Alteration of the tree–soil microbial system triggers a feedback loop that boosts holm oak decline

In anthropic savanna ecosystems from the Iberian Peninsula (i.e. dehesa), complex interactions between climate change, pathogen outbreaks and human land use are presumed to be behind the observed increase in holm oak decline. These environmental disturbances alter the plant–soil microbial continuum, which can destabilize the ecological balance that sustains tree health. Yet, little is known about the underlying mechanisms, particularly the directions and nature of the causal–effect relationships between plants and soil microbial communities. In this study, we aimed to determine the role of plant–soil feedbacks in climate-induced holm oak decline in the Iberian dehesa. Using a gradient of holm oak health, we reconstructed key soil biogeochemical cycles mediated by soil microbial communities. We used quantitative microbial element cycling (QMEC), a functional gene-array-based high-throughput technique to assess microbial functional potential in carbon, nitrogen, phosphorus and sulphur cycling. The onset of holm oak decline was positively related to the increase in relative abundance of soil microbial functional genes associated with denitrification and phosphorus mineralization (i.e. nirS3, ppx and pqqC; parameter value: 0.21, 0.23 and 0.4; p < 0.05). Structural equation model (χ2 = 32.26, p-value = 0.73), moreover, showed a negative association between these functional genes and soil nutrient availability (i.e. mainly mineral nitrogen and phosphate). Particularly, the holm oak crown health was mainly determined by the abundance of phosphate (parameter value = 0.27; p-value < 0.05) and organic phosphorus (parameter value = −0.37; p-value < 0.5). Hence, we propose a potential tree–soil feedback loop, in which the decline of holm oak promotes changes in the soil environment that triggers changes in key microbial-mediated metabolic pathways related to the net loss of soil nitrogen and phosphorus mineral forms. The shortage of essential nutrients, in turn, affects the ability of the trees to withstand the environmental stressors to which they are exposed. Read the free Plain Language Summary for this article on the Journal blog. © 2023 The Authors. Functional Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.This research has been mainly funded by the Spanish Government through the IBERYCA project (CGL2017‐84723‐P), its associated FPI scholarship BES‐2014‐067971 (ME‐V), the SMARTSOIL (PID2020‐113244GB‐C21) and SMARTHEALTH (PID2020‐113244GA‐C22) projects (both funded by MCIN/AEI/10.13039/501100011033). It has been further supported by the BC3 María de Maeztu excellence accreditation (MDM‐2017‐0714; the Spanish Government), by the BERC 2018–2021 and by the UPV/EHU‐GV IT‐1648‐22 (from the Basque Government). Additionally, this research was further supported through the grant Holistic management practices, modelling and monitoring for European forest soils—HoliSoils (EU Horizon 2020 Grant Agreement No 101000289) and the ‘Juan de la Cierva programme’ (MV; IJCI‐2017‐34640; the Spanish Government). We acknowledge the Nutrilab‐URJC (Mostoles, Spain) laboratory services for the soil chemical analyses and SGIker of UPV/EHU (Leioa, Spain) for the technical and staff support for the high‐throughput quantitative‐PCR analysis. We also thank the private owners of the dehesas for facilitating our access to their properties. We are thankful to Celia López‐Carrasco Fernández and the ‘Consejería de Agricultura, Medioambiente y Desarrollo rural de la Junta de Castilla‐La Mancha’ for all the logistical support. The ‘Tree’ icon by Hey Rabbit illustrator, from thenounproject.com were used to design the Graphical abstract. Open Access funding provided by the Univer

Integrative assessment of in situ combined bioremediation strategies applied to remediate soils spilled with sewage sludges

Landfills and waste disposal sites in the Basque Country are summarized in the inventory of soils that either currently support or have supported potentially polluting activities or facilities (Law 4/2015). Notably, “Landfill 17,” located in Gernika-Lumo, has been receiving, for decades, sewage sludges from the local wastewater treatment plant (WWTP) as agricultural amendment. In order to decontaminate and recover soil functionality, a combination of bioremediation (which involved bioagumentation and phyto- and vermitechnologies) and complementary bioremediation strategy (i.e., promotion and maintenance of the native vegetation) was implemented in situ. Physicochemical and ecotoxicological characterization were achieved. Furthermore, an ecotoxicological assessment of the soils upon flora and fauna was carried out through the application of different bioassays and biomarkers. Additionally, an integrative biomarker response (IBR/n) index was calculated to provide a holistic view of the soil general status. Critical pollutants [Cd, Cr, Ni, Pb, benzo(a)pyrene, and dieldrin] were observed in most of the treated sites. Microbial parameters did not present remarkable differences among sites. However, plant indicators pointed the non-treated site (MN8) as the unhealthiest. This was also observed in earthworms’ immune system, where cytotoxicity appears when exposed to non-treated soils. In conclusion, this field study showed that the combination of bioaugmentation, phytoremediation with native species, and vermiremediation is highly useful in eliminating mixed contamination, improving soil health, and ultimately restoring ecosystem functionality and biodiversity

Reduction of hexavalent chromium by Ochrobactrum intermedium BCR400 isolated from a chromium-contaminated soil

Hexavalent chromium-resistant Ochrobactrum intermedium BCR400 was isolated from chromium contaminated soil collected from Vadodara, Gujarat. It reduced 100 mg Cr(VI)/L completely in 52 h with initial Cr(VI) reduction rate of 1.98 mg/L/h. The Cr(VI) reduction rate decreased with increase in Cr(VI) concentration from 100 to 500 mg/L. The addition of anthraquinone-2-sulphonic acid (AQS) to culture O. intermedium BCR400 significantly enhanced its chromium reduction rate. The activation energy of AQS-mediated Cr(VI) reduction (120.69 KJ/mol) was 1.1-fold lower than non-mediated Cr(VI) reduction. An increase in the activities of quinone reductase and chromate reductase in cells grown in presence of AQS/AQS + Cr(VI) suggests their role in reduction of Cr(VI) by O. intermedium. Both chromate reductase and quinone reductase activities were FAD independent, required NADH as reductant, displayed maximum activity at pH (7.0) and temperature (30 °C). Thus Cr(VI) bioremediation potential of O. intermedium can be enhanced by augmentation of system with AQS as redox mediator

Nitrate and phosphate uptake from water by free-living and immobilized cells of the cyanobacterium Phormidium laminosum

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