杉木、火力楠纯林及其混交林生态系统C、N贮量

C and N stocks under three plantation forest ecosystems of Chinese-fir,Michelia macclurei and their mixture

研究比较第2代连载杉木纯林、杉木与火力楠混交林以及火力楠纯林3种人工林生态系统的C、N贮量。结果表明,杉木与火力楠混交林生态系统C贮量要高于杉木纯林和火力楠纯林,而生态系统N贮量是火力楠纯林和杉木与火力楠混交林高于杉木纯林;生态系统C和N贮量的空间分布基本一致,土壤层占主要部分,其次为乔木层,再次是根系,林下植被层和凋落层所占比例最小;相关分析表明,土壤C、N贮量分别和林下植被生物量以及与森林凋落物现存量之间都具有良好的线性关系,说明林下植被和森林凋落物对土壤C、N贮量有着深刻的影响。

Chinese fir （Cunningharnia lanceolata）, a type of subtropical fast-growing conifer tree, widely distributed in South China, and its plantation area in China is more than 7 × 10^6 hm^2, accounting for 24% of total area of plantation forest in China. In recent decades, the system of successive plantation of Chinese fir is widely used in the southern china for an anticipated high economic return. However, recent studies have documented that the practice of this system led to dramatic decreases in soil fertility and forest environment as well as in productivity. Some forest ecologists and managers recognize the ecological role performed by broadleaf trees growing in mixtures with conifers, and a great deal of studies on mixtures effects have been conducted, particularly on mixture species of temperate and boreal forest, but these research results were not completely consistent. Maybe the mixtures effects depend in large part on specific site conditions, the interactions among species in mixtures and biological characteristics of species, etc.. Although some researchers also studied the effects of mixtures of Chinese fir and broadleaf tree species on soil fertility, forest environment and tree growth status, little information is available about the effects of Chinese fir and its mixtures with broadleaves on carbon and nitrogen stocks. The experimental site was situated at Huitong Experimental Station of Forest Ecology, Chinese Academy of Sciences, Hu＇nan Province （N 26°40′-27°09′ latitude and E 109°26′- 110°08′ longitude）. It locates at the transition zone from the Yunnan-Guizhou Plateau to the low mountains and hills of southern bank of Yangtz River at an altitude of 300-1100 m above mean sea level and at the same time, it is also a member of the Chinese Ecosystem Research Network （CERN）, sponsored by the Chinese Academy of Sciences （CAS）. This region has a humidmid-subtropical monsoon climate with a mean annual precipitation of 1200-1400 mm, most of the rain falling between April and August, and a mean temperature of 16.5℃ with a mean minimum of 4.9℃ in January and a mean maximum of 26.6℃ in July. The soil of the experimental field is red-yellow soil. After a clear-cutting of the first generation Chinese-fir （Cunninghamia lanceolata） plantation forest in 1982, three different plantation forest ecosystems, viz. mixture of Michelia macclurei and Chinese fir （MCM）, pure Michelia macclurei stand （PMS） and pure Chinese-fir stand （PCS）, were established in spring of 1983. Comparative study on C and N stocks under these three plantation forest ecosystems was conducted in 2004. The results showed that, the carbon stocks were greater under the mixtures than under the pure Chinese fir forest and the pure broad-leaved forest, and the broadleaves and the mixtures showed higher values in the nitrogen stocks compared with the pure Chinese fir forest. The spatial distribution of carbon and nitrogen stocks was basically consistent, the value being greater in soil layer, followed by tree layer, roots, understory and then litter layer. The carbon and nitrogen stocks in soil layer were, respectively both highly correlated with the biomass in understory and litter layer, indicaing understory and forest litterfall exerted a profound effect on soil carbon and nitrogen stocks under plantation ecosystems. However, correlations between soil carbon, nitrogen stocks and belowground biomass of stand have not been observed in this study.