Role of rhizosphere microflora in potassium solubilization

Abstract

The K+ is not just the essential nutrient required to support optimal plant growth and yield, it is also an important signaling agent mediating a wide range of plant adaptive responses to abiotic and biotic stresses such as drought, salinity, oxidative stress, and apoptosis. The main source of K+ for plant is soil which is taken up by the plant roots through the epidermal and cortical cells and transported to the shoot and distributed to the leaves. Movement of K+ is facilitated by transport systems present in the cell membrane and the availability of which strongly determines crop yield. It is important to note that only a small percentage of the total K+ of the soil exists in a form available for plant uptake. The remainder is in complex with other elements and organic matter, making it unavailable and even intensive agricultural practices is adding to K+ deficiency in soil. It is already reported that large agricultural areas of world are deficient in K+ availability which is a major concern today. In this connection, efforts to understand the K+ uptake by plants and its solubilization from the K-bearing minerals such as waste muscovite, biotite, feldspars, orthoclase, illite, and mica have been undertaken. Recent investigations have shown that organic exudates of some microorganisms such as Pseudomonas spp., Burkholderia spp., Acidithiobacillus ferrooxidans, Bacillus mucilaginosus, B. edaphicus, B. megaterium, and Aspergillus spp., and even plant roots play a key role in releasing non-available K+ from the minerals. The list of rhizosphere microflora with potassium solubilization is increasing, and hence the present chapter discusses the mechanism of K+ solubilization and its role in signaling its uptake system in plants. Plant species effective in K+ uptake and K+-solubilizing microbial populations may be further key factors that control the K+ release from soil minerals.