Elevated [CO2] and growth temperature have a small positive effect on photosynthetic thermotolerance of Pinus taeda seedlings

摘要

Growth temperature had little effect on the response of net photosynthesis to high temperatures (up to 47 A degrees C). On the other hand, elevated [CO (2) ] increased net photosynthesis at high temperatures. We investigated whether Pinus taeda seedlings grown under elevated CO2-concentration ([CO2]) and temperature would be able to maintain positive net photosynthesis (A (net)) longer than seedlings grown under ambient conditions when exposed to temperatures up to 47 A degrees C. Additionally, we investigated whether a locally applied temperature increase would yield the same short-term gas exchange response to temperatures up to 47 A degrees C as a naturally occurring latitudinal temperature increase of equal magnitude. Growth conditions were applied for 7 months (February to August) in treatment chambers constructed at two sites in the native range of P. taeda in the southern US. The sites were located 300 km apart along a north-south axis with a natural temperature difference of 2.1 A degrees C. Seedlings were grown under ambient temperature and [CO2] conditions at both sites. At the northern site, we also applied a temperature increase of 2 A degrees C (T (E)), ensuring that this treatment equalled the mean temperature at the southern site. Additionally, at the northern site, we applied a treatment of elevated [CO2] (C (E)). Gas exchange was measured on all plants in walk-in environmentally controlled chambers. Under C (E), there was no difference in A (net) of seedlings grown in ambient or ambient +2 A degrees C temperatures at any measurement temperature, while differences were present under ambient [CO2]. Furthermore, A (net) was higher under C (E) than under ambient [CO2]. At 47 A degrees C, A (net) was negative in all seedlings except those in the C (E) and ambient temperature treatment combination. Seedlings at the northern site in the T (E) treatment showed no significant differences in A (net) compared with seedlings grown at ambient temperature at the southern site, indicating that the plants responded equally to a manipulated temperature increase and a latitudinal increase in temperature. Our results suggest that elevated [CO2] increases photosynthetic thermotolerance at high temperature (> 41 A degrees C), but this effect diminishes as temperature increases further. Temperature manipulations could provide accurate information on the effect of latitudinal differences in temperature on leaf gas exchange of P. taeda