Alice Courtois E., Stahl C., Burban B., Van Den Berge J., Berveiller D., Bréchet L., Larned Soong J., Arriga N., Peñuelas J., August Janssens I. (2019) Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest. Biogeosciences. 16: 785-796.LinkDoi: 10.5194/bg-16-785-2019
Measuring in situ soil fluxes of carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO 2 flux chamber system (LI-8100A) with a CH 4 and N 2 O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2 min was sufficient for a reliable estimation of CO 2 and CH 4 fluxes (100% and 98.5% of fluxes were above minimum detectable flux - MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N 2 O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25 min was more appropriate for reliable estimation of most N 2 O fluxes (85.6% of measured fluxes are above MDF±0.002 nmolm -2 s -1 ). Our study highlights the importance of adjusted closure time for each gas. © Author(s) 2019.
Andivia E., Zuccarini P., Grau B., de Herralde F., Villar-Salvador P., Savé R. (2019) Rooting big and deep rapidly: the ecological roots of pine species distribution in southern Europe. Trees - Structure and Function. 33: 293-303.LinkDoi: 10.1007/s00468-018-1777-x
Key message: The rapid production of a large, deep root system during seedling establishment is critical for pines to colonize dry Mediterranean locations. Abstract: Root properties can influence plant drought resistance, and consequently plant species distribution. Root structure strongly varies across biomes partly as a result of phylogeny. However, whether the spatial distribution of phylogenetically close plant species is linked to differences in root properties remains unclear. We examined whether root properties mediate the strong correlation between summer drought intensity and the spatial segregation of pine species native to southern Europe. For this, we compared the seedling root growth and structure of five ecologically distinct pine species grown in 360 L rhizotrons for 19 months under typical hot and dry Mediterranean conditions. We studied the mountain and boreo-alpine pines Pinus sylvestris and Pinus nigra, and the Mediterranean pines Pinus pinaster, Pinus pinea, and Pinus halepensis. Mediterranean pines formed deep roots faster than mountain pines, their shoots and roots grew faster and had higher root growth, especially P. halepensis, at low air temperature. By the end of the study, Mediterranean pines had larger root systems than mountain pines. Neither distribution of root mass with depth nor root-to-shoot mass ratio varied significantly among species. Across species, minimal annual rainfall to which species are exposed in their range related negatively to root growth but positively to specific root length and the time needed for roots to reach a depth of 40 cm. This study highlights the importance of root growth as a driver of pine distribution in southern Europe and suggests that rapidly producing a large, deep root system may be a key attribute for pines to colonize dry Mediterranean locations. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Andrés P., Rosell-Melé A., Colomer-Ventura F., Denef K., Cotrufo M.F., Riba M., Alcañiz J.M. (2019) Belowground biota responses to maize biochar addition to the soil of a Mediterranean vineyard. Science of the Total Environment. 660: 1522-1532.LinkDoi: 10.1016/j.scitotenv.2019.01.101
Biochar is a high carbon material resulting from biomass pyrolysis that, when applied to croplands, can increase soil carbon and soil water retention. Both effects are of critical importance in semi-arid regions, where carbon decline and desertification are the main drivers of soil degradation. Since most environmental services provided by soil are mediated by belowground biota, effects of biochar on soil microbial and invertebrate communities must be evaluated under field conditions before its agricultural application can be recommended. We tested maize biochar for its mid-term effect on soil microbes and micro-arthropods of a Mediterranean vineyard. We applied biochar to three field plots with neutral sandy loam soils at a dose of 5 Mg ha−1. During two years, we monitored the abundance of functional groups of soil micro-arthropods and estimated the biomass of soil microbial groups. We also analyzed the δ13C value of microbial PLFA biomarkers to determine biochar-C utilization by each microbial group taking advantage of the δ13C natural abundance differences between the applied biochar and the soil. Biochar addition significantly reduced soil microbial biomass but did not alter the functional microbial diversity nor the abundance or biodiversity of soil micro-arthropods. The contribution of biochar-C to the diet of most microbial groups was very low through the monitoring period. However, two gram-negative bacterial groups increased their biochar-derived carbon uptake under extreme soil dryness, which suggests that biochar-C might help soil microbes to overcome the food shortage caused by drought. The decrease in microbial biomass observed in our experiment and the concomitant decrease of SOM mineralization could contribute to the carbon sequestration potential of Mediterranean soils after biochar addition. © 2019 Elsevier B.V.
Azpiazu C., Bosch J., Viñuela E., Medrzycki P., Teper D., Sgolastra F. (2019) Chronic oral exposure to field-realistic pesticide combinations via pollen and nectar: effects on feeding and thermal performance in a solitary bee. Scientific Reports. 9: 0-0.LinkDoi: 10.1038/s41598-019-50255-4
Pesticide use is one of the main causes of pollinator declines in agricultural ecosystems. Traditionally, most laboratory studies on bee ecotoxicology test acute exposure to single compounds. However, under field conditions, bees are often chronically exposed to a variety of chemicals, with potential synergistic effects. We studied the effects of field-realistic concentrations of three pesticides measured in pollen and nectar of commercial melon fields on the solitary bee Osmia bicornis L. We orally exposed females of this species throughout their life span to 8 treatments combining two neonicotinoid insecticides (acetamiprid, imidacloprid) and a triazole fungicide (myclobutanil) via pollen and sugar syrup. We measured pollen and syrup consumption, longevity, ovary maturation and thermogenesis. Pesticide intake was three orders of magnitude higher via syrup than pollen. At the tested concentrations, no synergistic effects emerged, and we found no effects on longevity and ovary maturation. However, all treatments containing imidacloprid resulted in suppressed syrup consumption and drastic decreases in thoracic temperature and bee activity. Our results have important implications for pesticide regulation. If we had measured only lethal effects we would have wrongly concluded that the pesticide combinations containing imidacloprid were safe to O. bicornis. The incorporation of tests specifically intended to detect sublethal effects in bee risk assessment schemes should be an urgent priority. In this way, the effects of pesticide exposure on the dynamics of bee populations in agroecosystems will be better assessed. © 2019, The Author(s).
Bagaria G., Rodà F., Pino J. (2019) Extinction and colonisation of habitat specialists drive plant species replacement along a Mediterranean grassland-forest succession. Journal of Vegetation Science. 30: 331-340.LinkDoi: 10.1111/jvs.12722
Questions: Land-use change causes shifts in species richness, which can be delayed. However, beta-diversity patterns and especially the relative role of species replacement and nestedness in these situations with time-lagged extinctions and colonisations remain unknown. We aim to (a) quantify beta-diversity change, species replacement and nestedness for vascular plants along a grassland–forest succession with time-lagged biodiversity change for more than 50 years; (b) check its consistency between all species, grassland specialists and forest specialists, and (c) identify the role of forest encroachment relative to other drivers. Study site: Prades Mountains, Catalonia (NE Iberian Peninsula). Methods: We sampled 18 sites representing a gradient in past and current grassland area and connectivity, and in forest encroachment intensity, to obtain plant composition of all species, grassland specialists and forest specialists. We quantified overall beta-diversity and its components at each species classification group along the forest encroachment gradient and other drivers. Then, we used general linear models to study (a) the change rate of beta diversity along the forest encroachment gradient and (b) the relative importance of the drivers in explaining beta diversity. Results: Following the forest encroachment gradient, we found an overall noticeable species replacement, while nestedness was the main component for habitat specialists. Landscape differences contributed to explaining most compositional differences (both nestedness and replacement), while soil characteristics and geographic distance had a more restricted contribution. Conclusions: Species replacement due to environmental sorting occurred over the succession, triggered by selective extinctions of grassland specialists and selective colonisations of forest specialists. Nonetheless, historical landscape characteristics, current landscape characteristics and geographic distance modulate plant extinctions and colonisations, suggesting biological inertia, mass effects and habitat isolation, respectively. Partitioning beta-diversity into nestedness and replacement components and exploring the extinction and colonisation patterns of habitat specialist groups might provide relevant insight into the drivers and processes of community shift after land-use change. © 2019 International Association for Vegetation Science
Baldocchi D., Penuelas J. (2019) The physics and ecology of mining carbon dioxide from the atmosphere by ecosystems. Global Change Biology. : 0-0.LinkDoi: 10.1111/gcb.14559
Reforesting and managing ecosystems have been proposed as ways to mitigate global warming and offset anthropogenic carbon emissions. The intent of our opinion piece is to provide a perspective on how well plants and ecosystems sequester carbon. The ability of individual plants and ecosystems to mine carbon dioxide from the atmosphere, as defined by rates and cumulative amounts, is limited by laws of physics and ecological principles. Consequently, the rates and amount of net carbon uptake are slow and low compared to the rates and amounts of carbon dioxide we release by fossil fuels combustion. Managing ecosystems to sequester carbon can also cause unintended consequences to arise. In this paper, we articulate a series of key take-home points. First, the potential amount of carbon an ecosystem can assimilate on an annual basis scales with absorbed sunlight, which varies with latitude, leaf area index and available water. Second, efforts to improve photosynthesis will come with the cost of more respiration. Third, the rates and amount of net carbon uptake are relatively slow and low, compared to the rates and amounts and rates of carbon dioxide we release by fossil fuels combustion. Fourth, huge amounts of land area for ecosystems will be needed to be an effective carbon sink to mitigate anthropogenic carbon emissions. Fifth, the effectiveness of using this land as a carbon sink will depend on its ability to remain as a permanent carbon sink. Sixth, converting land to forests or wetlands may have unintended costs that warm the local climate, such as changing albedo, increasing surface roughness or releasing other greenhouse gases. We based our analysis on 1,163 site-years of direct eddy covariance measurements of gross and net carbon fluxes from 155 sites across the globe. © 2018 John Wiley & Sons Ltd
Barba J., Poyatos R., Vargas R. (2019) Automated measurements of greenhouse gases fluxes from tree stems and soils: magnitudes, patterns and drivers. Scientific Reports. 9: 0-0.LinkDoi: 10.1038/s41598-019-39663-8
Tree stems exchange CO 2 , CH 4 and N 2 O with the atmosphere but the magnitudes, patterns and drivers of these greenhouse gas (GHG) fluxes remain poorly understood. Our understanding mainly comes from static-manual measurements, which provide limited information on the temporal variability and magnitude of these fluxes. We measured hourly CO 2 , CH 4 and N 2 O fluxes at two stem heights and adjacent soils within an upland temperate forest. We analyzed diurnal and seasonal variability of fluxes and biophysical drivers (i.e., temperature, soil moisture, sap flux). Tree stems were a net source of CO 2 (3.80 ± 0.18 µmol m −2 s −1 ; mean ± 95% CI) and CH 4 (0.37 ± 0.18 nmol m −2 s −1 ), but a sink for N 2 O (−0.016 ± 0.008 nmol m −2 s −1 ). Time series analysis showed diurnal temporal correlations between these gases with temperature or sap flux for certain days. CO 2 and CH 4 showed a clear seasonal pattern explained by temperature, soil water content and sap flux. Relationships between stem, soil fluxes and their drivers suggest that CH 4 for stem emissions could be partially produced belowground. High-frequency measurements demonstrate that: a) tree stems exchange GHGs with the atmosphere at multiple time scales; and b) are needed to better estimate fluxes magnitudes and understand underlying mechanisms of GHG stem emissions. © 2019, The Author(s).
Barbeta A., Camarero J.J., Sangüesa-Barreda G., Muffler L., Peñuelas J. (2019) Contrasting effects of fog frequency on the radial growth of two tree species in a Mediterranean-temperate ecotone. Agricultural and Forest Meteorology. 264: 297-308.LinkDoi: 10.1016/j.agrformet.2018.10.020
The performance and persistence of rear-edge tree populations are relevant issues for conserving biodiversity because these stands harbor high intraspecific biodiversity and play a key role during periods of climate change. The occurrence of these populations is associated with the influence of heterogeneous topography, creating suitable refugia with regionally rare environmental conditions. Climate is changing at a global-scale, but little is known about the long-term impact on local climatic singularities and the associated taxa. We analyzed tree-ring growth chronologies of the two species (Fagus sylvatica and Quercus ilex) forming the evergreen-deciduous forest ecotone, constitutive of the rear-edge of F. sylvatica distribution. The study area is a coastal range with frequent fog immersion, which has been hypothesized to favor the persistence of F. sylvatica in Mediterranean peninsulas. We analyzed the long-term effect of fog on tree growth along a topographical gradient and the sensitivity of growth to rainfall and temperature. The annual number of foggy days has decreased by 62% over the last four decades, concomitant with increasing temperatures. Fog frequency was a relevant factor determining tree growth; fog during summer had positive effects on F. sylvatica growth mainly through a temperature buffering effect. The positive effect of fog on the growth of Q. ilex, however, was likely caused by a collinearity with rainfall. Q. ilex growth was less sensitive to climate than F. sylvatica, but growth of both species was enhanced by a positive early-summer water balance. Our results indicate that a decrease in fog frequency and an increase in temperature may generally benefit Q. ilex in this forest ecotone. Although future changes in rainfall and temperature matter most for the fate of rear-edge tree populations, local climatic singularities such as fog should also be considered. Those can have complementary effects that can swing the balance in ecotones and rear-edge tree populations such as those studied here. © 2018 Elsevier B.V.
Bartumeus F., Costa G.B., Eritja R., Kelly A.H., Finda M., Lezaun J., Okumu F., Quinlan M.M., Thizy D.C., Toé L.P., Vaughan M. (2019) Sustainable innovation in vector control requires strong partnerships with communities. PLoS neglected tropical diseases. 13: 0-0.LinkDoi: 10.1371/journal.pntd.0007204
[No abstract available]
Batllori E., De Cáceres M., Brotons L., Ackerly D.D., Moritz M.A., Lloret F. (2019) Compound fire-drought regimes promote ecosystem transitions in Mediterranean ecosystems. Journal of Ecology. 107: 1187-1198.LinkDoi: 10.1111/1365-2745.13115
Understanding ecosystem responses to compound disturbance regimes and the influence of specific sequences of events in determining ecosystem shifts remains a challenge. We use a modelling framework for Mediterranean-type ecosystems to assess the effects of fire–drought interactions on long-term vegetation dynamics and to identify disturbance-driven changes in trait composition (tree seeder vs. tree resprouter prevalence) and ecosystem state (forest vs. non-forest). Changes in tree seeder and the tree resprouter dominance show nonlinear, threshold-type trends over gradients of increasing compound disturbance frequency. Vegetation composition thresholds mostly occur in a narrow range of the compound fire–drought disturbance space. Additionally, trait compositional switches and the likelihood of sudden changes in ecosystem state are promoted by fire-drought interactions. Distinct sequences of disturbance events cause vegetation transitions, disrupting ecosystem resilience, even under moderate recurrence of individual disturbances. An extreme drought year followed by one or two large fire events promotes shifts from resprouter- to seeder dominance. Contrastingly, a large crown fire followed by an extreme drought promotes changes from seeder to resprouter dominance. This disturbance sequence is also a mechanism strong enough to trigger sudden shifts in ecosystem state (from forest to non-forest). Synthesis. Thresholds of change in vegetation composition occur over a narrow range of the modelled gradients of compound fire-drought recurrence, and the loss of ecosystem resilience is contingent on particular sequences of disturbance events. Overall, our findings highlight that disturbance interactions define the relative location of tipping points in ecosystem state, and that effects and feedbacks of compound disturbance regimes increase the long-term likelihood of sudden ecosystem shifts and, therefore, uncertainty in predicting vegetation state. © 2018 The Authors. Journal of Ecology © 2018 British Ecological Society
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