July 21, 2021, by Lexi Earl

A tale of rhynes and reens in the South West corner: Part three in a botanical tale of exploring natural variation around us

This post is written by Kellie Smith. See her previous posts about the great duckweed hunt here.

The next exciting stop off point on our duckweed tour is the South West. In this case, the South West region refers to the ridge between Wales and England – Bristol, on the English side and Newport, on the Welsh side of the Bristol channel. This allows us to pose the question: do we find the same duckweed ecotypes on both sides?

Both areas are industrial and have ports on the river Avon and Usk. South Wales is of special interest for duckweed studies as it corresponds to early invasive Lemna minuta sightings and Lemna turionifera – a seed-producing, overwintering variety spotted there first in 2013.

Bristol and its surroundings are renowned for many ditches called rhynes. Given that these were unmanaged waters, it wasn’t surprising that we found huge expanses of duckweed blooms. We found duckweed communities of up to 3 species per site; species composition of the Bristol sites included ivy-leaved duckweed (Lemna trisulca), common duckweed (Lemna minor), lesser duckweed (Lemna minuta), and fat duckweed (Lemna gibba).

We found that duckweeds seemed to love the ditches, which form stagnant bodies of water, often open to sunlight. The ditches and sewers form a network connecting up to the Avon river mouth. Duckweeds can take advantage in early spring to establish large populations before they flow out through sluices to the river, and finally to their demise in fast-flowing water opening into the sea. We also found cases of duckweeds growing in a muddy basin of a rhyne totally lacking in water, and numerous duckweed accessions growing in the alkaline Bristolian waters!

Using the state-of-the-art Future Food Beacon’s Ionomics facility we will be able to see which minerals are differentially present in Bristol waters relative to other locations, and indeed find out if the duckweeds from this region have corresponding adaptations to tolerate growth in particular mineral repletion or depletion, related to the industrial background of the area.

We then travelled to Newport, approximately 30 land miles away from Bristol, separated by water, to complete the second half of our case study to look at reens. Here we also found numerous spots with full duckweed coverage.

The duckweed diversity of sites in Bristol and Newport provide an excellent case study for factors associated with maximal growth/biomass and photosynthesis. Duckweeds are considered to be shade seeking plants found near locks, bridges, crevasses and grates, but interestingly we found that many duckweeds had adapted to sun sites, which were receiving light of >1500 µmol m^-2 s^-1, in other words maximum direct sunlight at peak hours! Duckweed lawns came in varied mixes of green, red, and yellowy tones. They were sometimes white if senescent (dead) duckweeds are abundant in the population; examples of the various colours are shown in the above pictures. Sometimes duckweeds form layered or mixed canopies, for instance with ivy-leaved submerged plants hiding below floating common duckweeds. Given the diverse growing habitats, we expect to see differences in light-harvesting pigments between species and sites.

Duckweed physiology and identification of species using hyperspectral sensor tools

Hyperspectral cameras can be used to measure reflectance from duckweed biomass, forming signatures that can be used to diagnose composition and physiology. We want to know if we can successfully use remote sensing tools to compare duckweed health or differentiate between species, which has indeed been achieved for other much larger aquatic plants including mangroves. Can duckweed reflectance data predict any other performance factors in the lab such as growth rate, photosynthesis, or the composition of key light pigments: chlorophyll, carotenoid and antioxidants? Such traits are important for developing isolated duckweed candidates as a plentiful future food with nutritional benefits.

Big thanks to Carlos Robles-Zazueta and Laura Briers for significant contributions to this blog.

Please join me again next time for more duckweed adventures up in Scotland!

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