354 REICHLE, DINGER, EDWARDS, HARRIS, AND SOLLINS 



Lateral root production was estimated from the difference between maxi- 

 mum and minimum standing crop (Fig. 1). Between June and September, net 

 lateral root carbon increased by 290 g C/m . Lateral root carbon increase was 

 approximately 80% of the amount fixed in aboveground and stump material 

 (Table 2). Root-carbon decrease is likely an underestimate of root death because 

 of mortality and disappearance between sampling periods. For example, Cox 

 (1971) reported that 20% of roots <0.5 cm in diameter are dead at any time 

 during the growing season. 



Net change in carbon-pool size for the root compartment (again based on 

 differences in standing crop) between September and March (Fig. 1) indicates 

 root dieback of 360 g C/m 2 . Apparent root mortality during the dormant season 

 contributes carbon to the decomposer substrate and eventually to the soil 

 carbon pool, but loss of carbon is probably confounded with the vernal flux of 

 labile carbohydrates to the aboveground components. Subsequent calculations 

 assume that accumulation of lateral root carbon equals annual turnover to the 

 decomposer substrate. 



Foliage biomass was estimated from the allometric relation of total leaf 

 weight to DBH (Sollins, 1972). However, cumulative annual litterfall estimates 

 were 40% less than foliage weight determined allometrically. Comparison of unit 

 leaf weights of mature leaves (0.37 to 0.39 g per leaf, Dinger, unpublished data; 

 Reichle and Crossley, 1967) to unit leaf weight of abscissed foliage (Olson, 

 1971) suggests a net translocation of approximately 30% of mature foliage 

 weight prior to abscission — 56 g C m year . Other sources of carbon loss not 

 accounted for are leaching of organics during the season and in the litter traps. 



CARBON FLUXES IIM THE ECOSYSTEM 

 Foliar Carbon Dioxide Exchange 



Net photosynthesis and respiration of yellow poplar (Liriodendron 

 tulipifera) leaves were determined under natural temperature and light condi- 

 tions by means of a gaseous-exchange apparatus incorporating an infrared 

 analyzer and inflatable polyfilm chambers (Dinger, 1971). Data from 450 

 chamber hours of observations gave a mean "daylight" (i.e., light intensity 

 >0.015 cal cm 2 min" 1 ) C0 2 intake rate of 6.4 mg g (dry weight foliage) hr 

 (Table 4). "Dark" (<0.015 cal cm 2 min 1 ) respiration losses were 0.6 mg/hr. 

 On the basis of 12 hr of "daylight" and an equal "dark" period, mean daytime 

 C0 2 uptake rates would be 77 mg/g foliage and dark respiration losses 7.0 

 mg/g, resulting in a net diurnal C0 2 absorption of 70 mg/g. If we assume 

 these net absorption rates to be representative for the entire season (180 days), 

 annual net daily C0 2 fixation per unit dry weight foliage is 12.6 g/g, and dark 

 respiration removes 1.2 g/g, or 9.8% of total daily C0 2 uptake. 



Net carbon dioxide uptake for other canopy trees was calculated from the 

 literature (Table 4). Net daytime C0 2 uptake by yellow poplar (12.6 g/g) was 



