Effects Of Arbuscular Mycorrhiza Fungi And Ectomycorrhiza Fungi On Litter Decomposition And Microbial Saprotrophs

Different types of mycorrhizal fungi profoundly affect forest litter decomposition.The roots almost all tree species can form mutualistic symbiosis relationships with arbuscular mycorrhizal fungi（AMF）and/or ectomycorrhizal fungi（EMF）.There have been reports on the effects of mycorrhizal fungi on litter decomposition from the perspective of different mycorrhizal types,however,due to the different experimental conditions,the results of the studies have great differences.In addition,most of the effects of AMF are based on herbs or crops,there are few studies using forest trees as test objects.In order to draw a unified research conclusion,further explore the effects of AMF and EMF symbiotic with forest trees on litter decomposition,and analyze the mechanism in detail.In this study,two arbuscular mycorrhizal（AM）tree species（Fraxinus mandshurica,Juglans mandshurica）and three ectomycorrhizal（EM）tree species（Pinus koraiesis,Betula platyphylla,Larix gmelinii）commonly found in Northeast China were used in a two-chamber pot experiment as the research objects.The two-chamber pot experiment is to divide the test device into a plant growing and a litter decomposition room through the nylon mesh.Inhibition of mycorrhizal fungi by benomyl,setting the mycorrhizal fungi（M+）and benomyl treatment（M-）,the effects of AMF and EMF were analyzed under the same experimental conditions.Relevant indicators include forest litter mass loss,nutrient release,saprophytic microbial biomass and enzymatic activity,and effects of soil nutrients.The results show that:（1）AMF significantly promoted forest litter decomposition and nitrogen（N）release（p<0.05）,and EMF had a tendency to inhibit litter decomposition.M+treatment in AM significantly accelerated the loss of litter mass and the rate of decomposition,increased by13%and 0.016 g/d respectively at 90 day（d）,and as the longer the decomposition time,the greater the loss of litter.AMF significantly reduced the N content of the litter and affected the carbon nitrogrn ratio（C/N）,the N content decreased by 11.33 g/kg at 90 d.AMF accelerated the release of litter nutrients,which was more conducive to the further decomposition of litter.M+treatment in EM had a smaller litter mass loss rate,which was 2.8%decreased at 90 d,and significantly inhibited carbon（C）release from litter.The effects of EMF on other litter nutrient contents lacked consensus at the tree species level and significant differences.（2）AMF can significantly increase the biomass and enzyme metabolism of saprophytic microorganisms,and there are different trends in biomass and enzyme metabolism among the three EMF tree species.The activities ofβ-1,4-glucosidae（BG）、β-N-acetylglucosaminidase（NAG）and acid phoaphatase enzymes（ACP）in the litter decomposition chamber of the M+treatment in AM were significantly higher than those of the M-treatment（p<0.05）,especially the NAG enzyme activity increased by nearly 1.6～2.0 times,and microbial biomass carbon（MBC）、microbial biomass nitrogen（MBN）were increased.AMF-induced loss of litter mass was significantly positively correlated with NAG and ACP,and significantly negatively correlated with MBC/MBN and MBC/MBP（p<0.05）.The effect of EMF on the loss of litter mass was significantly negatively correlated with MBC（p<0.05）.The contents of MBC,BG,and NAG in the M+treatment were generally lower than those in the M-treatment.However,there is no consistency in the impact of enzyme activity and microbial biomass among the three EM tree species.（3）AMF and EMF increased soil nutrient content in litter decomposition chamber.M+treatment in AM significantly increased the contents of soil total carbon（TC）,total nitrogen（TN）,increased by 39.03 g/kg and 1.50 g/kg respectively at 90 d,and soil nitrate nitrogen（NO₃^--N）and soil available phosphorus（AP）content also increased.The effect of AMF on the contents of these nutrients was significantly positively correlated with the changes of TC and TN contents in litter（p<0.05）.M+treatment in EM significantly increased soil ammonium nitrogen（NH₃⁺-N）,NO₃^--N content,increased by 1.24 mg/kg and 5.43 mg/kg respectively at90 d,but had no significant effect on soil TC,TN,total phosphorus（TP）,AP content.In addition,there was no significant correlation between the effects of EMF on soil nutrients and effects on litter nutrients.To sum up,AMF symbiotic with forest trees promotes litter decomposition.AMF plays an important role in regulating litter decomposition by affecting the activities of microbial saprotrophs’extracellular enzymes（BG,NAG,ACP）.AMF by stimulating enzyme activity increases mass loss and N release of litter while improving soil nutrients.EMF showed an inhibitory trend on litter decomposition,mainly reducing litter mass loss and C release by affecting MBC.This indicated that under the same experimental conditions,the effect of mycorrhizal fungi on the decomposition of litter was related to the types of mycorrhizal fungi,and the effects of different types of mycorrhizal fungi on the litter were regulated by differences in soil microbial growth and extracellular enzyme activities.Therefore,compared with EM species,AM species are more beneficial to promote forest nutrient cycling and improve soil nutrient availability under long-term decomposition.