Effects Of Nitrogen Compounds Addition On Micronutrient In Grassland Soil Plant System

Nitrogen?N?input can result in soil acidification and affect bioavailability of micronutrients in terrestrial ecosystems.However,it remains poorly understood how changes in micronutrient availability in plant-soil system under N addition rates with different N compounds in the semi-arid grasslands.A manipulative experiment with 36treatments and eight replicates,including six addition rates(0,2,5,10,20,50 g N m^-2yr^-1),three compounds,i.e.,ammonium carbonate?NH₄HCO₃,CN?,ammonium nitrate?NH₄NO₃,NN?,and slow-released urea?SRU?,and mown or unmown,was conducted in a meadow grassland in Erguna Forest-Steppe Ecotone Research Station,Institute of Applied Ecology,Chinese Academy of Sciences,Inner Mongolia since 2014,to investigate the ecological responses in the soil-plant system.We examined DTPA-extractible iron?Fe?,manganese?Mn?,copper?Cu?,and zinc?Zn?,and related chemical properties in soil and plant micronutrient concentrations in four grass species,i.e.,Leymus chinensis,Stipa krylovii,Carex duriuscula,and Cleistongenes squarrosa,in2016.The results obtained are as follows:?1?DTPA-extractable Fe concentration in soil increased only with increasing addition rates of ammonium nitrate,but the additions the other two N compounds,i.e.,slow-released urea and ammonium carbonate,had no significant effects on DTPA-extractable Fe in soil.DTPA-extractable Mnconcentration increased with increasing N addition rates with addition of all the three N compounds,and the increase in DTPA-extractable Mn were in sequence of slow-released urea>ammonium nitrate>ammonium carbonate,Neither DTPA-extractablesoil Cu nor Zn consentration was affected by N addition rates or N compound types.With a same N compound and under a same N addition rate,biomass mown or not had no significant effcte on all the four micronutrients in soil after three year's treatment.DTPA-extractable Fe,Mn,Znconcentrations were negatively correlated with but Cu was not correlated with soil pH.DTPA-extractable Fe was negatively correlated with soil effective cation exchange capacity,while Mn was only negatively correlated with soil effective cation exchange capacity under unmown treatment.?2?The uptake of micronutrients by dominant plant species in the grassland was different among the four species.The uptake of micronutrients was more sensitive by L.chinensis,C.duriuscula,and C.squarrosa than by Skrylovii.With increasing N addition rates,Mn and Zn concentrations in the four dominant plant species,and Cu concentrations in L.chinensis increased significantly.With increasing N addition rates and the decline of surface soil pH,plant Mn concentration significantly increased by Fe concentration decreased,indicating indicating an antagonistic relationship between Fe and Mn uptake,i.e.,the increase in plant Mn uptake inhibited the uptake of Fe by plants.The concentrations of Fe,Mn and Cu in a same dominant plant species was not significantly differents betwwen mown and unmown treatments under a same N addition rate.