Long-term growth of ginkgo with CO2 enrichment increases leaf ice nucleation temperatures and limits recovery of the photosynthetic system from freezing

The importance of subzero temperature interactions with elevated CO2 on pla nt carbon metabolism has received rather little attention, despite their li kely role in influencing future vegetation productivity and dynamics. Here we focused on the critical issues of CO2-enrichment effects on leaf-freezin g temperatures, subsequent membrane damage, and recovery of the photosynthe tic system. We show that growth in elevated CO2 (70 Pa) results in a substa ntial and significant (P < 0.01) increase (up to 4 degrees C) in the ice nu cleation temperature of leaves of Maidenhair tree (Ginkgo biloba), which wa s observed consistently throughout the 1999 growing season relative to thei r ambient CO2 (35 Pa) counterparts. We suggest that increased sensitivity o f leaves to ice damage after growth in elevated CO2 provides an explanation for increased photoinhibition observed in the field early and late in the growing season when low nighttime temperatures are experienced. This new me chanism is proposed in addition to the earlier postulated explanation for t his phenomenon involving a reduction in the rate of triose-P utilization ow ing to a decrease in the rate of carbohydrate export from the leaf.