How harmful are exotic plantations for soils and its microbiome? A case study in an arid island

Abstract

Theplantationofexoticspecieshasbeenacommonpracticein(semi-)aridareasworldwideaimingtorestorehighly degradedhabitats.Theeffectsoftheseplantationsonplantcoverorsoilerosionhavebeenwidelystudied,whilelittle attentionhasbeenpaidtotheconsequencesonsoilqualityandbelowgroundbiologicalcommunities.Thisstudyevaluatesthelong-term(>60years)effectsoftheexoticspeciesAcaciacyclopsandPinushalepensisrevegetationonsoil properties,includingmicrobiome,inanaridisland.Soilsunderexoticplantationwerecomparedtobothdegraded soilswithaverylowcoverofnativespeciesandsoilswithwell-preservednativeplantcommunities.Sevenscenarios wereselectedinasmallarea(~25ha)withsimilarsoiltypebutdifferingintheplantcover.Topsoils(0–15cm)were analyzedforphysical,chemicalandbiochemicalproperties,andampliconsequencingofbacterialandfungalcommunities.Microbialdiversitywassimilaramongsoilswithexoticplantsandnativevegetation(Shannon'sindex=5.26 and5.34,respectively),whilethemosterodedsoilsexhibitedsignificantlylowerdiversitylevels(Shannon'sindex= 4.72).Bacterialandfungalcommunities'compositionindegradedsoilsgreatlydifferedfromthoseinvegetatedsoils (Canberraindex=0.85and0.92,respectively)likelyduetohighsoilsodicity,finetexturesandcompaction.Microbial communities'compositionalsodifferedinsoilscoveredwithexoticandnativespecies,toagreaterextentforfungi thanforbacteria(Canberraindex=0.94and0.89,respectively),duetohigherlevelsofnutrients,microbialbiomass andactivityinsoilswithnativespecies.Resultssuggestthatreforestationsucceededinavoidingfurthersoildegradationbutstillleadingtorelevantchangesinsoilmicrobialcommunitythatmayhavenegativeeffectsonecosystemstability.Informationgainedinthisresearchcouldbeusefulforenvironmentalagenciesanddecisionmakersaboutthe controversialreplacementofexoticplantsininsularterritories.