Decomposition of pine needles and twigs on and under the litter layer in the natural Korean pine broadleaved forests

The effects of forest litter layer on litter decomposition were examined by the measurement of mass remaining and N,P,K release after three years' exposure of Korean pine(Pinus koraiensis Sieb.et Zucc.) needles and twigs placed on and under the litter layer formed by the litter fall in the present year in natural P.koraiensis broadleaved forests.The microenvironment below the litter layer contributes to the decomposition rate and N,P,K release rates of the litter,but needles showed a significant higher decomposition rate and N,P,K release rates than those of twigs.The decomposition rate(k value) decreased continuously with the length of study period extended,and the k values were higher for needles and twigs on the litter layer than those under the layer.The mass remaining percentage of litter in this study was related to C/N,lignin/N,and the concentration of lignin and cellulose,but needles and twigs on the litter layer were regulated by litter chemical components from those under the litter layer.At later decomposition stage,lignin became the dominant factor affecting the litter decomposition for all litter types.Needles and twigs on the litter layer exhibited a higher N and P immobilization rate and lower mineralization rate compared with those under the layer.K was continuously mineralized during the study period and its mineralization rate was higher for needles than twigs as well as for needles and twigs under the layer than those on the layer.Our study proved that decomposition rate and C,N,P,K release rates of P.koraiensis would be underestimated if the microenvironment effects of litter layer were not taken into account.