1、原文

Key role of symbiotic dinitrogen fixation in tropical forest secondary succession

Nature 502, 224–227 (10 October 2013) doi:10.1038/nature12525
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA
Forests contribute a significant portion of the land carbon sink, but their ability to sequester CO2may be constrained by nitrogen, a major plant-limiting nutrient. Many tropical forests possess tree species capable of fixing atmospheric dinitrogen (N2), but it is unclear whether this functional group can supply the nitrogen needed as forests recover from disturbance or previous land use, or expand in response to rising CO2. Here we identify a powerful feedback mechanism in which N2 fixation can overcome ecosystem-scale deficiencies in nitrogen that emerge during periods of rapid biomass accumulation in tropical forests. Over a 300-year chronosequence in Panama, N2-fixing tree species accumulated carbon up to nine times faster per individual than their non-fixing neighbours (greatest difference in youngest forests), and showed species-specific differences in the amount and timing of fixation. As a result of fast growth and high fixation, fixers provided a large fraction of the nitrogen needed to support net forest growth (50,000kg carbon per hectare) in the first 12years. A key element of ecosystem functional diversity was ensured by the presence of different N2-fixing tree species across the entire forest age sequence. These findings show that symbiotic N2 fixation can have a central role in nitrogen cycling during tropical forest stand development, with potentially important implications for the ability of tropical forests to sequester CO2.

2、翻译文

共生固氮在热带次生林中的关键作用

普林斯顿大学生态与生物进化系新泽西州 08544美国

森林是陆地碳汇的重要来源。氮素是主要的植物生长限制性养分，森林吸收CO2的碳汇作用受制于土壤中的氮素匮乏。许多热带森林树种具备吸收固定大气中N2的能力，但这种固氮功能是否能为森林恢复提供所需氮素还不是很清楚。本文我们确认了一个强有力的反馈机制，固氮可以克服生态系统尺度氮素匮乏。本文我们确定了热带次生林恢复生物量快速积累阶段，固氮可以克服生态系统尺度氮素匮乏的强有力的反馈机制。在巴拿马，经历了300年的积累，巴拿马固氮树种积累碳的速度是哪些并不临近固氮树种的非固氮树种碳积累速度的9倍，尤其是对幼林差距很大。热带次生林恢复的前12年，生长迅速和固氮作用强烈，这为森林生长提供了大部分氮素支持。通过不同固氮树种在完整林龄序列中固氮作用研究，共生固氮作用成为森林生态系统功能多样性的重要指标被确定。这个发现表明，在热带次生林演替过程中，共生固氮在碳循环中处于中心地位，对于热带森林碳汇能力具有重要的潜在意义。

3、对我的启发

这是Nature上的最新的一篇论文，对我的启发很大。森林碳汇作用受制于土壤中氮素的匮乏。而具有共生固氮作用的植物能直接吸收空气中的氮气，进而促进了快速发育进而增进了碳汇作用。而且对周边树木具有育肥作用。

是否在北京山区也存在这种现象呢。北京土石山区土层浅薄，养分贫瘠。如果能将固氮植物与非固氮主导营林树种混交营林，不仅增加了生物多样性和稳定性，而且还可以提高生物群落的活性，提升碳汇作用。

接下来可以按照以下顺做开展。第一，通过文献资料查阅，看看北京山区主要的共生固氮植物种有哪些；第二，通过野外考察，寻找野外多种多年龄组的固氮植物；第三，通过固氮植物与周边非固氮植物土壤有机碳的采样分析，研究固氮植物对土壤有机碳的贡献差异；第四，进而提出通过共生固氮植物混交，提升生态系统活力与稳定性，增进人工林碳汇能力的营林模式。