The Activity of Enzymes in a Sandy Clay Soil at Different Levels of Salinity in the Presence vs. Absence of Plant

Plants and soil microbes are the main sources of most enzymes available in the environment. It is, therefore, anticipated that any change in the growth of soil biota in response to salinity, may reduce the synthesis and production of extra- and intra- cellular enzymes. As a result, a reduction in the growth of plants and the activity of soil microbes in saline environments may lessen the level and the activity of soil enzymes. Soil salinity may reduce microbial growth and activity in different ways. The aim of this study was to determine the direct effects (by reducing the osmotic potential and specific ion effect) and indirect effects of salinity (by changing quality and quantity of root exudates) on soil enzymes activity. As to prove these effects, an uncultivated soil was used to determine direct effects, while soils under clover and wheat were used to determine the indirect effects, of salinity on soil enzyme activities. In the study, five levels of salinity using NaCl, CaCl2, MgCl2 and KCl; and three soil media (non-cultivated soil, soil cultivated with wheat and clover) replicated three times constituted the factorial experiment arranged in a completely randomized design. The experiment was carried out in a sandy clay soil under greenhouse conditions and lasted for 120 days. Results indicated that salinity caused significant reduction (P<0.001) in enzyme activities in uncultivated soil, as well as in the rhizosphere of clover and wheat plantations. Enzymes activities had significant correlations (P<0.05) with the root biomass of the two plants. So, one may attribute the lowered enzyme activities to the reduction in root biomass. With increasing salinity, the reduction in clover root biomass was observed to be more than that in wheat biomass, indicating more reduction in soil enzyme activities in the clover rhizosphere being largely due to less development of its root biomass in saline environment. Furthermore, the data indicated that enzyme activities in the clover and wheat rhizosphere, at high salinity levels, were almost similar to those in uncultivated soils, there being a small difference in enzyme activities observed the three media at high salinity levels, suggesting that role of indirect effects might be less pronounced with increase in soil salinity....