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Title: GROWTH OF EASTERN COTTONWOODS IN ELEVATED CO2 STIMULATES STAND LEVEL RESPIRATION AND RHIZODEPOSITION OF CARBOHYDRATES, ACCELERATES SOIL NUTRIENT DEPLETION, YET STIMULATES ABOVE & BELOW GROUND BIOMASS PRODUCTION 1660

Author
item BARON-GAFFORD, G.
item Martens, Dean
item GRIEVE, K.
item McLain, Jean
item LIPSON, D.
item MURTHY, R.

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2005
Publication Date: 7/5/2005
Citation: Baron-Gafford, G., Martens, D.A., Grieve, K., Mclain, J.E., Lipson, D., Murthy, R. 2005. Growth of eastern cottonwoods (Populus deltoides) in elevated CO2 stimulates stand level respiration and rhizodeposition of carbohydrates, accelerates soil nutrient depletion, yet stimulates above & below ground biomass production. Global Change Biology. 11: 1-14.

Interpretive Summary: Understanding the impact of higher atmospheric CO2 concentrations on plant growth is vital as we are learning the rate of CO2 increase in our atmosphere maybe more rapid than previously understood. The research was conducted in the Biosphere 2 research facility from 2000 through the 2003 growing season with three levels of atmospheric CO2. Plant grown under elevated CO2 developed faster and produced greater biomass each of the 4 years of the study. The increased CO2 levels also increased soil respiration during the study and at conclusion, soil carbon and the nutrients, P, K, and Ca were significantly depleted. The work showed that long-term exposure to higher atmospheric CO2 levels will not increase soil C sequestration as short term experiments have suggested and the end result of higher CO2 concentrations will be a rapid depletion of soil nutrients followed by a rapid reduction in plant growth

Technical Abstract: We took advantage of the distinctive system-level measurement capabilities of the Biosphere 2 Laboratory (B2L) to examine the effects of prolonged exposure to elevated CO2 concentration on carbon flux dynamics, above- and belowground biomass changes and soil carbon and nutrient capital in plantation forest stands over 4 years. Annually-coppiced stands of eastern cottonwoods (Populus deltoides) were grown under ambient (400 ppm) and two levels of elevated (800 and 1200 ppm) atmospheric [CO2] in carbon and N-replete soils of the Intensive Forestry Mesocosm in the B2L. Elevated [CO2] significantly stimulated whole system maximum net CO2 influx by an average of 21 and 83% in years 3 and 4 of the experiment. Over the 4-year experiment cumulative belowground, foliar, and total aboveground biomass increased in both elevated [CO2] treatments, and all components of stand respiration (total system respiration, soil respiration with and without roots) were also stimulated. After 2 years of growth at elevated [CO2], early season stand respiration was decoupled from CO2 influx aboveground, probably due to increased fine root biomass and increased soil carbohydrates status under elevated [CO2] treatments. The increase in soil carbohydrates stimulated soil respiration as measured in the undisturbed soil block, and by soil collars in-situ, and substrate induced respiration in-vitro. Elevated [CO2] accelerated depletion of soil nutrients phosphorus, calcium and potassium after 3 years of growth, litter removal and coppicing, especially in the upper soil profile. Total N showed no change with elevated [CO2] and total soil carbon declined throughout the experiment. Enhancement of above and belowground biomass production by elevated [CO2] accelerated carbon cycling through the coppiced system and did not sequester additional carbon in the soil