Nutrient Characteristic By Stand Age In Larix Principis-ruppechtii Plantations In Taiyue Mountain, Shanxi, China

In this study, the biomass and the concentrations, accumulation, distribution and cycling patterns of four nutrient elements(C, N, P and K) were measured through the survey of sample plots, actual measurements of biomass and experiments, in order to interpret nutrient cycling and improve forest management in 33-year-old plantations of Larix principis-ruppechtii Magyr in HaodifangForesty of Taiyue Forest Bureau’s Shanxi, China. The results showed that:(1) The total biomass of L. principis-ruppechtii among the four stands were 43.47 t-hm-2,128.63 t·hm-2,179.82 t-hm-2 and 117.40 t-hm-2 respectively. The biomass was in the order of tree layer> herb layer> shrub layer. The concentration of C in different components of L. principis-ruppechtii was in the order of bark> branch> leaves> stem> root. The change of the concentrations of N, P and K was:leaves> branch> bark> root> stem. The nutrient retention of vegetation layer firstly increases and then decreased with the stand age. The nutrient accumulation in L. principis-ruppechtii of 35-year-old was the highest. With the increase of the stand age, the nutrient concentrations of shrub layer firstly decreased and then increased. The herb layer was the opposite. The nutrient concentrations of herb layer was higher than shrub layer.(2) The biomass of litter layer increased and then decreased with the increasing of forest age. The storage of undecomposed litter was the lowest among three layers. The concentration of nutrient elements in undecomposed litter was higher than semi-decomposed litter and decomposed litter. The total nutrient accumulation of litter layer among the four stands were 6.00×103 kg·hm-2,11.81×103 kg·hm-2,28.04×103 kg·hm-2 and 12.90×103 kg·hm-2 respectively. The 35-year-old plantation was the highest. As the stand age increased, the four nutrient accumulation increased first and then decreased. The leaf litter to the total litter fall was more than 50%. The nutrient content in leaf litter was higher than branch and fruit litter. With the increasing stand age, the nutrient concentration of annual litter firstly decreased, then increased. The nutrient resorption caused the nutrient content of annual litter was lower than vegetation layer. The annual nutrient return of litter layer in different stand ages were 940.65 kg·hm-2,1520.38 kg·hm-2,2193.83 kg·hm-2 and 925.03 kg·hm-2. The annual nutrient return of litter were proportional to the amount of annual litter.(3) The soil bulk density and pH value increased with the increasing of soil depth, while the opposite is true for the soil water content. The soil organic matter, total nitrogen (TN), total phosphorus (TP) and total potassium (TK) decreased with the increasing of soil depth. The four nutrient elements content of soil in 35-year-old stand was higher than other three ages plantations.Soil is a big nutrient pool. With the increasing of soil depth, the accumulation of C and N was decreased, while P and K was increased.(4) With the increasing of forest age, the annual nutrient retention increased and then decreased. The annual nutrient return was true in the opposite. As the biomass of herb layer in 15-year-old and 40-year-old was high, the nutrient return increased. Therefore, the cycling coefficient of 15-year-old and 40-year-old plantation was higher than 26-year-old and 35-year-old. While the recycling period was lower than that.