Effects of nitrogen addition on the early stage decomposition of Korean pine litter in the Changbaishan Mountains, northeastern China

Effects of external nitrogen(N) on the decomposition of early stage of Pinus koraiensis needle litter were studied in a 13 weeks laboratory incubation experiment.Three doses of external N(equal to 0,30 and 50 kg N/(hm²·year,respectively,as NH₄NO₃) were added to two types of P.koraiensis litter collected along elevation gradient in the Changbaishan Mountains,northeastern China.The results showed that the addition of external N increased the decomposition rate significantly(P<0.05).High external N treated samples showed greater weight loss and respiration rate than low N treated one and the control.Internal N was not an overriding constraint on litter decomposition,and lignin content controlled the decomposition rate of litters.The releases of dissolved organic carbon(DOC) were not significantly affected by external N input.The effect of N addition on dissolved organic nitrogen(DON) leaching is uncertain.In spite of part of inorganic N leaching,the litter still immobilized 40%-55% external N.The retention of inorganic N generally increases along the external N gradient.