Does desert time exist?

* The Swiss Institute for Dryland Environmental & Energy Research

*French Associates Institute for Agriculture and Biotechnology of Drylands  

Most plant species depend on insects, such as bees, butterflies, moths, and flies, for pollination services. To attract these pollinators, plants use visual signals, such as flower shape, size and color, the quality and quantity of nectar, and, of course, smell. The smell of flowers is attractive to insects and humans alike and is composed of several small volatile molecules. One of the more fascinating aspects of flower scent is that it is dynamic and changes throughout the day: some plant species begin emitting a scent early in the morning, while others are particularly fragrant at night. Researchers have claimed that these patterns follow the activity peaks of the plants’ particular pollinators. 

In a study conducted by the working groups of Dr. Vered Tzin French Associates Institute for Agriculture and Biotechnology of Drylands  and Prof. Merav Seifan The Swiss Institute for Dryland Environmental & Energy Research, and led by Dr. Alon Cna'ani and Efrat Dener, these researchers asked whether additional factors, including genetic and environmental ones, affect the composition and timing of scent release in desert plants.
Desert plants grow in highly stressful conditions, due to precipitation scarcity, sandy soil, and high temperatures. The project focused on plants from the species-rich Brassicaceae family, found in Israel’s arid regions, which also includes several domestic species, such as cabbage, broccoli, canola, and mustard. The researchers asked whether desert plants of this family, which are constantly exposed to stressful conditions, have adapted their smell-emission timing to ensure pollinator attraction, thus maximizing their reproductive success. To answer this question, several Brassicaceae species were collected along a geographical gradient in the Negev Desert. The flower smells of each plant were collected for 24 hours using specific columns, and the volatile molecules were quantified and identified in the lab. In addition, the phylogenetic relatedness between species, habitat conditions, and timing of pollinator visitation was recorded for each plant species.

The study’s findings showed that the timing and composition of scent emission were governed by the combination of genetic relatedness and two environmental factors: minimum winter temperature and the amount of sand in the plant’s growth site, probably because sand affects the immediate water availability to the growing plants. Overall, plant species whose distribution is associated mainly with arid regions, where water is more limited and temperatures are warmer, tended to emit smell in a more unified way, throughout the 24 hours, than species with a Mediterranean distribution, which emitted smell mainly during the day.

Pollinator observations showed that there is a direct connection between the timing and composition of smell emission and pollinator attraction to the plants. The researchers suggested that these findings indicate that species growing in desert habitats adapt their smell emission to better capture the more limited activity of pollinators under the limited resource availability in these regions. The study contributes to the general understanding of global climate change and its potential impact on plants, pollinators, and their interactions. Because climate change is predicted to increase winter temperatures and intensify desertification, it may significantly affect the timing and composition of smell emission, jeopardizing the effectiveness of pollination services.