2019-07-03 07:55国内新闻网编辑:admin人气:

每年多达1%。 )




Oxalicacid is a good stand-in for a whole suite of root compounds thatare excreted by plants in the root zone, Kleber said. "Rootsexcrete several compounds similar to oxalic acid. We can assumethat many root exudates act in a similar way."



"Thesignificance of this research," Kleber said, "is that we havedocumented for the first time a mechanism by which long-stored soilcarbon is cycled back into the system."

When theyanalyzed the water stored in the oxalic acid-treated soil, theresearchers saw there was eight times more dissolved carbon in itthan there had been before. Additional laboratory tests confirmedthe finding that the acids were breaking the carbon-mineralbonds.


"And thisis likely happening to a certain extent," he said. "But our bigsurprise was that the energy-poor oxalic acid generated a muchstronger response from the microbes than the energy-richglucose."

Prevailing theory, said Kleber, would predictthat the hungry microbes would respond most strongly to thenutritious glucose, which would give them the energy to tackle therest of the organic matter, including the carbon.


In thelaboratory, using a syringe and pump, they applied oxalic acid,acetic acid and glucose to soil taken from a dry-climateagricultural area and a wet-climate forest, both in Oregon. Theyconducted the experiment over 35 days to simulate a flush of rootgrowth in the spring.

Theresearchers tested three model compounds for common "rootexudates"--chemicals commonly excreted by plant roots--to see howstrongly each one stimulated the microbes that drive organic-matterdecomposition.


"But fromthe beginning, there was a question that made a lot of folksuneasy," said Kleber. "If carbon keeps going into the soil andstaying there, then why aren't we drowning in carbon? Isn't theresome process that takes it back into the cycle? That part was notvery well researched, and it was what we were trying tofind."


For thepast couple of decades, scientists have assumed that thesecarbon-mineral bonds amounted to a long-lasting "sink" for soilcarbon--keeping it out of the atmosphere by storing it in a stableform over many centuries.

Between60 and 80 percent of organic matter entering the soil gets brokendown within the first year in a chain of decomposition that endswith CO2, Kleber said. Most of the remaining carbon gets bound tothe soil's minerals through a variety of physical and chemicalmechanisms. When this happens, the carbon is protected because themicrobes can't get at it to break it down.



Onepercent may not sound like much, he added. "But think of it thisway: If you have money in the bank and you lose 1 percent per year,you would be down to two thirds of your starting capital after only50 years."

"There ismore carbon stored in the soil, on a global scale, than invegetation or even in the atmosphere," said Kleber. "Since thisreservoir is so large, even small changes will have serious effectson carbon concentrations in the atmosphere, and by extension onclimate."


CO2 is amajor driver of the current warming of Earth's atmosphere. Byfailing to account for accelerated soil-carbon decomposition, thestudy suggests, current climate-change models may beunderestimating carbon loss from soil by as much as 1 percent peryear.

"Our mainconcern is that this is an important mechanism, and we are notpresently considering it in global models of carbon cycling,"Kleber said.


It'slikely that a warming climate is speeding this process up, he said.As warmer weather and more carbon dioxide in the air stimulateplants to grow, they produce more root compounds. This will likelyrelease more stored carbon, which will enter the atmosphere asCO2--which could in turn accelerate the rate of climatewarming.



He saidthe study challenges the prevailing view that carbon bonded tominerals stays in the soil for thousands of years. "As these rootcompounds separate the carbon from its protective mineral phase,"he said, "we may see a greater release of carbon from its storagesites in the soil."

Thecarbon then passes into the atmosphere as carbon dioxide (CO2),said the study's coauthor, Markus Kleber, a soil scientist in OSU'sCollege of Agricultural Sciences.


In astudy published in this week's online edition of the journalNature Climate Change, the researchers showed thatchemicals emitted by plant roots act on carbon that is bonded tominerals in the soil, breaking the bonds and exposing previouslyprotected carbon to decomposition by microbes.

根据俄勒冈大学土壤科学家们的观点,便译成中文,土壤碳损失的问题已备受关注。昨天阅览科技日报发现了这篇文章, Soil,long thought to be a semi-permanent storehouse for ancient carbon,may be releasing carbon dioxide to the atmosphere faster thananyone thought, according to Oregon State University soilscientists.


Markus Kleber is a soil scientist at Oregon StateUniversity.

Climate change, plant roots may accelerate carbon loss fromsoils气候变化----植物根系会加速土壤中碳的流失