Environmental stress and genetics influence night-time leaf conductance in the C-4 grass Distichlis spicata

Growing awareness of night-time leaf conductance (g(night)) in many species, as well as genetic variation in gnight within several species, has raised questions about how genetic variation and environmental stress interact to influence the magnitude of gnight. The objective of this study was to investigate how genotype salt tolerance and salinity stress affect gnight for saltgrass [Distichlis spicata (L.) Greene]. Across genotypes and treatments, night-time water loss rates were 5-20% of daytime rates. Despite growth declining 37-87% in the high salinity treatments (300 mM and 600 mM NaCl), neither treatment had any effect on gnight in four of the six genotypes compared with the control treatment (7 mM NaCl). Daytime leaf conductance (g(day)) also was not affected by salinity treatment in three of the six genotypes. There was no evidence that more salt tolerant genotypes (assessed as ability to maintain growth with increasing salinity) had a greater capacity to maintain gnight or gday at high salinity. In addition, gnight as a percentage of gday was unaffected by treatment in the three most salt tolerant genotypes. Although gnight in the 7 mM treatment was always highest or not different compared with the 300 mM and 600 mM treatments, gday was generally highest in the 300 mM treatment, indicating separate regulation of gnight and gday in response to an environmental stress. Thus, it is clear that genetics and environment both influence the magnitude of gnight for this species. Combined effects of genetic and environmental factors are likely to impact our interpretation of variation of gnight in natural populations.