杉木(Cunninghamia lanceolata)、火力楠(Michelia macclurei)纯林及其混交林细根分布、分解与养分归还

用土钻法研究了杉木（Ｃｕｎｎｉｎｇｈａｍｉａｌａｎｃｅｏｌａｔａ）、火力楠（Ｍｉｃｈｅｌｉａｍａｃｌｕｒｅｉ）纯林和混交林的细根分布，用分解袋法研究了杉木和火力楠细根的分解，计算了３个林分中细根分解的Ｎ，Ｐ，Ｋ，Ｃａ，Ｍｇ的归还量。活细根的垂直分布以火力楠纯林层次性最强，混交林次之，杉木纯林最差。火力楠细根的养分含量比杉木细根高，而Ｃ／Ｎ比低。火力楠细根年分解率比杉木快，火力楠为５７．７％，而杉木为３２．７８％。细根分解的养分归还量多少顺序依次为：火力楠纯林、杉木火力楠混交林和杉木纯林。混交林中，细根分解的Ｎ，Ｐ，Ｋ，Ｃａ和Ｍｇ归还量分别为枯枝落叶的３３．３８％，５．８２％，２６９．３３％，３４．１２％和３７６．０８％。细根在３个林分的物质循环和周转中起着不可忽视的作用。

DISTRIBUTION,DECOMPOSITION AND NUTRIENT RETURN OF THE FINE ROOT IN PURE Cunninghamia lanceolata, Michelia macclurei AND THE MIXED PLANTATIONS

Soil corer was used to investigate the distribution of fine root and a traditional method of nylon litter bag to measure the decomposition in pure Cunninghamia lanceolata and Michelia macclurei var Sublanea ,and the mixed plantations.Nutrient returns of N,P,K,Ca and Mg in the above three plantations were estimated based on the decomposition experiment.The vertical distribution of live fine root for pure M.macclurei stand was the most superficial,the mixed stand was intermediate,pure C.lanceolata was the least.The fine root of M.macclurei decomposed more quickly than that of C.lanceolata because of its higher original nutrient content and lower C:N ratio.Nutrient return from fine root was largest in pure M.macclurei ,the mixed stand intermediate,and pure C.lanceolata the least.In the mixed stand,returns of N,P,K,Ca and Mg from fine root decomposition were 33 38%,5 82%,269 33%,34 12% and 376 08% of that from decomposition of leaf and twig litter respectively.It is suggested that fine root plays an important role in nutrient cycling of the stands.