关键词: 养分含量, 地表枯落物, 分解层, 生态化学计量比, 杉木, 人工林, 次生林

Abstract: [Objective] The objective was to investigate the stoichiometry of carbon (C), nitrogen (N) and phosphorus (P) in litter and soil in four forest types at different succession stages in subtropical region of China, in order to provide a scientific basis for understanding the mechanism of influence of restoration of subtropical secondary forest on soil nutrients and forest restoration. [Method] The study was conducted in a permanent observation plot in size of 1 hm² at Dashanchong Forest Park in Changsha County, Hunan Province, China. The method of spatial sequence was used instead of time successional sequence, four types of subtropical forests:plantation of Cunninghamia lanceolata, mixed forest of Pinus massoniana+Lithocarpus glaber, deciduous broad leaved forest of Choerospondias axillaris, and evergreen broad-leaved forest of L. glaber+Cyclobalanopsis glauca were chosen to represent successional stages of forest restortation in the region. Based on the status of litter decomposition, the litter of forest ground was divided into layers of un-decomposed, semi-decomposed and decomposed. within the permanent observation plot, 6 small sample plots (10 m×10 m) were established along the slope, and each was set at random with 2 sample squares (1 m×1 m), Within each of the sample squares, soil samples were collected from the three soil layers respectively with 0-10 cm, 10-20 cm, and 20-30 cm depth. Concentrations of C, N and P in litter and soil samples were analyzed and the ratios of C/N, C/P, and N/P were estimated. [Result] At the same litter decomposition layer, concentrations of C was decreased, while N and P contents were increased with successional stages and the increases of proportion of broad-leaved trees in the studied sites, except at the decomposed layer. Contents of C was decreased with litter decomposition progress in the four forest types. Specifically, N content ranked in an order of semi-decomposed layer > decomposed layer > un-decomposed layer in the mixed fores of P. massoniana+L. glaber, and in an order as semi-decomposed layer >un-decomposed layer >decomposed layer in the plantation of C. lanceolata, deciduous broad leaved forest of C. axillaris, and the evergreen broad-leaved forest of L. glaber+C. glauca. The distribution of P content was in an order of un-decomposed layer>semi-decomposed layer>decomposed layer in the deciduous broad-leaved forest of C. axillaries, and semi-decomposed layer>un-decomposed layer>decomposed layers (except the mixed forest of P. massoniana+L. glaber) in the plantation of C. lanceolata, the mixed forest of P. massoniana+L. glaber, evergreen broad-leaved forest of L. glaber+C. glauca. At the similar decomposition conditions, the ratios of C/N, C/P and N/P of litter were decreased along with forest successional progress. The C/N and C/P ratios of litter were decreased, but the N/P ratios were not significantly changed with the litter decomposition progress. The contents of C, N and P were increased with successional stages. The ratios of C/N and C/P were similar in 0-30 cm soil layer in the four subtropical forest types. It was found that the ratios of C/N and C/P were the highest in the evergreen broad-leaved forest of L. glaber+C. glauca, followed by the mixed forest of P. massoniana+L. glaber, and the lowest in the plantation of C. lanceolata. No significant differences of N/P ratios were found among the studied forests. There were significant negative correlations between C concentration at un-decomposed layer and C, N and P contents in 0-10 cm, 0-30 cm soil layers, while significant positive correlations were founded between N and P contents at un-decomposed layer and C, N (except N) and P contents in 0-10 cm, 0-30 cm soil layers. Significant negative correlations were found between the C/N, C/P and N/P ratios and C (except N/P), N and P contents in 0-10 cm, 0-30 cm soil layers. There were no significant correlations of C/N, C/P and N/P ratios between litter and soil in all four forest types. [Conclusion] The ratios of C/N, C/P and N/P were decreased, but C, N and P were increased along with the successional stages and the increase of proportion of broad-leaved trees in forests. The C, N and P contents and the C/N, C/P and N/P ratios in undecomposed layers significantly affected the contents of C, N, P in soil. As a consequence, it is a critical during forest management process to adjust the species composition of the forests in order to change the quality of litter layer.

Key words: nutrient concentration, forest floor litter, decomposed layer, ecological stoichiometric ratio, Cunninghamia lanceolata, plantation, secondary forest