Photosynthesis 



L. L. Tieszen, P. C. Miller, and W. C. Oechel 



INTRODUCTION 



The interception of solar radiation and the conversion of that energy 

 by photosynthesis into stable organic forms is essential for the mainten- 

 ance and growth of plants as well as for their vegetative or sexual repro- 

 duction. Accumulating information on photosynthesis of tundra plants 

 suggests that this process is highly adapted to the extreme conditions of 

 the tundra. This chapter describes photosynthesis in the coastal tundra at 

 Barrow and the sensitivity of carbon dioxide assimilation to abiotic and 

 biotic factors. Response patterns and internal and external controls over 

 photosynthesis in vascular plants and mosses are described in an attempt 

 to quantify those factors that govern rates of carbon dioxide uptake. The 

 objectives of Chapter 4 are to understand the controls over photosynthe- 

 sis, analyze the sensitivity of the system, and estimate community pro- 

 ductivity as reviewed in Chapter 3. 



Photosynthesis is a photochemical, diffusion, and enzymatic pro- 

 cess with a rate controlled by intrinsic and extrinsic factors. The process is 

 basically similar in all vascular plants and mosses, although variations in 

 component dark reactions have evolved and are most notable in the dis- 

 tinctions between C3 and C4 plants (Hatch et al. 1971). Tundra vegetation 

 consists mainly of C3 plants (Tieszen and Sigurdson 1973), and no signif- 

 icant differences would be expected in the basic mechanisms between Cj 

 plants in the Arctic and d plants in more temperate climates. However, 

 component reactions, e.g. at the enzyme level, have probably evolved 

 and could be manifest as quantitatively different response patterns. 



The amount of carbon dioxide assimilated is a function of the maxi- 

 mum capacity (rate) for carbon dioxide uptake, which may be related to 

 intrinsic factors such as component enzyme levels (Treharne 1972), the 

 concentrations of ribulose-l,5-diphosphate, nutrient status, innate leaf 

 growth, or development patterns. The extent to which this maximum 



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