To reveal the physiological and biochemical mechanism underlying graft union formation in pecan (Carya illinoinensis), dynamic changes content of nutrients, tannin, phytohormones together with key enzyme activities were investigated 0, 3, 5, 7, 10, 14, 18, 22, 31, 40 d after grafting (DAG), homograft unions. During formation, peroxidase (POD) activity increased at 7 - 10 DAG compared that 0 DAG...