Maintenance Respiration and Carbon Balance of Plants at Low Levels of Sodium Chloride Salinity

The daily course of carbon influx and efflux was measured inyoung plants of Phaseolus vulgaris, Xanthium strumarium, Zeamays, and Atriplex halimus, exposed to low levels of salinity(NaCl) and varying daytime light intensities. Maintenance respiration(R_M) was calculated. In Phaseolus, Xanthium, and Atriplex, R_Mrose with increasing salinity, approximately up to those levelsof salinity above which apparent signs of toxicity appear. Athigher levels of salinity R_M declined. There was no responseof R_M to salinity in Zea. At the levels of salinity tested,salinity did not affect the ratio of growth respiration to photosynthesis. At –5 x 10⁵ Pa of NaCl salinity, the increase in R_M inXanthium was calculated to account for 24% of the growth reductioncaused by salt. The remainder could be ascribed to reduced photosynthesis.The increase of R_M is considered to be indicative of an adaptivemechanism, not present in the very salt-sensitive Zea.