Joining empirical and modelling approaches to estimate dry deposition of nitrogen in Mediterranean forests

García-Gómez H., Izquieta-Rojano S., Aguillaume L., González-Fernández I., Valiño F., Elustondo D., Santamaría J.M., Àvila A., Bytnerowicz A., Bermejo V., Alonso R. (2018) Joining empirical and modelling approaches to estimate dry deposition of nitrogen in Mediterranean forests. Environmental Pollution. 243: 427-436.
Link
Doi: 10.1016/j.envpol.2018.09.015

Abstract:

In Mediterranean areas, dry deposition is a major component of the total atmospheric N input to natural habitats, particularly to forest ecosystems. An innovative approach, combining the empirical inferential method (EIM) for surface deposition of NO3 − and NH4 + with stomatal uptake of NH3, HNO3 and NO2 derived from the DO3SE (Deposition of Ozone and Stomatal Exchange) model, was used to estimate total dry deposition of inorganic N air pollutants in four holm oak forests under Mediterranean conditions in Spain. The estimated total deposition varied among the sites and matched the geographical patterns previously found in model estimates: higher deposition was determined at the northern site (28.9 kg N ha−1 year−1) and at the northeastern sites (17.8 and 12.5 kg N ha−1 year−1) than at the central-Spain site (9.4 kg N ha−1 year−1). On average, the estimated dry deposition of atmospheric N represented 77% ± 2% of the total deposition of N, of which surface deposition of gaseous and particulate atmospheric N averaged 10.0 ± 2.9 kg N ha−1 year−1 for the four sites (58% of the total deposition), and stomatal deposition of N gases averaged 3.3 ± 0.8 kg N ha−1 year−1 (19% of the total deposition). Deposition of atmospheric inorganic N was dominated by the surface deposition of oxidized N in all the forests (means of 54% and 42% of the dry and total deposition, respectively). The relative contribution of NO2 to dry deposition averaged from 19% in the peri-urban forests to 11% in the most natural site. During the monitoring period, the empirical critical loads provisionally proposed for ecosystem protection (10–20 kg N ha−1 year−1) was exceeded in three of the four studied forests. Dry deposition of atmospheric N in four forests of Quercus ilex represented 77% of the total deposition of N and it was dominated by the surface deposition of oxidized N. © 2018 Elsevier Ltd

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Climate change-driven extinctions of tree species affect forest functioning more than random extinctions

García-Valdés R., Bugmann H., Morin X. (2018) Climate change-driven extinctions of tree species affect forest functioning more than random extinctions. Diversity and Distributions. : 0-0.
Link
Doi: 10.1111/ddi.12744

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Aim: Climate change affects forest functioning not only through direct physiological effects such as modifying photosynthesis and growing season lengths, but also through indirect effects on community composition related to species extinctions and colonizations. Such indirect effects remain poorly explored in comparison with the direct ones. Biodiversity-ecosystem functioning (BEF) studies commonly examine the effects of species loss by eliminating species randomly. However, species extinctions caused by climate change will depend on the species' vulnerability to the new environmental conditions, thus occurring in a specific, non-random order. Here, we evaluated whether successive tree species extinctions, according to their vulnerability to climate change, impact forest functions differently than random species losses. Location: Eleven temperate forests across a gradient of climatic conditions in central Europe. Methods: We simulated tree community dynamics with a forest succession model to study the impact of species loss on the communities' aboveground biomass, productivity and temporal stability. Tree species were removed from the local pool (1) randomly, and according to (2) their inability to be recruited under a warmer climate or (3) their increased mortality under drier conditions. Results: Results showed that non-random species loss (i.e., based on their vulnerability to warmer or drier conditions) changed forest functioning at a different rate, and sometimes direction, than random species loss. Furthermore, directed extinctions, unlike random, triggered tipping points along the species loss process where forest functions were strongly impacted. These tipping points occurred after fewer extinctions in forests located in the coldest areas, where ecosystem functioning relies on fewer species. Main conclusions: We showed that the extinction of species in a deterministic and mechanistically motivated order, in this case the species vulnerability to climate change, strengthens the selection effect of diversity on ecosystem functioning. BEF studies exploring the impact of species loss on ecosystem functioning using random extinctions thus possibly underestimate the potential effect of biodiversity loss when driven by a directional force, such as climate change. © 2018 John Wiley & Sons Ltd.

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Root exudate metabolomes change under drought and show limited capacity for recovery

Gargallo-Garriga A., Preece C., Sardans J., Oravec M., Urban O., Peñuelas J. (2018) Root exudate metabolomes change under drought and show limited capacity for recovery. Scientific Reports. 8: 0-0.
Link
Doi: 10.1038/s41598-018-30150-0

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Root exudates comprise a large variety of compounds released by plants into the rhizosphere, including low-molecular-weight primary metabolites (particularly saccharides, amino acids and organic acids) and secondary metabolites (phenolics, flavonoids and terpenoids). Changes in exudate composition could have impacts on the plant itself, on other plants, on soil properties (e.g. amount of soil organic matter), and on soil organisms. The effects of drought on the composition of root exudates, however, have been rarely studied. We used an ecometabolomics approach to identify the compounds in the exudates of Quercus ilex (holm oak) under an experimental drought gradient and subsequent recovery. Increasing drought stress strongly affected the composition of the exudate metabolome. Plant exudates under drought consisted mainly of secondary metabolites (71% of total metabolites) associated with plant responses to drought stress, whereas the metabolite composition under recovery shifted towards a dominance of primary metabolites (81% of total metabolites). These results strongly suggested that roots exude the most abundant root metabolites. The exudates were changed irreversibly by the lack of water under extreme drought conditions, and the plants could not recover. © 2018, The Author(s).

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Inter- and intra-specific trait shifts among sites differing in drought conditions at the north western edge of the Mediterranean Region

Garnier E., Vile D., Roumet C., Lavorel S., Grigulis K., Navas M.-L., Lloret F. (2018) Inter- and intra-specific trait shifts among sites differing in drought conditions at the north western edge of the Mediterranean Region. Flora: Morphology, Distribution, Functional Ecology of Plants. : 0-0.
Link
Doi: 10.1016/j.flora.2018.07.009

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Identifying consistent and predictable associations between traits and environment is one of the oldest quest of ecology. Yet, there are few formal and robust quantification of such associations, which seriously impedes our capacity to predict how ecological systems respond to global changes, including climate. This study was designed to assess how differences in environmental conditions affect plant form and function in a wide array of species. Twelve traits were measured on 40 species in three Mediterranean sites differing in drought conditions. Some species being common among sites, 78 species belonging to four major Raunkiær life form categories were studied. These traits correspond to: (i) plant size: vegetative and maximum plant height, (ii) seed mass, (iii) leaf morpho-anatomical traits: leaf area, specific leaf area, dry matter content and thickness, (iv) leaf chemical composition: mass based nitrogen, phosphorus and carbon contents, and carbon isotopic fraction. On average, there was a shift in the phenotypic space towards more resource conservative and taller species in the drier sites. These changes were not always consistent for hemicryptophytes and chamaephytes on the one hand, and for phanerophytes on the other hand. This is interpreted as different species responding to different aspects of complex changes in environmental factors. Intraspecific trait variation differed among species, and was lower than interspecific variation. Changes in site-average trait values were therefore mostly driven by species turnover among sites. The traits selected do not respond strongly to the differences in environmental conditions however, resulting in a moderate shift in the phenotypic space between sites. We argue that traits more directly related to plant water economy should be considered for an improved description of plant phenotypic response to the environmental factors at stake. The implications for the prediction of plant responses to climate changes likely to occur in the Mediterranean Region are discussed. © 2018

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Habitat disturbance selects against both small and large species across varying climates

Gibb H., Sanders N.J., Dunn R.R., Arnan X., Vasconcelos H.L., Donoso D.A., Andersen A.N., Silva R.R., Bishop T.R., Gomez C., Grossman B.F., Yusah K.M., Luke S.H., Pacheco R., Pearce-Duvet J., Retana J., Tista M., Parr C.L. (2018) Habitat disturbance selects against both small and large species across varying climates. Ecography. 41: 1184-1193.
Link
Doi: 10.1111/ecog.03244

Abstract:

Global extinction drivers, including habitat disturbance and climate change, are thought to affect larger species more than smaller species. However, it is unclear if such drivers interact to affect assemblage body size distributions. We asked how these two key global change drivers differentially affect the interspecific size distributions of ants, one of the most abundant and ubiquitous animal groups on earth. We also asked whether there is evidence of synergistic interactions and whether effects are related to species’ trophic roles. We generated a global dataset on ant body size from 333 local ant assemblages collected by the authors across a broad range of climates and in disturbed and undisturbed habitats. We used head length (range: 0.22–4.55 mm) as a surrogate of body size and classified species to trophic groups. We used generalized linear models to test whether body size distributions changed with climate and disturbance, independent of species richness. Our analysis yielded three key results: 1) climate and disturbance showed independent associations with body size; 2) assemblages included more small species in warmer climates and fewer large species in wet climates; and 3) both the largest and smallest species were absent from disturbed ecosystems, with predators most affected in both cases. Our results indicate that temperature, precipitation and disturbance have differing effects on the body size distributions of local communities, with no evidence of synergistic interactions. Further, both large and small predators may be vulnerable to global change, particularly through habitat disturbance. © 2017 The Authors

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Weak isolation by distance and geographic diversity gradients persist in scottish relict pine forest

González-Díaz P., Cavers S., Iason G.R., Booth A., Russell J., Jump A.S. (2018) Weak isolation by distance and geographic diversity gradients persist in scottish relict pine forest. IForest. 11: 449-458.
Link
Doi: 10.3832/ifor2454-011

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Gene flow is one of the main factors shaping genetic diversity within and among tree populations, and occurs through pollen and seed dispersal. Recent findings of pollen-release asynchronies in distant populations of Scots pine (Pi-nus sylvestris L.) within Scotland suggest that gene dispersal among more distant populations might be less effective than previously thought. Limited gene dispersal is one of the major factors causing genetic structure for neutral markers, and pollen-release asynchrony could have driven isolation by distance (IBD) among Scottish populations. Previous studies of neutral markers found little differentiation among Scottish populations of Scots pine, however they did not consider IBD over the full Scottish range. We analysed data from 6 nuclear simple sequence repeats (SSR) and 5 chloroplast SSR loci in a total of 540 individuals of Scots pine from 18 populations across Scotland. Our aim was to assess contemporary levels and distribution of genetic variation and to test if the distribution of genetic diversity was consistent with IBD. We also analysed patterns of gene flow that could have contributed to the observed patterns of variation. Levels of genetic diversity were high, for both nuclear and chloroplast markers within populations, and there was no significant differentiation among populations. A weak signal of IBD was present. We found an increase in nuclear diversity towards the East along with greater gene flow in a West-East direction commensurate with the prevailing winds. Our findings suggest that this wind-driven gene flow is dominant over genetic drift and prevents differentiation among the Scottish populations. It may also counteract any pollen-release asynchronies among populations. © SISEF.

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Do asynchronies in extinction debt affect the structure of trophic networks? A case study of antagonistic butterfly larvae–plant networks

Guardiola M., Stefanescu C., Rod F., Pino J. (2018) Do asynchronies in extinction debt affect the structure of trophic networks? A case study of antagonistic butterfly larvae–plant networks. Oikos. 127: 803-813.
Link
Doi: 10.1111/oik.04536

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Habitat loss and fragmentation affect species richness in fragmented habitats and can lead to immediate or time-delayed species extinctions. Asynchronies in extinction and extinction debt between interacting species may have severe effects on ecological networks. However, these effects remain largely unknown. We evaluated the effects of habitat patch and landscape changes on antagonistic butterfly larvae–plant trophic networks in Mediterranean grasslands in which previous studies had shown the existence of extinction debt in plants but not in butterflies. We sampled current species richness of habitat-specialist and generalist butterflies and vascular plants in 26 grasslands. We assessed the direct effects of historical and current patch and landscape characteristics on species richness and on butterfly larvae–plant trophic network metrics and robustness. Although positive species- and interactions–area relationships were found in all networks, structure and robustness was only affected by patch and landscape changes in networks involving the subset of butterfly specialists. Larger patches had more species (butterflies and host plants) and interactions but also more compartments, which decreased network connectance but increased network stability. Moreover, most likely due to the rescue effect, patch connectivity increased host-plant species (but not butterfly) richness and total links, and network robustness in specialist networks. On the other hand, patch area loss decreased robustness in specialist butterfly larvae–plant networks and made them more prone to collapse against host plant extinctions. Finally, in all butterfly larvae–plant networks we also detected a past patch and landscape effect on network asymmetry, which indicates that there were different extinction rates and extinction debts for butterflies and host plants. We conclude that asynchronies in extinction and extinction debt in butterfly–plant networks provoked by patch and landscape changes caused changes in species richness and network links in all networks, as well as changes in network structure and robustness in specialist networks. © 2017 The Authors

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Phylogeny of the ant genus Aphaenogaster (Hymenoptera: Formicidae) in the Iberian Peninsula, with the description of a new species

Gómez K., Martínez D., Espadaler X. (2018) Phylogeny of the ant genus Aphaenogaster (Hymenoptera: Formicidae) in the Iberian Peninsula, with the description of a new species. Sociobiology. 65: 215-224.
Link
Doi: 10.13102/sociobiology.v65i2.2099

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A phylogenetic tree of the Iberian Aphaenogaster species - except for A. splendida (Roger) - and a key to the worker caste of all Iberian Aphaenogaster species are proposed. The position of A. striativentris Forel and A. cardenai Espadaler is discussed, stating the possibility that this second species may belong to a new, undescribed genus. Aphaenogaster ulibeli n. sp. is described from the Iberian Peninsula. Its closest relatives are A. gibbosa (Latreille) and A. striativentris. Its habitat seems to be restricted to caducifolia forests in the Western Central Massif. © 2018 Universidade Estadual de Feira de Santana. All rights reserved.

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Earwigs and woolly apple aphids in integrated and organic apple orchards: responses of a generalist predator and a pest prey to local and landscape factors

Happe A.-K., Roquer-Beni L., Bosch J., Alins G., Mody K. (2018) Earwigs and woolly apple aphids in integrated and organic apple orchards: responses of a generalist predator and a pest prey to local and landscape factors. Agriculture, Ecosystems and Environment. 268: 44-51.
Link
Doi: 10.1016/j.agee.2018.09.004

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Organic management, connective woody habitats, and landscape complexity are supposed to enhance beneficial arthropods and biological pest control in agro-ecosystems. We studied earwigs (Dermaptera: Forficulidae) as generalist predators and aphids (Hemiptera: Aphididae) as key pests serving as earwig prey in a total of 58 commercial apple orchards differing in management (integrated production (IP) versus organic) in Germany and Spain. We focused on the effects of local agri-environmental structures, orchard management, and composition of the surrounding landscape on earwig populations and on tree infestation by the woolly apple aphid (WAA), Eriosoma lanigerum. Surprisingly, the common earwig, Forficula auricularia, did not benefit from organic management in either country, and we found even slightly higher earwig abundances in IP than in organic orchards in Germany. In Spain, we found a negative impact of IP compared to organic management on abundance of the earwig Forficula pubescens, whereas orchard management did not affect the abundance of F. auricularia. The presence of woody habitats adjacent to the orchard reduced the abundance of F. auricularia in IP but not in organic orchards in Germany. We did not study the effects of woody habitats in Spain, where these structures were very scarce. There was no effect of high plant species richness at the orchard boundary or compositional landscape heterogeneity on earwig abundance in either country. In Germany, WAA infestation was very low and driven by landscape characteristics rather than orchard management. In Spain, WAA infestation differed strongly between management types (higher in organic orchards). There were no strong, consistent correlations between earwig abundance and WAA infestation in either country. Our study shows that adjacent woody structures and orchard management may affect earwigs in perennial cropping systems. The consequences of orchard management, however, seem to strongly depend on earwig species. Our study suggests that woody elements may serve as sink habitats – potentially attracting earwigs by providing alternative prey and shelter – in IP (but not in organic) orchards. © 2018 Elsevier B.V.

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Research frontiers for improving our understanding of drought-induced tree and forest mortality

Hartmann, H., Moura, C.F., Anderegg, W.R.L., Ruehr, N.K., Salmon, Y., Allen, C.D., Arndt, S.K., Breshears, D.D., Davi, H., Galbraith, D., Ruthrof, K.X., Wunder, J., Adams, H.D., Bloemen, J., Cailleret, M., Cobb, R., Gessler, A., Grams, T.E.E., Jansen, S., Kautz, M., Lloret, F., O'Brien, M. (2018) Research frontiers for improving our understanding of drought-induced tree and forest mortality. New Phytologist. 218: 15-28.
Link
Doi: 10.1111/nph.15048

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