100. 



ex: 

 a 



eSO. -- 



JUNE 70 I JUL! TO I 



Figure 14. Seasonal primary production values, site 2 control plots, Barrow, Alaska. 



<2 cm thick, between 60 and 85% of the living material consisted of rhizomes and stem bases. 

 Rhizome material in the top 5 cm of mineral soil constituted from 20 to 60% of the total living 

 phytomass. Up to 77% of the living material in the second 5 cm increment of mineral soU consis- 

 ted of rhizomes. There were no rhizomes in deeper increments. Between 80 and 99% of the total 

 living subsurface phytomass occurred in the top 12 cm of soU (includes the organic mat). These 

 data indicate that subsurface vascular plant activity primarily occurs in the upper part of the active 

 layer, in that part of the soU. having early and rapid thaw, warmer temperatures, and higher oxygen 

 contents. Maintenance of a large subsurface standing crop requires either long-lived structures or 

 rapid turnover with high annual input of photosynthate. 



The absence of high numbers of lemmings for several years has resulted in an accumulation 

 of standing dead material. Careful physical observations allowed a separation of this material 

 into age classes by year of production. In this material, caloric content was distinctly lower as 

 the age d the material increased. Thus, there is an apparent leaching or decomposition of organic 

 materials in the standing dead compartment. The extent and mechanism of the removal of materials 

 from this compartment by these means remains to be determined. 



Of the species found on site 2, Dupontia fischeri, Eriophorum angustifolium, and Carex aquatilis 

 were the most abundant and accounted for the majority of the production. In contrast to these 

 species, in which growth was continuous during the season, some of the producers revealed dis- 

 tinct seasonality in production. Seasonal production in the cryptogams could not be followed due 

 to methodolc^ical problems. However, the total standing crop of live portions of cryptogams at 

 the peak of the season was measured in one plot. A foliose lichen provided an average of 2 g/m', 

 polytrichum-type moss an average of 3 g/m^ and aU other mosses an average of 40 g/m^ Thus, 

 production in this layer is quite substantial and significant. 



Chlorophyll determinations were made as an indication of the amount of photos ynthetic tissue 

 in the community, as a unit for comparison with laboratory photosynthesis studies, and as an indi- 

 cation of onset and degree of senescence. Chlorophyll content in the community decreased rapidly 

 after 15 July, suggesting a rapid loss of photosynthetic capacity and an onset of senescence in 

 some leaves (Fig. 15). This was also indicated by the detailed growth studies on Dupontia lischeri, 

 Alopecurus alpinus, and other grasses where the first leaf of the season was decreasing in photo- 

 synthetic activity by 15 July. Chlorophyll varied by a factor of 2 among the species; its distri- 



30 



