Biophysical Processes and Primary Production 67 



The energy exchange processes are significant in determining the rates of 

 primary production, the temperatures of the plants and soil, and the 

 rates of water loss from vascular plants and mosses. The metabolic term 

 is small relative to the total energy exchanged by physical processes, but 

 is important in maintaining all biological processes. The effect of the 

 energy exchange processes is mainly through absorbed solar energy for 

 photosynthesis and through influences on plant temperatures. Tempera- 

 tures at the Biome research area, even during the growing season, are 

 almost always below the optimum for physiological processes in most 

 plants. Therefore, physiological adaptation of plants to low tempera- 

 tures, and morphological adaptation that increases plant temperature, 

 should be more evident in the vegetation of the coastal tundra at Barrow 

 than in temperate regions. 



PRIMARY PRODUCTION IN THE BARROW 

 WET MEADOW TUNDRA 



Standing Crop and Primary Productivity 



Primary productivity in the tundra at Barrow has been estimated by 

 the harvest method for the aboveground vascular vegetation (Webber 

 1978), by cuvette measurements for vascular plants (Tieszen 1975, 1978b) 

 and mosses (Oechel and Sveinbjornsson 1978), by photosynthesis models 

 for vascular plants (Miller et al. 1976) and mosses (Miller et al. 1978a), 

 and by the aerodynamic method for the total ecosystem (Coyne and 

 Kelley 1975). Based on these different measurements, gross above- and 

 belowground primary production for the Biome research area in 1972, a 

 year of nearly normal temperature and precipitation, was 465 gdw m"\ 

 including 358 gdw m"^ for vascular plants, 106 gdw m'^ for mosses, and 

 about 1 gdw m"^ for lichens. 



Net primary productivity, which is gross productivity minus the esti- 

 mated respiratory costs for plant maintenance and growth, was about 

 230 gdw m"^ yr"', including 162 gdw m"^ yr"' for vascular plants, 66 gdw 

 m"^ yr"' for mosses, and less than 1 gdw m'^ yr"' for lichens. For these 

 calculations growth respiration was calculated as 0.3 of the new biomass 

 for both vascular plants and mosses. Maintenance respiration was calcu- 

 lated as 0.0054 gdw gdw"' day"' for 35 days for aboveground vascular 

 material, 0.0027 gdw gdw"' day"' for 60 days for belowground vascular 

 material, and 0.003 gdw gdw"' day"' for 60 days for mosses. The daily 

 maintenance cost was calculated using protein percentages of 9, 4.5 and 

 4.8 for above- and belowground vascular and moss material respectively 

 (Penning de Vries 1974, Chapter 5). The overall value is composed of the 

 separate productivities of different plant growth forms in eight vegetation 



