Belowground carbon budget and nutrient uptake of temperate forest species in response to elevated carbon dioxide and temperature

The growth of ponderosa pine (Pinus ponderosa Douglas. Ex Laws.) in elevated atmospheric CO₂ may be mitigated by an increase in temperature. There was a significant increase in relative growth rates (RGR) of the plants grown in elevated CO₂ up to 1100 μ1 1 −1. The specific utilisation rate of nitrogen (SUR_N) increased with increasing CO₂ concentration, whereas the specific absorption rate of nitrogen (SAR_N) was unchanged. The SUR _p and SAR_p showed an increasing trend with rising atmospheric CO2 concentrations, which was related to the increase in mycorrhizal infection of the roots. The uptake of nutrients by ponderosa pine to support the growth response in elevated CO₂ appears to have been facilitated by an increase in root growth and nutrient-use efficiency.; The allocation of carbon belowground in forest ecosystems is predicted to increase in response to elevated atmospheric CO₂. The fixation of carbon aboveground in loblolly pine (Pinus taeda) mesocosms was increased in elevated CO₂ and temperature by an increase in photosynthesis and leaf area index (LAI). Fine root biomass, mortality, decomposition and turnover were greatest in the high temperature treatment. An increase in fine root biomass in elevated CO₂ resulted in a non-significant increase in belowground NPP (net primary productivity). The high turnover of carbon belowground in response to elevated temperature will mitigate the small increases in soil carbon storage in elevated CO₂.; A large proportion of carbon in forest ecosystems is lost from belowground through root respiration. Maintenance respiration of attached fine roots was measured on mature loblolly pine and sweetgum (Liquidambar styraciflua ) growing in atmospheric CO₂ elevated by 200 μ1 1 −1 above ambient. Fine root maintenance respiration on a mass basis was significantly lower in the elevated CO₂ treatment for loblolly pine, but was not significantly different for sweetgum. Annual growth respiration was significantly higher in the elevated CO₂ treatment for loblolly pine because of significantly greater construction respiration and fine root production. Maintenance respiration was 98% of total respiration leaving a small proportion of energy for growth and nitrogen-uptake. The reduction in annual total fine root respiration of loblolly pine in elevated CO ₂ will result in more carbon being stored belowground.