Abundance, production and mortality of fine roots under elevated atmospheric CO 2 in an oak-scrub ecosystem

Abstract

Atmospheric carbon dioxide levels are increasing and are predicted to double this century. The implications of this rise on vegetation structure and function are not well understood. Measurement of root growth response to elevated atmospheric carbon dioxide is critical to understanding plant responses and soil carbon input. We investigated the effects of elevated carbon dioxide on fine root growth using open top chambers with both ambient and elevated (700 ppm) CO 2 treatments in an oak-palmetto scrub ecosystem at Kennedy Space Center, FL. Minirhizotron tubes installed in each elevated and control chamber were sampled for root length density (mm cm −2) every 3 months. Carbon dioxide enrichment of the chambers began May 15, 1996. By December 1997, root length density (RLD) increased to 7.53 mm cm −2 for the control chambers and 21.36 mm cm −2 for the enriched chambers in the top 101-cm of soil. Vertical distribution of fine roots was unchanged under elevated carbon dioxide. Fine root production increased with elevated carbon dioxide, and mortality and turnover were higher in the elevated chambers by the last sample date in 1997. The increased rates of fine root growth coupled with no change in decomposition rate suggest a potential increased rate of carbon input into the soil. However, these results only represent the first 21 months post-fire and recovery to root closure could just be faster in the elevated CO 2 atmosphere.