Heat-wave events have been increasing in recent decades, and more frequent, intense, and longer-lasting heat waves are predicted for the high-CO2 warmer world of the future. Little is known about how heat-wave events impact carbon and nitrogen relations in plants under elevated CO2. I investigated the effect of 5-day-long heat wave (10°C above the normal daytime growth temperature) on gas-exchange, growth, and carbon and nitrogen relations in various tissues (i.e., new leaf, mature leaf, old leaf, stem, and root) of sunflower and corn grown under both current and elevated CO2.
In sunflower, heat wave (~ 4hrs) initially had a negative impact on net photosynthesis (Pn) under low, but not high, CO2, highlighting the protective effect of elevated CO2 on Pn during high-temperature events. In corn, however, the heat wave initially stimulated Pn under both CO2 concentrations. The heat wave increased respiration rate (R) in corn under elevated CO2, but did not affect R under low CO2 in corn and under both the CO2 concentrations in sunflower. But Pn (corn) and R (corn and sunflower) were not affected by the heat wave on day 5 under both the CO2 concentrations in both the species.
The heat wave did not affect total biomass in either species, or root/shoot (R/S) ratio in corn, under both the CO2 concentrations. But in sunflower, the heat wave increased R/S under elevated CO2. These alterations of Pn, R and R/S by heat wave or CO2 may alter the C cycling.
In sunflower, the heat wave tended to increase %N in its tissues under both the CO2 concentrations, but five days after termination of heat wave, %N was reduced in tissues of heated plants under high CO2. In corn, the heat wave increased %N in shoots under elevated CO2 and decreased %N in all the tissues except old leaves under low CO2 by the end of heat wave, but the effects disappeared 5 days after termination of the heat wave.
In sunflower, the heat wave increased %C in roots under both the CO2 concentrations, and decreased %C in roots and mature leaves under elevated CO2 five days after heat-wave termination. In corn, the heat wave increased and decreased %C in tissues under low and high CO2, respectively, by the end of the heat wave. Five days after termination of the heat wave, the tissues of heated plants had higher %C under both the CO2 concentrations in corn.
In sunflower, heat wave tended to decrease C:N ratio in shoots by the end of heat wave under both the CO2 concentrations, but the heat wave tended to increase C:N ratio in shoots five days after termination of heat wave under high CO2. In corn, heat wave decreased C:N ratio in shoots under high CO2, but tended to increase C:N ratio in all the plant parts except old leaves under low CO2 by the end of the heat wave.
These alterations of %N and C:N ratio in plant tissues by heat wave under both current and elevated CO2 concentrations may impact plant-herbivore interactions, since herbivores are often affected by N concentration and C:N ratio of the tissues they consumes.
|Commitee:||Frantz, Jonathan, Gray, John|
|School:||The University of Toledo|
|School Location:||United States -- Ohio|
|Source:||MAI 57/05M(E), Masters Abstracts International|
|Keywords:||Carbon, Heat wave, High temperature, Nitrogen, Photosynthesis, Respiration|
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