Hie standard plot method was used to study the distribution and biological cycling of 10 nutrient elements( N,P,K,Ca, Mg, Fe, Mn,Zn,Cu and B) in the 7-year-old( middle-age) Acacia crassicarpa plantation. The results indicated that concentrations of the 10 nutrient elements in different organs of A. Crassicarpa plantation were in the order of leaves > bark > branch > root > stem. The contents of N were the highest, K and Ca the second, Mg and P the lowest for macro-elements, whereas Mn and Fe were the highest, B and Zn the second, and Cu the lowest for micro-elements. The nutrient storage of the plantation was 1 121.08 kg ? Hm~2, of which overstorey of A. Crassicarpa trees stored 848.94 kg ? Hm~2 accounting for 75. 72% .forest floor 116. 05 kg ? Hm'2 account for 10. 35% ,and standing litter 156. 08 kg ? Hm"2 account for 13. 92%. The amounts of nutrient elements in different parts of trees was in the order of stem > leaves > branch > bark > root. The amounts of annual uptake, retention and return of 10 elements in the plantation were 261.87,140.59 and 121.28 kg ? Hm ~2, respectively. The cycling coefficient and recycling period were 0. 54 and 6. 04. As was observed,the nutrient utilization efficiency in middle-aged A. Crassicarpa plantation was lower,but the return rate was higher and the turnover period was shorter, resulting in the recovery and maintenance of forestland fertilization.%采用标准样地法研究了7年生(中龄林)厚荚相思Acacia crassicarpa人工林10种养分元素(N、P、K、Ca、Mg、Fe、Mn、Zn、Cu和B)的分布和生物循环特点.结果表明:1)厚荚相思不同器官营养元素含量为:树叶＞干皮＞树枝＞树根＞干材,各器官中大量营养元素含量以N最高,其次是Ca或K,然后是Mg,P最低,微量元素含量则以Mn和Fe最高,其次是Zn和B,Cu最低；2)厚荚相思人工林养分贮存量为1 121.07 kg·hm-2,其中乔木层、林下植物层和凋落物层积累量依次为848.94、116.05和156.08 kg·hm-2,分别占总积累量的75.72％、10.35％和13.92％,林木中不同器官养分元素贮存量排序为:干材＞树叶＞树枝＞干皮＞树根；3)厚荚相思人工林养分年吸收量、归还量、存留量分别为261.87、140.59和121.28 kg hm-2·年-1,循环系数为0.54,周转期为6.04年.因此,厚荚相思中龄林的营养元素利用率较低,归还速率较快,周转期较短,有利于林地地力的恢复和维持.
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