Control of Tundra Plant Allocation Patterns and Growth 159 



of a plant compartment is the balance between the rates of photosynthe- 

 sis, respiration, and death and the net translocation flux to that compart- 

 ment. Growth also involves the accumulation and incorporation of nutri- 

 ents. The rate of change in nutrient content of a plant compartment is the 

 balance among the rate of uptake from soil, the net translocation flux, 

 and losses from the living system due to leaching, exudation, grazing and 

 death. There is inadequate information currently available to allow 

 growth to be analyzed in terms of nutrient costs. 



Respiration provides energy for a number of distinct metabolic pro- 

 cesses and can be separated into at least three components: maintenance 

 respiration, growth respiration and translocation respiration. Mainten- 

 ance respiration provides the energy required to sustain the existing live 

 biomass at its present level of metabolic activity. Maintenance respira- 

 tion includes the energy requirement of basic metabolic processes and the 

 replacement or turnover of structural and functional substances, particu- 

 larly of proteins, and is assumed to be proportional to protein content 

 and turnover (Penning de Vries 1975). The proportionality constants of 

 maintenance respiration have been calculated (Miller 1979) for various 

 plant parts according to the relationship derived for crop plants (McCree 

 1974, Penning de Vries 1975) and corrected for values measured in plants 

 from the Biome research area (Chapin et al. 1975, Billings et al. 1978), 

 The relatively high protein content of graminoids in the tundra at Barrow 

 (Chapin et al. 1975) suggests a high maintenance respiration and is in 

 agreement with the high shoot respiration rates measured (Tieszen 1975). 

 Leaves have a higher proportionality constant of maintenance respira- 

 tion (0.012) than do roots or rhizomes (0.006) because of higher protein 

 content, which is consistent with the higher respiration rate measured in 

 leaves than in roots. 



Growth respiration provides the energy required to synthesize vari- 

 ous components of new tissues from glucose (Penning de Vries 1972b; 

 Table 5-5). Although plants contain a variety of sugars that function as 

 metabolic intermediates, these will be viewed as glucose equivalents for 

 the sake of simpHcity. The investment in new tissue is equal to the quan- 

 tity of glucose equivalents contained in the added biomass plus that glu- 

 cose respired in the synthetic process, the growth respiration (Figure 5-8). 

 The total growth respiration for production of new biomass is calculated 

 from the increase in biomass and a constant c that apportions the cost of 

 synthesis among the biochemical constituents of the new tissue (Table 

 5-5): 



c = 1.1 5(% lignin) + 0.17(% cellulose) + 2.03(07o lipids) + 



-l-0.59(<7o protein) + 0.17(% polysaccharide) + 0.09(% sucrose). 



