Leaf senescence of Quercus myrtifolia as affected by long-term CO2 enrichment in its native environment

摘要

The long-term effects of elevated (ambient plus 350 mu mol mol(-1)) atmospheric CO2 concentration (C-a) on the leaf senescence of Quercus myrtifolia Willd was studied in a scrub-oak community during the transition from autumn (December 1997) to spring (April 1998). Plants were grown in large open-top chambers at the Smithsonian CO2 Research Site, Merritt Island Wildlife Refuge, Cape Canaveral, Florida. Chlorophyll (a + b) concentration, Rubisco activity and N concentration decreased by 75%, 82%, and 52%, respectively, from December (1997) to April (1998) in the leaves grown at ambient C-a. In contrast, the leaves of plants grown at elevated C-a showed no significant decrease in chlorophyll (a + b) concentration or Rubisco activity, and only a 25% reduction in nitrogen. These results indicate that leaf senescence was delayed during this period at elevated C-a. Delayed leaf senescence in elevated C-a had important consequences for leaf photosynthesis. In elevated C-a the net photosynthetic rate of leaves that flushed in Spring 1997 (last year's leaves) and were 13 months old was not different from fully-expanded leaves that flushed in 1998, and were approximately 1 month old (current year's leaves). In ambient C-a the net photosynthetic rate of last year's leaves was 54% lower than for current year's leaves. When leaves were fully senesced, nitrogen concentration decreased to about 40% of the concentration in non-senesced leaves, in both CO2 treatments. In April, net photosynthesis was 97% greater in leaves grown in elevated C-a than in those grown at ambient. During the period when elevated C-a delayed leaf senescence, more leaves operating at higher photosynthetic rate would allow the ecosystem dominated by Q. myrtifolia to gain more carbon at elevated C-a than at ambient C-a. [References: 32]