香港桃金娘群落植物的养分分配、季节动态和生物循环

THE DISTRIBUTION,SEASONAL DYNAMICS ANDBIOLOGICAL CYCLING OF PLANT NUTRIENTS INRHODOMYRTUS TOMENTOSA SHRUBLAND OF HONG KONG

研究香港桃金娘灌木林中植物的Ｎ、Ｐ、Ｋ养分，结果表明：（１）生物量和养分贮量的分配格局明显不同。桃金娘茎和枝的生物量占地上部生物量的６６．３％，其Ｎ、Ｐ、Ｋ贮量分别只占地上部Ｎ、Ｐ、Ｋ贮量的３８．０％、３７．６％和５１．６％；叶子的生物量占地上部生物量的１８．９％，其Ｎ、Ｐ、Ｋ贮量却分别占３９．９％，３５．４％和２８．０％。（２）常绿的桃金娘叶子终年保持相对高的养分贮量；花和果的养分贮量则存在有规律的季节变化，从４月到７月其养分贮量迅速增加，９月之后则突然下降。（３）群落净第一性生产量中的Ｎ、Ｐ、Ｋ量分别为６８４４，４７２和４３７９ｍｇ／ｍ２．ａ。对于桃金娘来说，叶子的净第一性生产量最大，所占的养分贮量也最大；花和果的净第一性生产量最小，却占净生产量中养分的第二位。（４）凋落物归还的Ｎ、Ｐ、Ｋ养分贮量分别为２８１５，１６４和８９２ｍｇ／ｍ２．ａ，地上部净第一性生产中所需Ｎ、Ｐ的４４．７％，５０．８％来自养分的内部循环。

The N,P,K nutrients of plant in Rhodomyrtus tomentosa shrubland of Hong Kong have been studied and the results show that:(1) The resource distribution patterns of phytomass and nutrients were significantly different.Although the stems and branches of R.tomentosa comprised 66.3% of aboveground phytomass,they contained only 38.0%,37.6% and 51.6% of N,P,K,respectively,Conversely,the foliage which comprised only 18.9% of the phytomass had 39.9% of the N,35.4% of the P and 28.0% of the K.(2) Evergreen R.tomentosa moved N,P,K into new foliage gradually throughout the growing season.There remained a relatively large amount of nutrients in the leaves throughout the year.In contrast to foliage,the contents of N,P and K of reproductive structures increased relatively fast from April to July and declined suddenly after September.(3) For R.tomentosa,the largest fractions of major nutrients in net primary production(NPP) went into foliage which made up the largest NPP of the components.However,the second largest fractions of nutrients in NPP went into reproductive structures although reproductive structures made up the smallest NPP.N,P,K mass in NPP of shrubland were respectively 6844,472 and 4379 mg/m^2 a.(4)On average for two years,the return of N,P,K by litterfall was respectively 2815,164 and 892 mg/m^2 a.44.7% and 50.8% of the N and P requirement in aboveground NPP came from internal cycling.