Effect of smoke on plant physiology: Is smoke bad for tobacco too?

Background/Question/Methods Smoke is well known to increase seed germination rates in many species, especially those endemic to fire prone environments. Given such a strong physiological effect of smoke on this early life stage, it is reasonable to expect that smoke will alter physiology of later plant stages as well. Large wildfires produce copious amounts of smoke, much of which lingers around the unburned vegetation adjacent to the fires. In some cases this smoke may remain in these areas for several days, not only reducing light levels, but also exposing plant to volatiles and particulate matter contained in the smoke. The effects of these volatiles and particulates on plant physiology and growth has yet to be examined in depth. To assess the impact of smoke on photosynthesis, we exposed tobacco plants to coast live oak (Quercus agrifolia) litter smoke. Each plant was exposed to the smoke generated by combusting 0.4 g of litter, which was then circulated in a smoke chamber for 20 minutes. Control plants were placed in a separate chamber at the same time, also for 20 minutes, to mimic the handling and light regime. Within an hour of the initial exposure we generated an A-Ci curve for each individual using a Licor 6400 gas analyzer. Instantaneous measures of photosynthesis were done 48 hours later to assess the duration of effect. We also performed rapid light curves within 24 hours of exposure to assess the status of the electron transport chain. Lastly, plants were grown to maturity harvested and dry mass compared between treatments.

Results/Conclusions A-Ci curve showed photosynthesis rates were significantly depressed in plants exposed to smoke compared to controls. Rapid light curves also differed significantly 18-20 hours after exposure suggesting an effect of smoke on electron transport or light harvesting ability. However, after 48 hours instantaneous photosynthesis did not differ between treatment and control plants. Conflicting results were found in final plant dry biomass, with one set of replicates showing significantly higher dry biomass in treatments while other replicates were not different. These results suggest that smoke can have a large, short-term effect on plant function. This work is the first to show the results of A-Ci curves and chlorophyll fluoresce on plants exposed to smoke and begin to elucidate the mechanisms of how smoke affect adult plants.