Algalization of acid soils with acid‐tolerant strains: Improvement in pH, carbon content, exopolysaccharides, indole acetic acid and dehydrogenase activity

Abstract

Widespread occurrence of acid soils across the globe is a serious issue in agriculture that has been generally managed with intensive use of chemical amendments.Although green microalgae are the primary colonizers of soils even under extreme acid conditions, only a few investigations focused on their role in health improvement of such soils. In this study we tested the hypothesis: that acid-tolerant microalgae have the potential for ameliorating soil acidity and enhancing soil health through enrichment of carbon content, exopolysaccharides, indole acetic acid besides stimulating dehydrogenase activity in acid soils. Inoculation of two acid soils collected from Australian fields with acid-tolerant microalgae, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, alone or in combination, resulted initially in the development of a soil algal crust as evidenced by significant increase in chlorophyll a in both the soils. Also, there was a significant increase (>200%) in the release of exopolysaccharides that facilitated soil aggregate stability. The increase in soil pH was about one unit (from 4.8 to 5.6 in soil A or 4.3-5.3 in soil B) under the influence of individual or co-cultures of the microalgal strains after 90 days. Algalized acid soils exhibited a significant increase in carbon content (29-57%), dehydrogenase activity (>500%) and production of indole acetic acid (200-500%). Thus, the present study reports for the first time on the great potential of green microalgae in amelioration of acid soils besides improving soil health and fertility.acid soils, acid-tolerant microalgae, algalization, pH increase, soil health indicators | INTRODUCTIONSoil is an important component of Earth's biosphere for food production and maintenance of global environmental quality (Doran & Zeiss, 2000). One of the intrinsic soil characteristics is pH, which influences the soil quality and nutrient availability (De Caritat, Cooper, & Wilford, 2011). Globally, 35-40% of soils (about 3,950 million ha) are acidic, and such an extent of soil acidification is due to the natural phenomenon of biogeochemical cycles at the interface of soil and plant, and the release of H + ions in the cyclic process (Sumner & Noble, 2003). These acid soils are distributed in regions notably in

Algalization of Acid Soils with Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3 Enriches Bacteria of Ecological Importance

“…The genus Nitrosococcus of δ- Proteobacteria was prominent in soil A, and the genus Enterobacter was prevalent in soil B. Nitrobacter and Nitrosococcus are ammonia-oxidizing bacteria, which are crucial in the nitrification process in the biogeochemical cycling of nitrogen . Hu et al observed that the abundance ratio of ammonia-oxidizing bacteria to Archea decreased with an increase in pH, which supports our earlier report of pH increase by 1.0 unit . In addition, the genera Brevibacillus and Enterococcus of the phylum Firmicutes were observed in algalized soils, while Brevibacillus was prominent in both the soils.…”

“…Indiscriminate application of chemical fertilizers in acid soils that are widely distributed in several regions across the globe significantly affects the indigenous microbes. , Several reports indicate the microbial phenotypic changes under the influence of algalization that include abundant production of extracellular polysaccharides that act as a carbon source for bacteria in soil. ,, In this study, we demonstrated the role of acid-tolerant microalgae in influencing bacterial diversity in acid soils. Interestingly, both the algalized soils exhibited almost similar DNA concentrations, less reads compared to nonalgalized controls, but the total number of genera observed was significantly higher in soil A than in soil B. Lv et al attributed the enhanced richness of microbial community such as bacteria and fungi in rhizosphere of plant inoculated with Scenedesmus quadricauda to biochemicals, mainly proteins.…”

“…Actinobacteria , being predominantly heterotrophic, are widely present in neutral soils of semiarid regions on a cyanobacterial crust . Thus, all of the above also support the fact that algalization promotes bacterial phyla based on the soil crust development and nutrient leaching in terms of polysaccharides . However, biochar-amended soils failed to enhance the abundance of Proteobacteria , Actinobacteria , and Cyanobacteria …”

“…MAS3, harvested from the cultures maintained in modified Bold’s basal medium (BBM). The set of “algalized” soil samples that received a final microalgal biomass of 2.0 g m –2 soil was incubated at a light intensity of 60 μ mol s –1 as described previously . Soil samples that received no inoculum of microalgae and incubated either in the dark or light (60 μ mol s –1 ) served as controls.…”

“…36−38 When applied to acid soils, the above microalgal strains improve soil health, measured in terms of soil pH, dehydrogenase activity, indole acetic acid production, aggregate stability, and extracellular polysaccharide production within 90 days of incubation. 39 The novelty of the present study is to demonstrate the impact of algalization of acid soils with two acid-tolerant microalgae, Desmodesmus sp. MAS1 and Heterochlorella sp.…”