| Atmospheric carbon dioxide (CO2) is rising at unprecedented rates to levels not experienced in the last 420,000 years. Plants have adapted to CO2 fluctuations accompanying past glacial/interglacial cycles, but how plants and ecosystems will respond to current increases is uncertain. Three ways that CO2 may shape forest dynamics include impacts on forest succession, plant fitness, and nutrient turnover. Forest succession is important for biodiversity and net ecosystem productivity (NEP), but how it will be affected by rising CO2 is unknown. Second, plants may exhibit genetic variation in response to CO2, but the geographical scale at which this variation is expressed (family through provenance) is unclear, yet critical for understanding CO2 effects on competitive dynamics and evolutionary potential. Third, previous work has observed changes in turnover rates of foliage produced under elevated CO2, but how biomass produced under paleo-levels of CO2 decomposes is ambiguous, as is whether genetic variation in decomposition responses may affect future ecosystem functioning.; I examined growth and survivorship of woody understory plants under ambient (∼360 mul/1) and elevated CO2 (∼560 mul/l) at the Duke Forest Free-Air CO2 Enrichment (FACE) facility in North Carolina. When protected from herbivores, population biomass grew faster (g/m 2/yr) with CO2 enrichment. Shade-tolerant, less productive tree species exhibited the greatest responses to CO2, suggesting future forests may be less productive than today. However, when available to herbivores neither ambient nor elevated populations grew over time, suggesting a lack of recruits able to attain future canopy dominance.; At the Duke University Phytotron I grew Acer rubrum (red maple) individuals from different families, populations, and provenances for two years under four levels of CO2: representing Pleistocene (180 mul/1) through future (600 mul/1) conditions. Germination, growth, and survivorship responses to CO2 depended on family and regional identities, implying red maple may evolve in response to rising CO2 and the way trees in one region respond to CO2 may not inform predictions for other regions. Foliage from these trees was decomposed in situ for one year. I found genetic variation in decomposition responses, and tissue produced under paleo-CO2 levels had much higher rates of nutrient turnover than today. |
