GROWTH, BIOMASS ALLOCATION AND PLANT NITROGEN CONCENTRATION IN CHILEAN TEMPERATE RAIN-FOREST TREE SEEDLINGS - EFFECTS OF NUTRIENT AVAILABILITY

Seedlings of nine southern Chilean trees were grown at three nutrient supply rates, to examine the roles of growth rate, biomass distributio n and nutrient use traits in determining species natural distributions on resource gradients. Relative growth rate (RGR) showed no overall r elationship with species site requirements, although RGR of fertile-si te species tended to be more responsive to nutrient supply In the low- nutrient treatment, infertility-tolerant Fitzroya cupressoides showed a higher RGR rank than a fertility-demanding species (Laurelia philipp iana) which outgrew it substantially at the highest supply rate. This reversal of RGR ranks was associated with divergent nutrient use respo nses: at high nutrient supply both spp. had similar plant nitrogen con centrations (PNC), whereas at the low supply rate Fitzroya's productio n of biomass per unit of assimilated N was twice that of Laurelia's. H owever, this pattern does not appear to serve as a general explanation of the respective distributions. of the study species, as RGR ranks o f most species were unaltered by nutrient supply. At low nutrient avai lability, no clear differences in shoot:root ratio (SRR) were apparent between poor-site and fertile-site species. However, at high nutrient availability, SRR was markedly higher in the latter, resulting from d ifferences in biomass allocation to stems (not leaves). Leaf area rati os (LAR) were higher in fertile-site species than in those tolerant of low fertility, because of differences in specific leaf area rather th an leaf weight ratio. Very high LAR at high nutrient supply was charac teristic of most shade-tolerant angiosperms, but not of shade-tolerant conifers. Although PNC showed no overall differences between poor- an d fertile-site species, sensitivity of PNC to external supply rate was greatest in two infertility-tolerant conifers. In contrast, the angio sperm Weinmannia trichosperma, although tolerant of low fertility, res ponded to increased nutrient supply with greatly increased RGR and lit tle change in PNC. Results show little trait convergence between conif ers and angiosperms in adaptation both to shade and to infertile soils ; i.e. fitness of different taxa in a given environment may hinge on d ifferent trait combinations.