Growth and Carbon Partitioning in Rainforest and Eucalypt Forest Species of South Coastal New South Wales, Australia

Abstract

Rainforest, ecotone and eucalypt forest species were grown for 22 weeks in glasshouse conditions under light, water and nutrient treatments. Plant biomass, leaf area and leaf biomass per plant increased in Eucalyptus sieberi, Eucalyptus fastigata, Pittosporum undulatum, Callicoma serratifolia, Elaeocarpus reticulatus, Backhousia myrtifolia and Ceratopetalum apetalum at high irradiance (1230-1670 μ-mol PAR m^-2 s^-1). Both E. sieberi and E. fastigata inhabit the relatively high light environments of northern aspects, upper southern aspects and ridge tops in the gully systems of south coastal New South Wales. Callicoma serratifolia, P. undulatum and E reticulatus are pioneer species of the ecotone around rainforest patches, and B. myrtifolia and C. apetalum are rainforest canopy species. Mean plant biomass under high irradiance was ranked: eucalypt species > ecotone species and B. myrtifolia > C. apetalum. At low irradiance (200-530 μ-mol PAR m^-2 s^-1) the trend observed was reversed where rainforest canopy and ecotone species produced greater plant biomass. Plant response to different water and nutrient treatments under glasshouse conditions showed that, while the light environment primarily governed plant response, interaction between treatments occurred which resulted in maximum plant biomass at relatively high levels of soil moisture and nutrients.

Carbon partitioning was used as an indication of relative response to light treatments. The proportion of plant mass partitioned to leaves did not change between experimental treatments. The magnitude of the response of leaf area ratio and specific leaf weight to light treatment, however, was ranked: eucalypt species > ecotone species > rainforest canopy species. This suggested that species naturally growing outside the rainforest canopy maximised leaf area in proportion to plant mass for a given irradiance, presumably to maintain high growth rates.