The Influence of Earthworm and Arbuscular Mycorrhizal Fungi on Microbial Biomass Carbon and Enzyme Activity in a Soil Contaminated with Cadmium in Sunflower (Helianthus annuus L.) Cultivation

Soil biota such as earthworms and arbuscular mycorrhizal fungi (AMF) play an important role in the stability of ecosystem، and the bioavailability of soil elements، in particular heavy metals، in soils. To examine the effects of these organisms، a 3×2×3 factorial experiment arranged as randomized complete design was set up to study the individual and combined influence of earthworms (Lumbricus rubellus L.) and AMF (Glomus mosseae and Glomus intraradices) on soil organic matter (OM)، dissolve organic carbon (DOC)، soil respiration، microbial biomass carbon (MBC)، soil enzyme activity and glomalin production in a calcareous soil contaminated with 0، 10، 20 mg of Cd kg-1 soil cropped with sunflower (Helianthus annuus L.) with three replications. Both earthworms and mycorrhizal fungi were able to survive in all the treatments with added Cd. Results showed that Cd pollution decreased all the measured microbial activities and properties in soil. Earthworm treatment increased DOC by 4-10% at all Cd levels. The amount of soil MBC in mycorrhizal treatments was greater (1. 9-2. 4 times) than that in non-mycorrhizal treatment، and AMF inoculation increased MBC/TOC ratio from 23% to 53% in Cd-polluted soils. Earthworm and AMF enhanced soil enzyme activity/MBC ratio، 10-18 and 40-54% for soil alkaline phosphatase and 4-9 and 40-55% for soil urease، respectively. The glomalin production increased at 20 mg kg-1 and was about 15% greater in G. mosseae than in G. intraradices species. Although soil respiration was decreased substantially with Cd pollution، inoculation of either earthworms or AMF enhanced soil respiration when compared with the corresponding controls.