Phenological changes in rate of respiration and annual carbon balance in a perennial herbaceous plant, Primula sieboldii.

Primula sieboldii E. Morren is a clonal herbaceous species with a short foliar period from spring to early summer. We have studied the temperature-dependence of the rate of respiration at the whole-ramet level throughout the phenological stages of P. sieboldii to reveal its photosynthate-utilization strategy. P. sieboldii ramets were grown in a chamber enabling simulation of seasonal changes in temperature. Rates of respiration were measured at three phenological stages--the foliar period, the before-chilling defoliated (BCD) period, and the after--chilling defoliated (ACD) period. In the foliar period the rate of respiration, on a biomass basis at 20 degrees C (R (20)), of the above-ground plant parts was 2.5 times that of the below-ground parts. The R (20) of the below-ground parts in the foliar period was 6.5 times that in the BCD period and 1.6 times that in the ACD period. Estimation of the ramet carbon balance under these growth conditions showed that ramets respired 87% of total photosynthate production during the experimental period (8.5 months). Respiratory consumption in the foliar period accounted for 70% of the yearly total, whereas 24 and 6% were consumed in the BCD and ACD periods, respectively. An extremely low rate of respiration during the long defoliated period led to a positive net annual carbon balance for P. sieboldii ramets.