The Relative Importance of Presence and Absence of Plant Root in Changing the Ratio of Soil Enzymatic Activity to Microbial Biomass

Soil microbiological criteria are a complex reflection of interactive metabolic processes that may not be evaluated only by measuring a single parameter but rather it requires the simultaneous determination of more parameters and combining them. The objective of this research was to study enzyme activities: microbial biomass carbon ratios in salinized and none-saline soils in the presence and absence of plant's rooting system. This ratio indicates the amount of enzyme activity per unit of microbial biomass. In this study, five levels of salinity using NaCl, CaCl2, MgCl2 and KCl; with 2:1:1:1 ratio and three soils (unplanted soil, soil planted with wheat and clover) replicated three times consisted our factorial experiment arranged in a completely randomized design. Results showed that salinity caused significant reduction in enzyme activities: microbial biomass ratio in all three soils. Furthermore, at all salinity levels, unplanted and planted treatments had a significant effect on urease activity: microbial biomass carbon ratio and arylsulphatase activity: microbial biomass carbon ratio. However, there were no significant differences in ß-glucosidase: microbial biomass carbon ratio and alkaline phosphatase: microbial biomass carbon ratio among the three soils at all salinity levels. In the other words, the presence of plant did not have any substantial effect in increasing or reducing microbial ability to produce and synthesize these enzymes. The effect of planted and un-planted treatments on the ratio of L-glutaminase, saccharase and acid phosphatase to microbial biomass carbon in different salinity treatments were variable. In summary, results showed that the presence of plants may support the synthesis of some enzymes by soil microorganisms. But the synthesis of some other enzymes is not affected by the presence and absence of plants living roots. In other words, the effect of roots and its exudates on moderating the effect of salinity on the amount of the enzymes synthesized by soil microbes depends on the salinity level, plant type and enzyme.