Nitrogen Cycling In Ecosystems Of Latin America And The Caribbean

The large and rapidly expanding body ofliterature related to nitrogen cycling in both managed and native terrestrial ecosystems reflects the importance accorded to the behaviour of this vital and often limiting nutrient. Research at the organism, ecosystem and landscape levels commonly addresses questions concerning nitrogen acquisition, internal cycling and retention. Goals for this research include increased agricultural productivity and a better understanding of human impact on local, regional and global nitrogen cycles. Nitrogen cycle research in tropical regions has a long and distinguished history. Research on different aspects of nitrogen cycling in ecosystems of the tropics has been carried out in many regions. In relatively few instances has there, however, been a focus on the biogeochemical cycles at the ecosystem level. The meeting resulting in this volume was an attempt to bring together existing information on nitrogen cycling in ecosystems of Latin America and the Caribbean and discuss this in an ecosystem context.

The large and rapidly expanding body ofliterature related to nitrogen cycling in both managed and native terrestrial ecosystems reflects the importance accorded to the behaviour of this vital and often limiting nutrient. Research at the organism, ecosystem and landscape levels commonly addresses questions concerning nitrogen acquisition, internal cycling and retention. Goals for this research include increased agricultural productivity and a better understanding of human impact on local, regional and global nitrogen cycles. Nitrogen cycle research in tropical regions has a long and distinguished history. Research on different aspects of nitrogen cycling in ecosystems of the tropics has been carried out in many regions. In relatively few instances has there, however, been a focus on the biogeochemical cycles at the ecosystem level. The meeting resulting in this volume was an attempt to bring together existing information on nitrogen cycling in ecosystems of Latin America and the Caribbean and discuss this in an ecosystem context.

This book contains the proceedings of the `8th Nitrogen Workshop' which was held at the University of Ghent, Belgium, from 5 to 8 September 1994. Although nitrogen dynamics in different ecosystems have been studied for several decades, new orientations and other emphases have recently emerged. Previously, nitrogen was considered as an essential element mostly in terms of productivity, but now, more emphasis is attached to environmental consequences. More than 100 contributions in this book tackle recent developments within the fields of nitrogen advice systems, plant response to fertilization, immobilization and mobilization, nitrification, denitrification, leaching, ammonia volatilization and biological nitrogen fixation. A large number of papers is devoted to the formation of gaseous nitrogen compounds, while mineralization-immobilization is another topic of important interest. The book also contains the reports of discussion groups on different aspects of the nitrogen cycle.

Inputs of nitrogen to terrestrial and aquatic ecosystems have increased several-fold over the last one hundred and fifty years, with the steepest increases during the last four decades. The expansion of fertilizer manu facture and use, the increase in fossil fuel combustion, the intensification of animal husbandry, and widespread cultivation of N2 fixing crops have all contributed to the dramatic increase in N inputs. The increase has been most rapid in Northern Hemisphere (NH) temperate ecosystems, but presently subtropical and tropical regions of Asia are also experiencing an explosive increase in N inputs to terrestrial ecosystems (W. Chameides, pers. comm. ; Galloway et al. 1996). Projected increases in N deposition for these trop ical and subtropical regions, with a high natural background of N inputs, exceed increases projected for temperate and arctic regions (Cleveland et al. submitted; Galloway et al. 1994; Holland & Lamarque 1997a). Compared to biological N fixation, N deposition is becoming a proportionately greater source of N to terrestrial and aquatic ecosystems worldwide (Vitousek et al. 1997). 6 The nitrogen contained in the atmosphere as N , 3. 9 * 10 Tg (Tg = 2 12 10 g), is the largest reservoir of N in the Earth system (Warneck 1988). However, this paper focuses on the nitrogen emissions and deposition that have been transformed from N2 into reactive forms that are biologically avail able (e. g. Vitousek et al. 1997).

The success of shifting cultivation systems developed by subsistence farmers testifies to the resilience of the "natural" soil-plant ecosystems to recover from the offtake of nutrients in crops and loss of soil struc ture. By contrast, the development of intensive cropping systems requires large inputs especially of nitrogen, together with phosphorus, sulphur and other essential elements in order to maintain the nutrient levels needed for abundant crop yields. As Dr. Cooke ably pointed out in his introductory lecture, the dis coveries and experiments of the 19th century encouraged farmers in temperate zones to rely greatly on chemical fertilizers supplements. However, the work of Charles Da{win on soil mixing by earthworms and the discovery by Hellriegel and Wilfarth in 1886 that the nodules on legume roots contain colonies of symbiotic bacteria able to "capture" atmospheric nitrogen molecules to the benefit of the host plant heralded a growing realization of the importance of soil biota in fertility studies. Biological fixation of nitrogen has been the theme of many meetings and publi~ations hitherto but at this Conference, convened on the delightful campus of Reading University, attention was mainly focussed on other biological processes in soil fertility. These Proceedings record the dominant themes and include six keynote addresses delivered at plenary sessions and seven introductory lectures to paper reading sessions by invited individuals plus 22 of the proferred papers, in six sections as tabled in the contents list.

From the research results and discussions presented in this book it becomes clear that a profound understanding of the various interrelationships of the nutritional aspects allows the implementation of specific management strategies to improve stability and productivity of forest ecosystems. In particular the effects of environmental changes as related to the impacts of air pollution, global change and land use on nutrient uptake and cycling processes in forest ecosystems are dealt with in detail. The book is divided into six main issues and each topic contains reviews as well as selected results of recent studies.

Viewed from space, the Earth appears as a globe without a beginning or an end. Encompassing the globe is the atmosphere with its three phases- gaseous, liquid, and solid--moving in directions influenced by sunlight, gravity, and rotation. The chemical compositions of these phases are determined by biogeochemical cycles. Over the past hundred years, the processes governing the rates and reactions in the atmospheric biogeochemical cycles have typically been studied in regions where scientists lived. Hence, as time has gone by, the advances in our knowledge of atmospheric chemical cycles in remote areas have lagged substantially behind those for more populated areas. Not only are the data less abundant, they are also scattered. Therefore, we felt a workshop would be an excellent mechanism to assess the state of-knowledge of the atmospheric cycles of sulfur and nitrogen in remote areas and to make recommendations for future research. Thus, a NATO Advanced Research Workshop '~he Biogeochemical Cycling of Sulfur and Nitrogen in the Remote Atmosphere" was held at the Bermuda Biological Station, St. Georges, Bermuda, from 8-12 October 1984. The workshop was attended by 24 international scientists known for their work in atmospheric cycling in remote areas. This volume contains the back ground papers and the discussions resulting from that workshop. The workshop was organized along the lines of the atmospheric cycle. There were working groups on emission, transport, transformation, and deposi tion.