Potential ecosystem-level effects of genetic variation among populations of Metrosideros polymorpha from a soil fertility gradient in Hawaii

This study assessed intrinsic differences in tissue quality and growth rate among populations of Metrosideros polymorpha native to sites with a range of soil fertilities. We collected seedlings from three Hawaiian mesic fores ts that were either phosphorus-limited, nitrogen-limited, or relatively fer tile. These individuals were grown in a common garden under a factorial hig h/low, N/P fertilization regime for 1.5 years and then harvested to determi ne genetic divergence; aboveground growth rate; and lignin, N, and P concen trations in leaves and roots. Allozyme analyses indicated that the three gr oups had genetically diverged to some degree (genetic distance = 0.036-0.05 3 among populations). Relative growth rate did not differ significantly amo ng the populations. Senescent leaves from the fertile-site population had t he highest N concentrations (due to low N resorption) and had lower lignin concentrations than plants from the N-limited site. Across treatments, P co ncentrations in senescent leaves were highest in plants from the fertile an d P-limited site. Root tissue quality did not generally differ significantl y among populations. Since decomposition rate of senescent leaves in this s ystem is related positively to N concentration and negatively to lignin con centration, senescent leaves from the fertile-site population may have a ge netic tendency toward faster decay than the others. The intrinsic qualities of the three populations may provide positive feedbacks on nutrient cyclin g at each site-nutrient availability may be raised to some degree at the fe rtile site, and reduced at the N- or P-limited sites. Our results suggest t hat even a small degree of genetic differentiation among groups can influen ce traits related to nutrient cycling.