生物谷报道：对西欧和美国的森林生态系统所做的一项研究解决了一个长期存在的争议，同时也提出了很多新问题。所研究的问题是，氮沉积对全球碳循环的影响，尤其是人类活动所扮演的角色。这项新的研究表明，通过森林管理的直接影响，以及通过氮肥的使用和汽车及工业等所产生的氮氧化物的间接影响，人类活动对碳平衡或生态系统的净生产（即生态系统通过光合作用所进行的固碳作用及碳随后通过植物和土壤呼吸所进行的排放之间的平衡）具有一个深远的、基本上是积极的效应。在为这篇论文所配发的News and Views中，Peter Högberg考虑了这些发现对于诸如为森林施用氮肥的做法是否正确等实际问题的意义。
英文原文：
Nature 447, 849-851 (14 June 2007) | doi:10.1038/nature05847; Received 13 November 2006; Accepted 11 April 2007
The human footprint in the carbon cycle of temperate and boreal forests
Federico Magnani1, Maurizio Mencuccini2, Marco Borghetti3, Paul Berbigier4, Frank Berninger5, Sylvain Delzon4, Achim Grelle6, Pertti Hari7, Paul G. Jarvis2, Pasi Kolari7, Andrew S. Kowalski4, Harry Lankreijer8, Beverly E. Law9, Anders Lindroth8, Denis Loustau4, Giovanni Manca10,11, John B. Moncrieff2, Mark Rayment2, Vanessa Tedeschi3, Riccardo Valentini10 & John Grace2
Department of Fruit Tree and Woody Plant Science, University of Bologna, Bologna I-40127, Italy
School of GeoSciences, University of Edinburgh, Edinburgh EH93JU, UK
Department of Crop Systems, Forestry and Environmental Sciences, University of Basilicata, Potenza I-85100, Italy
INRA, UR1263 EPHYSE, Villenave d'Ornon F-33883, France
Departement des Sciences Biologiques, University of Québec à Montréal, Montréal, Quebec, H3C 3P8, Canada
Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, SE-75007 Uppsala, Sweden
Department of Forest Ecology, University of Helsinki, FIN-00014 Helsinki, Finland
Department of Physical Geography and Ecosystems Analysis, Lund University, S-223 62 Lund, Sweden
College of Forestry, Oregon State University, Corvallis, OR 97331, USA
Department of Forest Resources and Environment, University of Tuscia, Viterbo I-01100 Italy
Present address: Institute for Environment and Sustainability—Climate Change Unit, Joint Research Center, European Commission, I-21020 Ispra, Italy.
Correspondence to: Federico Magnani1 Correspondence and requests for materials should be addressed to F.M. (Email: federico.magnani@unibo.it).
Abstract
Temperate and boreal forests in the Northern Hemisphere cover an area of about 2 107 square kilometres and act as a substantial carbon sink (0.6–0.7 petagrams of carbon per year)1. Although forest expansion following agricultural abandonment is certainly responsible for an important fraction of this carbon sink activity, the additional effects on the carbon balance of established forests of increased atmospheric carbon dioxide, increasing temperatures, changes in management practices and nitrogen deposition are difficult to disentangle, despite an extensive network of measurement stations2, 3. The relevance of this measurement effort has also been questioned4, because spot measurements fail to take into account the role of disturbances, either natural (fire, pests, windstorms) or anthropogenic (forest harvesting). Here we show that the temporal dynamics following stand-replacing disturbances do indeed account for a very large fraction of the overall variability in forest carbon sequestration. After the confounding effects of disturbance have been factored out, however, forest net carbon sequestration is found to be overwhelmingly driven by nitrogen deposition, largely the result of anthropogenic activities5. The effect is always positive over the range of nitrogen deposition covered by currently available data sets, casting doubts on the risk of widespread ecosystem nitrogen saturation6 under natural conditions. The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly (through forest management) or indirectly (through nitrogen deposition).
