By Dennis O'Brien,
The effect of climate change on some trees harvested for paper and wood may not be quite as severe as expected, according to U.S. Department of Agriculture (USDA) scientists in Auburn, Ala.
Climate change is expected to increase levels of carbon dioxide (CO2) in the atmosphere. A key question is whether rising CO2 levels will increase the severity of tree diseases.
Agricultural Research Service (ARS) plant pathologist Brett Runion and his colleagues at the agency's National Soil Dynamics Laboratory in Auburn exposed loblolly pine and red oak seedlings to twice the normal levels of CO2 in open-top field chambers for six weeks, then inoculated them with the fungal pathogens that cause pitch canker and fusiform rust, two common tree diseases. They then placed the seedlings back in the chambers to grow for seven months.
Results showed that both types of seedlings grown under elevated CO2 were larger in diameter, height and weight than seedlings grown under normal CO2 levels. The researchers expected to see fusiform rust increase under elevated CO2 levels because the added biomass would give the pathogen more tissue for infection. They also expected to see reduced levels of pitch canker because the trees would be healthier and better able to defend themselves against the disease. Instead, they found that the incidence of both diseases declined under elevated CO2, while disease severity was unaffected.
Higher CO2 levels may have caused the trees to produce higher levels of tannins and phenols, which can help plants fight off infections, according to Runion. The higher CO2 also altered the timing of the fusiform rust reproductive cycle in a beneficial way. Fusiform rust moves from red oak to pine trees by way of spore dispersal. Pine tissues don't stay highly susceptible for long, and it's possible a delay in spore formation on the oaks, caused by higher CO2, means spores were dispersed after the pine tissues had hardened and were less susceptible.