Submitted to: Journal of Sugarbeet Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2006
Publication Date: 12/29/2006
Citation: Haagenson, D.M., Klotz, K.L., Campbell, L.G., Khan, M.F. 2006. Relationships between Root Size and Postharvest Respiration Rate. Journal of Sugarbeet Research. 43(4):129-144. Interpretive Summary: Sugarbeet root size is controlled by many external and internal factors. During postharvest storage, the beet uses sucrose to provide energy through respiration, and the influence of root size on postharvest respiration is not clear. The mechanisms regulating beet respiration were studied by evaluating root respiration across a wide range of root sizes. Small beets had increased respiration rate when compared to big beets. Respiration rate decreased as root size increased until a critical mass was reached where increasing mass did not further reduce respiration rates. The association between root size and respiration rate suggests that gas diffusion may be a factor limiting respiration. An association between surface area and total beet respiration was also observed and is consistent with the theory that most respiration is occurring in the outermost tissues of the beet. Beet size and surface area are important factors that affect sugarbeet respiration; however, respiration is a complex process and other, as yet unknown factors are likely to influence it.
Technical Abstract: Sugarbeet root size is dependent on genetics, environmental conditions, and cultural factors. To evaluate the effect of root size on respiration rate and explore possible physiological mechanisms that regulate respiration in sugarbeet roots, the relationship of root mass, surface area, and the ratio of surface area to mass (specific surface area) with respiration rate and the relationship between surface area and total respiration were determined using three field-grown sugarbeet varieties. Root mass, surface area, and specific surface area were significantly associated to respiration rate by a sigmoidal relationship. The variation in respiration rate among KW 2249, VDH 46177, and Beta 4818 was best explained by root mass alone (R2 = 0.55, 0.40, and 0.43), or the specific surface area (R2 = 0.57, 0.34, and 0.33). For each variety, there was a critical root size above which size had little impact on respiration. Below this critical size, root respiration increased dramatically as root mass or surface area decreased. This critical beet size, determined by the inflection point was 0.68, 0.50, and 0.92 kg for KW 2249, VDH 46177, and Beta 4818, respectively. Total respiration, i.e. respiration per beet, was linearly associated with surface area for KW 2249 (R2 = 0.70) and VDH 46177 (R2 = 0.46), but not for Beta 4818 (R2 = 0.11). The relationships observed are consistent with the theories that root respiration occurs largely at the root surface and that root respiration is limited by gas diffusion through the bulky taproot. However, the low coefficient of determinations present in this study suggest other unknown physiological mechanisms may contribute to respiratory regulation.