Some crops tolerate ozone pollution better than others: Study

New Delhi: Certain crop plants are less prone to harm caused by ground-level ozone pollution, according to a study that opens the door to better models for predicting crop responses to the effects of climate change.

The findings, published in the journal Proceedings of the National Academy of Sciences, also pave the way for developing more resilient varieties that can sustain humanity's increasing demand for food, feed, fibre and fuel.

A team of scientists at Agricultural Research Service (ARS) and University of Illinois Urbana-Champaign (UIUC), US found that the so-called "C4" crops like corn and sorghum tolerate increased ozone levels better than "C3" crops, like rice or snap beans.

A crop is designated as C3 or C4 depending on whether the CO2 it captures from the air is initially converted into a 3-carbon or 4-carbon compound, they said.

The general ability of C4 crops to tolerate increases in ground-level (or “tropospheric”) ozone better than C3 crops has long been suspected but not widely tested under actual field conditions, said Lisa Ainsworth, a research molecular biologist at ARS.

Together with ARS research plant physiologist Christopher Montes and a UIUC team led by Shuai Li—Ainsworth conducted an extensive analysis of both published and unpublished data.

They culled the first dataset from 46 journal papers and the second set from 20 years' worth of open-air experiments conducted in the US, India and China.

Their analysis focused on the responses of five C3 crops (chickpea, rice, snap bean, soybean and wheat) and four C4 crops (sorghum, corn, giant miscanthus and switchgrass) to both ambient levels of ozone and increased concentrations of the gas, ranging from 40 to 100 parts per billion.

Of particular interest were changes in the crops' photosynthetic capacity, chlorophyll content and fluorescence (a form of measurement for the pigment), antioxidant leaf activity, biomass material and seed yield.

C3 and C4 crops differ in how their leaves capture carbon dioxide from the air as a key component of photosynthesis.

It is the process by which plants use sunlight to convert carbon dioxide into glucose, a sugar that helps power their growth, repair and development—and, in turn, sustain other forms of life on the planet, including humankind.

While both C3 and C4 crops use the enzyme called rubisco to convert carbon dioxide into sugars, C4 crops isolate rubisco in specialised cells where the concentration of carbon dioxide is very high.

This enables higher rates of photosynthesis and greater efficiency of water use. Thus, C4 plants have lower stomatal conductance, resulting in less diffusion of carbon dioxide and ozone into leaves.

The team found that exposure to increased ozone levels correlated with reduced chlorophyl content, fluorescence and seed yield in C3 crops more than the C4 group.

But there were differences within the two categories of crops as well, with snap bean, rice, wheat, chickpea, soybean, maize, giant miscanthus, sorghum and switchgrass being ranked the most to least ozone sensitive.