Is C-4 photosynthesis less phenotypically plastic than C-3 photosynthesis?

C-4 photosynthesis is a complex specialization that enhances carbon gain in hot, often arid habitats where photorespiration rates can be high. Certain features unique to C-4 photosynthesis may reduce the potential for phenotypic plasticity and photosynthetic acclimation to environmental change relative to what is possible with C-3 photosynthesis. During acclimation, the structural and physiological integrity of the mesophyll-bundle sheath (M-BS) complex has to be maintained if C-4 photosynthesis is to function efficiently in the new environment. Disruption of the M-BS structure could interfere with metabolic co-ordination between the C-3 and C-4 cycles, decrease metabolite flow rate between the tissues, increase CO2 leakage from the bundle sheath, and slow enzyme activity. C-4 plants have substantial acclimation potential, but in most cases lag behind the acclimation responses in C-3 plants. For example, some C-4 species are unable to maintain high quantum yields when grown in low-light conditions. Others fail to reduce carboxylase content in shade, leaving substantial over-capacity of Rubisco and PEP carboxylase in place. Shade-tolerant C-4 grasses lack the capacity for maintaining a high state of photosynthetic induction following sunflecks, and thus may be poorly suited to exploit subsequent sunflecks compared with C-3 species. In total, the evidence indicates that C-4 photosynthesis is less phenotypically plastic than C-3 photosynthesis, and this may contribute to the more restricted ecological and geographical distribution of C-4 plants across the Earth.