PHYSIOLOGICAL AND MORPHOLOGICAL VARIATION IN METROSIDEROS-POLYMORPHA,A DOMINANT HAWAIIAN TREE SPECIES, ALONG AN ALTITUDINAL GRADIENT - THEROLE OF PHENOTYPIC PLASTICITY
S. Cordell et al., PHYSIOLOGICAL AND MORPHOLOGICAL VARIATION IN METROSIDEROS-POLYMORPHA,A DOMINANT HAWAIIAN TREE SPECIES, ALONG AN ALTITUDINAL GRADIENT - THEROLE OF PHENOTYPIC PLASTICITY, Oecologia, 113(2), 1998, pp. 188-196
Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystem
s, occupies a wide range of habitats. Complementary field and common-g
arden studies of M. polymorpha populations were conducted across an al
titudinal gradient at two different substrate ages to ascertain if the
large phenotypic variation of this species is determined by genetic d
ifferences or by phenotypic modifications resulting from environmental
conditions. Several characteristics, including ecophysiological behav
ior and anatomical features, were largely induced by the environment.
However, other characteristics, particularly leaf morphology, appeared
to be mainly determined by genetic background. Common garden plants e
xhibited higher average rates of net assimilation (5.8 mu mol CO2 m(-2
) s(-1)) and higher average stomatal conductance (0.18 mol H2O m(-2) s
(-1)) than their field counterparts (3.0 mu mol CO2 m(-2) s(-1), and 0
.13 mol H2O m(-2) s(-1) respectively). Foliar delta(13)C of most commo
n-garden plants was similar among sites of origin with an average valu
e of -26.9 parts per thousand. In contrast, mean values of foliar delt
a(13)C in field plants increased substantially from -29.5 parts per th
ousand at low elevation to -24.8 parts per thousand at high elevation.
Leaf mass per unit area increased significantly as a function of elev
ation in both field and common garden plants; however, the range of va
lues was much narrower in common garden plants (211-308 g m(-2) for co
mmon garden versus 107-407 g m(-2) for field plants). Nitrogen content
measured on a leaf area basis in common garden plants ranged from 1.4
g m(-2) to 2.4 g m(-2) and from 0.8 g m(-2) to 2.5 g m(-2) in field p
lants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% wit
h increasing elevation in field plants and only 20% in plants from you
ng substrates in the common garden. This was a result of higher rates
of net CO2 assimilation in the common garden plants. Leaf tissue and c
ell layer thickness, and degree of leaf pubescence increased significa
ntly with elevation in field plants, whereas in common garden plants,
variation with elevation of origin was much narrower, or was entirely
absent. Morphological characteristics such as leaf size, petiole lengt
h, and internode length decreased with increasing elevation in the fie
ld and were retained when grown in the common garden, suggesting a pot
ential genetic basis for these traits. The combination of environmenta
lly induced variability in physiological and anatomical characteristic
s and genetically determined variation in morphological traits allows
Hawaiian M. polymorpha to attain and dominate an extremely wide ecolog
ical distribution not observed in other tree species.