It's the timing of water that matters to plants

A new study has shown that plants are more receptive to the timing of when they are watered, rather than how much water they receive. This is especially ithe case in Palm Springs, where a research team created artificial rainfall to study the effects on plants over two years. This region has both winter and summer growing seasons impacted by both drought and extreme rain events. 

Normally, some desert wildflowers and grasses grow in December, and die by June. Afterwards, a new community of plants sprouts in July and flowers in August. Study lead author Marko Spasojevic is a plant ecologist at the University of California Riverside. 

“We wanted to understand whether one season is more sensitive to climate change than another,” said Spasojevic. “If we see an increase or decrease in summer rains, or winter rains, how does that affect the ecosystem?”

The team observed 24 plots of land at the Boyd Deep Canyon Desert Research Center, in the Palm Desert area. Some plots were watered by natural rainfall, while others were covered and allowed to receive rain only in one season. A third group of plots received additional collected rainwater. 

The results showed that during the summer, plants grow more when given extra water, including natural rainfall. However, this was not the case during the winter.

While adding water in summer resulted in higher plant biomass, it did not increase the diversity of plants that grew. Decreasing rainfall had negative effects on plants in both the summer and winter, but may lead to some increased growth during the off-seasons.

The study demonstrates the importance of understanding the availability of water resources beyond just plant growth. Whole communities of animals depend on these plants, such as pollinators, and they play a big role in controlling erosion and movement of soils by wind. 

“Studies like this one are critical for understanding the complex effects of climate change to dryland ecosystems,” said study co-author Darrel Jenerette.

Desert plants also play an important role in removing carbon dioxide and nitrogen from the atmosphere. Microbes that live in the soil can use the carbon and nitrogen released by plant roots, then send it back into the atmosphere where it can affect the climate. 

“Drylands cover roughly a third of the land surface, so even small changes in the way they take in and emit carbon or nitrogen could have a big impact on our atmosphere,” said study co-author Peter Homyak.

The research team plans to continue this research and expect to see changes in soil carbon and nitrogen cycling, given that plants are already being affected by changes in seasonal rainfall, as this research shows. 

“Can changes in precipitation patterns alter the feedback between plants and microbes, destabilizing the carbon locked in soils and sending more of it into the atmosphere? We are working on figuring that out,” said Homyak. 

The study is published in the journal Elementa Science of the Anthropocene.

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By Katherine Bucko, Earth.com Staff Writer