# Thermal performance of Wolffia globosa under climate change: heatwaves impair population growth

## TL;DR

Wolffia globosa, a tropical duckweed used for food, shows reduced growth during heatwaves despite thriving under higher average temperatures.

## Contribution

The first thermal performance curve for Wolffia globosa population growth under climate change conditions is presented.

## Key findings

- Constant high temperatures under future climate scenarios do not significantly reduce growth rates.
- Heatwave-like temperature fluctuations significantly lower growth rates due to increased frond death.
- Wolffia globosa may recover faster from extreme heat events compared to other crops due to its fast growth rate.

## Abstract

Climate change impacts on temperature may alter the availability of plants used for food. Some species may have asymmetric responses to temperature, with growth rates that fall rapidly at temperatures above the optimum. As a result, even if mean temperatures increase towards optimal conditions, fluctuations about this mean can substantially decrease growth. We use Wolffia globosa, a tropical duckweed harvested for food in Southeast Asia, to examine the impacts of predicted changes in temperatures. This aquatic plant has a fast growth rate, a high protein content, and is also a source of important nutrients. Therefore, it could play an important role in food security under climate change. For constant temperatures there is no significant difference between growth at current conditions and those predicted in the next 40 years according to the high emissions scenario (SSP5-8.5 scenario) in Thailand, Laos and Myanmar. However, when temperatures are allowed to fluctuate about the mean in a pattern similar to recent heatwave conditions in Thailand, we find significantly lower growth rates at the optimum than at current mean temperatures. This decrease is driven by an increase in frond death at higher temperatures. Nevertheless, given the fast growth rate of this species relative to other food crops, and the mitigating impact of water on the magnitude of temperature fluctuations, it seems likely that W. globosa may more rapidly recover from extreme heat events than other crop species, and is therefore a suitable candidate for adapting food systems to climate change impacts.

We present the first thermal performance curve for the population growth rates of Wolffia globosa, a high protein aquatic plant harvested for food in SouthEast Asia. Optimal constant temperatures are quite high, and produce very fast population growth. However, we find that the asymmetric thermal response interacts with temperature variation during heatwave conditions. Therefore, changes to mean and variance of temperatures under climate change are likely to cause population crashes.