Influence of Salinity on Soil Enzyme Activities

Abstract

Efforts were made to assess the levels of soil enzyme activities that have a specific role in the N, C, P, and S cycles of saline soils. Fieldmoist soil samples were treated with four rates of CaCl2, NaCl, and Na2SO4 solutions applied to produce electrical conductivity readings of saturation extracts (ECe) ranging up to 22 mmho/cm. The range of ECe values included threshold salinity levels associated with reduced yields of agronomic crops. After 7 d of equilibration, the following soil enzymes were assayed: amidase, urease, acid phosphatase, alkaline phosphatase, phosphodiesterase, inorganic pyrophosphatase, arylsulfatase, rhodanese, α‐glucosidase, α‐galactosidase, dehydrogenase, and catalase.Soil enzyme activities decreased with increasing ECe; however, the degree of inhibition varied among the enzymes assayed and the nature and amounts of salts added. Dehydrogenase activity was severely inhibited by salinity, whereas, the hydrolases showed a much lesser degree of inhibition. Generally, the inhibition of soil enzyme activities by the salt solutions decreased in the following order when compared at the same ECe level: NaCl > CaCl2 > Na2SO4. Reduced enzyme activities in saline soils may be due to the osmotic desiccation of microbial cells releasing intracellular enzymes which become vulnerable to attack by soil proteases, a “salting‐out” effect modifying the ionic conformation of the active site of the enzyme‐protein, and specific ion toxicities causing nutritional imbalances for microbial growth and subsequent enzyme synthesis.

Interactions between arbuscular mycorrhizal fungi and phosphate-solubilizing fungus (Mortierella sp.) and their effects on Kostelelzkya virginica growth and enzyme activities of rhizosphere and bulk soils at different salinities

“…Therefore, we have only determined neutral and alkaline phosphatase activities since soil pH was 7.3. Catalase (Frankenberger and Bingham 1982), alkaline phosphatase (Garcia and Hernandez 1996), invertase, and urease (Omar et al 1994) activities were inhibited by increasing soil salinity. Similarly, we have observed that soil enzyme activities of control soil decreased proportionately by increasing salinity.…”

Effect of Soil Water Contents on Urea Hydrolysis and Nitrification in a Newly Reclaimed Tidal Soils

“…Katyal and Carter (1988) also found that increased hydrolysis rates were closely related with increasing time of submergence. Especially in a newly reclaimed tidal soils containing high salt content, urea hydrolysis can be delayed by the salts due to reduction in urease activity (Frankenberger and Bingham, 1982;Galstyn, 1960).…”

Distribution of phosphatase activity in marsh sediments along an estuarine salinity gradient

“…A salt-induced inhibition of phosphatase was observed by Frankenberger & Bingham (1982), who attributed the effect to osmotic desiccation or specific ion toxicity of soil microbes, or to a salting-out effect on the enzymes themselves. Alternatively, the results of our cross-habitat comparison can be explained by differences in the clay and organic matter content, which decreased as salinity increased.…”