Document: DAR-3-32-35

Variation in water availability and plant physiological characteristics among species occupying a substrate and rainfall matrix in Hawaii.

SANDQUIST, D.*

California State University, Fullerton, CA, U.S.A. ¹

Abstract:
Variation of rainfall amount and substrate texture combine to affect water availability and thus influence ecosystem processes. In addition, interspecific differences of plant responses to water availability may add variation to these processes. Over a rainfall gradient on the island of Hawaii, water potential of early successional plants on two contrasting lava types, 'a'a (rough) and pahoehoe (smooth), was examined. Concurrently, photosynthesis within and among species was measured to evaluate how water availability may affect vegetation differences found between these two substrates and to determine if physiological variation among species might contribute to productivity differences among ecosystems. Few differences were found in water potential and photosynthetic rate of plants growing on 'a'a vs. those on pahoehoe. Of the comparisons that were different, neither 'a'a nor pahoehoe was consistently more favorable. There was, however, a slight trend showing greater water stress in 'a'a communities when water availability was lower, and in communities of greater biomass in sites where rainfall is typically higher. Within a community there were usually distinct differences among species for water potential and photosynthesis, but the species-by-lava effect was rarely significant, indicating that each species was responding similarly to what differences there may be between 'a'a and pahoehoe.

Keywords: water potential, photosynthesis, species diversity, Hawaii

This abstract is being presented at: 3:30 PM in session:
WATER RELATIONS