162 F. S. Chapin III et al. 



lipids than do plants in warm soil (Kedrowski and Chapin 1978). The 

 high lipid content reported for arctic and alpine plants (Bliss 1962b) is 

 probably associated with membrane lipid for metabolism or for anti- 

 herbivore defense, such as resins, and not with an energy storage func- 

 tion, as previously assumed. 



Lignin and cellulose, two important structural compounds, also dif- 

 fer strikingly in their carbon cost of synthesis. Neither is significantly 

 broken down for retranslocation during senescence. Lignin should be an 

 important component of a tissue only where strong support is essential or 

 where selection has led to strategies to discourage herbivory. Neither 

 selective force appears to have led to a high lignin content in tundra 

 graminoids. 



The implications of biosynthetic cost for successful adaptation to 

 the tundra environment are discussed in Chapter 6. 



It is of interest, especially when considering the relatively anaerobic 

 soil conditions of the coastal tundra, that biosynthetic processes under 

 anaerobic conditions are 18-fold less efficient because of the incomplete 

 oxidations that can be performed. In addition, toxic end products must 

 be excreted, requiring additional energy expenditures. Although the 

 native graminoids appear to have efficient oxygen transport systems and 

 thus circumvent such problems, introduced plants and some dicoty- 

 ledons may be severely stressed by the saturated soils and anaerobic con- 

 ditions characteristic of many arctic soils. 



Biomass Flux Analyses for Dupontia 



A detailed picture of the fluxes involved in growth and allocation of 

 carbohydrates and nutrients through the season can be built from simu- 

 lations of the seasonal courses of dry matter accumulation, percentage 

 composition, and metabolic cost estimates in Dupontia (Figure 5-9), 

 Estimates of photosynthesis and respiration derived from the flux analy- 

 sis can be compared with direct measurements of net photosynthesis and 

 respiration. Analyses of this type are essential to a thorough understand- 

 ing of the way the plant uses available resources to grow and produce 

 offspring in a particular environment. Biomass changes provide an indi- 

 cation of biosynthetic activity but the costs of biosynthesis, transloca- 

 tion, uptake, and maintenance must be known to truly understand the 

 allocation pattern and overall physiological balance. The following des- 

 cription is based upon simulations of translocation, respiration and 

 growth. 



In a newly initiated tiller (VO), simulated rates of translocation and 

 growth generally increase steadily through the season until about 20 

 August. Subsequently, the rate of growth falls as maintenance respiration 



