As editor of the two-part Volume V on photosynthesis in RUHLAND''S Encyclopedia, the forerunner of this series published in 1960, I have been approached by the editors of the present volume to provide a short preface. The justification for following this suggestion lies in the great changes which have been taking place in biology in the two decades between these publications, changes which are reflected in the new editorial plan. Twenty years ago it appeared convenient and formally easy to consider photo­ synthesis as a clearly separated field of research, which could be dealt with under two major headings: one presenting primarily photochemical and biochemical prin­ ciples, the other physiological and environmental studies. Such a partition, however, as far as aims and opinions of the authors were concerned, resulted in a rather heterogeneous volume. Today, the tendency in experimental biology is towards a merger of previously distinct disciplines. Biochemists and biophysicists have developed their methods to such an extent that, over and above the analysis of individual reaction sequences, work on the manifold interrelationships among cellular activities has become in­ creasingly possible. Joining them in growing numbers are the physiologists and ecologists with their wealth of information on activity changes in vivo and on the variability and efficiency of the organisms concerned. Furthermore, biochemists, biophysicists and physiologists also now share a lively interest in ultrastructure research, the results and implications of which, through continually improving methodology, have generated important stimuli for the work in the field of cell function.

As editor of the two-part Volume V on photosynthesis in RUHLAND'S Encyclopedia, the forerunner of this series published in 1960, I have been approached by the editors of the present volume to provide a short preface. The justification for following this suggestion lies in the great changes which have been taking place in biology in the two decades between these publications, changes which are reflected in the new editorial plan. Twenty years ago it appeared convenient and formally easy to consider photo­ synthesis as a clearly separated field of research, which could be dealt with under two major headings: one presenting primarily photochemical and biochemical prin­ ciples, the other physiological and environmental studies. Such a partition, however, as far as aims and opinions of the authors were concerned, resulted in a rather heterogeneous volume. Today, the tendency in experimental biology is towards a merger of previously distinct disciplines. Biochemists and biophysicists have developed their methods to such an extent that, over and above the analysis of individual reaction sequences, work on the manifold interrelationships among cellular activities has become in­ creasingly possible. Joining them in growing numbers are the physiologists and ecologists with their wealth of information on activity changes in vivo and on the variability and efficiency of the organisms concerned. Furthermore, biochemists, biophysicists and physiologists also now share a lively interest in ultrastructure research, the results and implications of which, through continually improving methodology, have generated important stimuli for the work in the field of cell function.

Nitrogen and sulfur compounds are continuously synthetized, degraded and converted into other forms in nature. There are many similarities in the principle problems and basic mechanisms of the biology of inorganic nitrogen and sulfur. Many details are not yet understood and hence are the subject of active investigation the world over. In May, 1980, a conference was held in Bochum, Federal Republic of Germany, at which attempts were made to discuss and compare all aspects of both the nitrogen and the sulfur cycle. Lectures were given by internationally recognized experts on the physiology, biochemistry, genetics, and ecology of dinitrogen fIXation, of assimilatory and dissimilatory nitrate and sulfate reduction, and of ammonia and sulfide oxidation. In addition, important data were communicated by German scientists of the national program on the Metabolism of Inorganic Nitrogen and Sulfur Compounds, supported by the Deutsche Forschungsgemeinschaft. This book contains all the contributions to the meeting and consequently should be of interest to researchers, teachers, and students in the field. The members of the German national program on the Metabolism of Inorganic Nitrogen and Sulfur Compounds would like to thank the Deutsche F orschungsgemeinschaft for their generous fmancial support of the scientific projects during the past four years and for the conference itself. Without this help, the present book would not have been written. The members express their appreciation particularly to Dr. A. Hoffmann of the Deutsche Forschungsgemeinschaft for her invaluable skill and patience in taking care of the projects and scientists.

As editor of the two-part Volume V on photosynthesis in RUHLAND''S Encyclopedia, the forerunner of this series published in 1960, I have been approached by the editors of the present volume to provide a short preface. The justification for following this suggestion lies in the great changes which have been taking place in biology in the two decades between these publications, changes which are reflected in the new editorial plan. Twenty years ago it appeared convenient and formally easy to consider photo­ synthesis as a clearly separated field of research, which could be dealt with under two major headings: one presenting primarily photochemical and biochemical prin­ ciples, the other physiological and environmental studies. Such a partition, however, as far as aims and opinions of the authors were concerned, resulted in a rather heterogeneous volume. Today, the tendency in experimental biology is towards a merger of previously distinct disciplines. Biochemists and biophysicists have developed their methods to such an extent that, over and above the analysis of individual reaction sequences, work on the manifold interrelationships among cellular activities has become in­ creasingly possible. Joining them in growing numbers are the physiologists and ecologists with their wealth of information on activity changes in vivo and on the variability and efficiency of the organisms concerned. Furthermore, biochemists, biophysicists and physiologists also now share a lively interest in ultrastructure research, the results and implications of which, through continually improving methodology, have generated important stimuli for the work in the field of cell function.

As editor of the two-part Volume V on photosynthesis in RUHLAND'S Encyclopedia, the forerunner of this series published in 1960, I have been approached by the editors of the present volume to provide a short preface. The justification for following this suggestion lies in the great changes which have been taking place in biology in the two decades between these publications, changes which are reflected in the new editorial plan. Twenty years ago it appeared convenient and formally easy to consider photo­ synthesis as a clearly separated field of research, which could be dealt with under two major headings: one presenting primarily photochemical and biochemical prin­ ciples, the other physiological and environmental studies. Such a partition, however, as far as aims and opinions of the authors were concerned, resulted in a rather heterogeneous volume. Today, the tendency in experimental biology is towards a merger of previously distinct disciplines. Biochemists and biophysicists have developed their methods to such an extent that, over and above the analysis of individual reaction sequences, work on the manifold interrelationships among cellular activities has become in­ creasingly possible. Joining them in growing numbers are the physiologists and ecologists with their wealth of information on activity changes in vivo and on the variability and efficiency of the organisms concerned. Furthermore, biochemists, biophysicists and physiologists also now share a lively interest in ultrastructure research, the results and implications of which, through continually improving methodology, have generated important stimuli for the work in the field of cell function.

Nitrogen and sulfur compounds are continuously synthetized, degraded and converted into other forms in nature. There are many similarities in the principle problems and basic mechanisms of the biology of inorganic nitrogen and sulfur. Many details are not yet understood and hence are the subject of active investigation the world over. In May, 1980, a conference was held in Bochum, Federal Republic of Germany, at which attempts were made to discuss and compare all aspects of both the nitrogen and the sulfur cycle. Lectures were given by internationally recognized experts on the physiology, biochemistry, genetics, and ecology of dinitrogen fIXation, of assimilatory and dissimilatory nitrate and sulfate reduction, and of ammonia and sulfide oxidation. In addition, important data were communicated by German scientists of the national program on the Metabolism of Inorganic Nitrogen and Sulfur Compounds, supported by the Deutsche Forschungsgemeinschaft. This book contains all the contributions to the meeting and consequently should be of interest to researchers, teachers, and students in the field. The members of the German national program on the Metabolism of Inorganic Nitrogen and Sulfur Compounds would like to thank the Deutsche F orschungsgemeinschaft for their generous fmancial support of the scientific projects during the past four years and for the conference itself. Without this help, the present book would not have been written. The members express their appreciation particularly to Dr. A. Hoffmann of the Deutsche Forschungsgemeinschaft for her invaluable skill and patience in taking care of the projects and scientists.