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EVOLUTION OF C 3 AND C 4 PLANTS ALONG AN ENVIRONMENTAL MOISTURE GRADIENT: PATTERNS OF PHOTOSYNTHETIC DIFFERENTIATION IN HAWAIIAN SCAEVOLA AND EUPHORBIA SPECIES
Author(s) -
Robichaux Robert H.,
Pearcy Robert W.
Publication year - 1984
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1984.tb12492.x
Subject(s) - biology , photosynthesis , botany , habitat , euphorbia , range (aeronautics) , photosynthetic capacity , ecology , materials science , composite material
The endemic Hawaiian species of Scaevola and Euphorbia grow in a wide variety of native habitats and exhibit a wide range of variation in photosynthetic responses. Light‐saturated photosynthetic capacities range from 12.0 to 24.7 μmol CO 2 m −‐2 s −‐1 in the Scaevola species and from 18.2 to 51.4 μmol CO 2 m −‐2 s −‐1 in the Euphorbia species. Within each genus, differences in light‐saturated photosynthetic capacity are paralleled by differences in mesophyll and leaf conductances to CO 2 . Within each habitat, the C 4 Euphorbia species exhibits a significantly higher photosynthetic capacity and a significantly higher mesophyll conductance than the corresponding C 3 Scaevola species. These differences are greatest in the dry scrub habitat and least in the wet forest habitat. One photosynthetic characteristic that exhibits little variation among the species within each genus, yet that exhibits a consistently large difference between the species within each habitat, is photosynthetic water‐use efficiency. The C 4 Euphorbia species possess water‐use efficiencies that are 2–3½ times as high as those of the C 3 Scaevola species, regardless of whether these species are native to very dry or very wet habitats. At present, the ecological significance of this large inherent difference in photosynthetic water‐use efficiency is unknown. Indeed, it appears that neither photosynthetic pathway has imposed any major inherent constraints on the ability of the Scaevola and Euphorbia species to diversify into a wide variety of habitats.