Nitrate reductase activity, nitrogenase activity and photosynthesis of black alder exposed to chilling temperatures

Christoph S. Vogd and Jeffrey O. DawsomVogel, C. S, and Dawson, J, O. 1991, Nitrate reductase activity, nitrogenase activityand photosynthesis of black alder exposed to chilling temperatures, - Physiol, Plant,82: 551-558,Actinorhizal (/^ran/rifl-nodulated) black alder [Alnus glutinosa (L.) Gaertn,] seed-lings fertilized with 0,36 mM nitrate (low nitrate fertilizer treatment) or 7,14 mMnitrate (high nitrate fertilizer treatment) and acclimated in a growth chamber for 2weeks were exposed to 2.5 h of night-time chilling temperatures of —1 to 4°C. Coldtreatment decreased nitrogenase activity (acetylene reduction activity) 33% for lownitrate fertilized plants and 41% for high nitrate fertilized plants. Recovery ofnitrogenase activity occurred within 7 days after chilling treatment. In contrast, invivo nitrate reductase (NR) activities of leaves and fine roots increased immediatelyafter chilling then decreased as nitrogenase activities recovered. Fine roots of alderseedlings exhibited NR activities proportional to the amounts of nitrate in the rootingmedium. In contrast, the NR activities of leaves were independent of substrate andtissue nitrate levels and corresponded to nitrogenase activity in the root nodules. In aseparate experiment, net photosynthesis (PS) of similarly treated black alder seed-lings was measured before and after chilling treatments. Net PS declined in responseto ehiUing by 17% for plants receiving low nitrate fertilizer and 19% for plantsreceiving high nitrate fertilizer. After chilling, stomatal conductance (gj decreasedby 39% and intemal CO'2 concentration (c^) decreased by 5% in plants receiving thehigh nitrate fertilizer, whereas plants receiving the low nitrate fertilizer showed noebange in gs and a 13% increase in q. Results indicate that chilhng stimulates stomatalclosure only at the high nitrate level and that interference with bioehemtcal functionsis probably the major impact of chilling on PS,Key words - Aetinorhizal, Alnus glutinosa, black alder, chilling temperatures, di-nitrogen fixation, Frankia, nitrate reductase, nitrogenase, photosynthesis.C. S. Vogel and J. O. Dawson (corresponding author), Dept of Forestry, Univ. ofIllinois, 1301 West Gregory Dr., Urbana, IL 61801, USA.ing temperatures began to occur and after the leaves ofIntroduction associated woody deciduous broad-leaved trees haveBlack alder \Alnus glutinosa (L.) Gaertn,] is a temper- been shed (Neave et al, 1989),ate deciduous tree that forms symbiotic dinitrogen fix- Leaf N resorption in black alder during the autumning root nodules in association with soil actinotnycetes can be affected by soil fertility and Frankia nodulation,of the genus Frankia. Black alder sheds its leaves much Cote et al. (1989) demonstrated that N-fertili2ed blacklater and resorbs less net leaf N during autumnal se- alder seedlings lacking Nj-fixing nodules showed no netnescence than do most other temperate deciduous trees resorption of leaf N during autumn, while alders de-(C6te and Dawson 1986, Gote et al, 1989, Dawson and pendent on N derived from symbiotic fixation resorbedFunk 1981, Dawson etal, 1980), This delay in autumnal 38% of their leaf N prior to leaf abscission. The declinesenescence apparently allows leaf physiological proc- in leaf N coincided with the temperature-dependentesses to continue longer, since photosynthesis (PS) in decrease in nitrogenase activity. Fertilized plants lack-black alder may cotitinue for up to a month after freez- irtg nodules continued to absorb and utilize availableReceived 5 November, 1990; revised 26 March, 1991