Forests

Abstract

: In order to relieve the effects of stand ages and densities on litter nutrients changes and its returns in planted Pinus massoniana forests, we selected four forest types of stand ages (Young stand, Half-mature stand, Mature stand, and Over-mature stand) and four forest types of stand densities (Low density, Middle-low density, Middle-high density, and High density) as the research object (total 8 stands) in Zhenlong Forest Farm of Hengxian County, Nanning, Guangxi Zhuang Autonomous Region; and we measured litter carbon, nitrogen and phosphorus contents and its ratios in the early and latter degradation period of litter. The results were as follows: (1) C contents in early degradation period of litter were relatively higher in Mature and Over-mature stands, N contents were relatively higher in Over-mature and Half-mature stands, but P contents and N:P ratios were not different among four stands, C:N and C:P ratios were highest in mature stand. It indicated that the growth rates were relatively faster in Young stand and Half-mature stand, resulting in Pinus massoniana needing large amounts of N and P in the two stands. (2) In early degradation period of litter, C contents increased but P contents decreased with the increasing stand densities, N contents were not different among four densities. C:P and N:P ratios were relatively higher in Middle-high and High density stands, resulting in Pinus massoniana needing large amounts of N and P and higher P reabsorption in these stands. (3) The C contents and C:N, C:P, and N:P ratios in latter degradation period of litter were lower than those in early degradation period of litter, but N and P contents were adverse. It indicated that N and P were enriched to litters along the advancing degradation periods. (4) The difference of C contents between the early and the latter degradation period of litter was relatively higher in Half-mature, Middle-high, and High density stands, but C:N and C:P ratios was relatively lower, indicating that the degradation rates of litters C were relatively higher in these stands. The above results suggested that Pinus massoniana may need large amounts of N and P in Half-mature, Middle-high, and High density stands, and resulting in high nutrient resorption efficiency; additionally, there were high potential degradation rates of litter carbon, which was beneficial to return litter C to soils in these forest stands.