The Effects Of The Addition Of Stellera Chamaejasme Root Aqueous Extracts, Litters, And Nitrogen On Soil Hydrolase Activities In Leymus Chinensis Rhizosphere

In degraded grasslands,a large number of poisonous plants compete with edible forage grasses for nutrient resources and reduce the utilization value of grassland.Stellera chamaejasme L.is a common poisonous plant in the northern grassland of China,which has strong ecological adaptability and a certain competitive advantage.S.chamaejasme coexists with excellent forage grass Leymus chinensis in the degraded typical steppe and degraded meadow steppe.The root exudates and litters of S.chamaejasme have allelopathic effects on many plants.Soil enzymes play an important role in mediating soil nutrient cycling and utilization.However,the response of enzyme activity to the allelopathic effects of S.chamaejasme as well as its role in mediating the interspecific relationship between S.chamaejasme and L.chinensis are still unclear.Furthermore,how the increasing atmospheric nitrogen（N）deposition and continuous grassland degradation may affect the interspecific relationship between S.chamaejasme and L.chinensis remain poorly understood.To study the effects of the root aqueous extracts and litters of S.chamaejasme on the growth of L.chinensis and the activity of soil hydrolase in rhizosphere under the background of increasing N deposition,as well as to elucidate the mechanism of S.chamaejasme affecting the growth of L.chinensis,we conducted a two-year experiment.In this experiment,L.chinensis was used as the research object,and we conducted two-factor interaction experiments,including the addition of aqueous extract of S.chamaejasme root and N;the addition of S.chamaejasme litter and N,respectively.The aqueous extract of S.chamaejasme root was set with four gradients,including WN（no aqueous extract）,W20（twenty-fold dilution）,W5（five-fold dilution）,W0（original solution）;N addition was set with three gradients,including N0(0g·N·m^-2 yr^-1),N1(10g·N·m^-2 yr^-1),N2(20g·N·m^-2 yr^-1);S.chamaejasme litter was set with four gradients,including L0（0g per pot）,L2(2g per pot,66.7 g·m^-2 yr^-1),L4(4g per pot,133.3 g·m^-2 yr^-1),L8(8g per pot,266.7 g·m^-2 yr^-1).We tested seven types of soil hydrolase activities closely related to the cycle of carbon,nitrogen,and phosphorus,includingα-glucosidase（αG）,β-glucosidase（βG）,β-xylosidase（βX）,cellobiohydrolase（CBH）,N-acetylglucosaminidase（NAG）,L-leucine aminopeptidase（LAP）,and acid phosphatase（aP）,as well as soil physicochemical properties.The research results are as follows:（1）The aqueous extracts of S.chamaejasme root decreased the activities of soil C-and N-degrading enzymes（NAG）.N addition also decreased the activities of soil C-（βG,βX,CBH）and N-degrading enzymes（NAG）to some extent,while high N treatment had stronger inhibitory effects.The interaction between the two treatments had a"superposition"inhibitory effect on the activities of C-and N-degrading enzymes.（2）The S.chamaejasme litter increased the activities of soil C-,N-and P-degrading enzymes.Furthermore,the addition of N and S.chamaejasme litter interactively affected different types of soil enzyme activities.In other words,increasing N addition changed the effects of S.chamaejasme litter on soil enzyme activities.（3）LAP showed the strongest response to aqueous extracts of S.chamaejasme root,and S.chamaejasme litters interacted with N addition.Therefore,LAP can be potentially used as an important indicative variable to reveal the mechanism of interspecific relationship between S.chamaejasme and neighboring forage grasses in degraded grassland under the background of N deposition and can be used as an indicator of N deposition and allelopathic effects of S.chamaejasme.（4）The key factors affecting soil hydrolase activities were soil N,P content,and soil pH under the conditions of aqueous extracts of S.chamaejasme root and S.chamaejasme litters interacted with N addition.In conclusion,the results of two years of the addition of N,root aqueous extracts and litters of S.chamaejasme treatments showed that S.chamaejasme may affect the growth of L.chinensis by altering soil enzyme activity and nutrient availability directly or indirectly through the release of the allelochemicals from the root.This process is the potential mechanism by which S.chamaejasme affects the growth of L.chinensis in the same community in degraded grasslands.The"superposition"inhibitory effect of the addition of N and aqueous extract of S.chamaejasme root on soil enzyme activity means that the potential allelopathic effects of S.chamaejasme on L.chinensis may be strengthened by the increase of atmospheric N deposition in the future.This study expounded the allelopathic mechanism of S.chamaejasme on L.chinensis from the perspective of soil enzyme activity and soil nutrient dynamics,which is of considerable significance to reveal the mechanism of the interspecific relationship between poisonous plants and edible forage grasses in degraded grassland under the background of intensified atmospheric N deposition.Furthermore,it provides a new way to study the interspecific relationship of grassland plants.