Effects of temperature regime and water deficit on leaf
physiology and biomass productivity
Temperature regime showed significant effects on gas exchange variables
including light saturated photosynthetic rate (Asat; P
<0.001), stomatal conductance (gs, P
<0.001) and the ratio of intercellular to ambient
CO2 (Ci/Ca; P
<0.001) (Figure 1 and 2; Table 1 and S1). Compared with plants
grown under cool daytime temperatures, Asat,
gs and Ci/Ca increased
by 31.5%, 105.6% and 10.5%, respectively, under warm day growth
temperatures. In addition, rates of leaf dark respiration
(Rn) were significantly increased by growth temperature
(P <0.001), with Rn being 30.3% higher in
warm grown plants than in cool grown plants, although this pattern was
less clear in the well-watered treatment (Figure 1, Table S1). On the
other hand, water deficit treatment did not alter most gas exchange
variables, except for Rn, which was decreased by 11% in
response to water deficit stress, on average. A significant interaction
was detected for temperature and water treatment on leaf level carbon
balance represented by the difference between Asat and
Rn (Asat-Rn; P
<0.001). However, the variation of leaf carbon balance across
treatments was primarily driven by growth temperature rather than water
availability, given that Asat-Rnincreased by 10.7% in warm grown plants compared with cool grown
plants, but decreased by 2% in the well-watered treatment relative to
water deficit treatment, on average.
Warmer growth temperature had significant effects on the optimum
temperature of photosynthesis (Topt; P =0.02) (Figure 3,
Table 2). Topt of plants grown under
28/22oC was higher than Topt of the
other temperature treatments (ca . +1oC);
nonetheless, the variation in Topt across temperature
treatments was relatively minor. There was a significant interaction
between growth temperature and water treatment on photosynthetic rate at
Topt (Aopt; P =0.03). Growth temperature
was the main determinant of the variation across treatments given that
the difference induced by the water treatment was small for all
temperature treatments.
Both temperature regime and water treatment showed significant main
effects on the number of days required for plant height to reach 50% of
its maximum height (H50; P <0.01 for both
treatments); H50 was higher at cool temperatures and in
the well-watered treatment on average (Figure 4; Table 1 and S2). Growth
temperature and water regime showed significant interactive effects on
the dry mass of vegetative organs (P <0.01), as well as total
aboveground dry mass (P <0.05). Although the pattern of
variation across treatment combinations was less evident, both variables
were generally decreased by elevated growth temperature and water
deficit stress. In addition, growth temperature and water independently
affected the fruit biomass (P <0.001 for both treatments),
with values lower under the warm temperature regimes (-15.6%) and water
deficit treatment (-11.8%) compared with cool temperature regimes and
well-watered treatment, respectively (Table S2).