Seedlings of subtropical rainforest species from similar successional guild show different photosynthetic and morphological responses to varying light levels

Restoration using rainforest species in Australia and elsewhere has been limited to a small number of widely known species, mainly pioneer or early successional species, Using the presumed successional status as a guideline for species selection in reforestation should be taken with a caveat since a species' capacity to adjust to light gradients is not easily predicted. This study examined the photosynthetic and growth responses of four Australian subtropical rainforest species in the context of using late successional species in restoration programs. Since the selected species [Sloanea australis ((Benth.) F. Muell.), Cinnamomum oliveri (F. M. Bailey),Caldcluvia paniculosa ((F. Muell.) Hoogland) and Geissois benthamiana (F. Muell.)] are considered late-successional species, this study also discussed the possibility of separating these species according to their acclimation level towards light gradients. Seedlings of four species were grown under four light treatments using neutral density shade cloth (5, 33, 64 and 80% irradiance) during summer November 2014 to February 2015. All species demonstrated a narrow range of photosynthetic acclimation to different light levels, experienced photoinhibition and photodamage in 80% irradiance and allocated more biomass to leaves in 5% irradiance, supporting their classification as late successional species. Cinnamomum oliveri was the only species able to utilize higher irradiance, with a higher light saturated rate of photosynthesis than the other species. Canonical analysis of principal coordinates revealed that the degree of plasticity of each species in response to contrasting irradiance levels varied. This analysis separated the species into three light tolerance classes: obligate shade-adapted species (S. australis and G. benthamiana), high light-adapted species (C. paniculosa) and the generalist (C. oliveri). Overall, this study suggests that the four species can be planted and will grow well under 33-64% irradiance since either lower or higher irradiance inhibits growth, and additionally that C. paniculosa and C. oliveri can be possibly planted in early phase of restoration planting with other early-successional species.