Composition of rhizomes of forest herbaceous plants in relation to morphology, ecology, and burial by tephra

Nine herbaceous species of variable but known belowground morphology were sampled in subalpineforests of the Cascade Range, Oregon and Washington. We measured variation of belowground concentra-tions of energy, ash, carbohydrates (starch plus sugar), nutrients, and water among morphological typesand between areas with and without recent volcanic tephra. Chemical composition of belowground partsvaried among species and, to a lesser extent, among morphological groups, with season, and followingburial by tephra. Some aspects of rhizome chemistry were related to rhizome length and degree of shootperenniality: (1) short rhizomes contain more resources because of their greater mass per unit length, al-though chemical concentrations do not differ with rhizome length, and (2) species with ephemeral shootscontain higher proportions of mobile macronutrients, compared with other elements, than those with pe-rennial shoots. Even so, many chemical differences among rhizomes cannot be predicted from morphology.Plants recently buried by volcanic tephra contained more ash, water, K, S, Fe, and Cu than those elsewhere.Water and often carbohydrate content declined during the growing season. Tissue near shoots in long-rhizomatous species had higher concentrations of water, N, and P and, in tephra, of carbohydrates. Com-position of belowground organs varied among species to a degree and with a pattern that indicates adaptivesignificance. Explanations of behavior of forest understory plants that ignore belowground differences arelikely to be inadequate because of chemical as well as morphological differences among species.