a r t i c l e i n f o Monte Carlo simulation testing of the sensitivity of the Fickian diffusion model used for paleo-PCO 2 proxies indicates that assuming annual average soil respiration rate results in over-estimation of PCO 2. In all cases, the natural variability of the factors of the model, including soil porosity and inverse tortuosity and the δ 13 C value of the soil produced CO 2 were n...

To determine whether long-term growth in enriched CO(2) atmospheres changes the woody tissue respiration component of aboveground carbon budgets, we measured woody tissue respiration of stems of 3-year-old ponderosa pine (Pinus ponderosa Laws.) grown in ambient (350 ppm) or twice ambient (700 ppm) atmospheric CO(2) concentrations in open-top field chambers located in Placerville, CA. Total resp...

Increased root exudation and a related stimulation of rhizosphere-microbial growth have been hypothesised as possible explanations for a lower nitrogen(N-) nutritional status of plants grown under elevated atmospheric CO2 concentrations, due to enhanced plantmicrobial N competition in the rhizosphere. Leguminous plants may be able to counterbalance the enhanced N requirement by increased symbio...

The distribution of resources between enzymes of photosynthetic carbon metabolism might be assumed to have been optimized by natural selection. However, natural selection for survival and fecundity does not necessarily select for maximal photosynthetic productivity. Further, the concentration of a key substrate, atmospheric CO(2), has changed more over the past 100 years than the past 25 millio...

Green alder (Alnus viridis ssp. fruticosa) is a dominant understory shrub during secondary successional development of upland forests throughout interior Alaska, where it contributes substantially to the nitrogen (N) economy through atmospheric N2 fixation. Across a replicated 200? year old vegetation chronosequence, we tested the hypotheses that green alder has strong effects on soil chemical ...

chemical vapor deposition (cvd) is one of the most important methods for producing carbon nanotubes (cnts). in this research, a numerical model, based on finite volume method, is investigated. the applied method solves the conservation of mass, momentum, energy and species transport equations with aid of ideal gas law. using this model, the growth rate and thickness uniformity of produced cnts,...

Chloroplasts isolated by methods similar to that described by Arnon et al. (1) are capable of incorporating acetate carbon into both lipid and n)on-lipid materials when fortified with appropriate cofactors (2, 3,4, 5). The actual rate of incorporation of acetate carbon in these preparations was, however, very small compared with the normal rate of photosynthesis (1-2 jumoles/mg chlorophyll'hr) ...

Rhizobia and legume plants establish symbiotic associations resulting in the formation of organs specialized in nitrogen fixation. In such organs, termed nodules, bacteria differentiate into bacteroids which convert atmospheric nitrogen and supply the plant with organic nitrogen. As a counterpart, bacteroids receive carbon substrates from the plant. This rather simple model of metabolite exchan...

Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochem...

The present study assesses the contribution of dark carbon fixation to the primary production in the oxic/anoxic interface of a shallow estuarine environment that develops a salt-water wedge with the presence of sulfide. Primary production was partitioned into oxygenic photosynthesis, anoxygenic photosynthesis and dark fixation. The results show the importance of dark fixation in the oxic/anoxi...