Effect of mycorrhizal fungi on the absorption of phosphorus and zinc by two alfalfa varieties in cadmium contaminated soils

Abstract

Some agricultural and industrial practices such as mining activities, waste materials of industrial factories, other pollutants and the application of wastewater on farmlands contaminate the agricultural soils. Cadmium is one of the most common heavy metals which accumulates in agricultural soils as a result of the application of phosphorus fertilizers and can easily be absorbed by plants even at very low concentrations with detrimental effects on the living systems. Alfalfa requires high rates of phosphorus fertilizer and therefore the soils under alfalfa are more prone to contamination of cadmium. Arbuscular Mycorrhizal fungi exist as obligate symbiotic organisms on roots of more than 80% of plant families and enhance the growth of the host plant by providing water and nutrients when the plant growth limited by environmental stresses. In order to evaluate the effect of Mycorrhiza symbiosis on nutrient absorption by alfalfa under the cadmium pollution, a factorial experiment base on completely randomized design conducted by using two alfalfa varieties (2122 and Hamadani cultivars); Glomus intraradices fungi; and four levels of cadmium (0, 5, 10 and 20 mg kg -1 soil) with four replications in green house on 2005. The plants cut at 50% bloom to determine root and shoot dry matter as well as mineral nutrient absorption by using standard laboratory procedures. The soil material rhyzosphere collected to determine colonization percent. Results showed that phosphorus and iron absorption of 2122 was superior under normal growing conditions. However, under cadmium stress Hamadani performed superior where it also proved none suitable as a host plant for symbiosis with Mycorrhiza. Fungi significantly (a = %1) increased the absorption of nitrogen, phosphorus and zinc by shoots and phosphorus even in the presence of cadmium adverse effects. Time of harvest also significantly improved the uptake of all the nutrients by the shoots as well as the dry matter production by shoots.