NASA Maps How Nutrients Affect Plant Productivity

Nutrients are known to be essential for plant growth. Plants will grow normally until they run short of one nutrient. Then growth is limited by the availability of that nutrient. If the nutrients are deficient, or too abundant, then plants will be discolored or deformed.

A research team led by JPL research scientist Josh Fisher, have come up with a new analysis that estimates how much the growth of plants worldwide is limited by amount of nutrients available in their soil.

The analysis was based on the 19 years data from NASA, National Oceanic and Atmospheric Administration and international satellites in order to assess the maximum possible growth of vegetation all over the world based upon available water and light conditions. 

This is the first time such an analysis is being conducted where the scientists cross-compared the potential maximum with observed vegetation productivity as measured by satellites.

The researchers have come up with certain maps that will be useful in evaluating how carbon dioxide Earth's ecosystems may be able to soak up as greenhouse gas levels increase.

The maps clearly list the places where the vegetation productivity was less than the potential maximum.  They conclude that the reason for the limited vegetation in those places was due to the availability of the soil nutrients.

Using measurements of nutrients taken at ground validation sites in Hawaii, the results of the study was evaluated.

"There are many regions on Earth where vegetation struggles to reach optimum productivity because of sparse nutrients, such as nitrogen or phosphorus," said Fisher. "This reduces global vegetation productivity by nearly a quarter compared to vegetation in a completely fertile Earth."

Fisher said the research is valuable for studying the global carbon cycle. "Current global carbon cycle models do not, for the most part, account for the cycling of nutrients, so the terrestrial biosphere (forests and other ecosystems) is expected to absorb an increasing amount of atmospheric carbon dioxide," he said. "Our approach provides a way to assess the performance of global carbon models that incorporate the cycling of nutrients to ensure that they accurately reflect the impacts that sparse nutrients have on plant growth."

On conducting an analysis the researchers noticed that tropical forests were more nutrient-limited than boreal forests, though the range in the amount of nutrients was much larger for boreal forests than tropical forests. North American forests were more nutrient-limited than Eurasian forests. Savannas, grasslands and shrublands had the fewest nutrients, and croplands had the most.

"We were able to detect known regional gradients in nutrient levels -- an East-West gradient across Amazonia, fertilization differences between 'developed' and 'developing' countries, and the migration of trees in boreal North America, for example," said co-author Grayson Badgley of Stanford University, Palo Alto, Calif.

"It is interesting that we can glean insight on global nutrient cycles from satellite observations of global water and carbon cycles," said co-author Eleanor Blyth of the UK Centre for Ecology and Hydrology, Wallingford.

The maps were published recently in the journal Global Biogeochemical.