Plants use nitrogen from the atmosphere in unexpected ways. writes Kat Kerlin
Trees need nitrogen to grow, and they would prefer to get it from the soil. But in a pinch, when soils are poor, they will look to the atmosphere as sort of a nitrogen “food pantry,” grabbing it from the sky, according to a UC Davis study. However, amid rising levels of carbon dioxide, that back-up source of nitrogen is harder for the trees to access, limiting their growth.
The study, published in the journal Nature Scientific Reports, helps explain why rising CO2 levels are not accompanied by a boom in tree growth, as scientists formerly expected.
“If we were to include the effect of soils and nitrogen from the air, it would radically change the predictions of how plants respond to elevated CO2,” said lead author Lucas Silva, a researcher in the Department of Land, Air and Water Resources at UC Davis.
Silva’s colleague, UC Davis Plant Sciences professor Arnold Bloom, showed in a 2010 Science study and a 2014 Nature study how rising CO2 threatens human nutrition in grain crops. Inspired by that work, Silva wanted to understand how elevated CO2 would influence how trees use nutrients from the soil and the air.
He and his research team grew coffee trees at the UC Davis Controlled Environment Facility, exposing the trees to different levels of CO2 and nitrogen.
The team found that, when exposed to increased levels of CO2, trees growing in soils with readily available nitrogen grew bigger and took up less nitrogen from the atmosphere. Trees growing in poorer soils were smaller, and take more of their nitrogen from the air. But increasing the amount of CO2 in the air decreased the ability of the plants to take up nitrogen from the air through their leaves.
This showed Silva that plants use nitrogen from the atmosphere in ways previous studies hadn’t anticipated.
On the one hand, this could be a good thing: Trees are able to take up through their canopies nitrogen that would otherwise have been lost from terrestrial ecosystems.
“The bad news is, in a world where we have rising CO2 levels, we will likely see less and less nitrogen uptake from the air,” Silva said. “And, if soils are limiting, we could see a widespread decrease in tree growth.”
This work was developed in collaboration with the National Center for Coffee Research, Manizales, Colombia and supported by the Fulbright Exchange Program and by LAWR professor William Horwath’s J.G. Boswell Endowed Chair in Soil Science.
Follow Kat Kerlin on Twitter at @UCDavis_Kerlin.