Warming Climate Threatens Photosynthesis of Forest Trees

Biologist Rakesh Tiwari at Uppsala University's Department of Ecology and Genetics is using an infrared greenhouse gas analyzer to measure photosynthesis by manipulating a leaf's environmental conditions. The portable instrument allows the researchers to measure the interaction of light intensity, carbon dioxide concentration in the air, and temperature to gain insights into how plants respond to the changing climate.

Rakesh, a postdoctoral researcher, shares that he and other researchers have seen a clear degradation in the efficiency of photosynthesis in natural tropical environments. In 2017, he participated in a research project in the Amazon conducted by the University of Leeds to find out how rising temperatures threaten the rainforest's ability to function. He explained that they saw a clear pattern that trees in the Amazon are already experiencing air temperature conditions that can affect their photosynthesis machinery. The research team discovered that some plant species were working at the limit of their heat tolerance. During especially hot and dry periods, photosynthesis rates dropped to some of the lowest levels recorded in tropical forests.

Rakesh said that the photosynthetic efficiency of a majority of Earth's plants is down to at most 5 percent, and one of the biggest causes of this inefficiency is photorespiration, a side reaction that occurs when the enzyme rubisco binds oxygen instead of carbon dioxide. Another factor is the small stomata in the plant's leaves that regulate carbon dioxide absorption and water exchange. In extreme heat, the stomata close to save water, but this reduces their photosynthesis rate. In some trees, stomata open at higher temperatures to make use of evaporative cooling as a leaf-cooling mechanism.

The researchers call to preserve the existing natural systems to preserve the environment. Planting more trees is not enough, according to Rakesh.

For more details about this study, read the article in Uppsala University News.