Controls on CO 2 Exchange in Two Polytrichum Moss Species. 2. The Implications of Belowground Plant Parts on the Whole-Plant Carbon Balance

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Abstract
P. commune Hedw. and P. alpinum Hedw. growing on the tundra near Barrow, Alaska [USA], were studied with respect to biomass partitioning, above- and belowground carbohydrate reserves and stem respiration. The biomass of belowground parts constituted .apprx. 30% of the total living biomass in both species. Sugar concentrations were highest in the green shoots, but starch concentration was highest in belowground parts. Respiration rates were similar in the belowground parts of both species and increased linearly with temperature over the temperature range observed. The proportion of the diel C gain by the aboveground shoot which was respired by the belowground parts sometimes exceeded 30%. This CO2 loss is considered to affect the pattern of both the diel and seasonal CO2 uptake and result in net seasonal dry matter accumulation of .apprx. 250 mg g-1 dry wt of the whole plant.