Wheat Root Exudation and Soil Nitrogen Transformations in Farmland Reclaimed From Coal Gangue

To investigate fundamental mechanisms of coal gangue affecting winter wheat (Triticum aestivum) root exudation and nitrogen transformations, a field experiment was conducted on a tract of farmland reclaimed from coal gangue. Exudates from wheat roots, soil N transformation rate, and activities of two extracellular enzymes at various growth stages of the crop in the farmland were analyzed and determined. Results show that: (1) The existence of coal gangue significantly decreased root length, root biomass and root activity of the crop wheat throughout its growth season; (2) The existence of coal gangue decreased root exudation rate Ⅰ by 25.47%, 23.71% and 9.95%, respectively, and root exudation rate Ⅱ by 39.83%, 25.81% and 10.84%, respectively at the jointing stage, flowering stage and maturing stage, and root exudation rate Ⅲ decreased significantly by 23.71% at the jointing stage as compared with that of the crop in a control field. Root exudation rate Ⅲ(y) was found to be positively related to root activity(x) and the correlation could be fitted with the regression equation of y=0.012x-0.43, R²=0.874(P<0.05, n=30); (3) Coal gangue inhibited significantly N transformations and soil enzyme activities at all the growth stages, and the two were positively related to root exudation rate Ⅲ (P<0.05), which suggests that coal gangue decreases N transformation rate by inhibiting crop root exudation, thus reducing the supply of available N and then restraining growth of the crop.