Nitrogen‐limited growth of lettuce is associated with lower stomatal conductance.

Summary: • C assimilation (A) has been shown to limit the growth of young Lactuca sativa (lettuce) plants following an interruption in their external N supply. Further data from these plants were used to test two hypotheses: that N‐limited growth of lettuce is associated with lower stomatal conductance (gs); and that reductions in gs result from adjustments to stomatal frequency or distribution.• The photosynthetic characteristics, nitrate and organic N‐concentrations, as well as epidermal and stomatal distributions, were determined in leaves of hydroponically grown lettuce plants supplied continuously with N or with N removed for up to 14 d.• Although N‐limited plants had lower maximum rates of A, comparisons at equivalent values of gs showed that A was not directly limited by organic‐N but by gs. Reductions in gs under N‐limiting conditions did not associate with adjustments to stomatal frequency or distribution.• Associations between plant N and A could arise either through stomata responding directly to signals induced by N deprivation or to increased CO2 partial pressure at the sites of carboxylation. [ABSTRACT FROM AUTHOR]