PSO. 



UJ 



0-1 



g 

 Siso. 



e 



-so. -- 



Figure 15. Seasonal chlorophyll contents, site 2 control plots, Barrow, Alaska. 



bution in blade and non-blade material also varied. For example, at the peak of the season 

 Eriophorum angustifolium possessed 20 times more chlorophyll in the blades than in the remainder 

 of the plant while in Carex aquatilis nearly a third of the chlorophyll was in non-blade material. 

 Field photosynthesis determinations with a portable "COj technique indicated that these stems 

 and green flowering structures were active in the uptake of COj. 



Table XII contains the seasonal data for these above ground production parameters. The plant 

 nutrient data for the three principal species show several distinct seasonal trends, particularly 

 for the more mobile elements: phosphorus, nitrogen and potassium. Phosphorus showed an initial 

 increase followed by a leveling off, a gradual decline and late season increase (Fig. 16). The 

 phosphorus values from site 2 were lower than those reported from other previously sampled Barrow 

 sites. The low values compare favorably with other low lemming years. Nitrogen showed a more 

 consistent increase, followed by a late season decline and subsequent rise (Fig. 17). Other 

 elements (Ca, Mg, Fe, Mn, Zn) showed no clear trends. Late summer values for nitrc^en and 

 phosphorus were higher than the spring's standing dead. Again this suggests nutrient leaching 

 prior to initiation erf the foUowir^ growing season. 



The mechanistic approach to an understanding and modeling of primary production requires a 

 thorough knowledge of leaf position and orientation in the canopy. These considerations are neces- 

 sary to calculate and predict energy exchange and photosynthesis in individual leaves, intact plants, 

 and entire stands through one entire growing season. The 1970 plant studies utilized an inclined 

 point frame system to estimate for each species leaf area indices (LAI) as a function of position 

 in the canopy. 



The leaf area index is a measure of the amount of leaf cover, and may be thought of as the 

 ratio of the area c^ leaf surface to the area of groimd. Thus a leaf area index of 0.8 means that 80% 

 of the surface is covered by leaves. These indices were determined at six sampling periods through 

 the growing season with a frame consisting of 39 pins at 2.5 cm intervals. Usually the contacts of 

 at least 500 pins were recorded upon pushing the pins through the entire depth of the canopy. 

 Slight changes in microrelief resulted in a few contacts below mean ground level, and in this report 

 these contacts are grouped in the increment "-X to -0.1." 



31 



