PHYSIOLOGICAL PERTURBATION IN JACK PINE (PINUS-BANKSIANA LAMB.) IN THE PRESENCE OF COMPETING HERBACEOUS VEGETATION

The effects of herbaceous competing vegetation on two containerized st ocktypes of jack pine (Pinus banksiana Lamb.) were investigated to ass ess their relative competitive tolerance in the first year after plant ing. Stocktypes were of similar genetic origin and age, but differed i n initial size. First-season survival of Multi-pot(TM) 1-67 and 6-45 s eedlings was 37% and 60%, and diameter increment was 0.25 mm and 0.33 mm, respectively, in the presence of competition. Competitive toleranc e was reflected in mid-to late-season physiology: the larger stocktype maintained higher macronutrient concentration and photosynthetic perf ormance, as well as greater capacity to protect tissues from photooxid ative damage. The 1-67 trees had lower net photosynthetic rate, glutat hione (GSH) concentration, and foliar macronutrients particularly N, K , and Ca in the presence of grass. Both stocktypes had high nonphotoch emical quenching in grass plots which likely served a protective funct ion, but in 6-45 trees GSH was also increased which would have provide d additional protection from risk of photooxidative damage. These find ings contribute to our understanding of how size-based differences in competitive ability may be manifested physiologically. (C) 1998 Elsevi er Science B.V.