Schulze E-D, Gebauer G, Ziegler H, Lange O L
Lehrstuhl Pflanzenökologie, Universität Bayreuth, Box 101251, W-8580, Bayreuth, Federal Republic of Germany.
Institut für Botanik und Mikrobiologie, TU München, Arcisstrasse 21, W-8000, München, Federal Republic of Germany.
Oecologia. 1991 Nov;88(3):451-455. doi: 10.1007/BF00317592.
Nitrogen (N) fixation was estimated along an aridity gradient in Namibia from the natural abundance of N (δN value) in 11 woody species of the Mimosacease which were compared with the δN values in 11 woody non-Mimosaceae. Averaging all species and habitats the calculated contribution of N fixation (N ) to leaf nitrogen (N) concentration of Mimosaceae averaged about 30%, with large variation between and within species. While in Acacia albida N was only 2%, it was 49% in Acacia hereroensis and Dichrostachys cinerea, and reached 71% in Acacia melifera. In the majority of species N was 10-30%. There was a marked variation in background δN values along the aridity gradient, with the highest δN values in the lowland savanna. The difference between δN values of Mimosaceae and non-Mimosaceae, which is assumed to result mainly from N fixation, was also largest in the lowland savanna. Variations in δN of Mimosaceae did not affect N concentrations, but higher δN-values of Mimosaeae are associated with lower carbon isotope ratios (δC value). N fixation was associated with reduced intrinsic water use efficiency. The opposite trends were found in non-Mimosaceae, in which N-concentration increased with δN, but δC was unaffected. The large variation among species and sites is discussed.
通过纳米比亚沿干旱梯度分布的含羞草科11种木本植物中氮的自然丰度（δN值）估算固氮量，并与11种非含羞草科木本植物的δN值进行比较。对所有物种和生境进行平均计算，含羞草科固氮（N ）对叶片氮（N）浓度的贡献平均约为30%，物种间和物种内差异很大。在阿拉伯胶树中，N 仅为2%，而在赫氏金合欢和银合欢中为49%，在聚果相思中达到71%。大多数物种的N 为10%-30%。沿干旱梯度，背景δN值有显著变化，低地稀树草原的δN值最高。含羞草科和非含羞草科的δN值差异（假定主要由固氮导致）在低地稀树草原也最大。含羞草科δN的变化不影响N浓度，但含羞草科较高的δN值与较低的碳同位素比率（δC值）相关。固氮与内在水分利用效率降低有关。在非含羞草科中发现了相反的趋势，其中N浓度随δN增加，但δC不受影响。文中讨论了物种和地点间的巨大差异。
