Washington [US], August 14 : Researchers at the University of New Hampshire discovered that water use efficiency has plateaued since 2001, implying that plants are absorbing less CO2 and consuming more water, which could have implications for carbon cycling, agricultural production, and water resources.
“We observed an overall significant increase in water use efficiency throughout 1982 to 2016, with a substantial rise from 1982 to 2000, but after that water use efficiency seems to have stalled,” said Jingfeng Xiao, research professor at UNH’s Earth Systems Research Center.
“An increase in CO2 allows green plants to grow faster and use water more efficiently but this study shows that some of the nature-based methods that scientists thought might be in place to help achieve carbon neutrality may be undermined by the adverse effects of climate warming and that plants are not using water as efficiently as scientists might have expected.”
The multifaceted dynamics involved in the complex trade-off between carbon gain and water loss as temperatures rise and atmospheric CO2 levels rise remain unknown. Researchers used satellite and micrometeorological FLUXNET data, as well as machine learning/AI, to develop 24 models for five major vegetation types: forests, shrublands, savannas, grasslands, and croplands in their study, which was recently published in the journal Science.
They investigated the potential influences and limitations on CO2 uptake in each ecosystem and discovered that satellite-driven models indicated a weakening response in plant growth and a sustained increase in plant water use since 2001, possibly due to rising vapour pressure deficit (VPD), which is the amount of water actually in the air versus the amount of water vapour the air could hold.
As VPD increases, it has the potential to slow or suppress photosynthesis while increasing plant water consumption, thereby weakening plant growth and decreasing water use efficiency in global ecosystems.
According to the researchers, this trend may indicate that rising temperatures caused by climate change, as well as projected increases in VPD, may have an impact on future global land carbon levels, which are primarily stored in forests and other ecosystems and can affect water cycles and plant growth.
They note that several factors were considered, and WUE saturation did not appear to be the result of changes in vegetation regrowth, land cover, or nutrient constraints on such as too much or too little nitrogen or phosphorus.
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