Fungi mat­ter

First-of-its-kind global study shows soil fungi can di­rectly im­pact cli­mate change

Down to Earth - - CONTENTS - VI­JAY RAVIKU­MAR

A global study on fun­gal bio­di­ver­sity shows how soil fungi di­rectly af­fect cli­mate change

Ftime they in­hab­ited the land­masses ROM THE some 500 mil­lion years ago, fungi have played a fun­da­men­tal role in Earth’s geo­chem­i­cal cy­cles. They are im­por­tant in­gre­di­ents for healthy and agri­cul­tur­ally vi­able soil as they de­com­pose dead or­ganic mat­ter to pro­vide nec­es­sary nu­tri­ents to plants.The bal­ance of fun­gal com­mu­ni­ties can even di­rectly af­fect the car­bon cy­cle and, thereby, the pace of cli­mate change. Yet, due to their con­cealed ex­is­tence—most fungi are mi­cro­scopic and live be­neath the soil—we know very lit­tle of their global ecol­ogy.

In the re­cent past, sev­eral stud­ies have sought to ad­vance our un­der­stand­ing of fun­gal ecosys­tems and high­light the im­por­tant role soil fungi play in sus­tain­able soil man­age­ment, for­est preser­va­tion and cli­mate change mit­i­ga­tion. Now, in a first-of-its-kind study, a team of sci­en­tists, led by Leho Ted­er­soo of the Uni­ver­sity of Tartu, Es­to­nia, sam­pled the mi­cro­bial life of the soil at 365 lo­ca­tions across six con­ti­nents to know about the ba­sic driv­ers of fun­gal bio­di­ver­sity. They stud­ied the dis­tri­bu­tion of fun­gal com­mu­ni­ties at each site along with soil pH, rain­fall pat­tern, plant di­ver­sity and spa­tial vari­ables.

Global fun­gal bio­di­ver­sity

Ted­er­soo and his team col­lected and stud­ied 40 soil cores from each of the 365 sites in over 40 coun­tries, in­clud­ing In­dia and Sri Lanka. The mas­sive work re­quired the co­or­di­na­tion of 35 re­search in­sti­tutes. Soil sam­ples were taken from a di­verse set of ecosys­tems, in­clud­ing the Ama­zon rain­for­est, the Hi­malayas and Siberia. The team stud­ied the fun­gal dna in th­ese sam­ples. They found that fun­gal

di­ver­sity is not pri­mar­ily determined by plant di­ver­sity. The study shows that mean an­nual pre­cip­i­ta­tion is the strong­est driver of species di­ver­sity among soil fungi, mean­ing a more di­verse set of soil fun­gal com­mu­ni­ties will be present in ar­eas with large amounts of rain or snow. Soil pH and soil cal­cium con­cen­tra­tion also sig­nif­i­cantly in­crease di­ver­sity.The over­all fun­gal di­ver­sity in­creases to­wards the Equa­tor, with the no­table ex­cep­tion of cer­tain fun­gal groups such as ec­to­my­c­or­rhizal fungi.

There are about 100,000 known fun­gal species, and nearly half of them were ob­served in the study, which is the most ex­ten­sive anal­y­sis of fun­gal dis­tri­bu­tion to date, ac­cord­ing to Colin Averill, who stud­ies fun­gal ecol­ogy at the Uni­ver­sity of Texas, Austin. He was not part of the study, which was pub­lished on Novem­ber 28,2014,in the jour­nal Science.

Im­pact on cli­mate change

This un­der­stand­ing of fun­gal bio­di­ver­sity as­sumes sig­nif­i­cance in the face of cli­mate change. In a com­ment on the study pub­lished in the same is­sue of Science, David War­dle from the Depart­ment of For­est Ecol­ogy and Man­age­ment and Björn Lin­dahl from the Depart­ment of Soil and En­vi­ron­ment, Swedish Uni­ver­sity of Agri­cul­tural Sciences, write, “Im­proved knowl­edge about links be­tween macro­cli­mate and fun­gal com­mu­ni­ties will help pre­dict how global cli­mate change is likely to af­fect the rel­a­tive abun­dance of key fun­gal groups and thereby al­ter fun­gal-driven eco­log­i­cal pro­cesses.”

The study clas­si­fies fungi into groups on the ba­sis of their eco­log­i­cal role.Two of th­ese groups fig­ure promi­nently in the car­bon cy­cle.The first group con­sists of “sapro­trophs” or de­com­posers, which re­cy­cle the ni­tro­gen in dead plant mat­ter and re­lease it back into the at­mos­phere as car­bon diox­ide (CO2). The sec­ond group con­sists of “ecto-my­c­or­rhizal” (ecm) fungi, which grow in ex­ten­sive fil­a­ment net­works around the roots of cer­tain woody plants like birch, wil­low, pine and rose. They are clas­sic sym­bionts, ex­chang­ing ni­tro­gen for car­bo­hy­drates man­u­fac­tured by plants through pho­to­syn­the­sis.

Earth’s soil can store three times the car­bon as the at­mos­phere. But a 2014 pa­per in Na­ture by Averill and sci­en­tists at the Smith­so­nian Trop­i­cal Re­search In­sti­tute shows that soil with ecm fungi can store 70 per cent more car­bon than soil with­out ecm fungi. The study sug­gests that ecm fungi snatch ni­tro­gen from dead plant mat­ter be­fore sapro­trophs can get to it, leav­ing less ni­tro­gen to sapro­tro­phes for de­com­po­si­tion.The end re­sult is more car­bon in the soil and less in the at­mos­phere.

In other words, the rel­a­tive bal­ance of sapro­trophs and ecm fungi de­ter­mines the amount of car­bon stored in the soil and the rate at which car­bon is re­leased into the at­mos­phere as CO2. Since th­ese fungi are di­rectly re­spon­si­ble, a bet­ter un­der­stand­ing of the driv­ers of their global di­ver­sity is nec­es­sary to fight cli­mate change.

For ex­am­ple, the study shows that ecm fungi are driven pri­mar­ily by host plant di­ver­sity and high soil pH, while sapro­troph di­ver­sity is cor­re­lated to mean an­nual pre­cip­i­ta­tion. Ac­cord­ing to Ted­er­soo, dry­ing and de­ser­ti­fi­ca­tion due to cli­mate change will have a di­rect im­pact on th­ese fun­gal com­mu­ni­ties. “Con­cur­rent changes in veg­e­ta­tion may fur­ther al­ter the func­tional com­po­si­tion of fungi,” he says. His study sug­gests that preva­lent cli­mate change might re­duce ecm fun­gal di­ver­sity and abun­dance. This re­duc­tion could, in turn, ex­pe­dite the re­lease of CO2 into the at­mos­phere, quick­en­ing the pace of cli­mate change.

But fur­ther re­search is re­quired. “We know very lit­tle about how other fun­gal species or func­tional groups of fungi af­fect car­bon cy­cling and stor­age. If we did, we might be able to make bet­ter pre­dic­tions about how th­ese fungi re­spond to cli­mate change and in turn af­fect the rate at which car­bon diox­ide is re­leased into the at­mos­phere,” Averill says.

The bio­di­ver­sity pat­tern of soil fungi was also ex­plored by Richard Bard­gett of the Uni­ver­sity of Manch­ester and Wim van der Put­ten of the Nether­lands In­sti­tute of Ecol­ogy in the Novem­ber 2014 is­sue of Na­ture. The au­thors con­clude that there is lit­tle ev­i­dence to prove that bio­di­ver­sity of soil or­gan­isms fol­lows the same pat­tern as plant or in­sect di­ver­sity. “It is im­por­tant to un­der­stand the bio­di­ver­sity of soil fungi be­cause soils with many fungi are in gen­eral more re­sis­tant to ex­treme events, such as drought. Soil fungi pro­vide struc­ture to soil which is im­por­tant for soil fer­til­ity,” Put­ten ex­plains. He adds that in a heav­ily pop­u­lated coun­try like In­dia, sus­tain­able soil man­age­ment should be high on the agenda .

SI­IRI J RIS JA LEHO TED­ER­SOO

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