Effect of Simultaneous Biological and Foliar Treatments with Silicon on Growth, Morphological and Physiological Traits of Coriander under Pb Stress

One of the major environmental problems is heavy metal contamination of agricultural soils, especially in developing countries. The transfer of pollutants to human via plants endangers people helth in community. Lead (Pb) with higher shelf life toxicity in soil has a more devastating decrese on the biological activities in soils. Same application of silicon and biological treatments under heavy metal stresses rarely investigated before. In this study, it was tried to evaluate the feasibility of their simultaneous use on the properties of coriander.

This factorial experiment was conducted in a completely randomized design with four levels of Pb stress (0, 500, 1000 and 1500 mg.Kg), four levels of biological treatments (Without bacteria, strains 6, 19 bacteria and mycorrhizal fungi Glomus mosea) and three levels of silicon nano particles (0, 1.5 and 3 mM) on coriander plants. At the end of the experiment, traits including plant height, root and shoot weight, root length, leaf area, leaf dry weight, photosynthesis pigment (Chlorophyll a, b, and total, carotenoid), electro leakage, proline, and carbohydrate were measured in coriandrum sativum. Also, basal and induced respiratory and percentage of mychorizha colonization in soil were measured.

The results of this study showed that both mycorrhizae symbiosis and bacterial isolates inoculation were acceptable population even at high intensities, such that high amoun of Pb decresed population. Both application of Silicon nano particles and biological treatments showed desirable results in most of the studied traits. Morphological traits including fresh and dry weight of plant, leaf area, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid under both experimental treatments were partially offset by Pb treatment. The amount of electro lekage and proline under Pb stress, especially at high concentrations, was significantly increased, but the combination of silicon nano particles and biological treatments decreased this treatments significantly. Also, Pb increased the carbohydrate content of coriander plants, and the interesting thing was that it increased as a result of their joint application of silicon nano particles and biological treatments. It seems that the biological treatments in this study improved the growth of Coriandrum sativum under Pb contamination by affecting the root system and subsequently the effect on photosynthetic pigments.

In general, Pb, especially at high concentrations, caused significant deficiency in measured traits in Coriander. In this study, mycorrhizal and isolates 6 showed better results in most morphological and physiological conditions, although at lower concentrations of Pb in some isolates 19 also showed good results. Combining the microorganisem treatment with 3 mM silicon nanoparticles were better results in these traits. Simultaneous application of biological treatments and silicon in coriander is recommended for their individual application, although their mechanism has not been elucidated and needs further study. Key word: Silicon, PGPR, Morphological traits, basal respiration, Induced respiration.