NASA’s map on nutrient limitation and plant productivity; Research

Scientists from NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif. made an analysis for the first time to estimate the effect of nutrients available in the soil to the growth of plants in the world.

This research has been published online in the journal Global Biogeochemical Cycles.

Researchers have developed a map to check for the utilization of carbon dioxide by the Earth’s ecosystems as the greenhouse gas levels increase.

Global map depicting nutrient limitation affecting plant productivity

This research team has been led by JPL research scientist Josh Fisher. They used 19 years of data from NASA, National Oceanic and Atmospheric Administration and international satellites to check for the maximum possible growth of the plants based on the available status of water and light. They then compared the potential maximum with observed plant productivity measured by satellites and found the places with less productivity than the potential maximum. They concluded that the limited amount of nutrients in the soil is the cause of limited vegetation.

Ground validation sites in Hawaii are used for the evaluation of the measurements of the nutrients and the vegetation productivity.

“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.”

According to the research, boreal-forests have more nutrients than the tropical forests but tropical forests have less range in the amount of the nutrients. Croplands had more amounts of the nutrients whereas Savannas, grasslands and shrublands had fewer nutrients. North American forests were more nutrient-limited than Eurasian forests.

“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.

You can read the abstract of the paper here,

Most vegetation is limited in productivity by nutrient availability, but the magnitude of limitation globally is not known. Nutrient limitation is directly relevant not only to ecology and agriculture, but also to the global carbon cycle by regulating how much atmospheric CO2 the terrestrial biosphere can sequester. We attempt to identify total nutrient limitation in terrestrial plant productivity globally using ecophysiological theory and new developments in remote sensing for evapotranspiration and plant productivity. Our map of nutrient limitation qualitatively reproduces known regional nutrient gradients (e.g., across Amazonia), highlights differences in nutrient addition to croplands (e.g., between “developed” and “developing” countries), identifies the role of nutrients on the distribution of major biomes (e.g., tree line migration in boreal North America), and compares similarly to a ground-based test along the Long Substrate Age Gradient in Hawaii, U.S.A. (e.g., foliar and soil nutrients, litter decomposition). Nonetheless, challenges in representing light and water use efficiencies, disturbance, and comparison to ground data with multiple interacting nutrients provide avenues for further progress on refining such a global map. Global average reduction in terrestrial plant productivity was within 16–28%, depending on treatment of disturbance; these values can be compared to global carbon cycle model estimates of carbon uptake reduction with nutrient cycle inclusion.

Reference:

Joshua B. Fisher, Grayson Badgley, Eleanor Blyth, (2012). Global nutrient limitation in terrestrial vegetation. Global Biogeochemical Cycles, DOI: 10.1029/2011GB004252

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