Control of Tundra Plant Allocation Patterns and Growth 145 



dra graminoids is 5 to 10 °C higher than average summer shoot tempera- 

 ture in the field. Transplant studies show that Barrow graminoids and 

 other arctic species do grow faster in warmer climates (Warren Wilson 

 1966a, Chapin and Chapin, pers. comm.) than in their natural environ- 

 ment, indicating that arctic plant growth is limited in part by temperature 

 despite adaptations that permit rapid growth at low temperature. 



The similarity of relative production rates between tundra and mid- 

 latitude grasses in the field suggests that the metabolic cost associated 

 with this production (i.e. growth respiration) may also be similar, assum- 

 ing comparable production efficiencies. This hypothesis is supported by 

 laboratory studies showing that arctic plants have a higher respiratory 

 rate than mid-latitude plants when measured at some standard tempera- 

 ture, but that the respiration rates of various populations at their respec- 

 tive habitat and growth temperatures may be comparable (Mooney and 

 BiUings 1961, Billings et al. 1971). High rates of mitochondrial oxidation 

 are the cause of high respiration rates measured in intact plants (Klikoff 

 1966). Because respiration is temperature-dependent, a high respiratory 

 capacity would be required for arctic plants to maintain their observed 

 growth rates at low ambient temperature. The high respiratory capacity 

 of arctic plants is determined both genetically and environmentally, al- 

 though genetic factors appear more important than acclimation in ex- 

 plaining this temperature compensation (Klikoff 1966, Billings et al. 

 1971). 



Many authors (e.g. Bliss 1962a, Billings and Mooney 1968) have 

 commented upon rapid spring shoot growth of tundra species. However, 

 Warren Wilson (1966a) found lower growth rates in the high Arctic than 

 in England. Further critical studies of relative growth rates of arctic 

 plants are needed. 



Rhizome Growth 



Simulations suggest that the rapid early-season leaf growth of 

 Dupontia is correlated with a corresponding decrease in the biomass of 

 the rhizome and to a lesser degree of the stem base (Figure 5-4). This has 

 been corroborated in measurements of temperate and upland tundra 

 sedges (Bernard 1974, Chapin et al. 1980). Later in the season there is 

 substantial allocation of biomass to belowground organs and probably a 

 retrieval of materials from senescing leaves to the rhizome and 

 sheath/stem base in preparation for the following season. This agrees 

 with conclusions of the carbon dioxide budgets (Chapter 12) and '"C and 

 '^P autoradiography (Allessio and Tieszen 1975a, Chapin and Bloom 

 1976). The main growth phase of new VO tillers is from mid-July onward 

 in contrast to the mid-June onset of leaf production. The delay of below- 



