Influence of Nerium oleander L. Leaves on Soil Microbial Populations and Enzyme Activities

Nerium oleander L. (Common oleander, Apocynaceae) is an ornamental shrub in Mediterranean Region and all parts of this plant were toxic as it was reported in previous. In ten decades, many reports showed that this toxic plant have also antimicrobial and antifungal compounds. Th us, it has become essential to investigate the eff ects of oleander leaves on microbial populations and their enzyme activities in soil. Effects of oleander leaves on soil microbial populations (total aerobic bacteria and fungi) and enzyme (cellulase and xylanase) activities were determined under diff erent moistures in present study. Oleander soils were taken from Cukurova University Campus in February 2014. Some soil physical and chemical properties with leaf carbon and nitrogen contents were determined. Soils were mixed with oleander leaves at doses of half (L0.5), same (L1) and double (L2) of soil organic carbon content and humidified at their 80% and 60% of field capacities (80%FC and 60%FC). Soils without oleander leaves humidified at same field capacities were used as controlled. All soils were incubated for 30 days at 28°C. Soil microbial populations and their cellulase and xylanase activities were measured on 15th and 30th days of incubation. All doses of oleander increased soil microbial populations compared to controls under both field capacities. Bacteria populations were highest at L1 dose on 15th days and at L0.5 dose on 30th days under both FC. Same L1 and L0.5 doses were significantly higher than controls (p<0.05). Fungi populations were generally increased as Oleander leaf doses increased in all days under both FC. Fungi was highest at L1 dose on 15th days and L2 dose on 30th days under both FC. In general, these same doses significantly increased fungi populations compared to controls (p<0.05). It was expected that as soil moisture decreased, soil microbial population would decrease in this study. However, effects of field capacities on soil aerobic bacteria were variable but fungi under 80%FC was generally higher than 60%FC in all doses. One of the main results in microbial populations was that time was more dominant factor than field capacity and leaf doses. Both soil bacteria and fungi populations were higher on 15th day than 30th day. Soil enzyme activities were generally increased by all leaf doses. In general, highest enzyme activities were measured at L2 dose that was significantly higher than control on both days and field capacities (p