Zanetti S, Hartwig U A, van Kessel C, Lüscher A, Hebeisen T, Frehner M, Fischer B U, Hendrey G R, Blum H, Nösberger J
Institute of Plant Sciences, Swiss Federal Institute of Technology, 8092 Zurich, Switzerland fax: ++41-1-632-1153; e-mail:
Department of Agronomy and Range Science, University of California, Davis, CA 95616, USA, , , , , , US.
Oecologia. 1997 Sep;112(1):17-25. doi: 10.1007/s004420050278.
The extent of the response of plant growth to atmospheric CO enrichment depends on the availability of resources other than CO. An important growth-limiting resource under field conditions is nitrogen (N). N may, therefore, influence the CO response of plants. The effect of elevated CO (60 Pa) partial pressure (pCO) on the N nutrition of field-grown Lolium perenne swards, cultivated alone or in association with Trifolium repens, was investigated using free air carbon dioxide enrichment (FACE) technology over 3 years. The established grassland ecosystems were treated with two N fertilization levels and were defoliated at two frequencies. Under elevated pCO, the above-ground plant material of the L. perenne monoculture showed a consistent and significant decline in N concentration which, in general, led to a lower total annual N yield. Despite the decline in the critical N concentration (minimum N concentration required for non-N-limited biomass production) under elevated pCO, the index of N nutrition (ratio of actual N concentration and critical N concentration) was lower under elevated pCO than under ambient pCO in frequently defoliated L. perenne monocultures. Thus, we suggest that reduced N yield under elevated pCO was evoked indirectly by a reduction of plant-available N. For L. perenne grown in association with T. repens and exposed to elevated pCO, there was an increase in the contribution of symbiotically fixed N to the total N yield of the grass. This can be explained by an increased apparent transfer of N from the associated N-fixing legume species to the non-fixing grass. The total annual N yield of the mixed grass/legume swards increased under elevated pCO. All the additional N yielded was due to symbiotically fixed N. Through the presence of an N-fixing plant species more symbiotically fixed N was introduced into the system and consequently helped to overcome N limitation under elevated pCO.
植物生长对大气中二氧化碳浓度升高的响应程度取决于除二氧化碳之外其他资源的可利用性。在田间条件下，一种重要的生长限制资源是氮（N）。因此，氮可能会影响植物对二氧化碳的响应。利用自由空气二氧化碳富集（FACE）技术，在3年的时间里研究了二氧化碳分压（pCO）升高至60帕对单独种植或与白三叶混种的田间多年生黑麦草草地氮营养的影响。对已建成的草地生态系统设置了两个施氮水平，并以两种频率进行刈割。在pCO升高的情况下，多年生黑麦草单作地上部分植物材料的氮浓度持续显著下降，总体上导致年度总氮产量降低。尽管在pCO升高的情况下临界氮浓度（非氮限制生物量生产所需的最低氮浓度）有所下降，但在频繁刈割的多年生黑麦草单作中，pCO升高时的氮营养指数（实际氮浓度与临界氮浓度之比）低于环境pCO时。因此，我们认为pCO升高时氮产量降低是由植物可利用氮的减少间接引起的。对于与白三叶混种并暴露于pCO升高环境下的多年生黑麦草，共生固定氮对草地总氮产量的贡献增加。这可以通过从相关的固氮豆科物种向非固氮禾本科植物的氮表观转移增加来解释。在pCO升高的情况下，禾本科/豆科混合草地的年度总氮产量增加。所有额外产生的氮都来自共生固定氮。通过固氮植物物种的存在，更多的共生固定氮被引入系统，从而有助于克服pCO升高时的氮限制。
