| A large number of toxic plants that grow in degraded grassland not only compete with other plants for mineral nutrients and space,but also release allelochemicals that affect the growth of other plants directly or indirectly.Stellera chamaejasme is one of the main toxic plants in the grasslands of northern China.It often coexists with the excellent forage Leymus chinensis in the degraded typical steppe and degraded meadow steppe.Arbuscular mycorrhizal fungi(AMF)can be mutually beneficial with L.chinensis,but rarely infect the root system of S.chamaejasme.However,little is known about how the S.chamaejasme litter in degraded grassland affects forage growth and the characteristics of AMF in the rhizosphere soil.In order to test the effects of S.chamaejasme litter on the clonal growth of L.chinensis and the characteristics of AMF in the rhizosphere soil,to explore the mechanism of the influence of S.chamaejasme litter on L.chinensis,the two-factor interaction experiment of adding S.chamaejasme litter and nitrogen was carried out.The main conclusions of the two-year experiment are as follows:(1)Nitrogen addition alone significantly promoted the number of ramets and the biomass of L.chinensis,but showed a certain inhibitory effect on the length of the spacer.The S.chamaejasme litter addition had a promoting effect on the number of ramets and the biomass of L.chinensis.The interaction between Nitrogen and S.chamaejasme litter addition had a promoting effect on the number of ramets and the biomass of stems and leaves.In general,the addition of S.chamaejasme litter had a positive effect on the growth of L.chinensis.(2)Nitrogen addittion had the effect of lowering soil pH,changing soil conductivity,and increasing siol available nitrogen and soil available phosphorus.The addition of S.chamaejasme litter increased soil pH,soil conductivity,and soil biomass carbon content to a certain extent,and the addition of high litter amount significantly increased soil available phosphorus content.The addition of litter and nitrogen changed the effect of litter only on soil chemical characteristics.In general,the addition of S.chamaejasme litter had a positive effect on the soil nitrogen and phosphorus content.(3)High nitrogen treatment significantly reduced the AMF infection rate,infection intensity and AMF spore density of rhizosphere soil.The effect of adding S.chamaejasme litter on the AMF infection rate,infection intensity and AMF spore density of rhizosphere soil were significantly different between years.In general,under the conditions of no nitrogen and low nitrogen,the addition of S.chamaejasme litter had a positive effect on AMF infection rate and AMF infection intensity(4)The soil available nitrogen content had a significant or extremely significant negative correlation with the AMF infection rate,infection intensity of L.chinensis roots and AMF spore density of rhizosphere soil.The available phosphorus content was only significantly negatively correlated with AMF spore density in the second year.pH,soil conductivity and soil microbial biomass carbon content were significantly associated with certain characteristics of AMF only in the first year.The soil available nitrogen content is a key factor affecting the AMF characteristics of L.chinensis.In summary,the experimental results of adding S.chamaejasme litter and nitrogen to L.chinensis for two consecutive years showed that the effects of adding S.chamaejasme litter on the growth of L.chinensis and the contents of soil nitrogen and phosphorus were positive.However the effect of the AMF in the rhizosphere of L.chinensis showed greater uncertainty.The results suggested that the promotion of S.chamaejasme to L.chinensis is mainly achieved by increasing the availability of nitrogen and phosphorus content in soil.This means that the litter of S.chamaejasme may be beneficial to the coexistence of L.chinensis and S.chamaejasme in degraded grassland.This conclusion is of great significance for a comprehensive and objective understanding of the competition and coexistence mechanism between S.chamaejasme and neighboring plants in degraded grassland. |
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