water availability, temperature) and stand characteristics (age, type of leaf). Gross primary production and ecosystem respiration were strongly correlated with mean annual temperature and precipitation only when precipitation and temperature were not limiting factors. Finally, our results suggest a global convergence in mean resource-use efficiencies. © 2013 Springer-Verlag Berlin Heidelberg.

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Nutrient availability as the key regulator of global forest carbon balance

Fernandez-Martinez M., Vicca S., Janssens I.A., Sardans J., Luyssaert S., Campioli M., Chapin Iii F.S., Ciais P., Malhi Y., Obersteiner M., Papale D., Piao S.L., Reichstein M., Roda F., Penuelas J. (2014) Nutrient availability as the key regulator of global forest carbon balance. Nature Climate Change. 4: 471-476.
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Doi: 10.1038/nclimate2177

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Forests strongly affect climate through the exchange of large amounts of atmospheric CO 2 (ref.). The main drivers of spatial variability in net ecosystem production (NEP) on a global scale are, however, poorly known. As increasing nutrient availability increases the production of biomass per unit of photosynthesis and reduces heterotrophic respiration in forests, we expected nutrients to determine carbon sequestration in forests. Our synthesis study of 92 forests in different climate zones revealed that nutrient availability indeed plays a crucial role in determining NEP and ecosystem carbon-use efficiency (CUEe; that is, the ratio of NEP to gross primary production (GPP)). Forests with high GPP exhibited high NEP only in nutrient-rich forests (CUEe = 33 ± 4%; mean ± s.e.m.). In nutrient-poor forests, a much larger proportion of GPP was released through ecosystem respiration, resulting in lower CUEe (6 ± 4%). Our finding that nutrient availability exerts a stronger control on NEP than on carbon input (GPP) conflicts with assumptions of nearly all global coupled carbon cycle-climate models, which assume that carbon inputs through photosynthesis drive biomass production and carbon sequestration. An improved global understanding of nutrient availability would therefore greatly improve carbon cycle modelling and should become a critical focus for future research. © 2014 Macmillan Publishers Limited.

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Opposite metabolic responses of shoots and roots to drought

Gargallo-Garriga A., Sardans J., Pérez-Trujillo M., Rivas-Ubach A., Oravec M., Vecerova K., Urban O., Jentsch A., Kreyling J., Beierkuhnlein C., Parella T., Peñuelas J. (2014) Opposite metabolic responses of shoots and roots to drought. Scientific Reports. 4: 0-0.
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Doi: 10.1038/srep06829

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Shoots and roots are autotrophic and heterotrophic organs of plants with different physiological functions. Do they have different metabolomes? Do their metabolisms respond differently to environmental changes such as drought? We used metabolomics and elemental analyses to answer these questions. First, we show that shoots and roots have different metabolomes and nutrient and elemental stoichiometries. Second, we show that the shoot metabolome is much more variable among species and seasons than is the root metabolome. Third, we show that the metabolic response of shoots to drought contrasts with that of roots; shoots decrease their growth metabolism (lower concentrations of sugars, amino acids, nucleosides, N, P, and K), and roots increase it in a mirrored response. Shoots are metabolically deactivated during drought to reduce the consumption of water and nutrients, whereas roots are metabolically activated to enhance the uptake of water and nutrients, together buffering the effects of drought, at least at the short term.

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A tethered-balloon PTRMS sampling approach for surveying of landscape-scale biogenic VOC fluxes

Greenberg J.P., Penuelas J., Guenther A., Seco R., Turnipseed A., Jiang X., Filella I., Estiarte M., Sardans J., Ogaya R., Llusia J., Rapparini F. (2014) A tethered-balloon PTRMS sampling approach for surveying of landscape-scale biogenic VOC fluxes. Atmospheric Measurement Techniques. 7: 2263-2271.
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Doi: 10.5194/amt-7-2263-2014

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Landscape-scale fluxes of biogenic gases were surveyed by deploying a 100 m Teflon tube attached to a tethered balloon as a sampling inlet for a fast-response proton-transfer-reaction mass spectrometer (PTRMS). Along with meteorological instruments deployed on the tethered balloon and a 3 m tripod and outputs from a regional weather model, these observations were used to estimate landscape-scale biogenic volatile organic compound fluxes with two micrometeorological techniques: mixed layer variance and surface layer gradients. This highly mobile sampling system was deployed at four field sites near Barcelona to estimate landscape-scale biogenic volatile organic compound (BVOC) emission factors in a relatively short period (3 weeks). The two micrometeorological techniques were compared with emissions predicted with a biogenic emission model using site-specific emission factors and land-cover characteristics for all four sites. The methods agreed within the uncertainty of the techniques in most cases, even though the locations had considerable heterogeneity in species distribution and complex terrain. Considering the wide range in reported BVOC emission factors for individual vegetation species (more than an order of magnitude), this temporally short and inexpensive flux estimation technique may be useful for constraining BVOC emission factors used as model inputs. © 2014 Author(s).

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A screening study of leaf terpene emissions of 43 rainforest species in Danum Valley Conservation Area (Borneo) and their relationships with chemical and morphological leaf traits

Llusia J., Sardans J., Niinemets U., Owen S.M., Penuelas J. (2014) A screening study of leaf terpene emissions of 43 rainforest species in Danum Valley Conservation Area (Borneo) and their relationships with chemical and morphological leaf traits. Plant Biosystems. 148: 307-317.
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Doi: 10.1080/11263504.2013.770803

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We have conducted a screening study of leaf terpene emissions for 43 rainforest woody species of Borneo. To the best of our knowledge, this study reports for first time the terpene emission capacity of 43 species belonging to 22 genera of rainforest woody plant species. We have used a general lineal model with phylogenetic control by the phylogenetic distance matrix when necessary. The proportion of the species that emitted terpenes in this set of Borneo woody species was 95% and the species average total terpene emissions of emitting species were 0.04-11.6 μg g-1 h-1, which is in the range of the reported emissions in similar screening studies conducted in other biomes. Altogether, 85 terpene compounds were detected, and 11 common monoterpenes and sesquiterpenes were identified and quantified. Only two of the terpenes, ocimene and γ-terpinene, of the 11 determined compounds showed a phylogenetic signal. No significant relationships were found between the terpene emissions and the physiological, chemical and morphological foliar traits and the data also showed a lock of constant applicability of the "excess carbon" hypothesis for this set of species. This evidence suggests multiple and diverse factors and conditions driving plant chemistry in the tropical forests. © 2013 © 2013 Società Botanica Italiana.

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Physiological and antioxidant responses of Quercus ilex to drought in two different seasons

Nogues I., Llusia J., Ogaya R., Munne-Bosch S., Sardans J., Penuelas J., Loreto F. (2014) Physiological and antioxidant responses of Quercus ilex to drought in two different seasons. Plant Biosystems. 148: 268-278.
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Doi: 10.1080/11263504.2013.768557

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Climate change projections forecast a warming and an associated change in the distribution and intensity of rainfalls. In the case of the Mediterranean area, this will be reflected in more frequent and severe drought periods in the future. Within a long-term (9 years) manipulation experiment, we aimed to study the effect of the soil drought projected for the coming decades (an average of 10% soil moisture reduction) onto photosynthetic rates and water relations, and onto the antioxidant and anti-stress defense capacity of Quercus ilex, a dominant species in Mediterranean forests, in two different seasons, spring and summer. Results showed that photosynthesis was limited by stomatal closure in summer. However, a decrease in photosynthesis as a consequence of drought was observed only during spring, possibly due to a low pigment concentration and to an insufficient antioxidant protection. In summer, the increased resistance to CO2 entry reduced photosynthesis in control and drought-treated leaves, though the higher pigment content and antioxidant levels in summer leaves prevented a further decrease in photosynthesis as a consequence of drought. Also total monoterpene emission rates were higher in summer than in spring, though they did not change with drought, as happened with photosynthetic pigments. On the other hand, the antioxidant defense system was induced by drought in both studied seasons, indicating an efficient activation of defense responses aiming at scavenging reactive oxygen species produced in Q. ilex leaves under drought. © 2013 © 2013 Società Botanica Italiana.

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Removal of floral microbiota reduces floral terpene emissions

Peñuelas J., Farré-Armengol G., Llusia J., Gargallo-Garriga A., Rico L., Sardans J., Terradas J., Filella I. (2014) Removal of floral microbiota reduces floral terpene emissions. Scientific Reports. 4: 0-0.
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Doi: 10.1038/srep06727

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The emission of floral terpenes plays a key role in pollination in many plant species. We hypothesized that the floral phyllospheric microbiota could significantly influence these floral terpene emissions because microorganisms also produce and emit terpenes. We tested this hypothesis by analyzing the effect of removing the microbiota from flowers. We fumigated Sambucus nigra L. plants, including their flowers, with a combination of three broad-spectrum antibiotics and measured the floral emissions and tissular concentrations in both antibiotic-fumigated and non-fumigated plants. Floral terpene emissions decreased by ca. two thirds after fumigation. The concentration of terpenes in floral tissues did not decrease, and floral respiration rates did not change, indicating an absence of damage to the floral tissues. The suppression of the phyllospheric microbial communities also changed the composition and proportion of terpenes in the volatile blend. One week after fumigation, the flowers were not emitting β-ocimene, linalool, epoxylinalool, and linalool oxide. These results show a key role of the floral phyllospheric microbiota in the quantity and quality of floral terpene emissions and therefore a possible key role in pollination.

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