184 F. S. Chapin III et al. 



SUMMARY 



The component processes of growth and allocation in graminoids of 

 the coastal tundra at Barrow have compensated for low temperature to 

 such an extent that these processes occur at nearly the same rates in situ 

 as those observed in temperate grasslands. Temperature compensation 

 may be achieved at substantial carbon and protein cost and thus be ac- 

 companied by lowered reproductive output. Latitudinal temperature 

 compensation has been demonstrated for shoot growth, photosynthesis, 

 respiration and phosphorus uptake, but requires documentation for 

 growth of belowground organs. Because the air warms faster than the 

 soil, shoot growth and photosynthesis predominate early in the season, 

 whereas root growth and uptake continue well after shoot senescence. 

 Nutrients absorbed in one year have their most pronounced effect upon 

 growth and reproduction in subsequent years. 



The lower levels of annual plant production in tundra than in com- 

 parable temperate communities are more a consequence of shortness of 

 the growing season than of the difference in ambient summer tempera- 

 ture. This hypothesis is supported by computer simulations but has not 

 been tested by field experiments or long-term observations. 



Allocation patterns are altered genetically and environmentally in a 

 way that minimizes limitation to growth by any one environmental re- 

 source but maximizes long-term survival through vegetative and sexual 

 reproduction. Growth is limited simultaneously by several factors. Ex- 

 perimental manipulatipns under field conditions indicate that phosphor- 

 us and nitrogen strongly limit plant growth. Simulations predict that 

 light, carbon dioxide concentration, and water availability also limit 

 growth to a lesser extent. Low temperature limits production in a com- 

 plex fashion involving all of the above environmental variables. The high 

 root-to-shoot ratio of the graminoids compensates for low nutrient avail- 

 ability. The environmental and genetic determinants of typical allocation 

 patterns remain to be determined. 



Plant growth at Barrow is generally more strongly limited by an in- 

 adequate supply of certain nutrients, especially nitrogen and phosphor- 

 us, than by inadequate carbohydrate. Available carbohydrate levels are 

 high in the graminoids, particularly in habitats of low nitrogen and phos- 

 phorus availability. Carbohydrate levels are reduced by fertilization. We 

 suggest that the low radiation environment of the Arctic limits plant 

 growth more strongly by the indirect effects of low temperature upon nu- 

 trient availability than by a direct effect upon photosynthesis. Shoots 

 also become photosynthetically self-sufficient quite early in the season 

 and depend upon rhizome reserves for nutrients more than for carbohy- 

 drate. The decrease in rhizome weight that coincides with early season 



