LUXURY UPTAKE AND STORAGE OF NITROGEN IN THE RHIZOMATOUS ALPINE HERB,BISTORTA BISTORTOIDES

The patterns of luxury uptake and storage of nitrogen were studied in the rhizomatous alpine herb, Bistorta bistortoides (Pursh.). Nitrogen pools in the rhizome and shoot were measured in fertilized and nonfert ilized plants over two growing seasons (3-4 growing seasons after fert ilization began). Fertilized plants stored more N in the rhizome throu ghout both seasons than did nonfertilized plants. Inflorescence, folia r, and preformed bud N concentrations and biomass production rate did not increase in response to fertilization. The increased storage of N without a concomitant influence on biomass production demonstrates tha t luxury uptake occurs in this species. Increased N storage in fertili zed plants was accommodated by an increase in the amino acids arginine , the nonprotein amino a acid, delta-acetylornithine, glutamine, and g lutamate. Luxury uptake was accommodated entirely through filling of e xisting rhizome cells; no increased cell proliferation was found. Sucr ose concentration was significantly lower in the recently produced rhi zome tissue of fertilized plants, possibly reflecting the carbon costs of storing the additional N. During the first half of the season, fer tilized plants relied more on stored N to drive growth, with transloca tion from reserves accounting for 56% and 100% of the aboveground N re quirement in nonfertilized and fertilized plants, respectively. In fer tilized plants, the complete reliance on stored N indicates a decrease in current-season uptake of N during the period normally associated w ith net N uptake in this species. This is interpreted as either (1) a seasonal shift in N uptake, or (2) a negative feedback between stored N and uptake that would constrain the continued accumulation of excess N and eliminate any long-term benefits of luxury N uptake in this spe cies.