Photosynthesis and leaf structure in domesticated cassava (Euphorbiaceae) and a close wild relative: Have leaf photosynthetic parameters evolved under domestication?

Broad patterns across wild plant species show that leaf composition and morphology vary predictably among habitats, richer habitats favoring resource-acquisition strategies and poorer habitats favoring resource-conservation strategies. Domestication is often accompanied by a shift to richer habitats, and might thus be expected to lead to a shift in leaf composition and morphology and hence in photosynthetic parameters. We compared leaf photosynthetic parameters in domesticated cassava (Manihot esculenta) and a close wild relative, using greenhouse-grown plants. In domesticated cassava, CO2 exchange rate expressed per unit mass and specific leaf area (SLA, m(2)/kg dry mass) were greater than in the wild relative, whereas leaf dry matter content (LDMC, dry mass/fresh mass) was lower in the domesticate. These results suggest that SLA and net photosynthetic rates may both have increased in the evolution of cassava under domestication, enabling more rapid growth in relatively resource-rich and protected agricultural habitats. Previous comparisons of photosynthetic rates in domesticated plants and wild relatives have usually considered only leaf area-based measures. Here, we discuss the interest of using mass-based rates to study the evolution of ecological strategies under domestication.