Search

The connection between olive genetic responses to environmental and agro-climatic conditions and the composition, structure and functioning of host-associated, belowground microbiota has never been studied under the holobiont conceptual framework. Two groups of cultivars growing under the same environmental, pedological and agronomic conditions, and showing highest (AH) and lowest (AL) Actinophytocola relative abundances, were earlier identified. We aimed now to: i) compare the root transcriptome profiles of these two groups harboring significantly different relative abundances in the above-mentioned bacterial genus; ii) examine their rhizosphere and root-endosphere microbiota co-occurrence networks; and iii) connect the root host transcriptome pattern to the composition of the root microbial communities by correlation and co-occurrence network analyses. Significant differences in olive gene expression were found between the two groups. Co-occurrence networks of the root endosphere microbiota were clearly different as well. Pearson's correlation analysis enabled a first portray of the interaction occurring between the root host transcriptome and the endophytic community. To further identify keystone operational taxonomic units (OTUs) and genes, subsequent co-occurrence network analysis showed significant interactions between 32 differentially expressed genes (DEGs) and 19 OTUs. Overall, negative correlation was detected between all upregulated genes in the AH group and all OTUs except of Actinophytocola. While two groups of olive cultivars grown under the same conditions showed significantly different microbial profiles, the most remarkable finding was to unveil a strong correlation between these profiles and the differential gene expression pattern of each group. In conclusion, this study shows a holistic view of the plant-microbiome communication., Supported by grants AGL2016-75729-C2-1-R and AGL2016-75729-C2-2-R from the Spanish Ministerio de Economía, Industria y Competitividad/Agencia Estatal de Investigación, and grant PID2019-106283RB-I00 from the Spanish Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación, all of them cofinanced by the European Regional Development Fund (ERDF). These funding sources had no involvement in this work preparation.

The objective of this study was to determine whether native and invasive plants harbor different bacterial communities in their rhizospheres and whether there are bacterial indicator species associated with the invasive rhizosphere. Additionally, physico-chemical, biochemical, and biological properties have been determined in the native and invasive rhizospheres in order to ascertain the relationships between these soil properties and the rhizosphere bacterial communities. We carried out a study in five independent locations under Mediterranean semiarid conditions, where the native Hyparrhenia hirta is being displaced by Pennisetum setaceum. Partial 16S rRNA genes of the rhizosphere bacterial communities were amplified and 454-pyrosequenced. Principal coordinate analysis revealed differences in the composition and structure of the rhizosphere bacterial communities between native and invasive plants, the values of the richness index being higher in the invasive microbial community. Rhizosphere microbial community structure was also influenced by invaded location. The indicator species analysis showed a higher number of indicators for the invasive community at all the taxonomic levels studied, the genus Ohtaekwangia being the most abundant indicator. As shown by canonical correspondence analysis, the protease and dehydrogenase activities and soil respiration were related to the rhizosphere bacterial community of invasive plant. However, only protease activity was significantly affected by the plant type, being higher in the invasive plant rhizosphere. Our results show that P. setaceum invasion has produced an intense interaction with the soil bacterial community, shifting its structure, composition, and protease activity related to N cycling, which may be altering the function of the invaded ecosystem., R.C.G. acknowledges a predoctoral fellowship (“Ayudas para contratos predoctorales para la formación de doctores 2013”) from the Spanish Ministry of Economy and Competitiveness. This research was supported by the Spanish Plan Nacional-FEDER Project CGL-2015-64168-R.

A solution for environmentally wiser agriculture is the use of composted organic wastes as soil amendments. Just as this alleviates the problem of recycling organic residues, it provides necessary nutrient input for food production. The objective of this work was to study the effect that 13 years of applying three different composted organic wastes or organic amendments have had on soil quality, GHG emissions and the dynamics of its microbial communities 15 days after the annual application. For this purpose, in 1996 a field trial was set up in a Tempranillo vineyard. Since 1998, the applied organic amendments have been as follows: 1. a pelletized organic compost (PEL) made from plant, animal and sewage sludge residues; 2. a compost made from the organic fraction of municipal solid waste (OF-MSW); 3. a compost made of stabilized sheep manure (SMC); 4. a mineral fertilizer (NPK); and 5. an unaltered control. The mean annual doses applied since 1998 have been 3700 kg ha−1 fresh weight (FW) of PEL, 4075 kg ha−1 FW of OF-MSW, 4630 kg ha−1 FW of SMC, and 340 kg ha−1 of NPK treatment. Soil quality was consistently enhanced by amendment application over the 13 years. Total nitrogen was significantly increased in PEL (0.1%), OF-MSW (0.09%) and SMC (0.1%) compared to control (0.06%). Nutrient content was also improved in a similar way, e.g. the most significant increase in P Olsen (80.7 mg kg−1) and K2O (473.8 mg kg−1) was found on SMC. The overall enzyme activity was also increased 15 days after the annual application and OF-MSW had the highest rate (95.9) compared to control (51.3). This increase in metabolic activity was also recorded in GHG emissions. CO2 equivalents per hectare were 1745 kg for OF-MSW and it was the only significant difference found. PEL with 1598 kg and SMC with 1591 kg were not different from the Control (1104 kg). Even though GHG emissions in the soil increased because of the application, soil organic matter content increased significantly (at least 35% more in all organic treatments compared to control) and this rise in organic matter was consistent over the years. According to the results, 85% of the sequences corresponded to 5 main phyla: Proteobacteria, Actinobacteria, Bacteroidetes, Acidobacteria and Gemmatimonadetes, with unclassified material making up for 10.9% (average) of the sequences. Bacterial diversity by Shannon and Chao1 indices was not affected 15 days after the application. However, slight changes in the bacterial community were recorded 15 days after application only in OF-MSW treatment. Assessing soil quality using these three factors allows the relevant agronomical capabilities of the soil to be integrated with the potential effect of this practise on global warming.

We investigated the effect of soil microclimate on the structure and functioning of soil microbial communities in a Mediterranean Holm-oak forest subjected to 10 years of partial rain exclusion manipulations, simulating average drought conditions expected in Mediterranean areas for the following decades. We applied a high throughput DNA pyrosequencing technique coupled to parallel measurements of microbial respiration (RH) and temperature sensitivity of microbial respiration (Q10). Some consistent changes in the structure of bacterial communities suggest a slow process of community shifts parallel to the trend towards oligotrophy in response to long-term droughts. However, the structure of bacterial communities was mainly determined by short-term environmental fluctuations associated with sampling date (winter, spring and summer) rather than long-term (10 years) shifts in baseline precipitation. Moreover, long-term drought did not exert any chronic effect on the functioning of soil microbial communities (RH and Q10), emphasizing the functional stability of these communities to this long-term but mild shifts in water availability. We hypothesize that the particular conditions of the Mediterranean climate with strong seasonal shifts in both temperature and soil water availability but also characterized by very extreme environmental conditions during summer, was acting as a strong force in community assembling, selecting phenotypes adapted to the semiarid conditions characterizing Mediterranean ecosystems. Relations of climate with the phylogenetic structure and overall diversity of the communities as well as the distribution of the individual responses of different lineages (genera) to climate confirmed our hypotheses, evidencing communities dominated by thermotolerant and drought-tolerant phenotypes.

A local characterization of Schwarzschild metrics is made by showing the space-time is locally a 2 by 2 warped product and admitting a static reference frame on its certain open subsets under some assumptions on the global analytic structure and stress-energy tensor of the space-time, such as, assuming the existence of solutions to certain partial differential equations and the existence of a radiation stress-energy tensor consistent with these solutions on the space-time.

Nitrate reductase (NR) activity was detected in the cytosol and membranes from bacteroids of Bradyrhizobium japonicum strain L-236 isolated from nodules of soybean ( Glycine max , Merr., cv. Williams) plants that were only N 2 -dependent. The molecular mass ( M ) of the NR from each source was estimated by gel filtration to be about 76 kDa. Treatment of plants with 20 mM KNO 3 induced NR activity in the bacteroid cytosol, but did not affect rates of activity in the membranes. Furthermore, the M of the cytosolic enzyme was 160 kDa, while that of the NR from the membranes was 76 kDa. When bacteroids that had been isolated from nodules of plants not receiving nitrate were incubated microaerobically (2 % O 2 v/v) in both the absence and presence of nitrate, the M of the membrane-bound NR enzyme was calculated to be 230 kDa; in bacteroids incubated in the absence of nitrate, the M of the soluble enzyme was 76 kDa, whereas that of bacteroids incubated with nitrate was about 160 kDa. Incubation of bacteroids under aerobic conditions with nitrate induced NR activity in the soluble fraction, and the M of the enzyme was 160 kDa; in the absence of nitrate the M of the soluble NR was 76 kDa. No NR activity was found in membranes from aerobically incubated bacteroids.