N2-fixation by Alnus and Colletia

English. Acetylene reduction by detached nodules of Alnus cordeta, A. glutinosa and Colletia paradoxa was tested with respect to the effect of temperature on nitrogenase activity. Nodules were incubated at temperatures from 5 deg C to 45 deg C, exposed to C(,2)H(,2) generally for 1 hr, and sampled for C(,2)H(,4). The maximum of activity occurred in all three species tested at about 25 deg C. The C(,2)H(,2) reduction rapidly declined at temperatures above the optimum and stopped at 40 deg C for A. glutinosa and 45 deg C for A. cordata and Colletia paradoxa. Nodules of A. cordata subjected to 5 deg C recovered nitrogenase activity within 1 hr when the temperature was raised to 25 deg C, whereas lots of activity was irreversible at 45 deg C. A. cordata nodules tested in different seasons of the year showed similar activities in April and October with a slightly lower rate in April and October with a slightly lower rate in August and a very much lower activity in January.

Italian. E stata misurata l'attivita nitrogenasica nei noduli escissi di Alnus cordata, A. glutinosa e Colletia paradoxa, mediante il metodo della riduzione dell'acetilene. I noduli, incubati a temperature tra 5 grad e 45 grad C, hanno presentato, per tutte le tre specie, una attivita nitrogenasica massima a circa 25 grad C, e decrescente con l'aumento della temperatura, fino a divenire nulla a 40 grad C per A. glutinosa ed a 45 grad C per A. cordata e C. paradoxa. I noduli di A. cordata, dopo 1 hr di incubazione a 5 grad C, reincubati a 25 grad C, recuperavano immediatamente l'attivita nitrogenasica; quelli incubati a 45 grad C, invece, perdevano irreversibilmente l'attivita nitrogenasica. I noduli di A. cordata, esaminati in varie stagioni dell'anno, mostravano attivita nitrogenasica simili in primavera, estate ed autunno, con valori leggermente piu bassi in estate; una attivita nettamente inferiore risultava in inverno quando l'Alnus e a riposo.