Abstract
Nodule conductance to O
2 diffusion has been involved as a major factor of the inhibition of N
2 fixation by soil salinity that severely reduces the production of grain legumes. In order to determine the effect of this constraint on the nodule conductance, oxygen uptake by the nodulated roots of
Cicer arietinum was measured by recording the concentration of O
2 as a function of
pO
2 in a gas-tight incubator. After germination and inoculation with the strain
Mesorhizobium ciceri UPMCa7, the varieties Amdoun 1 and INRAT 93-1 were hydroponically grown in a glasshouse on 1
L glass bottles filled with nutrient solution containing 25
mM NaCl. Salinity induced a marked decrease in shoot (30% versus 14%), root (43% versus 20%), and nodule biomass (100% versus 43%) for Amdoun 1 relative to INRAT 93-1. Although salinity completely prevented nodule formation in the sensitive variety Amdoun 1
, nodule number and biomass were higher in the first than in the second variety in the absence of salt. This effect was associated with a significantly higher O
2 uptake by nodulated root (510 versus 255
μmol
O
2
plant
−1
h
−1) and nodule conductance (20 versus 5
μm
s
−1) in Amdoun 1 than in INRAT 93-1. Salinity did not significantly change the nodule conductance and nodule permeability for INRAT 93-1. Thus, the salt tolerance of this variety appears to be associated with stability in nodule conductance and the capacity to form nodules under salt constraint.