Millett J, Millard P, Hester A J, McDonald A J S
The Macaulay Institute, Craigiebuckler, Aberdeen, UK.
New Phytol. 2005 Nov;168(2):413-22. doi: 10.1111/j.1469-8137.2005.01510.x.
Deciduous trees recycle nitrogen within their tissues. The aim of this study was to test the hypothesis that reductions in plant growth, caused by competition and herbivory, reduce the sink strength for N during autumn nutrient withdrawal, and reduce the storage capacity and hence the amount of N remobilized in the following spring. We used (15)N-labelled fertilizer to quantify N uptake, leaf N withdrawal and remobilization. Betula pubescens saplings were grown with either Molinia caerulea or Calluna vulgaris, and subjected to simulated browsing damage. Competition reduced B. pubescens leaf N withdrawal and remobilization, with C. vulgaris having a greater effect than M. caerulea. However, simulated browsing had no significant effect on sapling N dynamics. The patterns of leaf N withdrawal and remobilization closely followed sapling dry mass. We conclude that the effect of competition on sapling mass reduces their N-storage capacity. This reduces sink strength for leaf N withdrawal and the source strength for remobilized N. The ability of saplings to compensate for browsing damage removed any potential effect of browsing on N dynamics.
落叶树在其组织内循环利用氮。本研究的目的是检验以下假设：由竞争和食草作用导致的植物生长减少，会在秋季养分吸收过程中降低对氮的库强，并降低储存能力，从而减少次年春季氮的再迁移量。我们使用氮 - 15标记肥料来量化氮的吸收、叶片氮的吸收和再迁移。将欧洲白桦幼树与蓝禾本科草或帚石楠一起种植，并对其进行模拟啃食损伤。竞争减少了欧洲白桦叶片氮的吸收和再迁移，帚石楠的影响比蓝禾本科草更大。然而，模拟啃食对幼树的氮动态没有显著影响。叶片氮的吸收和再迁移模式与幼树干质量密切相关。我们得出结论，竞争对幼树质量的影响降低了它们的氮储存能力。这降低了叶片氮吸收的库强和再迁移氮的源强。幼树补偿啃食损伤的能力消除了啃食对氮动态的任何潜在影响。
