Net N mineralization and nitrification were determined using the closed-top PVC tube in situ incubation method in a subalpine meadow (Saussurea iodostegia Hance+ Carex capillaris L.)→shagspine peashrub (Caragana jubata (Pall.) Poir) shrubland→ribbed birch (Betula costata Trautv.) successional sere. The ability of the three communities to supply available N was comparatively studied. The results showed that there were apparent seasonal changes in the inorganic N pools (including NH+4-N and NO-3-N) and net N mineralization and nitrification rates in the three sites. There were generally no significant differences in the inorganic N pools among sampling events. But the NH+4-N concentration in both birch (P<0.01) and meadow (P<0.01) sites was significantly higher than that in peashrub site in June 1996, and the NO-3-N concentration in peashrub site was significantly higher than that of meadow site (P<0.05) in August 1996. The annual net N mineralization and nitrification rates in peashrub site (16.01 kg·hm-2) were higher than in birch (12.05 kg·hm-2) and meadow sites (1.64 kg·hm-2). The annual net nitrification rate in peashrub site (11.37 kg·hm-2) was higher than in meadow site (10.90 kg·hm-2) and much lower than in birch site (14.36 kg·hm-2). We conclude that the ability of peashrub shrubland soil to supply available N for plant uptake and the ability to prevent available N from denitrification and leaching were higher than that of the other two sites. The leguminous peashrub might play a potential role in supplying more N, which in turn facilitate the invasion of birch saplings during the successional processes.
箭叶锦鸡儿群落加速亚高山草甸-箭叶锦鸡儿-硕桦林演替系列的演替进程
苏波 韩兴国 渠春梅 黄建辉
（中国科学院植物研究所植被数量生态学研究开放实验室，北京100093）
摘要：利用PVC管顶盖埋管原位培育法测定了东灵山顶亚高山草甸 (紫苞风毛菊(SaussureaiodostegiaHonce) +丝柄苔草 (CarexcapillarisL .)_箭叶锦鸡儿 (Caraganajubata (Pall.Poir.) )灌丛_硕桦林 (BetulacostataTrautv .)演替序列中土壤有机N的年度净矿化与硝化作用 ,并以之作为土壤供氮能力的指标 ,比较了锦鸡儿灌丛与硕桦林和草甸土壤的供氮能力和维持氮素的能力。结果表明 ,3个生态系统土壤无机氮库 (包括NH+ 4 N和NO-3 _N)及净N矿化与硝化速率都存在明显的季节变化 ;除 1996年 6月硕桦林 (P 0 .0 1)和草甸NH+ 4_N显著高于锦鸡儿灌丛 (P 0 .0 1) ,1996年 8月锦鸡儿灌丛NO-3 _N显著高于草甸 (P 0 .0 5 )外 ,在不同取样时期无机氮库大小在 3个生态系统之间都不存在显著差异 ;锦鸡儿灌丛每公顷的年度总矿化量 (16 .0 1kg·hm-2 )高于硕桦林 (12 .0 5kg·hm-2 )和草甸 (1.6 4kg·hm-2 ) ;净硝化量 (11.37kg·hm-2 )略高于草甸 (10 .90kg·hm-2 ) ,低于硕桦林 (14.36kg·hm-2 )。尽管锦鸡儿灌丛土壤无机氮含量 ,矿化、硝化速率并不明显高于硕桦林和草甸 ,但其总年度净矿化量最高 ,所以锦鸡儿灌丛土壤的供氮能力在 3个群落中最强。此外 ,由于锦鸡儿灌丛的总年度硝化量低于硕桦林 ,略高于草甸 ,因此 ,锦鸡儿灌丛维持无机氮素的能力也较硕桦林强。总之，锦鸡儿灌丛通过提高氮素的可利用性而推动该序列的演替展。
关键词： 净9 矿化与硝化作用；锦鸡儿灌丛；演替
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