[C and N allocation patterns in planted forests and their release patterns during leaf litter decomposition in subalpine area of west Sichuan].

With the planted forest ecosystems of Cercidiphyllum japonicum, Betula utilis, Pinus yunnansinsis, and Picea asperata in subalpine area of west Sichuan as test objects, their total biomass and the C and N contents in soils and tree organs were determined. The results showed that the allocation of C in tree organs had less correlation with the age of the organs, while that of N and C/N ratio had closer relationship with the age. The N content in young organs was higher than that in aged ones, whereas the C/N ratio was higher in aged organs than in young organs, and higher in the leaf litters of needle-leaved forests than in those of broad-leaved forests. There was an obvious enrichment of C and N in the topsoil of test forests. The accumulated amounts of C and N in the whole planted forest ecosystem, including tree, litter, and 0-40 cm soil layer, were 176.75-228.05 t x hm(-2) and 11.06-16.54 t x hm(-2), respectively, and the nutrients allocation ratio between soil-litter and tree was (1.9-3.3):1 for C and (15.6-41.5):1 for N. Needle-leaved forests functioned as a stronger "C-sink" than broad-leaved forests. The decomposition rate of the leaf litters in needle-leaved forests was larger than that in broad-leaved forests, with the turnover rate being 2.2-3.7 years and 3.9-4.2 years, respectively. During the decomposition of leaf litter, the C in all of the four forests released at super-speed, with the turnover rate being 1.9-3.4 years. As for N, it also released at super-speed in C. japonicum and B. utilis forests, with the turnover rate being 1.9-3.2 years, but released at low speed in P. yunnansinsis and P. asperata forests, with the turnover rate being 6.7-8.5 years.

[Effects of leaf litter replacement on soil biological and chemical characteristics in main artificial forests in Qinling Mountains].

Through 2 years leaf litter replacement experiments in 4 typical artificial pure forests Larix kaempferi, Pinus tabulaeformis, Catalpa fargesii, and Quercus aliena var. acuteserrata in Qinling Mountains of China, this paper studied the effects of leaf litter replacement on soil biological and chemical characteristics and the interspecific relationships between different tree species. The results showed that the annual decomposition rate of broad-leaved litter was 33.70% higher than that of needle-leaved litter. The annual decomposition rate of needle-leaved litter increased by 8.35%-12.15% when replaced to broad-leaved forests, whereas that of broad-leaved litter decreased by 5.38%-9.49% when replaced to needle-leaved forests. Leaf litter replacement between needle and broad-leaved forests could increase the contents of soil organic-C and available N, P and K, and the increments were obviously higher in needle-leaved forests (8.70%-35.84%) than in broad-leaved forests (3.73%-10.44%). In needle-leaved forests, the increments with the replacement of C. fargesii litter (24.63%-35.84%) were higher than those with the replacement of Q. aliena var. acuteserrata litter (8.70%-28.15%). Furthermore, the replacement of broad-leaved litter could make the soil pH in needle-leaved forests changed from light-acid to neutral, and increase soil enzyme activities, microbial amounts, and microbial biomass C and N contents. The increments with the replacement of C. fargesii litter were higher than those with the replacement of Q. aliena var. acuteserrata litter. The soil enzyme activities, microbial amounts, and microbial biomass C and N contents in broad-leaved forests after the replacement of needle-leaved litter differed with broadleaved tree species. Q. aliena var. acuteserrata forest had the higher soil enzyme activities and microbial biomass C and N contents, while C. fargesii forest was in adverse. It was suggested that in the control of soil degradation under artificial pure forests, much attention should be paid to the direction of interspecific relationship in mixed forestation and leaf litter replacement.