Photosynthesis is vital for life on Earth. However, researchers anticipate that climate change will alter how plants undergo this crucial chemical process. To prepare ecosystems and industries that rely on plants for these changes, scientists are exploring how rising temperatures influence energy production and stress responses in leaves of different species. Most work to date has focused on agricultural crops and extrapolated the findings to towering trees that stand tall through seasonal changes, despite the differences in the temperatures they endure.
Rakesh Tiwari studies how different tree species respond to increased temperatures with photorespiration.
Pragya Tiwari
According to Rakesh Tiwari, a plant physiologist and postdoctoral fellow at Uppsala University, this approach limits researchers’ ability to accurately predict and understand how trees respond to temperature changes. Tiwari got his first clue into this issue during his PhD research where he explored how increasing temperatures affected photosynthesis in trees of the Amazon rainforest. “During the peak summer period, they are already getting pushed to their limits.”
Normally, photosynthesis occurs in two reactions to turn light energy into carbon fuel. In the first step, called the light reaction, photons help the plant produce electron carriers and ATP. The second stage uses this ATP and carbon dioxide (CO2) from the air to synthesize glucose with the help of the enzyme rubisco.1 Rubisco can also catalyze oxygen by mistake, creating toxic byproducts; a process called photorespiration undoes this catastrophic chemical reaction, releasing CO2.2
In his work, Tiwari saw that photosynthesis slowed down in high heat, but a complex of proteins in the light reaction remained active.3 “The light is not stopping. [The leaves are] still doing the light reaction. There’s no blinds or curtains for the leaves to hide from the light.”
Without photosynthesis continuing through catalyzing CO2, toxic byproducts begin to build up in the cells. “In this situation, photorespiration is a blessing,” Tiwari said. In the absence of CO2, rubisco binds oxygen, and then photorespiration uses the energy products from the light reaction to break down these products and release CO2.
In his current research, Tiwari studies how trees use photorespiration as a protective mechanism in eight different species in tropical forests of Western Ghats in India under natural conditions. Working with colleagues studying trees in Puerto Rico and Sweden, the team is fleshing out the distinct responses to higher temperatures in these long-standing plants.
“The variation of photorespiration across these species is way beyond what we think it is,” Tiwari said. He said that he and his team have observed some species that don’t use photorespiration at all to those where the rate of this process exceeds that of photosynthesis.
Yet, Tiwari added, “All the models, all the calculations of standard photosynthesis models, or vegetation models, use a fixed value for photorespiration, or at best, the ones measured from short duration crops that dramatically minimizes or ignores the whole world of diversity that is out there in the tropical forest and in the rest of the vegetation.”
Understanding this variation and the role of photorespiration better, he added, could improve climate models and offer other solutions to improving temperature tolerance in these enduring plants.
