Arizona’s glassed-in rainforest offers unique chance to study how plants endure during drought
Two years ago, KNAU reporter Melissa Sevigny joined an international science team at the Biosphere 2, a series of ecosystems trapped under glass in Southern Arizona. The director of rainforest research, Laura Meredith, gave her a behind-the-scenes tour. The rainforest was in the middle of an artificial drought. Scientists simply turned the rain off to find out how rainforests will respond as the global climate heats up. Melissa Sevigny caught up with Laura Meredith to hear about the findings, published last month in the journal Science. She's an assistant professor in the School of Natural Resources and the Environment at the University of Arizona.
So you put the rainforest inside the Biosphere through a drought for more than two months, am I remembering right?
Yeah, it was 65 days that we just shut off the sprinkler system that creates the rain. Usually the rainforest would get rain every 2 or 3 days, so a 65 hiatus in rain was a really severe stress to this forest.
Tell me what happened, maybe starting with the trees and the plants, how did they respond?
What we were really interested to watch, because we were not only tracking the whole ecosystem response, but we were measuring individual trees and how they were behaving in terms of their leaf photosynthesis… we actually started to see that they fell into two different groups…. We had a set of plants that were sensitive to drought and really initially, just with the dry air and initial drying of the surface soil, they shut down their activity very quickly… whereas there was another group of plants that was more drought tolerant, and they didn’t change their activity much as all, they had other strategies for dealing with the stress.
What kinds of strategies, what sorts of things did they do?
The plants that were tolerant to the drought, we saw they were accessing deep water reserves, and in terms of their root structure, we have another study that’s in review right now where we saw they actually created different chemical profiles in their roots belowground… It was important there were these two different groups of plants that had different strategies for dealing with the drought and were functionally diverse in their strategies. That diversity meant there was still ecosystem function, there was still ecosystem carbon cycling and water cycling, even under the most severe stages of drought, it was still a carbon sink…. When the rains came back, the drought-sensitive plants were immediately ready to make use of their water and start their activity again, whereas the tolerant plants sort of slowly just kept doing the same thing. That meant the sensitive plants were really important in having the ecosystem fully recover… and get back on the right foot once rain was available again.
I was with the team when you shut it down during the drought, but I wasn’t there when the rain came back. Can you describe to me what was the initial reaction of the ecosystem to the rain coming back?
I can say the scientists were really excited. In some ways, we were having some empathy for the plants and were feeling the stress of the drought too. It was a beautiful day, we rained during the day, and it was wonderful to see the raindrops falling on the cracked soil and the dried litter and start bringing the system back to life.
Do you feel, after doing this experiment, more hopeful about the fate of rainforests or are you still worried about things?
I think there is some signs of hope in our results for the fate of rainforests, that there is biodiversity in our tropical rainforests, and that may help these ecosystems deal with drought stress. I think there is still reason for caution, because our rainforests are not just dealing with the stress of drought. They’re dealing with the stress of drought and the stress of rising temperatures, or the stress of drought and the stress of land use change, which can completely overhaul an ecosystem from being biodiverse to one that is a monoculture of crops. It’s an important step in understanding that the diversity of drought responses is important to ecosystem resilience, but we’d also like to run additional experiments in the future to see how interactions between drought stress and temperature, or drought stress and land use change, really are affecting the real tropical forests around the globe.
Laura Meredith, thank you so much for speaking with me.
It’s been a pleasure, thank you.