Effects Of Nitrogen And Phosphorus Additions And AMF Inoculation On The Rhizosphere Ecology Of Chinese Fir Seedlings

At present,atmospheric nitrogen deposition is becoming severe.Nitrogen deposition increases soil phosphorus fixation,making it difficult for plants to absorb and utilize.Arbuscular mycorrhizal fungi(AMF)can promote soil nutrient activation.Chinese fir is a plantation tree species with a relatively high planting area in China,and its growth is limited by nitrogen deposition and phosphorus deficiency.The effect of nitrogen deposition,phosphorus addition and inoculation of AMF on the root ecology are unclear.In this study,one-year potted Chinese fir seedlings were used as the research object,and three types of treatments were set: nitrogen addition(N0,0 kg N.hm-2.yr-1;N30,30 kg N.hm-2.yr-1;N60,60 kg N.hm-2.yr-1);phosphorus addition(P0,0 mg P.kg-1;P20,20 mg P.kg-1;P40,40 mg P.kg-1)and inoculation of AMF.Then,the physical and chemical properties of soil,root exudates,and soil enzyme activities were studied.The main research results are as follows:(1)Nitrogen or phosphorus addition significantly increased soil total carbon(TC)and available phosphorus(AP)contents.Inoculation of AMF can significantly increase soil TC and soil organic carbon(SOC).When the AMF was inoculated and nitrogen was added at the same time,soil SOC content was significantly decreased and soil organic carbon decomposition was accelerated.Together with AMF,nitrogen and phosphorus addition could result in the decrease of SOC.(2)Nitrogen or phosphorus fertilization decreased the secretion of total organic acid(TA)when inoculated with AMF.Application of nitrogen,phosphorus or inoculation of AMF increases the content of fir root secretions.N60 treatment significantly increased the secretion of oxalic(OA)and hydroxybenzoic acid(HBA).P40 significantly increased the secretion of HBA,p-hydroxycinnamic acid(HA),ferulic acid(FA)and TA in roots of Chinese fir seedlings.AMF significantly increased the secretion of FA,citric acid(CA).(3)Nitrogen application can cause reduction of β-glucosidase(BG)enzyme and the increase of acid phosphatase(ACP)enzyme activity.Phosphorus addition increased Nacetyl-β-D-glucosidase and leucine aminopeptidase(NAG+LAP)enzyme activities,urease(UE)enzyme activities,and decreased peroxide(POD)enzyme activities.Inoculation of AMF decreased soil BG and cellulose(CL)enzyme activities and increased ACP enzyme activities.Inoculation of AMF and nitrogen addition at the same time caused the decreased of BG,ACP enzyme activity,and the increase of POD enzyme activity.Together of phosphorus application and the inoculation of AMF decreased the activity of BG and increased the activity of NAG+LAP.In the non-AMF treatment,NAG+LAP,UE,ACP enzyme activity was significantly positively correlated with TC and SOC content.Under the inoculation of AMF,NAG+LAP was significantly positively correlated with soil TP and AP content,while ACP was significantly positively correlated with soil organic carbon and root secretions(HA,FA and TA).In summary,nitrogen and phosphorus addition and inoculation of AMF could affect the physical and chemical properties,root secretions,and soil enzyme activities of Chinese fir seedlings.Each treatment increased soil carbon content.Applying nitrogen,phosphorus or inoculation of AMF alone could increase the content of root secretions.The interaction of three factors would inhibit the secretion of root secretions,which may be related to changes in soil physicochemical properties.The effect of each treatment on soil enzyme activity showed that nitrogen application decreased BG enzyme activity,and phosphorus application increased NAG+LAP enzyme activity.The changes of enzyme activity may be related to soil physicochemical properties and root exudates.