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The degree of degradation of soils can be measured by reference to a variety of chemical, physical, biochemical and biological properties, the last two being particularly sensitive to the changes that take place. Among these parameters, those related with the soil carbon content, such as total organic carbon and microbial biomass carbon, are of the greatest interest although others are also important indicators of microbial activity, including ATP and phosphatase activity. This study looks at the microbial activity of various soils in SE Spain which present different degrees of plant cover. The results demonstrate that vegetation is of fundamental importance for the development of microbial populations and their activity since soils with a substantial vegetal cover showed higher values for the above parameters than those with a reduced cover, which are more degraded. A seasonal study of the soil properties showed that the time of year exercises an important influence on the parameters that are indicative of microbial activity.

Changing climatic conditions (warming and decreasing precipitation) have been found to be a threat to the agricultural sustainability of Mediterranean croplands. From the climate change perspective, biochar amendment may interact with the effects of warming and drought stresses on soil ecosystems. However, the responses of soil microbial communities to the joint effects of climate change and biochar in Mediterranean croplands are not sufficiently known. To help fill this knowledge gap, in this work we used a field experiment to determine the effects of partial rain exclusion alone or combined with a soil temperature increase in biochar-amended (20 t ha) and unamended plots under crop rotation on soil chemical properties, enzyme activities, and the microbial community activity, structure, composition, abundance, and functions. The biomass, composition, and activity of the soil bacterial and fungal communities were more responsive to biochar addition than to climate manipulation. Thus, soil chemical parameters, enzyme activities and the relative abundances of bacterial populations were not responsive to the interaction of biochar and climate manipulation, while the predicted functionality of the bacterial community was modified by both factors. Soil β-glucosidase activity significantly decreased in response to biochar addition and climate manipulation, while urease activity was significantly increased by biochar, and protease activity was significantly decreased by climate manipulation. Gram negative and fungal biomasses were significantly affected by the interaction of biochar with climate manipulation. Climate manipulation produced changes in the composition of the soil fungal community without loss of diversity. This study illustrates how the interactions between biochar amendment and future climate change scenarios influence microbially-driven ecosystem services related to the maintenance of nutrient cycles and biodiversity in a Mediterranean agroecosystem. This research was financially supported by the Spanish MICINN MINECO, AEI, FEDER, EU), through the research projects CGL2015-65162-R and AGL2016-75752-R. The authors are also grateful for the AEPP CSIC funds (2020AEP004). We also thank the Spanish Ministry and FEDER funds for the project AGL2017–85755-R (AEI/FEDER, UE), the i-LINK + 2018 (LINKA20069) from CSIC.

14 páginas.- 4 figuras.- 4 tablas.- referencias.- Supplementary data to this article can be found online at https://doi.org/10.1016/j.apsoil.2024.105383 Here, a degraded soil, located in a semi-arid Mediterranean region, was characterized 17 years after organic amendment with sludge or compost (differing in their stabilization degree) for restoration purposes. To do this, (i) soil physicochemical properties and plant cover, (ii) soil organic matter (SOM) content and composition, (iii) soil basal respiration and enzymatic activities, and (iv) abundance, taxonomic composition, and functionality (shotgun metagenomics) of microbial communities were studied. Increased SOM and nutrient contents were found in soil from amended plots with respect to the control, with no differences between amendment types. This is explained by the lasting effects of organic amendments and the higher plant cover. Thermal and pyrolytic analyses showed that the restoration process enriched soil mainly with SOM of intermediate recalcitrance and of high chemical diversity. SOM composition did not differ between amendment types. Increased microbial abundances and activities were found in the amended plots, without differences between compost and sludge. Shotgun metagenomics showed that microbial communities changed in taxonomic and functional terms between amended and unamended plots, but these differences were rather limited. The taxonomic differences between treatments were mainly driven by increasing abundances of Actinobacteria and decreasing abundances of Proteobacteria in soil from amended plots. Soil microbial communities in amended plots showed some functional adaptation to the increased nutrient contents and predominant nutrients forms. This, together with the higher microbial abundances detected, explained the conspicuous soil enzymatic activities reported in amended plots. The effectiveness of the studied soil restoration process was confirmed here from an integrative perspective. This publication is part of the I + D + I project PID2020-114942RB-I00 funded by MCIN/AEI/10.13039/501100011033. This study formed part of the AGROALNEXT programme and was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Fundación Séneca with funding from Comunidad Autónoma Región de Murcia (CARM). J.A.S acknowledges the support of the program “Juan de la Cierva Incorporación” of the “Ministerio de Ciencia, Innovación y Universidades” (agreement no. IJC2018-034997-I). We thank A. Vera (CEBAS-CSIC) for assistance on FAME analysis. EJP Soil has received funding from the European Union's Horizon 2020 research and innovation programme: Grant agreement No 862695. Peer reviewed

Water shortage and low organic carbon content in soil limit soil fertility and crop productivity. The use of desalinated seawater is increasing as an alternative source of irrigation water. However, it has a high boron (B) content that could cause toxicity in the plant-soil microbial system. Here, we evaluated the responses of the soil microbiota and lemon trees to 3 irrigation B doses (0.3, 1, and 15 mg L-1) under two types of soil management (conventional, CS; and organic, OS) in a 180-days pot experiment. High B doses promoted B accumulation in soil, reaching harmful concentrations that affected soil biodiversity. Our results suggest a close interaction between B and organic labile fractions that increased B availability in soil solution. Besides, B addition to soil impacted on microbial biomass. The bacterial community showed sensitivity to the B dose. Organic amendment did not increase B soil adsorption but it favored B plant uptake. The highest B dose had a detrimental impact on plant physiology, finally resulting lethal for the plants. Our study provides a comprehensive assessment of the microbes-plant interactions in soils irrigated with water with high B content. This will be fundamental in the design of future fertirrigation strategies.

The increasing use of silver nanoparticles (AgNPs) due to their well-known antimicrobial activity, has led to their accumulation in soil ecosystems. However, the impact of environmental realistic concentrations of AgNPs on the soil microbial community has been scarcely studied. In this work, we have assessed the impact of AgNPs, that mimic real concentrations in nature, on tropical soils cultivated with Coffea arabica under conventional and organic management systems. We evaluated the biomass, extracellular enzyme activities, and diversity of the soil microbial community, in a microcosm experiment as a function of time. After seven days of incubation, we found an increase in microbial biomass in an AgNPs-concentration-independent manner. In contrast, after 60-day-incubation, there was a decrease in Gram+ and actinobacterial biomass, in both soils and all AgNPs concentrations. Soil physico-chemical properties and enzyme activities were not affected overall by AgNPs. Regarding the microbial community composition, only some differences in the relative abundance at phylum and genus level in the fungal community were observed. Our results suggest that environmental concentrations of AgNPs affected microbial biomass but had little impact on microbial diversity and may have little effects on the soil biogeochemical cycles mediated by extracellular enzyme activities.