Featured Research

from universities, journals, and other organizations

Floods didn't provide nitrogen 'fix' for earliest crops in frigid north

Date:
November 6, 2013
Source:
University of Washington
Summary:
Floods didn't make floodplains fertile during the dawn of human agriculture in the Earth's far north because the waters were virtually devoid of nitrogen. Instead, the hardy Norsemen and early inhabitants of Russia and Canada can thank cyanobacteria in the floodplains themselves for the abundant grasses that fed game and cattle, a process that continues today.

Sedges and willow trees get the nitrogen they need from cyanobacteria living in the sediments of pristine boreal floodplains found at 60 degrees latitude and north into the Arctic Circle.
Credit: T DeLuca/U of Washington

Floods didn't make floodplains fertile during the dawn of human agriculture in Earth's far north because the waters were virtually devoid of nitrogen, unlike other areas of the globe scientists have studied.

Instead, the hardy Norsemen and early inhabitants of Russia and Canada have microorganisms called cyanobacteria to mostly thank for abundant grasses that attracted game to hunt and then provided fodder once cattle were domesticated. The process is still underway in the region's pristine floodplains.

The new findings are surprising because it's long been assumed that nitrogen crucial to plant growth mainly arrived with floods of river water each spring, according to Thomas DeLuca, a University of Washington professor of environmental and forest sciences and lead author of a paper in the Nov. 6, 2013 issue of the journal PLOS ONE.

Discovering that cyanobacteria in the floodplains were responsible for nitrogen fixation -- that is taking it from the atmosphere and "fixing" it into a form plants can use -- partially resolves the scientific debate of how humans harvested grasses there for hundreds of years without fertilizing, DeLuca said. It raises the question of whether farmers today might reduce fertilizer use by taking advantage of cyanobacteria that occur, not just in the floodplains studied, but in soils around the world, he said.

It also might lead to more accurate models of nitrogen in river systems because none of the prominent models consider nitrogen being fixed in floodplains, DeLuca said. Scientists model nitrogen loading of rivers, especially where industrial fertilizers and effluent from wastewater-treatment plants cause dead zones and other problems in the lower reaches and mouths of rivers.

Ten rivers and 71 flood plains were studied in northern Fennoscandia, a region that includes parts of Scandinavia and Finland. The rivers were chosen because their upper reaches are pristine, haven't been dammed and are not subject to sources of human-caused nitrogen enrichment -- much like river systems humans encountered there hundreds of years ago, as agriculture emerged in such "boreal" habitats. Boreal habitat -- found at 60 degrees latitude and north all the way into the Arctic Circle, where it meets tundra habitat -- is the second largest biome or habitat type on Earth.

In the northern regions of the boreal, the surrounding hillsides have thin, infertile soils and lack shrubs or herbs that can fix nitrogen. In these uplands, feather mosses create a microhabitat for cyanobacteria, which fix a modest amount of nitrogen that mostly stays on site in soils, trees and shrubs. Little of it reaches waterways. On the floodplains, high rates of nitrogen fixation occur in thick slimy black mats of cyanobacteria growing in seasonably submerged sediments and coating the exposed roots and stems of willows and sedges.

"We joke and call the floodplains the 'mangroves of the North' because there are almost impenetrable tangles of willow tree roots in places, like a micro version of the tropical and subtropical mangroves that are known to harbor highly active colonies of cyanobacteria," DeLuca said.

"It turns out there's a lot of nitrogen fixation going on in both," he said. For example, the

scientists discovered that in spite of the dark, cold, snowy winters of Northern Sweden, the cyanobacteria there fix nitrogen at rates similar to those living the life in the toasty, sun-warmed Florida Everglades.

The amount of nitrogen provided by the cyanobacteria to unharvested willows and sedges is perhaps a quarter of what U.S. farmers in the Midwest apply in industrial fertilizers to grain crops and as little as a sixth of what they apply to corn.

Human-made fertilizers can be fuel-intensive to produce and use, for example, it takes the energy of about a gallon of diesel to produce 4 pounds of nitrogen fertilizer. In developing countries in particular, nitrogen fertilization rates are spiraling upward, driving up fossil-fuel consumption, DeLuca said. Meanwhile, cyanobacteria naturally occurring in farm soils aren't fixing nitrogen at all in the presence of all that fertilizer, they just don't expend the energy when nitrogen is so readily available, he said.

"Although modest in comparison to modern fertilization, the observation that cyanobacteria could drive the productivity of these boreal floodplain systems so effectively for so long makes one question whether cyanobacteria could be used to maintain the productivity of agricultural systems, without large synthetic nitrogen fertilizer inputs," he said.

Co-authors on the paper are Olle Zackrisson and Ingela Bergman with the Institute for Subarctic Landscape Research, Sweden, Beatriz Díez with Pontificia Universidad Católica, Chile, and Birgitta Bergman with Stockholm University.


Story Source:

The above story is based on materials provided by University of Washington. The original article was written by Sandra Hines. Note: Materials may be edited for content and length.


Journal Reference:

  1. Thomas H. DeLuca, Olle Zackrisson, Ingela Bergman, Beatriz Díez, Birgitta Bergman. Diazotrophy in Alluvial Meadows of Subarctic River Systems. PLoS ONE, 2013; 8 (11): e77342 DOI: 10.1371/journal.pone.0077342

Cite This Page:

University of Washington. "Floods didn't provide nitrogen 'fix' for earliest crops in frigid north." ScienceDaily. ScienceDaily, 6 November 2013. <www.sciencedaily.com/releases/2013/11/131106201842.htm>.
University of Washington. (2013, November 6). Floods didn't provide nitrogen 'fix' for earliest crops in frigid north. ScienceDaily. Retrieved August 21, 2014 from www.sciencedaily.com/releases/2013/11/131106201842.htm
University of Washington. "Floods didn't provide nitrogen 'fix' for earliest crops in frigid north." ScienceDaily. www.sciencedaily.com/releases/2013/11/131106201842.htm (accessed August 21, 2014).

Share This




More Plants & Animals News

Thursday, August 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Possible Ebola Patient in Isolation at California Hospital

Possible Ebola Patient in Isolation at California Hospital

Reuters - US Online Video (Aug. 20, 2014) — A patient who may have been exposed to the Ebola virus is in isolation at the Kaiser Permanente South Sacramento Medical Center. Linda So reports. Video provided by Reuters
Powered by NewsLook.com
Flower Power! Dandelions Make Car Tires?

Flower Power! Dandelions Make Car Tires?

Reuters - Business Video Online (Aug. 20, 2014) — Forget rolling on rubber, could car drivers soon be traveling on tires made from dandelions? Teams of scientists are racing to breed a type of the yellow flower whose taproot has a milky fluid with tire-grade rubber particles in it. As Joanna Partridge reports, global tire makers are investing millions in research into a new tire source. Video provided by Reuters
Powered by NewsLook.com
Unsustainable Elephant Poaching Killed 100K In 3 Years

Unsustainable Elephant Poaching Killed 100K In 3 Years

Newsy (Aug. 20, 2014) — Poachers have killed 100,000 elephants between 2010 and 2012, as the booming ivory trade takes its toll on the animals in Africa. Video provided by Newsy
Powered by NewsLook.com
Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Newsy (Aug. 19, 2014) — Scientists have developed a new device that mimics the way octopuses blend in with their surroundings to hide from dangerous predators. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins