Spencer, W.E., R.G. Wetzel, and J. Teeri, 1994. Acclimatization of Photosynthetic Phenotype to Environmental Heterogeneity, University of Alabama.

Reprinted from Ecology (1994) 75(2): 301-314

Acclimatization of Photosynthetic Phenotype to Environmental Heterogeneity

Abstract
Inducible C₄-like photosynthetic metabolism in Hydrilla verticillata leaf tissue elicits variability in photosynthetic phenotype expressed as CO₂ compensation point (G). We conducted a field and laboratory study to investigate the ecological and adaptive significance of this physiological phenomenon Spatial horizontal environmental heterogeneity was observed within in clonally populations of H verticillata in Florida. USA. Measured at midday the edge habitat at the expanding periphery of the clone exhibited a dissolved inorganic carbon (DIC) concentration of 0.7 mmol/L, pH 7.1 a dissolved oxygen (DO) level el of 0.13 mmol/L. and biomass of 0.2 kg/m². The mat habitat, Iocated 200 cm towards the interior of the surface mat, exhibited DIC 0.1 mmol/L, pH 10.2 DO 0.48 mmol/L. and biomass 0.8 kg/m². DIC depletion and DO supersaturation characterized the mat habitat for most of the day and much of the growing season. Furthermore, net photosynthesis daily carbon gain, and relative growth rate (RGR) of H. verticillata were reduced 80% by mat conditions compared to edge conditions. Gs of H. verticillata were positively correlated with CO₂ and bicarbonate concentration, and negatively correlated with pH, DO, and biomass. Low and high G photosynthetic phenotypes were associated with the mat and edge habitats, respectively. Photosynthetic phenotype of H. verticillata appears to acclimate to environmental heterogeneity within a clone in the field.

Net photosynthesis and daily carbon gain of low r phenotype H. verticillata was 128% and 40% greater than the high r phenotype when measured in the mat habitat, but was 219r lower than the high G photosynthetic phenotype when measured in the edge habitat under low quantum flux. Laboratory experiments showed a negative curvilinear relationship between the G of H. verticillata and plant density. The data demonstrate that plasticity in photosynthetic phenotype of H. verticillata is a density-dependent, physiological response that optimizes carbon gain within a stressful heterogeneous environment. Evolution of facultative C₄ -like photosynthetic metabolism in  H. verticillata may have been an adaptation to the constraints imposed upon carbon gain by DIC and quantum flux limitation in the mat habitat.

Entire Paper
Contact: Robert Wetzel, University of Alabama, Department of Biological Sciences, Tuscaloosa, AL 35487
Key Words: Hydrilla, Basic_biology, Aquatic_plant_management
Product Type: Research, Basic_biology
User Type: Resource Management