Poster

         Ecophysiology

Does CAM explain C4-like d13C values in Bulnesia retama (Zygophyllaceae), a non-Kranz, non-succulent desert shrub?

Presenting Author
Daniel Mok
Description
Isotopic screens of herbarium material designed to detect C4 species in the family Zygophyllaceae identified three distinct clusters of plants having C4-like isotopic values, one in the Zygophyllum simplex group (now Tetreana simplex), one in the Tribuloideae subfamily  (Tribulus, Kallstroemia, and Tribulopis), and one in the species Bulnesia retama (subfamily Larreoideae) a drought deciduous desert shrub from Argentina.  Tetreana and the Tribuloids are confirmed as C4 plants with distinct Kranz anatomy and C4 gas exchange traits. Bulnesia retama, however, shows no evidence of C4 anatomy or gas exchange signatures in leaf or stem, including single cell C4 photosynthesis. We considered CAM photosynthesis as an explanation for the high isotopic values, which range between -16‰ and -20‰. Clear succulence is lacking in all tissues, including stems; however, stems show tight packing of the photosynthetic cortical cells in a CAM-like manner. Leaves show typical non-succulent C3 anatomy. We therefore tested the hypothesis that B. retama is facultative CAM, which if true could explain the high isotopic values. If so, Bulnesia retama would represent a new CAM family, genus and species. The results of these tests will be presented in this poster.