Publication Date

2010-05-03

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Biology (Arts and Sciences)

Date of Defense

2010-04-09

First Committee Member

David P. Janos - Committee Member

Second Committee Member

Leonel Sternberg - Committee Member

Third Committee Member

Guillermo Goldstein - Mentor

Fourth Committee Member

David W. Lee - Outside Committee Member

Abstract

Hemiepiphytes are important components of tropical forests and are attractive to scientists due to their unique epiphytic growth habit during some period of their life cycle. Unique characteristics in plant water relations and carbon economy have been found in hemiepiphytic plants; however, to further understand this group of species on an evolutionary basis it is necessary to carry out comparative studies between hemiepiphytes and their close relatives. In this dissertation I conduced a comparative study in a suite of functional traits related to plant water relations and photosynthesis between hemiepiphytic and non-hemiepiphytic tree species from a single genus-Ficus. Great differentiation in functional traits has been found between species of the two growth forms both during juvenile and adult stages. Seedlings of hemiepiphytic Ficus species (H) had significantly lower xylem hydraulic conductivity, stomatal conductance, net light saturated CO2 assimilation, and higher water use efficiency than congeneric non-hemiepiphytic species (NH), which are adaptive to a drought-prone epiphytic growth conditions under natural conditions. The conservative water use adaptation in H species is likely crucial to the drought tolerance and survival in the forest canopy but is related to much lower growth rates than NH species. Species of the two growth forms both showed relatively large plasticity in responding to variation in light level as in typical light-demanding species. Surprisingly, the NH species showed characteristics related to higher light demand than H species, which is opposite from the prediction that H species are more light-demanding than NH species. Thus, although commonly accepted, it is likely that light was not the selective pressure for the evolution of hemiepiphytism in Ficus. Using adult trees grown in a common garden, I found that H species showed characteristics of more conservative water use even after they established connections to the soil. Moreover, H species showed significantly different traits in photochemistry compared to NH species due to hydraulic-photosynthetic coordination. The evolution of an epiphytic growth habit during the juvenile stage of a life cycle in the hemiepiphytic Ficus species thus involved changes in a suite of functional traits that persist during their terrestrial growth stages.

Keywords

Strangler Fig; Photosynthesis; Long-distance Water Transport; Leaf Hydraulics; Hydraulic Conductivity; Drought Tolerance

Share

COinS