Effects of Diurnal Variation in Light and Temperature on the Acetylene Reduction Activity (Nitrogen Fixation) of Subterranean Clover¹

Abstract

Singly, or in combination, both light intensity or temperature can limit symbiotic N fixation. Most reported studies have been done to investigate the effects of only one of these factors. The present study was done to determine N fixation response to variation in both light and temperature for an annual range legume which, during its normal growing season, may be subject to growth limiting levels of both environmental factors. Plants of subterranean clover (Trifolium subterraneum L., ‘Mt. Barker’) were grown from seed to the sixth trifoliolate leaf stage in sand with N‐deficient nutrient solution. Plant containers were designed to permit sampling of the rooting atmosphere for acetylene reduction assay during treatment conditions, which were maintained with controlled‐environment facilities. During the treatment phase light and temperature were investigated by: 1) varying both diurnally; 2) varying light diurnally under constant temperature; 3) varying temperature diurnally under constant light; and 4) maintaining both light and temperature constant. Apparent N2 fixation (acetylene reduction) showed diurnal fluctuations under: 1) constant light; and 2) 12/12 hour light/dark regimes when root and air temperature fluctuated by 7 and 14 C, respectively. In constant temperature and either normal photoperiods or constant light, however, no significant diurnal fluctuation of acetylene reduction was measured. Under both constant temperature regimes a gradual increase in acetylene reduction activity, which may have been an artifact, was observed. These results show that diurnal changes in acetylene reduction by subterranean clover result more from fluctuations in temperature than from diurnal changes in light and suggest that N2 fixation by root nodules of this species is buffered against short‐term changes in photosynthate supply.

High nitrogen contribution by Gunnera magellanica and nitrogen transfer by mycorrhizas drive an extraordinarily fast primary succession in sub‐Antarctic Chile

“…The daily pattern found here and at other sites showed a night‐time depression that was due to low temperature rather than changes in light (removal of leaves, for example, had no effect on the N‐fixation rates; data not shown). This has also been shown for other N‐fixing symbiotic plants (Eckart & Raguse, ; Schweitzer & Harper, ). Cyanobacteria are poor performers at subzero temperatures not just for N‐fixation but also for photosynthesis (Lange, ; Antoine, ).…”

Agronomical and physiological responses of white clover(Trifolium repens)and perennial ryegrass(Lolium perenne)to nitrogen fertiliser applied in autumn and winter

“…This supports the view that N2 fixation is primarily controlled by the availability of photosynthate in the nodules (Hardy & Havelka 1976), therefore, diurnal fluctuations in either light intensity or temperature affecting photosynthate supply will influence N2 fixation (Eckart & Raguse 1980). These results suggest that in white clover temperature rather than N is a limiting factor in dry weight gain.…”

Nitrogen Fixation (Acetylene Reduction) by Forest Legumes: Sensitivity to Pre‐harvest and Assay Conditions

“…There was no account taken of diurnal variation in rates of acetylene reduction and lower rates at night would lower the conversion ratios further. However, diurnal variation is likely to be small as the roots were kept at constant temperature, and temperature effects are often more important in determining diurnal variation than the short-term periods of dark (Eckart & Raguse, 1980;Schweitzer & Harper, 1980). This conclusion is partly supported by results from the shading experiment (Table 2) where extension of the period in which carbohydrate supply could limit nitrogen fixation, by the heavy shading of plants for 1 d, caused losses in activity of only 33 to 55%.…”