Effect of Rice Husk Biochar and Piriformospora Indica Endophytic Fungus on corn yeild in Zn contaminated soil

The symbiotic relationship between endophytic fungi and plants due to its significant influences on the growth and yield of plants under the conditions of soil pollution has an effective role in heavy metal stress tolerance in plants. The purpose of this study is to investigate the effect of rice husk biochar and the endophytic fungus; Piriformospora indica; on some growth indicators (the shoot height, fresh weight and stem diameter) on corn and biological properties (microbial respiration and microbial biomass carbon) of a Zn-polluted soil under greenhouse condition. To do this research, suitable amount of soil from surface horizon (0-30) of a calcareous soil was collected, After air drying, samples were passed through a 2 mm sieve. This experiment was conducted in a completely randomized factorial design experiment with three factors including Zn (0, 50, 100, 200 and 300 mg kg-1 soil), rice husk biochar (0, 2 and 4 weight percent) and P. indica (non-inoculated and inoculation with fungi). Biochars were produced using the pyrolysis of rice husk (500 °C for 4 h) in the limited oxygen conditions. For propagation of fungi and production of sufficient amount of spores, the isolates of the fungus were cultured and stored at 24 °C in the incubator for 4 weeks. Before the corn was cultivated, after addition of biochar and zinc for 2 months, soil was incubated in field capacity moisture conditions at 25 °C. After 8 weeks of plant growth some biological and morphological characteristics were measured. At levels of 2 and 4 (% w/w) biochar, The shoot fresh weight, the shoot height, and stem diameter of the control plants and non-inoculated with P. indica significantly increased by 4.14 and 9.18 percent, 3.49 and 8.43 percent, 3.18 and 9.25 percent respectively.
Whereas in the same conditions, shoot fresh weight of plants inoculation of P. indica was 5.73 and 12.76 percent, the shoot height was 4.84 and 7.67 percent, and stem diameter showed a significant increase 6.71 and 22.61 percent compared to the control plants respectively. Also average microbial respiration and microbial biomass carbon in soil after corn harvesting in non-inoculated of P. indica plants in condition at levels of 2 and 4 (% w/w) biochar of the control (without biochar) 39.33 and 47.83 percent and 12.69 and 31.30 percent significant increase respectively (p<0.05). But the amount of these indicators of plants inoculation of P. indica at levels of 2 and 4 (% w/w) biochar of the control (without biochar) 40.85 and 46.63 percent and 2.96 and 26.48 percent significant increase respectively (p<0.05). Application of 2 and 4 (% w/w) biochar resulted in significant increases in the shoot height, fresh weight and stem diameter on corn plant as well as microbial respiration and microbial biomass carbon of the soil. While this increase is more in the plants inoculation with P. Indica fungi. Increasing biochar levels increases the nutrients absorption and improves plant growth. In addition, the P. indica fungi is likely to improve corn growth due to the production of growth stimulants and the increased nutritional capacity of the mineral nutrients for the plant. Also, the height, fresh weight and diameter of the shoots increased at levels of 50 and 100 mg kg-1 of Zn and decreased at higher levels (200 and 300 mg kg-1), possibly at high zinc levels due to decreased cytokinin, Iron, potassium and calcium, as well as increased ethylene and growth inhibitors inhibit corn growth