In extreme heat and drought, trees hardly benefit from increased atmospheric carbon dioxide

Last updated: 10 Mar, 2020

Edited from a press release.


The increase in the concentration of carbon dioxide (CO2) in the atmosphere does not compensate for the negative effects of climate change on trees – the more intense drought and heat become, the less the trees benefit from the greater supply of CO2. Researchers from the Karlsruhe Institute of Technology (KIT) published their study on Aleppo pines in New Phytologist.


Trees are increasingly exposed to extremes of drought and heat as a result of climate change. How the increased concentration of CO2 in the atmosphere affects the physiological reaction of trees in climatic stress is controversial. Plants convert CO2 and water into carbohydrates and biomass through photosynthesis using sunlight. However, periods of drought and heat subject trees to stress; roots struggle to access water, and leaves close their stomata to reduce losses to evaporation, which in turn absorb less CO2 from the air.


The experimental setup: Aleppo pine trees were exposed to rising temperatures in high-tech plant chambers (photo: Plant Ecophysiology Lab, KIT).


A team of researchers has investigated how the combination of an increased CO2 concentration and hot, dry weather affects carbon exchange and water use efficiency in Aleppo pine (Pinus halepensis). The scientists grew the trees from seed under atmospheric (421 ppm) and increased (867 ppm) CO2 concentrations. The trees were either well watered or allowed to dry out for a month. They were also exposed to rising from 25ºC to 40ºC over a period of 10 days. The researchers measured the exchange of gas and water from the trees continuously and analysed vital metabolic products.


Increased CO2 concentration reduced the trees' water loss and increased their water use efficiency under increasing temperatures. At the same time, net carbon intake declined sharply.


Read the paper: Birami, B., Nägele, T., Gattmann, M., Preisler, Y., Gast, A., Arneth, A. and Ruehr, N.K. (2020) Hot drought reduces the effects of elevated CO2 on tree water use efficiency and carbon metabolism. New Phytologist. doi: 10.1111/nph.16471