Abstract
The negative effects of more extreme pH conditions (soil acidity and alkalinity) are increasingly challenging crop production. Managing acidity and alkalinity in soils has been achieved through techniques such as the use of lime, afforestation, tillage, and addition of organic matter. The use of microbes to address this challenge is new and could increase agroecosystem sustainability while helping plants survive more extreme acidity and alkalinity, among other stresses. Use of plant growth promoting microbes (PGPM) has recently gained attention as these microbes afford plants several benefits, including nutrient acquisition and stress tolerance, both biotic and abiotic. Several methods of microbe application have been developed, all intended to maximize the benefits of plant-microbial interactions. The current study assessed the potential of changing microbial culture pH during production, followed by removal of cells to produce supernatant that enhances plant growth, specifically under acidity and alkalinity stresses. The study included L. helveticus. (EL2006H) and B. subtilis (EB2004S) which were cultured at three pH levels (5, 7, and 8) incubated for 24–48 h then centrifuged at 12 000 g to remove the cells. The cell-free supernatants obtained were used for seed germination and early seedling growth assays. The results indicated significant increase in seed germination rate, for both corn and tomato, compared to experimental controls. Supernatants produced at pH 5, for both strains, had greater effect than those produced at pHs 7 and 8. Similarly, the positive effect of these supernatants was observed in seedling growth as increased root length and volume. Their results indicate that there is potential in stressing microbes below or above optimum pH (~7) to induce production and excretion of favorable materials into the growth medium, as was evident in this study. To the best of our knowledge this would be the first attempt to look at this pH change to increase potential benefits related to plant growth promotion by microbes. It was interesting to learn that using the CFS of microbes cultured at pH 5 increased germination rate and seedling growth. These results provide an initial indication that support broadened research into PGPM under pH stressed conditions.
Highlights
Worldwide the effects of soil acidity and alkalinity are increasingly challenging crop production and the plant science community attempting to improve yields (Liu et al, 2019)
Except for the cell-free supernatants (CFS) obtained from pH5 of EB2004S, positive controls had lower germination percentages at 42 h than the respective 1% CFS concentration
While treating corn seeds with CFSs caused increased pH Effects Cell-Free-Supernatant Growth Stimulation germination, it was still lower for CFSs from pH 8 than the effect obtained from those at pH 5 and 7 at 42 h
Summary
Worldwide the effects of soil acidity and alkalinity are increasingly challenging crop production and the plant science community attempting to improve yields (Liu et al, 2019). 3% of the global geographic area is dominated by salinesodic soils (Singh et al, 2016) and about 30% of ice free land in the world is acidic (Mehmood et al, 2017). In America alone acidic soils cover about 40% of potential arable land (Von Uexküll and Mutert, 1995; Ngoune Tandzi et al, 2018), putting pressure on crop production management, productivity and sustainability. Acidity and alkalinity impact crop production; various severe effects are seen in plant root system damage and the resulting imbalance of nutrient availability from soil (Sapre et al, 2018). Acidity and alkalinity can be corrected by deploying techniques such as the use of lime, afforestation, tillage and addition of organic matter (OM) in soil (Machado and Serralheiro, 2017)
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