Nitrogen uptake by Eucalyptus regnans and Acacia spp. - preferences, resource overlap and energetic costs.
Nitrogen uptake by Eucalyptus regnans and Acacia spp. - preferences, resource overlap and energetic costs.
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DOI：
10.1093/treephys/tpn033
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发表时间：
2009-03
期刊：
影响因子：
4
通讯作者：
S. Pfautsch;H. Rennenberg;T. Bell;M. Adams
中科院分区：
文献类型：
--
作者：
S. Pfautsch;H. Rennenberg;T. Bell;M. Adams
在澳大利亚东南部，上层树种 Eucalyptus regnans F. Muell。通常与两种豆科林下树种 Acacia melanoxylon (R. Br. Ex Ait. f.) 或 Acacia dealbata (Link.) 一起生长。我们的目标是阐明主要桉树与其伴生金合欢树之间对于氮 (N) 源的相互作用。使用稳定的氮同位素作为示踪剂表明，铵是所有物种首选的土壤氮源，然而，不同物种的总氮吸收量差异很大。双标记 ((13)C/(15)N) 谷氨酰胺的研究表明，E. regnans 和金合欢属植物均少量摄取这种形式的有机氮。这些数据和其他数据表明，与北方森林相比，有机氮并不是山梣林氮营养的重要组成部分。现场和实验室研究提供的证据表明，金合欢树的固氮能力随林分发育而变化，固氮物种在森林生长的早期而非成熟阶段的氮营养中发挥着重要作用。对四个氮源和三个物种的氮吸收效率指数（每吸收单位氮消耗的氧气量）进行了比较。硝酸盐吸收是氮获取效率最低的形式，尤其是与成本低 30 倍的铵吸收相比。谷氨酰胺的吸收效率介于铵盐和硝酸盐之间。金合欢属植物对氮的吸收效率差异最为明显。至少对于 E. regnans 来说。我们得出的结论是，同域金合欢属植物的需求存在重叠。由于金合欢属生化策略的变化，特定土壤氮源的 E.regnans 可以被绕过。由林分发育过程中土壤氮浓度增加引发。进一步的研究可能会阐明这是否是复杂森林生态系统的共同特征，或者是桉树和金合欢树之间相互作用的特殊性。
In southeastern Australia, the overstory species Eucalyptus regnans F. Muell. commonly grows with either of the two leguminous understory trees, Acacia melanoxylon (R. Br. Ex Ait. f.) or Acacia dealbata (Link.). Our objective was to elucidate interactions between the dominant eucalypt and its companion acacias for nitrogen (N) sources. Use of stable N isotopes as tracers revealed that ammonium was the preferred soil N source for all species, nevertheless, total N uptake varied greatly among species. Studies with double-labeled ((13)C/(15)N) glutamine indicated the uptake of this form of organic N in small amounts by both E. regnans and the Acacia spp. These and other data imply that, in contrast to boreal forests, organic N is not a significant component of N nutrition in mountain ash forests. Field and laboratory studies provided evidence that N(2)-fixation capacity of acacias varies with stand development, with N-fixing species playing an important role in N nutrition during the early but not the mature stages of forest growth. An index of N-uptake efficiency - the amount of oxygen consumed per unit N taken up - was compared across four N sources and three species. Nitrate uptake was the least efficient form of N acquisition, especially compared with ammonium uptake which was up to 30-fold less costly. Efficiency of glutamine uptake was intermediate between that of ammonium and nitrate. Differences in uptake efficiency among N forms were most pronounced for the Acacia spp. and least for E. regnans. We conclude that an overlap in requirements among sympatric Acacia spp. and E. regnans for specific soil N sources can be bypassed because of changes in biochemical strategies of Acacia spp. triggered by increasing soil N concentrations during stand development. Further studies might elucidate whether this is a common feature of complex forest ecosystems, or a specialty of the interaction between eucalypts and acacias.