Effects of growth temperature, drought and heatwave on carbon
gain and biomass productivity
Strong interactive effects were observed among growth temperature and
heatwave treatments for gas exchange parameters, including
Asat, gs, Rn and
Ci/Ca (Figure 1, Table 4 and S1). For
all variables, the values were increased by the heatwave under cool
growth temperatures, with an opposite pattern observed for plants grown
under warm temperatures. In addition, temperature, water deficit and
heatwave conditions interactively affected the leaf carbon balance
(Figure 2, Table 4). The values of
Asat-Rn displayed a similar pattern to
that of other gas exchange variables across growth temperature and
heatwave treatments, yet the difference associated with water deficit
stress was small. The differences in gas exchange variables during the
heatwave remained detectable on the second day of recovery (Figure 5,
Table 4), with significant interactions between growth temperature and
heatwave on Asat and
Asat-Rn (P <0.001 for both
variables), but not gs (P =0.43). However, the
differences caused by the heatwave within each growth temperature and
water treatment was greatly diminished. Furthermore, the difference in
gas exchange variables related to the heatwave disappeared in some
growth temperature × water treatment combinations on the seventh day of
recovery (data not shown).
Temperature and heatwave interactively affected vegetative dry mass.
Heatwave increased vegetative mass production in three of the four
growth temperature treatments, with the exception of
28/22oC, in which vegetative growth was not altered by
the heatwave (Figure 6, Table 4 and S2). Fruit mass was decreased in
response to the heatwave across all growth temperatures, with the
negative effects more prominent for warm temperature regimes (-14.8%)
compared with cool temperature regimes (-7.1%), as well as across water
treatments (-10.4% and -11.1% for well-watered and water deficit
treatment, respectively), but the total aboveground biomass was not
changed by the heatwave (Table S2).