Stomatal Conductance is a Key Parameter to Assess Limitations to Photosynthesis and Growth Potential in Barley Genotypes

Abstract

Fourteen genotypes of barley were compared for response to salinity by monitoring the parameters gas exchange and chlorophyll fluorescence. We present relationships between stomatal conductance (g _s) gas exchange chlorophyll fluorescence parameters and aboveground dry matter (AGDM). We found that genetic variability provided a continuum of data for g _s across control and saline conditions. We used this continuum of g_s values to test the overall relationships between g _s and net photosynthesis (A), leaf internal CO₂ concentration (C _i), actual quantum yield of PSII electron transport (ΦPSII), relative electron yield over net CO₂ assimilation rate (ETR/A), and AGDM. The relationship between g _s and A was highly significant (p < 0.0001) for both control and saline treatments, while correlations between g _s and C _i, and C _i and A were significant only under control conditions. Unexpectedly, we found positive correlations between g _s and ΦPSII (p < 0.0001) for both conditions. A comparison between relationships of g _s and A, and g _s and ΦPSII seemed to indicate a possible acclimation to salinity at the chloroplastic level. Finally, the relationships between g _s and ETR/A were exceptionally strong for both growing conditions (p < 0.0001) indicating that, as g_s values were negatively affected in barley by genetics and salinity as main or interactive effects, there was a progressive increase in photorespiration in barley. Overall, we found that stomatal conductance was a key parameter in the study of barley responses to limiting situations for photosynthesis. We also found a strong relationship between AGDM and g _s regardless of growing conditions and genotypes. For breeding evaluations to select barley genotypes for salinity tolerance, it may be possible to replace all measurements of gas exchange and chlorophyll fluorescence by the simple use of a porometer.

Stomatal conductance - stomatal and non-stomatal limitations - salinity - chlorophyll fluorescence - photosynthesis - barley - yield potential

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Editor: J. T. M. Elzenga