New Phytologist has, throughout its history, been a forum for open debate – indeed, in his opening editorial (1902), Tansley referred to ‘easy communication and discussion’ as being the main ideas for the journal launch. The Internet now offers exciting new ways for sharing information, and this has challenged all information providers to reassess what they offer. It is our intention that the new Forum section in the journal should formalize our standing commitment, and encourage serious dialogue – through scientific commentary, correspondence and opinion.

As the journal approaches its hundredth year, so the need for dialogue is stronger than ever. More and more science is published, making it harder, year on year, to keep abreast of important developments. Science is also global, making discussion confined to those within one country or economic bloc to be too restrictive. And as the pressure to publish is as strong as it has ever been, so the free flow of original and unorthodox ideas can too easily become stifled.

New Phytologist, as a high-impact, high-quality journal, with its international scope and fierce independence – the Trust is not answerable to any society or commercial publisher – is a respected vehicle for such material. We invite you to participate, and to join us in helping the Forum to develop.

This paper discusses ways in which plant metabolism, development and survival influence, and are influenced by, gaseous pollutants. When amino acids are used as carbon and energy sources by plants and other organisms, reduced inorganic nitrogen is released, with wide-ranging implications for the N cycle. Plants can detect the presence and amounts of deposited N and ozone in the environment, not only by direct metabolic incorporation but probably also via distinct signalling systems. Low-nutrient communities and ecosystems, such as temperate conifer forest, are often protected against N overnutrition by adaptations that insulate plant metabolism and growth from the fertilizing effects of deposited pollutant N. Changes in ecosystem balance and biodiversity are not related in any simple way to differential injury responses of constituent species. The question of what happens when a particular component of a changing plant community fails is considered in terms of the relationship between phases of development and the turnover of tissues and organisms.

The final paper of the Symposium (delivered by Professor Raven) reviewed the rôle of nitrogen in the development of terrestrial life, and gave a timely reminder of the context of the current debate on the effects of anthropogenic N; current man-made perturbations of the N cycle are approaching the scale of catastrophic perturbations caused by major meteorite impacts.

Faced with such a stark evaluation of the current position one is forced to consider how the scientific community is reacting to the challenge of understanding and predicting the effects of man's activities.

A two-day Discussion Meeting of the Royal Society, ‘The Nitrogen Cycle’, held in London in June 1991 (Stewart & Rosswall, 1992) reviewed the considerable progress made in understanding the N cycle in agricultural, forest and aquatic systems. The meeting included some discussion of the concerns which were already being expressed at that time over nitrate in water supplies, and the impacts of nitrogenous gases on tropospheric chemistry, the greenhouse effect and the ozone layer. Since then, disquiet over the impacts of nitrogenous compounds on the environment has increased, and numerous papers have been published on many aspects of the problem. We now have much better understanding of the size and scale of the perturbation of the N cycle, and several review papers have highlighted the complexity of the formidable issues that are challenging environmental scientists (Vitousek, 1994; Galloway et al., 1995; Vitousek et al., 1997).

How plants gather their resources, harvest solar energy and convert raw materials into an increased biomass is one of the enduring fascinations of biological science. Just about every step has been charted by biochemists and few processes have escaped the determination of a rate constant by physiologists. Even the molecular biologist is busy identifying the genes that govern the processes of synthesis and assembly. Nevertheless, at higher levels of organization, of building populations and, especially, communities, the prediction of growth continues to be problematic. Thus, the development by Bright & Walsby (pp. 301–316 in this issue) of a method for calculating the daily growth of a photoautotroph in its natural environment is bound to command our attention. Their approach is ingenious and the veracity of their calculations compelling. This is exciting science.