INTRACLONAL NITROGEN ALLOCATION IN THE BUNCHGRASS SCHIZACHYRIUM-SCOPARIUM HUBB - AN ASSESSMENT OF THE PHYSIOLOGICAL INDIVIDUAL

The size of the physiological individual within the bunchgrass Schizachyrium scoparium Hubb. was investigated by evaluating the pattern and magnitude of N-15 allocation within and between individual ramet hierarchies (sequences of connected ramet generations). Nitrogen-15 was acropetally allocated throughout the three generation hierarchies within 24h regardless of the ramet generation or organ labelled. Both primary and secondary ramet generations allocated nitrogen to juvenile, tertiary ramets. Basipetal nitrogen allocation, from secondary to ontogenetically older pr mary ramets, was observed, but accounted for less than 1% of the N-15 mass in the ramet hierarchies at the end of the 5-day experiment. Foliarly labelled ramets exported less nitrogen intraclonally than did root labelled ramets indicating that a greater proportion of the nitrogen was rapidly incorporated into metabolic compounds. A majority (> 93%) of the N-15 introduced into the ramet hierarchies remained within the labelled hierarchies as opposed to being allocated to associated hierarchies within individual clones. Clones of this bunchgrass consist of an assemblage of autonomous physiological individuals, composed of a minimum of three connected ramet generations, as opposed to a system of completely integrated ramet hierarchies. The propensity for acropetal resource allocation appears to be the predominant factor limiting resource allocation between ramet hierarchies within young clones possessing complete vascular continuity.