EFFECTS OF NITROGEN AVAILABILITY ON NITROGEN ALLOCATION AND PLANT GROWTH IN EVERGREEN AND DECIDUOUS SPECIES OF VACCINIUM (ALASKA)

The evergreen shrub, Vaccinium vitis-idaea and the deciduous shrub Vaccinium uliginosum inhabit areas with low nitrogen availability. The purpose of this study was to (1) compare the role of remobilized nitrogen during shoot growth in the two growth forms and (2) test the hypothesis that deciduous species respond more to nitrogen fertilization.; Using ('15)N as a tracer, a comparison of nitrogen allocation patterns from single leaves was made. Both species were similar. Leaves of any position along the stem could supply any plant part with nitrogen during shoot growth; however, the strongest sink for leaf nitrogen was current production. Source-sink interaction was well developed between shoots as well as within a shoot. Leaf nitrogen allocation patterns did not change with leaf position. However, lower leaves transported a larger portion of the ('15)N label.; Both species had similar patterns of leaf nitrogen storage during winter and utilization of stored nitrogen for shoot growth. They could rely totally on nitrogen reserves for new shoot growth. Both growth forms stored most leaf nitrogen in the closest tissue extant over winter; the leaves in the evergreen, the stem subtending leaves in the deciduous species. During shoot growth both species relied most for stored nitrogen on the closest leaves and stems; not belowground tissue.; Nitrogen allocation patterns were not differentially affected by nitrogen fertilization in the two growth forms. Interdependence of all plant parts of both species for nitrogen existed under low nitrogen conditions. The interdependence decreased with increased nitrogen availability.; Both species responded similarly to nitrogen fertilization in terms of shoot population and nitrogen pool growth rates. Shoot population growth rate was increased with nitrogen fertilization, however, the mechanism differed with species. In the evergreen, the probability of a shoot branching increased with nitrogen fertilization. In the deciduous species, nitrogen fertilization increased shoot size. Larger shoots produced more daughter shoots. Hence, shoot population growth rate increased. Nitrogen pool growth rate was not affected by nitrogen fertilization. Moreover, nitrogen fertilization did not favor either the evergreen or the deciduous species in terms of shoot population or nitrogen pool responses.