1. Akkermans ADL, Abdulkadir S, Trinick MJ (1978) N2-fixing root nodules in Ulmaceae: Parasponia or (and) Trema? Plant Soil 49: 711–715
2. Albrecht SL, Maier RJ, Hanus FJ, Russell SA, Emerich DW, Evans HJ (1979) Hydrogenase in Rhizobium japonicum increases nitrogen fixation by nodulated soybeans. Science 203: 1255–1257
3. Appleby CA, Bergersen FJ, Macnicol PK, Turner GL, Wittenberg BA, Wittenberg JB (1976) Role of leghaemoglobin in symbiotic N2 fixation. In: Newton WE, Nyman CJ (eds) Proc 1st Int Symp Nitrogen Fixation, Vol I. Washington State Univ Press, Pullman, pp. 274–292
4. Ayanaba A, Dart PJ (eds) (1977) Biological nitrogen fixation in farming systems of the tropics. Wiley and Sons, New York, pp. 1–377
5. Belkin S, Padan E (1978) Hydrogen metabolism in the facultative anoxygenie cyanobacteria (blue–green algae) Oscillatoria limnetica and Aphanothece halophytica. FEBS Lett 94: 291–294