Trash or treasure: Rhizome conservation during drought

The role of storage carbohydrates in plant carbon economy is currently disputed as possibly passive accumulation when other resources are limiting growth, or part of a conservative growth strategy as insurance for regrowth and stress response. One indication may be the fate of carbohydrates in senescing rhizomes, as either translocated to be retained in the live and growing end of the rhizome or kept within the senescing rhizome end and lost into the soil for it to decompose.To examine carbohydrate storage in senescing rhizomes, eight rhizomatous species were grown in a split-pot design with one compartment containing the forward-growing and younger end of the rhizome and another containing the older end. Both compartments were either watered (control) or the older one was left un-watered (drought treatment) to trigger rhizome senescence and potential carbohydrate translocation. Plant growth, root traits, and non-structural carbohydrate types and concentrations were assessed in four sequential harvests.Drought treatment plants had higher rhizome dry matter content. Younger rhizome parts produced higher new rhizome and above-ground biomass than older rhizome parts. Carbohydrate concentrations in rhizomes remained consistent for both treatments, younger and older rhizome parts, and all harvests, probably because of the translocation of water from the watered to the dry compartment to prevent senescence and rhizome loss.Contrary to expectations, the experimental treatment did not trigger rhizome senescence: plants responded by conserving the rhizome and resources within, rather than by losing their older parts. The invariant composition and concentration of carbohydrates within the rhizome suggest that rhizomes are essential plant organs and the storage carbohydrates they contain are necessary for regrowth after stress.