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12 páginas.- 4 figuras.- 4 tablas.- 114 referencias.- Supplementary data to this article can be found online at https://doi.org/10.1016/j.soilbio.2022.108560., The loss of tree health is a global concern with many unknown cascading impacts on the diversity and function of forest ecosystems. Specifically, it is uncertain how the process of tree decline and mortality driven by exotic pathogens might alter the soil microbiome. Here we combined high-throughput sequencing, neighborhood models, and network analysis to explore the impacts of the decline of a Mediterranean tree species, Quercus suber, on the diversity, composition and network structure of soil fungal and bacterial communities in forests invaded by the exotic pathogen Phytophthora cinnamomi. The belowground footprint of pathogen-driven tree decline implied an increase in the taxonomic and phylogenetic diversity of both bacteria and fungi, but also a severe reduction of tree-symbiotic fungi and Proteobacteria known to have positive effects on plant growth and disease suppression. Moreover, we detected alterations of the topology of soil microbial networks in declining tree neighborhoods (lower connectivity, higher modularity), with implications for ecosystem function. Our findings reveal the large impacts that moderate levels of tree decline can have on the soil microbiome of invaded forests, and highlight the recovery of a functionally diverse and highly connected soil microbiome as a key target in the restoration of these disturbed systems., This research was supported by the Ministerio de Ciencia e Innovación (MICINN) projects INTERCAPA (CGL2014-56739-R) and MICROFUN (RTI2018-094394-B-I00). AJMP was supported by a post-doctoral fellowship funded by the Portuguese Foundation for Science and Technology (SFRH/BPD/111015/2015), JDB by a FPI-MEC grant (BES-2012-055113) and EVS by a FPU-MICINN grant (FPU16/04616).

14 páginas.- 2 figuras.- 1 tabla.- referencias.- Additional supporting information may be found in the online version of this article at http://onlinelibrary.wiley.com/doi/10.1002/ecy.3430/suppinfo, Interactions among plant species and their soil biota drive plant–soil feedbacks (PSFs) that play a major role in the dynamics and diversity of plant communities. Among the different components of the soil community, pathogens are considered to be the main drivers of negative PSFs. Despite this, the number of studies that have experimentally quantified the contribution of soil pathogens to PSFs remains considerably low. Here we conducted a greenhouse experiment with oomycete-specific fungicide to quantify the contribution of soil pathogens, and particularly oomycete pathogens, to individual and pairwise PSFs in forest communities. We used as a case study Mediterranean mixed forests dominated by Quercus suber and invaded by the oomycete pathogen Phytophthora cinnamomi. The fungicide treatment was crossed with a competition treatment to explore how conspecific neighbors might modify pathogen effects. To place the results of the experiment in a wider context, we also conducted a systematic review of published papers that explicitly used fungicide to explore the role of pathogens in PSF experiments. Our experimental results showed that oomycete pathogens were the main drivers of individual PSFs in the study forests. Oomycete effects varied among tree species according to their susceptibility to P. cinnamomi, driving negative PSFs in the highly susceptible Q. suber but not in the coexistent Olea europaea. Oomycete-driven PSFs were not modified by intraspecific competition. Oomycete pathogens were also major contributors to negative pairwise PSFs assumed to promote species coexistence. Results from the systematic review supported the novelty of our experimental results, since only three studies had previously used oomycete-specific fungicide in a PSF context and none in systems invaded by exotic oomycetes. Overall, our results provide novel evidence of oomycete pathogens (including the exotic P. cinnamomi) as fundamental drivers of negative individual and pairwise PSFs with implications for species coexistence in invaded communities. Although in the short-term invasive pathogens might contribute to species coexistence by causing self-limitation in dominant species, strong inter-specific variation in self-limitation might undermine coexistence in the long-term. Because of the increasing number of exotic oomycetes worldwide, further attention should be given to oomycetes as drivers of PSFs in plant communities., This research was supported by the MICINN projects CGL2011-26877 and CGL2014-56739-R. J. Domínguez-Begines was supported by a FPI-MEC grant (BES-2012-055113), and J. M. Ávila by a FPU-MEC grant (AP2010-0229).

13 páginas.- 4 figuras.- 4 tablas.- 93 referencias, Emergent diseases are an increasing problem in forests worldwide. Exotic pathogens are now threatening forests where pathogens have not traditionally been considered to be major ecological drivers of tree demography, such as water‐limited Mediterranean forests. However, how pathogens might limit regeneration in invaded forests is largely unknown. Here we used fungicide to analyse the impact of soil‐borne oomycete pathogens on seedling establishment at community level in Mediterranean forests invaded by the exotic oomycete Phytophthora cinnamomi . Fungicide effects were modelled as a function of the tree neighbourhood composition, the seed mass of the target species, and the abiotic environment. Fungicide application had positive effects on seedling performance that varied in magnitude and spatial structure among coexisting species. Seed mass predicted fungicide effects on seedling emergence, but not on survival or growth. Positive fungicide effects were modulated by levels of abiotic resources, mainly water, increasing with soil moisture. Our results support a novel role for soil‐borne oomycete pathogens as one more axis of the regeneration niche of woody species in water‐limited forests. Given the increasing numbers of exotic oomycete pathogens worldwide, more research is needed to understand the role of this relevant microbial group as a factor shaping seedling establishment., This research was supported by the Ministerio de Economía y Competitividad (MICINN) projects CGL2011-26877 and CGL2014-56739-R. JD-B was supportedby a FPI-MEC grant (BES- 2012-055113) and JMA by a FPU-MEC grant (AP2010-0229

16 páginas.-- 2 tablas.-- 5 figuras.--104 referencias.-- Additional supporting information may be found online in the Supporting Information section at the end of the article in http://dx.doi.org/10.1111/1365-2745.13091, 1.Tree defoliation and mortality have considerably increased worldwide during the last decades due to global change drivers such as increasing drought or invasive pests and pathogens. However, the effects of this tree decline on soil food webs are poorly understood. 2.In this study we evaluated the impacts of Quercus suber decline on soil food webs of Mediterranean mixed forests invaded by the exotic oomycete pathogen Phytophthora cinnamomi, using soil nematodes as bioindicator taxa. We used a spatially‐explicit neighborhood approach to predict the characteristics of the nematode community (diversity, trophic structure, and several indices indicative of soil food web conditions) as a function of the characteristics of the tree and shrub community (species composition, size and health status). 3.Our results indicate that the process of defoliation and mortality of Q. suber caused significant alterations in the nematode trophic structure increasing the abundance of lower trophic levels (bacterivores, fungivores and herbivores) and decreasing the abundance of higher levels (predators and omnivores). Furthermore, Q. suber decline altered the functional composition of soil communities, producing a setback of the ecological succession in the soil food web to an earlier stage (decrease in the maturity index and increase in the plant‐parasitic index), simplified soil food webs (decrease in the structure index), and shifts in the predominant decomposition channel (increase in the fungivores/bacterivores ratio). 4.We also detected contrasting characteristics of the nematode community in neighborhoods dominated by coexisting woody species, which suggests potential for long‐term indirect effects on soil food webs due to the substitution of Q. suber by non‐declining species. 5.Synthesis:Our study provides novel results that show the major impacts that ongoing health deterioration of dominant tree species can have on the structure and composition of soil food webs in forest systems invaded by exotic pathogens, with cascading consequences for soil biogeochemical processes in both the short‐ and long‐term, This research was supported by the Ministerio de Economía y Competitividad (MICINN) projects CGL2011-26877and CGL2014-56739-R. JDB was supported bya FPI-MEC grant [BES-2012-055113].

15 páginas.- 4 figuras.- 3 tablas.- 165 referencias.- Supplementary information accompanies this paper at https://doi.org/10.1038/s41598-019-45702-1, Droughts associated with climate change alter ecosystem functions, especially in systems characterized by low biodiversity, such as agricultural fields. Management strategies aimed at buffering climate change effects include the enhancement of intraspecific crop diversity as well as the diversity of beneficial interactions with soil biota, such as arbuscular mycorrhizal fungi (AMF). However, little is known about reciprocal relations of crop and AMF diversity under drought conditions. To explore the interactive effects of plant genotype richness and AMF richness on plant yield under ambient and drought conditions, we established fully crossed diversity gradients in experimental microcosms. We expected highest crop yield and drought tolerance at both high barley and AMF diversity. While barley richness and AMF richness altered the performance of both barley and AMF, they did not mitigate detrimental drought effects on the plant and AMF. Root biomass increased with mycorrhiza colonization rate at high AMF richness and low barley richness. AMF performance increased under higher richness of both barley and AMF. Our findings indicate that antagonistic interactions between barley and AMF may occur under drought conditions, particularly so at higher AMF richness. These results suggest that unexpected alterations of plant-soil biotic interactions could occur under climate change. © 2019, The Author(s)., This project was supported by the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, funded by the German Research Foundation (DFG; FZT 118). We acknowledge support from the German ResearchFoundation (DFG) and Leipzig University within the program of Open Access Publishing.

Comunicación oral (TS.20-O-6) presentada en the 1st Meeting of the Iberian Ecological Society (SIBECOL) & XIV AEET meeting. Barcelona, Spain, 4th – 7th February 2019, Forested landscapes are rapidly being transformed by increasing rates of tree mortality caused by global-change factors such as exotic pathogens or extreme droughts. Disturbance of tree communities can have cascading impacts on biodiversity at all organization levels. However, how soil microorganisms respond to tree dieback and the implications for ecosystem recovery is largely unknown. Here we combined spatially-explicit neighborhood models, DNA metabarcoding, and a field experiment to explore how the decline of the Mediterranean tree Quercus suber altered the diversity, composition and network structure of belowground fungal communities in forests invaded by the exotic pathogen Phytophthora cinnamomi, and whether such changes had cascading impacts on Q. suber recruitment. We found that Q. suber dieback caused a reduction of the taxonomic diversity of soil fungal communities but increased their phylogenetic diversity, likely due to the colonization of unhealthy soils by rare taxa not present in healthy soils. Tree neighborhoods dominated by defoliated or dead oaks had soil fungal communities with higher relative abundance of saprophytic and pathogenic fungi, lower abundance of ectomycorrhizal fungi, and very distinct network structure (e.g. lower modularity) than healthy neighborhoods. Such changes had negative feedbacks on Q. suber regeneration, since seedling performance was negatively related to fungal phylogenetic diversity but positively influenced by ectomycorrhizal abundance. Our results showed that oak dieback exerted a strong influence on the diversity and structure of soil fungal networks, promoting new assemblages impoverished in mutualistic taxa. This implies that oak dieback has far-reaching multi-trophic effects that may affect regeneration and ecosystem recovery