PREFACE

In the five years since the last C0₂-symposium, the expertise on CO₂ effects on crops, i.e. of fundamental processes as well as practical applications, has greatly increased. Also the technical facilities for CO₂ enrichment have developed further and become easily available. These factors have stimulated that in modern greenhouse industry, CO₂ enrichment has become a common practice. CO₂ is applied in many greenhouses in winter and in summer, at least during a part of summer days.

In horticultural research, simulation models are used on a wider scale. More than in the past, researchers are now able to integrate physiological and sometimes also technical knowledge. In this way basic knowledge can easily be made available for the solution of problems, for design and for optimization.

At the symposium the recent developments in research and application were presented and new ideas were discussed.

The first two sections of the CO₂ symposium dealt with the physiological aspects and crop responses of CO₂ enrichment Questions were discussed such as how dry matter production is influenced by CO₂; how stomata react on CO₂ concentrations; what the optimal level of temperature and humidity is during CO₂ enrichment and if adaptation and starch accumulation can reduce the effect of CO₂ enrichment.

Another section of the symposium dealt with the release and effects of phytotoxic gases from heating/CO₂ systems, burning fossil fuel. It is evident from research that NOx-gases and unsaturated hydrocarbons (e.g. ethylene) can cause production losses or even serious damage to crops. Technically improved burners have decreased the levels of injurious gases in greenhouses. But still it is crucial to obtain more knowledge about the effects of toxic gases on crops, in relation to cultivar, growing stage, climatic conditions and in relation to concentrations of other gases.

The last section of the symposium covered the technical aspects, management and control of CO₂ enrichment. Some practical limitations are to be dealt with, relater to the source of CO₂ used When CO₂ is produced by burning fuel, CO₂ enrichment is coupled with the production of heat. This can lead to problems in winter as well as in summer. Possible solutions were discussed. Important in this respect is also improvement of the CO₂ strategies, especially for summer conditions Some solutions for this problem have been developed in recent years.

At this symposium 'CO₂ in protected cultivation' fundamental work on the items mentioned, was presented, whereas much of the work will be useful for practical application. The symposium was set up in such a way that many discussions could take place, either in discussion groups, at posters, during excursions or at informal meetings.

The wish of the organizing committee is that the symposium has contributed to the exhange of thoughts and ideas between experts from many countries. We want to thank the authors of papers, all participants, the organizing committee, the editor and the sponsors for the cooperation and their contribution to the success of the symposium.

Elly Nederhoff
Chris van Winden
Conveners


NOTE OF THE EDITOR

For many years a discussion is taking place within the ISHS about ways to improve the quality of the Acta Horticulturae. During the last meeting of the council of the ISHS (1988) a proposal was made to offer authors on a voluntary basis the opportunity to have their paper refereed according to the standards of international scientific journals.

In the present edition of Acta Horticulturae this policy has been followed. Those contributions that have been accepted as a refereed paper are marked as such, in the contents by an asterisk and in the papers by the addendum "refereed paper" on the first page. The other papers, however, contribute to provide a good and general overview of the topic covered and as such are worthwhile to include in the Acta. This consideration, in fact, forms the background for the policy of accepting both types of contributions. I thank the authors for the extra time spent to improve the quality of this issue of the Acta and I hope that our efforts will be appreciated by the readers.

Hugo Challa, Editor
Department of Horticulture
Wageningen Agricultural University
P.O. Box 30, 6700 AA Wageningen
The Netherlands