Primary Producers 239 



capacity of the sediments (Figure 4-29) and not to the concentration of P 

 in the water. This binding capacity is likely related to the supply rate. In 

 contrast, in terrestrial soils at Barrow the production of vascular plants 

 was correlated with the phosphorus concentrations (Ulrich and Gersper 

 1978, Bunnell et al. 1975). This conclusion, however, was based on 

 standard methods of measuring available phosphorus and Chapin et al. 

 (1978) argued that the available phosphorus in the soluble pool is really so 

 small that it has a residence time of only 10 hours. They also argue that 

 microbial lysis provides most of the available phosphorus. No matter 

 which view is correct, there are differences between the reactions of the 

 terrestrial soils and pond sediments. 



Phosphorus 



Chapin (1974), in his study of phosphate absorption in plants at low 

 temperatures, found five adaptations: low temperature optima for root 

 initiation, elongation, and production; large surface-to-volume ratios of 

 roots; proportionately more nutrient absorbing tissue; higher phosphate 

 absorption capacities at given temperatures; and less temperature 

 sensitivity of the phosphate absorption system. One of the species he 

 studied, Carex aquatilis, was collected from a pond margin at Barrow. 

 Some of these adaptations, such as root growth at low temperatures and 

 high root-to-shoot ratios, have already been discussed. The only measure 

 of root diameter is given in Chapin (1974, his Figure 3). The diameters 

 of Carex aquatilis roots were significantly smaller in the Barrow pond 

 samples (soil temperature was 2°C) than in samples from the interior of 

 Alaska where average soil temperature was 18°C. Chapin also found that 

 the V^ax of P uptake per unit of biomass was 4 times greater at Barrow 

 than at the interior site. 



Even within the Barrow area there were significant differences in P 

 uptake by Carex roots from different sites (Figure 5-35). The relatively 

 high Vmax in the plants from the pond margin is further evidence that 



TABLE 5-10 Kinetic Parameters for Phosphate Uptake by Carex in Three 

 Barrow Environments at 10°C 



Source: Chapin and Bloom (1976). 



