Regan E. Dunn

Paleoecology & Paleobotany

Grass cell morphology and light environment

Regan E. Dunn, Thien-Y Le & Caroline Strömberg, in press, International Journal of Plant Sciences.

Grass phytoliths of both long and short cells are often preserved in fossil assemblages, and they show a variety of forms, some more undulate than others, some larger than others.

Examples of fossil grass phytoliths: A) long cell B) crenate short cell.
Examples of fossil grass phytoliths: A) long cell B) crenate short cell.

Some methods for reconstructing habitat openness using the presence of open habitat grass short cell phytoliths may lack the ability to accurately reconstruct habitat openness in cases where grasses grew under a forest canopy. Therefore, a morphological approach may be more informative.  I, along with then Undergraduate Researcher Thien-Y Le, tested how light environment effected epidermal cell shape, and thus phytolith shape in grass. Studies of epidermal cell shape in oak, ivy and tobacco leaves show that plants grown in shade have more undulated cell walls than plants grown in full sun. However, this pattern had not been confirmed in any monocotyledons.  We tested whether grasses conform to this general pattern by conducting a greenhouse experiment where we grew five species of grasses under four different light regimes in the University of Washington Biology Greenhouse.

The shade experiment in the University of Washington Biology greenhouse
The shade experiment in the University of Washington Biology greenhouse

With the help of a team of seven undergraduate researchers (Thien-Y Le, Aidan Loeser, Ross “Fletcher” Hill, Darshi Banan, Tony Jijina, Josh Johnson, and Terry Huang) we measured thousands of cells and calculated the cells’ relative degree of undulation and their size.

Epidermal peel of Sporobolus asper, one of the taxa grown in the shade experiment
Epidermal peel of Sporobolus asper, one of the taxa grown in the shade experiment

We found that grasses do not show the same variation in undulation as do some dicots, however cells of grasses grown in shade were significantly longer and larger in area than those grown in full sun. Can longer grass epidermal cells in fossil assemblages tell us more about how much over story vegetation there was? Stay tuned… This greenhouse experiment is currently in press in the International Journal of Plant Sciences.

The wave gang
“Team Wave” – Undergraduate researcher extraordinaires

This work highlighted the need to conduct more controlled growth experiments to understand cell morphology and its response to light across lineages (e.g. gymnosperms and ferns) and in relation to complicating variables such as photoperiod and moisture.

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