Abstract
The lower volumes and reduced total amino acid content of root pressure sap, collected from excised nodulated roots of C2H2 inhibited Alnus glutinosa, were consistent with the induction by C2H2 of changes in osmotic potential of the treated root systems. Values for the ratio of citrulline: total amino acids in sap from N2- fixing roots were an order of magnitude higher than from C2H2 root systems, confirming previous reports of the importance of this amino acid for transport of fixed N and the distinctiveness of such high values for N2- fixation in Alnus. Twice-daily exposure to C2H2 of nodulated roots of water culture Alnus, maintained in a gas flow-through system for 30 days, produced similar, but qualitatively less dramatic effects on root morphology to plants whose roots were exposed twice daily to C2H4. Reduced shoot growth in C2H2 and especially in C2H4 plants was balanced largely by an increase in root weight. Nodule dry weight was not affected significantly by treatment with C2H4 but in C2H2 plants the weight of nodules increased by 40%, compensating completely for a reduction in the N2 fixed per unit weight of nodules.