Two Western Pacific Tabernaemontana Species Contrast in Biomass Allocation and Leaf Physiological Plasticity to Sun and Shade

The ability of plants to modify biomass allocation and leaf phenotypes to best utilize available resources has been heavily studied. No Tabernaemontana species have been included in this research agenda. Therefore, Tabernaemontana pandacaqui Poir. and Tabernaemontana rotensis (Kaneh.) B.C. Stone plants were subjected to 24% or 100% sunlight and various traits were determined to compare the relative level of plasticity. Midday net carbon dioxide assimilation was greater for T. rotensis in sun-grown plants, but greater for T. pandacaqui in shade-grown plants. Saturating light intensity and midday Fv/Fm were greater for T. rotensis in sun-grown plants, but did not differ between the species for shade-grown plants. Light compensation intensity was greater for T. rotensis than T. pandacaqui in both light treatments. Apparent quantum yield was greater for T. pandacaqui shade-grown plants but was similar for the two species in sun-grown plants. Greater relative root growth in full sun compared with shade was exhibited by T. rotensis but not by T. pandacaqui. These findings indicated that T. pandacaqui develops functional traits that improve performance in shade-grown plants, and T. rotensis develops facultative traits that enable performance in sun-grown plants. These insights into how T. pandacaqui and T. rotensis respond to sun and shade conditions add to the knowledge needed to inform the selection of niche conditions when using them in managed mixed forest plantings such as conservation and restoration sites.