Abstract
This study addresses the unique functional features of duckweed via comparison of Lemna gibba grown under controlled conditions of 50 versus 1000 µmol photons m−2 s−1 and of a L. minor population in a local pond with a nearby population of the biennial weed Malva neglecta. Principal component analysis of foliar pigment composition revealed that Malva was similar to fast-growing annuals, while Lemna was similar to slow-growing evergreens. Overall, Lemna exhibited traits reminiscent of those of its close relatives in the family Araceae, with a remarkable ability to acclimate to both deep shade and full sunlight. Specific features contributing to duckweed’s shade tolerance included a foliar pigment composition indicative of large peripheral light-harvesting complexes. Conversely, features contributing to duckweed’s tolerance of high light included the ability to convert a large fraction of the xanthophyll cycle pool to zeaxanthin and dissipate a large fraction of absorbed light non-photochemically. Overall, duckweed exhibited a combination of traits of fast-growing annuals and slow-growing evergreens with foliar pigment features that represented an exaggerated version of that of terrestrial perennials combined with an unusually high growth rate. Duckweed’s ability to thrive under a wide range of light intensities can support success in a dynamic light environment with periodic cycles of rapid expansion.
Highlights
Small, floating plant species in the duckweed family (Lemnaceae) possess attractive nutritional features as they accumulate large quantities of high-quality protein throughout the plant [1]
As a consequence of the similar frond area accumulation under the two vastly different growth photon flux densities (PFDs), the ratio of frond area produced per incident PFD, which can be considered the light-use efficiency of frond area production, was dramatically greater (1733%) in fronds grown under 50 versus 1000 μmol photons m−2 s−1 (Figure 1C), in other words, almost proportional to the 20-fold difference in incident PFD
A greater amount of dry biomass (Figure 2A) and protein (Figure 2B) was accumulated on a frond area basis in plants growing under the higher PFD, but the fraction of dry biomass (% biomass in g g−1) that consisted of protein (Figure 2C) was greater under the lower PFD, which resulted in a remarkable 46% of dry biomass consisting of protein under the low growth PFD
Summary
Small, floating plant species in the duckweed family (Lemnaceae) possess attractive nutritional features as they accumulate large quantities of high-quality protein (with all essential amino acids for humans) throughout the plant [1]. We present further insight into how L. gibba is able to combine fast growth across a range of environments with high nutritional content including pronounced zeaxanthin accumulation as well as other essential nutrients for humans or livestock. We further broadened the range of growth PFDs to test whether duckweed’s phenotypic plasticity with respect to photoprotective capacity and maintenance of a high growth rate may extend to even more extreme growth PFDs. We compared features of L. gibba grown under very low (50 μmol photons m−2 s−1) or very high (1000 μmol photons m−2 s−1) intensity of continuous light under otherwise common, controlled conditions. CO2-saturated photosynthetic capacity was characterized under both saturating light and the respective contrasting growth PFDs, and photosynthesis as well as protein and all micronutrients were expressed on multiple reference bases (per frond area, biomass, and chlorophyll [Chl] content) for a fuller evaluation of both plant function and nutritional quality for the consumer
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