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

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

La reiteración de la biodesinfección controla la incidencia de la podredumbre radicular y del cuello del pimiento causada por Phytophthora y mejora la calidad del suelo

Phytophthora root and crown rot is a plant disease responsible for important economic losses in protected pepper crops. A greenhouse experiment was carried out in a temperate climate region (northern Spain) to assess the effects of repeated biodisinfection after three consecutive crop seasons with different organic amendments (a non-composted mixture of sheep manure and chicken litter, a semicomposted mixture of horse manure and chicken litter, Brassica carinata dehydrated pellets plus Sinapis alba fresh green manure) on disease incidence, crop yield and soil quality. Biodisinfection treatments were found to improve soil water properties through reduction in soil bulk density and increased water infiltration. Biodisinfested soils showed higher values of physicochemical and microbial properties than control (untreated) and plastic-mulched soils. In plots treated with the non-composted or semicomposted mixture, the observed higher levels of microbial activity were strongly related with an increase in soil microbial biomass. Brassica-Sinapis treatment had a weaker effect on soil properties than animal manure-based treatments. However, highest counts of total bacteria, actinomycetes and Pseudomonas spp. were found in Brassica-Sinapis-treated soils. It was concluded that repeated biodisinfection for the control of Phytophthora root and crown rot in protected pepper crops located in temperate climate regions can improve soil quality and suppressiveness, as well as allow for a reduction in the dose of organic amendment needed for biodisinfection. Among the studied organic amendments, the semicomposted amendment was the best option in terms of reduction in disease incidence.La podredumbre radicular y del cuello causada por Phytophthora es una enfermedad que genera importantes pérdidas económicas en cultivos de pimiento en invernadero. En una región de clima templado (norte de España) se realizó ensayo en invernadero para evaluar la reiteración de tratamientos de biodesinfección después de tres ciclos de cultivo consecutivos con diferentes enmiendas orgánicas (mezcla no-compostada de estiércol de oveja y gallinaza, mezcla semicompostada de estiércol de caballo y gallinaza, pellets deshidratados de Brassica carinata más Sinapis alba como abono verde fresco) sobre la incidencia de la enfermedad, la producción y la calidad del suelo. La biodesinfección mejoró las propiedades hídricas del suelo al reducir la densidad aparente y aumentar la infiltración. Los suelos biodesinfectados mostraron valores más altos en las propiedades físico-químicas y microbianas que los suelos control (no tratado) y acolchado con plástico. En las enmiendas no-compostada y semicompostada, los valores más altos de actividad microbiana estuvieron fuertemente relacionados con un aumento en la biomasa microbiana. La biodesinfección con Brassica-Sinapis tuvo menor efecto sobre las propiedades del suelo que con ambas enmiendas animales. No obstante, los recuentos de bacterias totales, actinomicetos y Pseudomonas spp. fueron más altos en los suelos tratados con Brassica-Sinapis. La biodesinfección reiterada para controlar la podredumbre radicular y del cuello causada por Phytophthora en cultivos de pimiento en invernadero en regiones de clima templado, puede mejorar la calidad del suelo y su supresividad, así como reducir dosis de enmienda requerida. La enmienda semicompostada fue la mejor en disminuir la incidencia de enfermedad

Aquatic macrophytes as biological indicators of environmental conditions of rivers in north-eastern Spain

The aim of this work was to evaluate the potential of aquatic macrophytes as biological indicators of the environmental conditions of rivers in north-eastern Spain. To this end, twenty five river basins were studied to assess the species composition and abundance of macrophytes, and to examine their relation with different geographic, morphometric, mineralization, and trophic status parameters. Of the twenty six macrophyte species found, five appeared to be useful as biological indicators of the environmental conditions of the rivers. L. minor was a good indicator of high mineralization (i.e., conductivity and Cl-) and high trophic state (especially, N-NO2-). C. stagnalis was a good indicator of high P-PO43- concentrations. P. crispus, P. polygonifolius, and R. penicillatus seemed to be useful indicators of high N-NO3- concentration. We conclude that, in our study area, aquatic macrophytes can indeed be used as biological indicators of the environmental conditions of rivers