Effects of tissue-type and development on dark respiration in two herbaceous perennials

Perennial plants go through a number of developmental stages during the growing season. Changes in metabolism during these phases have been documented in laboratory-grown plants but never in native plants growing in natural habitats. The purpose of this study was to describe the seasonal pattern of dark respiration in the above-ground tissues of two herbaceous perennials, Bistorta bistortoides (Pursh) Small and Campanula rotundifolia L., growing in the Rocky Mountains (USA). The effect of biomass accumulation on respiration rate and differences in respiration rate among tissues were measured. Respiration rate differed significantly among the above-ground tissues. Reproductive structures had the highest respiration rates, followed by leaves, then stems. Respiration rate decreased by 10-90 % over the growing season in these tissues but was generally not correlated with a decrease in biomass accumulation. The seasonal pattern of respiration rate varied significantly among tissues. Total tissue respiratory flux was calculated at 15 °C for each tissue. In both species, total above-ground respiratory flux was either relatively constant during the growing season with a marked decrease at seed dispersal or a maximum rate was reached at mid-season. In B. bistortoides, leaves had the highest total respiratory fluxes, and the respiratory fluxes of the stem and reproductive structures were similar to one another. In C. rotundifolia, leaf and stem respiratory fluxes were similar, while the respiratory flux of the reproductive structures was considerably lower than that of leaves and stems. This study emphasizes the importance of developmental processes and tissue-type on respiration rate and highlights the importance of including all plant tissues in predictive models of plant carbon balance.