AM Fungi Regulate The Allelopathy Of Neochamaejasmin B On The Growth Of Leymus Chinensis(Trin.)Tzvel.

A large number of poisonous plants that breed on degraded grasslands not only compete with pastures for water and mineral nutrition but also secrete allelochemicals to affect the growth of neighboring pastures.Stellera chamaejasme L.is a poisonous plant commonly found in grasslands in northern China.On degraded typical grasslands and meadow grasslands,S.chamaejasme often coexists with Leymus chinensis（Trin.）Tzvel.,a high-quality gramineous pasture.S.chamaejasme has allelopathic effects on the seed germination and seedling growth and development of various plants,and it also has a certain effect on rhizosphere soil microorganisms.As an important type of soil microorganism,AM fungi have multiple functions such as promoting plant growth and regulating nutrient cycling.At present,little is known about whether neojamajamin B（the main allelopathic component of S.chamaejasme）has an allelopathic effect on L.chinensis,and whether AM fungi have a modulating effect on this allelopathy and its mechanism is still poorly understood.In this study,L.chinensis was used as the test plant,and a two-factor randomized block experiment was designed with the addition of neochamaejasmine B and AM fungi treatment.Four concentration gradients were set for neochamaejasmine B,CK(0μg m L^-1),NCB₁₀(10μg m L^-1),NCB₂₀(20μg m L^-1),NCB₄₀(40μg m L^-1),and the AM fungi treatment was set two conditions,inoculation（AM+）and without inoculation（AM-）.Through potted control experiments,the growth and photosynthesis parameters of L.chinensis,the nitrogen and phosphorus content of the plant,seven kinds of soil hydrolase activities（α-1,4-glucosidase（αG）,β-1,4-glucosidase（βG）,β-1,4-xylosidase（βX）,β-D-cellobiosidase（CBH）,β-1,4-N-acetyl glucosaminidase（NAG）,L-leucine aminopeptidase（LAP）,acid phosphatase（a P））,and soil physical and chemical properties were determined.The following scientific hypotheses are to be tested:（1）neochamaejasmine B has an allelopathic inhibitory effect on the growth of L.chinensis,and can affect the growth of L.chinensis by changing soil hydrolase activity and soil physical and chemical properties;（2）AM fungi can regulate the allelopathy of neochamaejasmine B on the growth of L.chinensis.The main results are as follows:（1）Neochamaejasmine B has a significant allelopathic inhibitory effect on the phenotypic characteristics and photosynthesis of L.chinensis.First of all,neochamaejasmine B significantly reduced the fibrous root biomass of L.chinensis,and reduced the bud number by about 50%.The high concentration of neochamaejasmine B has a significant inhibitory effect on the length of the spacer and the total rhizome length of L.chinensis.Secondly,neochamaejasmine B reduced the net photosynthetic rate（P_n）and increased the intercellular CO₂ concentration of leaves（C_i）.（2）Neochamaejasmine B has significant effects on soil hydrolase activity and soil physical and chemical properties.The addition of neochamaejasmine B significantly increased the activities ofβG,βX,CBH,and a P.At the same time,it was found that the treatment with neochamaejasmine B significantly increased the soil p H and total nitrogen content（TN）and reduced the soil total phosphorus（TP）and soil total carbon（TC）.（3）The inoculation of AM fungi can promote the fibrous roots biomass of L.chinensis and the total carbon content of shoot of L.chinensis,and can increase the activities ofαG,βG,βX,CBH,NAG,and a P.AM fungi treatment also significantly increased soil p H,but reduced soil TP content.（4）The interaction between AM fungi and neochamaejasmine B has a significant effect on the total carbon content of shoot,P_n,and the activities ofβG,CBH,and a P,and significantly changed the p H,TN,TP of the rhizosphere soil.In general,the inoculation of AM fungi weakened the inhibitory effect of neochamaejasmine B on the growth of L.chinensis.To sum up,neochamaejasmine B has a significant allelopathic inhibitory effect on the growth of roots and leaf photosynthesis of L.chinensis,and neochamaejasmine B can indirectly affect the growth of L.chinensis by changing soil hydrolase activities and soil properties.In addition,AM fungi can regulate the allelopathic effect of neochamaejasmine B on L.chinensis by changing soil hydrolase activity and soil nutrient content.This study reveals the multi-pathway potential mechanism of neochamaejasmine B inhibiting the growth of L.chinensis and the mechanism of rhizosphere AM fungi regulating the allelopathy of S.chamaejasme.It has important theoretical significance for the in-depth understanding of the interspecific relationship between poisonous plants in degraded grasslands and adjacent pastures,and has a certain reference value for the control of poisonous plants in grasslands and the restoration of degraded grasslands.