Portulacaria afra: a Study in Photosynthetic Plasticity in a Changing Climate

Biologist Lonnie Guralnick presents his research at ASU Polytechnic campus March 29

Lonnie Guralnick, professor of biology at Roger Williams University, presents this March 29 colloquium, from 3–4 p.m. in Cooley Ballroom C of the Student Union at Arizona State University's Polytechnic campus. His research interests include the ecological and evolutionary physiology of C4 and Crassulacean Acid Metabolism photosynthesis, development of CAM photosynthesis of Portulacaria afra, the role of photorespiration in CAM plants, and the restoration of Portulacaria afra in the Spekboom thicket of South Africa and possible consequences of global climate change. Guralnick's work has received numerous NSF awards, including a $586,000 NSF S-STEM award.  

Portulacaria afra is a dominant facultative CAM species growing in the southeastern cape of South Africa and well adapted to regions of the Spekboom thicket in areas of limited and sporadic rainfall. Carbon isotope composition (13C/12C ratios) can be used to determine the contribution of the CAM photosynthetic pathway (nocturnal CO2 uptake) to the overall carbon balance. Analysis of carbon isotope values for P. afra plants at different locations found no direct correlation with rainfall or maximum or minimum day/night temperatures in the summer or winter.

The results provide evidence that CAM is a continuous trait in P. afra and operating at low levels during C3 photosynthesis, which may explain the high variability in its carbon isotope composition. P. afra populations illustrate a large phenotypic plasticity and further studies may indicate genotypic differences between populations. This may be valuable in ascertaining the genetic contribution to its water use efficiency and possible use in engineering higher water use efficiency in C3 plants. The results may explain P. afra’s ability to sequester carbon at high rates compared to more mesic species.

At Roger Williams University, Guralnick served as interim dean of the Feinstein College of Arts and Sciences and was assistant dean of Math and Natural Sciences for five years. He earned a doctorate in botany with a specialization in plant physiology and ecophysiology at UC–Riverside.   

Faculty and practitioners discuss their current research and field projects in the college’s Science and Mathematics Colloquium Series, held throughout the academic year at the ASU Polytechnic campus. All seminars are free and open to the public.

Faculty of Science and Mathematics, College of Integrative Sciences and Arts
Ryan Penton
Student Union, Cooley Ballroom C, Polytechnic campus
Polytechnic campus

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