Luxury Uptake and Storage of Nitrogen in the Rhizomatous Alpine Herb, Bistorta Bistortoides

Abstract

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 nonfertilized plants over two growing seasons (3—4 growing seasons after fertilization began). Fertilized plants stored more N in the rhizome throughout both seasons than did nonfertilized plants. Inflorescence, foliar, 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 that luxury uptake occurs in this species. Increased N storage in fertilized plants was accomodated byan increase in the amino acids arginine, the nonprotein amino acid, δmdash;acetylornithine, glutamine, and glutamate. Luxury uptake was accommodated entirely through filling of existing rhizome cells; no increased cell proliferation was found. Sucrose concentration was significantly lower in the recently produced rhizome tissue of fertilized plants, possibly reflecting the carbon costs of storing the additional N. During the first half of the season, fertilized plants relied more on stored N to drive growth, with translocation from reserves accounting for 56% and 100% of the aboveground N requirement in nonfertilized plants, respectively. In fertilized plants, the complete reliance on stored N indicates a decrease in current—season uptake of N during the period normally associated with 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 species.