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paper and on a rather long estimate of soil-organic-matter turnover time. Their 

 assumption that increased photosynthesis would lead to increased biomass 

 requires critical investigation. 



Several research suggestions regarding the influence of elevated CO2 levels on 

 photosynthesis are raised in the foregoing analysis. Some of these are listed 

 below: 



1. Plant responses to increased CO2 levels should be determined over ranges 

 and combinations of environmentally limiting conditions, such as temperature, 

 moisture, cloudiness, and atmospheric turbidity as they occur at present and as 

 they may accompany climatic changes with increases in CO2 content. 



2. Field studies should be conducted on the ultimate state of ecosystems 

 dominated by nonwoody plants, with and without grazing, under elevated CO2 

 stimulation. 



3. Determinations should be made of limiting factors for major ecosystems 

 of the world on a time budget followed by an estimation of the fraction of time 

 in which elevated CO2 might be stimulating. 



4. Simulation studies should be initiated to predict the amount of additional 

 C0 2 that would be fixed at increased levels of CO2 by terrestrial photosynthetic 

 plants, especially by forest plants. Included in these simulations should be the 

 response of plants to C0 2 concentration, the relative global population of the 

 plants involved, and the expected climate (temperature, moisture conditions, 

 cloudiness, atmospheric turbidity, and pollutants). The simulations should 

 integrate the effects of all aspects of microclimate, especially light absorption on 

 a community scale, in addition to the effects of large-scale climate factors. At 

 least one such comprehensive computer simulation has been devised to 

 accurately predict the C0 2 fixation by a monoculture. 1 7 This type of simulator 

 should be expanded to include mixed population systems with different 

 photosynthetic functions and stand architecture. Eventually it should be joined 

 to a large-scale climate model to give global predictions of CO2 uptake as 

 affected by CO2 concentration increase and any concomitant climate changes. 

 Once CO2 uptake rates are understood, or at least predictable, then more 

 reasonable estimates of biomass accumulation of carbon can be made. 



Environmental Toxification 



Although increased levels of atmospheric CO2 may enhance primary 

 productivity, other factors may act to decrease it. Such effluents as smog 

 and smelter fumes 20 appear to have mainly local effects; others, such as S0 2 and 

 NO x compounds may be of wide-scale significance. Indications are that 

 precipitation over the northeastern United States has become increasingly acid 

 over the past 20 years as increased quantities of S0 2 and NO x are oxidized and 

 hydrolyzed in the atmosphere. 21-23 Recent studies (R. H. Whittaker, in 

 preparation; Bormann, personal communication) strongly suggest that forest 

 growth over much of northern New England has declined since 1950, possibly as 

 a result of this increased acidity. 



