Ciclo Del N Hipotesis Gaia

SC IE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 0 ( 2 00 8 ) 3 4 4–3 55

a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m

w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v

A reappraisal of the terrestrial nitrogen cycle: What can we learn by extracting concepts from Gaia theory?
Malcolm S. Cresser a,⁎, Matthew J. Aitkenheadb , Ishaq A. Miana
a bEnvironment Department, University of York, Heslington, York YO10 5DD, UK Department of Plant & Soil Science, University of Aberdeen, Old Aberdeen AB24 2UE, UK

AR TIC LE I N FO
Article history: Received 6 May 2008 Received in revised form 25 June 2008 Accepted 25 June 2008 Available online 3 August 2008 Keywords: Nitrogen cycling Gaia Ammonium Nitrate Earth Weathering Biodiversity Evolution

ABS TRACT
Although soil scientists and most environmental scientists are acutely aware of the interactions between the cycling of carbon and nitrogen, for conceptual convenience when portraying the nitrogen cycle in text books the N cycle tends to be considered in isolation from its interactions with the cycling of other elements and water, usually as a snap shot at the current time; the origins ofdinitrogen are rarely considered, for example. The authors suggest that Lovelock's Gaia hypothesis provides a useful and stimulating framework for consideration of the terrestrial nitrogen cycle. If it is used, it suggests that urbanization and management of sewage, and intensive animal rearing are probably bigger global issues than nitrogen deposition from fossil fuel combustion, and that plantevolution may be driven by the requirement of locally sustainable and near optimal soil mineral N supply dynamics. This may, in turn, be partially regulating global carbon and oxygen cycles. It is suggested that pollutant N deposition may disrupt this essential natural plant and terrestrial ecosystem evolutionary process, causing biodiversity change. Interactions between the Earth and other bodies inthe solar system, and possibly beyond, also need to be considered in the context of the global N cycle over geological time scales. This is because of direct potential impacts on the nitrogen content of the atmosphere, potential long-term impacts of past boloid collisions on plate tectonics and thus on global N cycling via subduction and volcanic emissions, and indirect effects upon C, O andwater cycling that all may impact upon the N cycle in the long term. © 2008 Elsevier B.V. All rights reserved.

1.

Introduction

If there is a silver lining to the cloud of atmospheric pollution, it has to be the wake up call that it gave to the scientific community in the latter quarter of the twentieth century. It became transparently obvious that pollution impacts crossed internationalboundaries, but also that interdisciplinary approaches were essential to reliably quantify impacts if policy makers were to be convinced of the need to implement strict, and sometimes expensive, pollution abatement strategies. The need for interdisciplinary research stemmed from the realisation of the necessity to quantitatively assess impacts upon
⁎ Corresponding author. E-mail address:msc5@york.ac.uk (M.S. Cresser).

integrated ecosystem functioning over wide ranges of both spatial and temporal sales, incorporating all the often complex interactions that occur between the atmosphere, soils and/or outcropping rocks, the soil–plant communities and microflora and fauna, and drainage waters to surface waters and/or ground waters. In many respects this was a logical extension of the problemsfaced by soil scientists in earlier decades when attempting to define soil fertility, which similarly varies over time and space in three dimensions, and encompasses chemical, physical and biological parameters which interact not only with each other but also with environmental factors such as climate and topography. Soil scientists try to circumvent this

0048-9697/$ – see front matter © 2008...