Maximum Temperature for Nitrogen Fixation in Common Bean
- R. Hernandez-Armenta ,
- H. C. Wien and
- A. R. J. Eaglesham
The upper temperature limit for nodulation and N2 fixation by common bean (Phaseolus vulgaris L.) is not well defined. Controlled-environment experiments were conducted to address this issue and to determine the relative importance of shoot and root temperatures. Bean cultivars Redkloud and Jutiapa were grown in sand culture and exposed to day temperatures (13 h d−1) of 26, 32, and 38 °C from sowing or 26, 32, 34, 36, and 38 °C for 5 to 10 days during vegetative growth. In other experiments, day shoot-root temperatures of 26-26, 26-38, 38-26, and 38-38 °C were compared. Night temperature was 22 °C in all instances. Transferring plants from a 26 °C to a 38 °C environment resulted in elimination of acetylene reduction activity (ARA) (controls reached over 12 nmol plant−1 s−1), severe N deficiency (55 ± 3 mg shoot-N plant−1 after 10 d compared with 177 ± 7 mg in controls), and virtual cessation of leaf expansion. Ten days at 32 °C decreased (P ≤ 0.05) shoot-N content relative to controls. Nodulation was inhibited at 38 °C when treatment was started immediately after inoculation of established plants or seeds but not when it was applied after nodules were initiated. At root temperature of 38 °C, N2 fixation was inhibited regardless of shoot temperature. Conversely, at root temperature of 26 °C, nodulation and shoot-N accumulation were unaffected even when shoot temperature was 38 °C. It appears that only high soil temperature would constrain N2 fixation by bean; the critical temperature was 32 °C for nodule function and 38 °C for nodulation.
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