In thickets in the ditches, forests and riverbanks of Southern China, Saururus chinensis, sometimes known as Asian lizard’s tail, has developed a skill to aid pollination. Bo Song and his team have been investigating why its leaf colour changes for a period. What they found was the change from green to white amplified the visual signal from flowers to pollinators that the plant was ready to receive. However, they also found that S. chinensis had another trick to help after pollination.
Anyone who’s lived through an autumn isn’t going to be surprised that leaf colours can change. Gardeners will also be aware of other leaf changes in plants as they display warnings about being well-defended – or else turn colour when they come under attack from unwanted guests. For S. chinensis colour change might be something else.
The top few leaves on S. chinensis change colour from green to white. This change coincides with the plant flowering. After the flowering is over, the leaves return to green. It’s a clue that there’s something connected to reproduction going on, so the team devised experiments to see what was happening.
The simplest experiment was to see if pollinators were more attracted to plants with white leaves than not. For five days they randomly selected fifteen plants and divided them into three groups. Five plants were the control group. Another five had the white leaves taken from them. This might compare green and white displays, but maybe the pollinators would be put off by the damage on the plants. The final group of five plants had their white leaves covered by green leaves taken from other plants and taped over them with transparent tape. This method was the simplest way of changing the colour of the S. chinensis display back to green.
The results were clear. The plants with the white leaves attracted over twice the pollinators than the other two groups. So S. chinensis plants that could turn their top leaves white had a clear reproductive advantage – at least as far as attracting pollinators went. The colour change did have some costs though.
Another experiment examined what the cost to the plant of having white leaves was. There’s a reason that plants tend to have green leaves and that’s because it’s the result of chlorophyll, which turns sunlight, atmosphere and water into food for a plant. The white leaves did not have chlorophyll working in the same way as the green leaves, and this was seen in the results. The white leaves were less than half as effective at producing food than the green leaves. However, the leaves that had been white, but returned to green, were just as efficient.
The authors argue that this change back to green is important for the plant. Attracting pollinators is only one stage in reproduction. The fruits also need to be formed and the seeds within them provisioned. It is possible that these leaves are changing colour back to provide more energy for fruit set.
You can get the full details from Annals of Botany as this is a free access paper.