Effects of Elevated Atmospheric CO2 on Root Growth, Turnover and Decomposition in a Scrub Oak Ecosystem

Atmospheric carbon dioxide levels are increasing and 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 soil carbon input. I investigated the effects of elevated carbon dioxide on fine root growth and decomposition using open top chambers with both ambient and elevated (700 PPM) CO2 treatments in an oak-palmetto scrub ecosystem at Kennedy Space Center, Florida. Minirhizotron tubes were installed in each elevated and control chamber to allow observation of roots. Each tube was sampled for root length density (mm cm−2) every three months. Carbon dioxide enrichment of the chambers began May 15, 1996. By December 1998 root length density (RLD) increased to 19.1 mm cm−2 for the control chambers and 37.7 mm cm−2 for the enriched chambers in the top 101-cm of soil. Root distribution was unchanged under elevated carbon dioxide. Fine root production increased with elevated carbon dioxide and mortality was unaffected over 33 months. Root length elongation increased significantly over a one-month period in June 1997. I also measured the effects of elevated carbon dioxide on the decomposition rates of roots grown in ambient and elevated carbon dioxide. Fine root decomposition rates were obtained from root litterbags incubated from December 1996 to December 1998 and showed no significant treatment effect. Initial percent mass loss varied from 10.3% to 13.5% after three months; 55.5% to 38.3% of original mass had been lost after 828 days. A period of nitrogen immobilization occurred in both fine roots and rhizomes in the elevated CO2 treatment, which is potentially a mechanism for nitrogen conservation for this system in an elevated CO2 world. Significant fine root length-mass relationships were applied to minirhizotron measurements and a 180% increases in root biomass was calculated at the end of the study. 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

Avian Response to Forest Management and Military Training Activities at Fort Benning, Georgia

Evaluating intensity and effects of land use disturbance is difficult, espe­cially in sites with multiple land use. We conducted point counts to deter­mine if abundance of bird species could be used to assess military train­ing and forestry management practices at Fort Benning, Georgia. We evaluated heavy and light use sites in the 1st growing season after pre­scribed fire and in the 3rd growing season postfire. Results focus on species common to early successional habitats and pine-grasslands and on forest species and habitat generalists. In the 3rd growing season post­fire, Indigo buntings (Passerino cyanea) and northern bobwhites (Colinus virginianus) were more abundant in recently burned heavy use sites than in light use sites. Conversely, red-eyed vireos (Vireo olivaceus) were more abundant in light use sites in the 3rd growing season postfire than in recently burned, heavy use sites. Further study could help determine if these species are indicators of disturbance

The Effects of 11 Yr of CO2 Enrichment on Roots in a Florida Scrub-Oak Ecosystem

Uncertainty surrounds belowground plant responses to rising atmospheric CO2 because roots are difficult to measure, requiring frequent monitoring as a result of fine root dynamics and long-term monitoring as a result of sensitivity to resource availability. We report belowground plant responses of a scrub-oak ecosystem in Florida exposed to 11yr of elevated atmospheric CO2 using open-top chambers. We measured fine root production, turnover and biomass using minirhizotrons, coarse root biomass using ground-penetrating radar and total root biomass using soil cores. Total root biomass was greater in elevated than in ambient plots, and the absolute difference was larger than the difference aboveground. Fine root biomass fluctuated by more than a factor of two, with no unidirectional temporal trend, whereas leaf biomass accumulated monotonically. Strong increases in fine root biomass with elevated CO2 occurred after fire and hurricane disturbance. Leaf biomass also exhibited stronger responses following hurricanes. Responses after fire and hurricanes suggest that disturbance promotes the growth responses of plants to elevated CO2. Increased resource availability associated with disturbance (nutrients, water, space) may facilitate greater responses of roots to elevated CO2. The disappearance of responses in fine roots suggests limits on the capacity of root systems to respond to CO2 enrichment

The effects of 11 yr of CO 2

ground-penetrating radar, minirhizotrons