154 



F. S. Chapin III et al. 



Dupontia fisheri 



100 



50 





a> 



o 

 u 

 « 



100 



50 



i5 



100 r 



50 



I 





L 



_L 



Andromeda polifolia 



I 



M_^ 





Rubus chamaemorus 



s^ 



L 



I 



L 



i 



May Jun Jul Aug 



Labeling Date 



Root DUl Stem Base 



Rtiizome Q Aboveground Ports 



Root and Rhizome 



FIGURE 5-7. Distribution of 

 recovered '"C in different 

 plant parts of Dupontia fish- 

 eri in mesic meadow tundra 

 at Barrow (Allessio and Ties- 

 zen 1975a) and Andromeda 

 polifolia and Rubus cham- 

 aemorus in an arctic mire at 

 Stordalen, Sweden (Johans- 

 son 1974). Dupontia was har- 

 vested two days after label- 

 ing; the others were harvested 

 three weeks after labeling. 



highly dependent upon belowground mineral reserves. 



Gas exchange and harvest measurements indicate that over the en- 

 tire growing season only 34% of the annual carbon fixation is used in 

 shoot growth and respiration. The remaining 66% is presumably translo- 

 cated below ground, perhaps late in the season, to support growth and 

 maintenance of roots and rhizomes. A downward translocation of this 

 magnitude would be necessary to provide the energy source for the sub- 

 stantial root and rhizome respiration measured by Peterson and Billings 

 (1975). 



The retention of radiocarbon in shoots of labeled tillers and the sea- 

 sonal stability of the allocation pattern in Dupontia differ strikingly 

 from the allocation patterns of other growth forms (Figure 5-7) (Johans- 

 son 1974). In Andromeda polifolia, an evergreen shrub growing in 

 Swedish tundra, 75% of the fixed carbon was translocated below ground 

 early in the season. As leaf growth began, a larger proportion of the '"C 

 was retained in the shoot. Finally, at the end of the season, fixed carbon 



