PROGRAMMED TILLER DIFFERENTIATION, INTRACLONAL DENSITY REGULATION AND NUTRIENT DYNAMICS IN CAREX-BIGELOWII

The internal controls of tiller dynamics in 3 populations of Carex bigelowii along an altitudinal gradient in Swedish Lapland were examined. The 1st daughter tiller to be produced was usually ventral. These generally had long rhizomes (guerilla), while dorsally produced tillers had shorter rhizomes or no rhizome at all (phalanx). Rhizomes of laterally produced tillers were of intermediate length. Bud dormancy varied between 0-4 yr. Mean time between emergence aboveground of a parent and its 1st daughter was at least 2.2 yr. Ventral tillers had more vegetative offspring; dorsal tillers were more likely to flower. Large tillers, irrespective of tiller type, tillered more and were more likely to flower. After production of a daughter tiller, the parent shoot gradually declined in vigour and finally died. A fertilizing experiment revealed a strong response of C. bigelowii to increased levels of soil nutrients. Offspring production increased by 50% and the proportion of dorsal tillers increased from 20% to 36%. Amount of resorption from the leaf fraction into the tiller system was high for macronutrients, and ranged from 42% for N to 92% for K. Ventral tillers were costlier to produce than dorsal tillers in terms of nutrients and carbon, due to their biomass. The first daughter tiller being of a guerilla type maximizes the forward "search' for favourable patches. Should these be encountered, the increased nutrient availability increases the production of offspring, these being mainly of the phalanx type, thus efficiently exploiting the favourable micro-site. The phalanx type tillers are more likely to flower, while not producing vegetative offspring, using the extra nutrients for the requirements of the maturing seeds. -from Authors