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- Dá-lhe PPublication . Dias, Teresa; Munzi, Silvana; Melo, Juliana; Santana, Margarida; Barão, Lúcia; Cruz, Cristina
- Finding optimal microorganisms to increase crop productivity and sustainability under drought – a structured reflectionPublication . Rosa, Ana Paula; Dias, Teresa; Mouazen, Abdul M.; Cruz, Cristina; Santana, Margarida M.Considering the more frequent and longer drought events due to climate change, improving plant drought tolerance became a priority. The search for plant growth promoting rhizobacteria (PGPR) able to improve plant drought tolerance has been long addressed, but with inconsistent results. Here, we summarize the PGPR mechanisms that improve plant drought tolerance, identify the pitfalls in current PGPR isolation and selection routines, and discuss the key points to define new strategies to get optimal PGPR for plant drought tolerance. Drought and host genotype impact rhizo-communities, and host-mediated selection strategies may be used to obtain a drought-adapted rhizomicrobiome that can be a source for PGPR isolation. Alternatively, an integrated omics-level analysis can improve our knowledge on the mechanisms of rhizomicrobiome construction, and a targeted approach can be designed, which will be focused on key PGP traits. New strategies to build PGPR consortia for improvement of plant drought tolerance are also suggested.
- The Plant Growth-Promoting Potential of Halotolerant Bacteria Is Not Phylogenetically Determined: Evidence from Two Bacillus megaterium Strains Isolated from Saline Soils Used to Grow WheatPublication . Ait Bessai, Sylia; Cruz, Joana; Carril, Pablo; Melo, Juliana; Santana, Margarida; Mouazen, Abdul M.; Cruz, Cristina; Yadav, Ajar Nath; Dias, Teresa; Nabti, El-hafid1) Background: Increasing salinity, further potentiated by climate change and soil degra- dation, will jeopardize food security even more. Therefore, there is an urgent need for sustainable agricultural practices capable of maintaining high crop yields despite adverse conditions. Here, we tested if wheat, a salt-sensitive crop, could be a good reservoir for halotolerant bacteria with plant growth-promoting (PGP) capabilities. (2) Methods: We used two agricultural soils from Algeria, which differ in salinity but are both used to grow wheat. Soil halotolerant bacterial strains were isolated and screened for 12 PGP traits related to phytohormone production, improved nitrogen and phosphorus availability, nutrient cycling, and plant defence. The four ‘most promising’ halotolerant PGPB strains were tested hydroponically on wheat by measuring their effect on germination, sur- vival, and biomass along a salinity gradient. (3) Results: Two halotolerant bacterial strains with PGP traits were isolated from the non-saline soil and were identified as Bacillus subtilis and Pseudomonas fluorescens, and another two halotolerant bacterial strains with PGP traits were isolated from the saline soil and identified as B. megaterium. When grown under 250 mM of NaCl, only the inoculated wheat seedlings survived. The halotolerant bacterial strain that displayed all 12 PGP traits and promoted seed germination and plant growth the most was one of the B. megaterium strains isolated from the saline soil. Although they both belonged to the B. megaterium clade and displayed a remarkable halotolerance, the two bacterial strains isolated from the saline soil differed in two PGP traits and had different effects on plant performance, which clearly shows that PGP potential is not phylogenetically determined. (4) Conclusions: Our data highlight that salt-sensitive plants and non-saline soils can be reservoirs for halotolerant microbes with the potential to become effective and sustainable strategies to improve plant tolerance to salinity. However, these strains need to be tested under field conditions and with more crops before being considered biofertilizer candidates.
- Transformation of organic and inorganic sulfur– adding perspectives to new players in soil and rhizospherePublication . Santana, Margarida; Dias, Teresa; Gonzalez, Juan M.; Cruz, CristinaSulfur (S) is a macro-element required for life. S deficiency limits plant growth. Microorganisms carry out several essential steps in the recycling of organic and inorganic S in soils. Microbes and plants interact, mainly in the rhizosphere, but the mechanisms ruling these interactions and the extent of such relationships remain poorly understood. Here, we update current perspectives on the role of specific microorganisms involved in S cycling and the spatial interaction between plants and microbes. To contextualize the pitfalls of current approaches in studying soil S transformations, we review the current main established steps, redox reactions and microbial players in the S cycle. The incorporation of novel microbial taxa, namely those important for organic S mineralization, which may be important ecosystem players in terms of soil functionality, and of the spatial-temporal context at aggregate-level for the relevance of plant-microbe interactions, introduce important implications involving the role of microorganisms in the rhizosphere and require an integrated analysis. Herein, the rhizosphere is a focus – a habitat of selected low-abundance species, where important microbial groups act in S turnover and plant growth – while keeping a perspective on important microbial feedback S fluxes that may occur in bulk soils.
- Multiple modes of action are needed to unlock soil phosphorus fractions unavailable for plants: The example of bacteria- and fungi-based biofertilizersPublication . Basílio, Francisco; Dias, Teresa; Santana, Margarida; Melo, Juliana; Carvalho, Luís; Correia, Patrícia; Cruz, CristinaPhosphorus (P) is an essential macronutrient for all life forms. Therefore, meeting the needs of a growing human population and their changing consumption patterns drastically intensified the use of mineral P fertilizers in agriculture. As a result, the current use of mineral P fertilizers causes severe negative economic, environmental and health impacts, which creates an urgent need for more sustainable agronomic practices capable of maintaining crop yields while improving P use efficiency. We consider that agronomic options that recycle/reuse the accumulated unavailable P (turn the unavailable P accumulated in the soil into P forms available for crop uptake) are an efficient strategy for food security, food production autonomy and sovereignty, and environmental sustainability. Here, we review P cycling in the soil and plant strategies to improve P acquisition, with special emphasis on the role of soil microbes as plant allies, namely their contribution to plant P acquisition directly through the production of organic acids and phosphatases, and indirectly through the production of phytohormones. Finally, we discuss why and how the use of soil microbes (mostly bacteria and fungi) with multiple modes of action may be the key to unlock soil P fractions unavailable for crop uptake, and highlight the benefits of combining: i) high-throughput sequencing; ii) new culturing methods to isolate and cultivate novel isolates; and iii) soil ecology experiments to develop multi-strain biofertilizers with diverse, complementary, and redundant modes of action in improving plant P acquisition and other benefits.