Maize Zmasft double mutant versus wildtype
The enrichment of water at the sites of evaporation above source water
(Δ18Oe) was 4.1 times more responsive
to changes in RH than to changes in light intensity, meaning thate a/e i is a more
influential variable in determining
Δ18Oe thang s-driven changes in εk.
Δ18Oe did not differ between genotypes
in either RH or light intensity, while maize Zmasft double
mutants were less enriched in leaf water oxygen isotope enrichment
(Δ18OLW) than wildtype in every
treatment (14.24 ± 1.48 and 16.14 ± 1.41 ‰, respectively) (Table 1; Fig.
1a, b). In all treatments, Δ18OLW was
consistently less enriched in the Zmasft double mutants than
wildtype by 0.5 to 1 ‰ (Table 1; Fig. 1c, d). Additionally,
Δ18Oe values trended lower in
wildtype, contrary to what is expected if differences in
Δ18Oe were driving the genotypic
differences in Δ18OLW. Nonetheless,
Δ18Oe has a drastic effect on
Δ18OLW in that
Δ18OLW was 11.65 ± 0.65 ‰ lower at 80
% RH than at 50 % RH, ranging from 9.44 to 22.80 ‰. The response to
light intensity was much less in that
Δ18OLW was 2.90 ± 0.50 ‰ lower at 300
than at 1200 μmol photons m-2 s-1,
and there was no difference at 80 % RH (Table 1, S1; Fig. 1).
The fractional contribution of source water (unenriched xylem water;f sw) was slightly greater in Zmasftmutants (0.22 ± 0.03) than wildtype (0.16 ± 0.03). Alternatively, for
both genotypes f sw was greater under 1200
compared to 300 µmol quanta m-2 s-1(0.27 ± 0.1 and 0.1 ± 0.02, respectively) (Table 1; Fig. 2a) and RH
increased f sw under 300 but not 1200 µmol quanta
m-2 s-1 (Table 1; Fig. 2a).
Transpiration rate (E ; mol H2O
m-2 s-1) was greater in theZmasft double mutants than in wildtype across treatments (P
< 0.0001), and this difference was most apparent under high
light intensity. At high light intensity, E was higher than at
low light intensity, and RH only affected E at low light
intensity (Table 1; Fig. 2b). Similarly, stomatal conductance
(g s; mol H2O
m-2 s-1) was 44 % greater inZmasft double mutant, and this genotypic difference was most
apparent at high light intensity (Table 1).