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).