Influence of Different Salinity Levels on Some Microbial Indices in the Presence and Absence of Plant's Living Roots

Similar to plants, soil salinity may reduce microbial growth and activities in different ways. The aim of this study was to determine the effects of different levels of salinity on some microbial indices in the presence and absence of plant's living roots. In this study, five levels of salinity using NaCl, CaCl2, MgCl2 and KCl; and three soil media (soil with no plant, soil cultivated with wheat and clover) replicated three times consisted our factorial experiment arranged in a completely randomized design. Results show that salinity caused a significant reduction in accumulated microbial respiration, microbial biomass carbon, substrate-induced respiration, and carbon availability index in uncultivated soil and in the soils planted with clover and wheat. Results also show that salinity caused a significant increase in metabolic quotient (qCO2) in uncultivated soil, and soils planted with clover and wheat. Microbial activity of cultivated soils at high salinity levels was almost similar to that of the uncultivated soils. We observed a small difference in soil microbial activity among the three media at high salinity levels, indicating the role of indirect effects of salinity might be less important with increasing salinity levels. We also found out that at low salinity levels, the available carbon was not a limiting factor for soil microflora, while at high salinity levels the activity of soil microbes might be carbon-limited. The lower values of qCO2 in cultivated soils compared with the uncultivated soil support the positive influence of root and its exudates on soil microbial activity in saline soils. The existence of plants in saline environments may help in alleviating the detrimental influence of low to medium salinity on most soil microbial activities, likely via the added root exudates and root turnover.