| Stellera chamaejasme L.is a poisonous plant commonly found in the grasslands of north China,and it is generally to be the dominant species in some severely degraded native grasslands.S.chamaejasme coexists with other plants in most cases and their interspecific relationships are complex.There might be competition for light,water,mineral nutrients and space between S.chamaejasme and other species.According to previous studies,the allelopathic effects of S.chamaejasme affecting seed germination and seedling growth.However,the previous studies untested how these effects can change the relationship between the poisonous plant and other plants in degraded grassland.In order to reveal the relationships and mechanism between poisonous plants and dominant species of Songnen grasslands,we selected Leymus chinensis(Trin.)Tzvel.as our material and conducted a two-factorial interactive experiment including aqueous root extracts of S.chamaejasme(ARES)and nitrogen addition as two treatments.This report aims to investigate the effects of ARES on clonal growth and nitrogen utilization efficiency of L.chinensis.In this study,we crushed the dry root of S.chamaejasme and soaked it in distilled water to collect ARES(including three mass concentration gradients).Ammonium nitrate is used as nitrogen fertilizer(including two concentration gradients).a two-year period pot experiment was carried out in the greenhouse to answer the following scientific questions:(1)Does ARES promote or inhibit clonal growth of L.chinensis ?(2)How does ARES affect the influence of nitrogen addition on clonal growth of L.chinensis?(3)Does ARES affect the efficiency of nitrogen element utilization?The main results are summarized as follows:(1)Within no ARES and low ARES concentration treatments,branch number,total root number,shoot number and the height of L.chinensis were significantly increased by nitrogen application.The low concentration of the ARES had no noticeable effect on the efficiency of nitrogen utilization.(2)Within high ARES concentration treatment,the positive effects of nitrogen addition on L.chinensis were not shown.The high concentration of ARES decreased the utilization efficiency of nitrogen fertilizer,and the inhibition effect was more significantly under high nitrogen treatment.Therefore,the higher concentration of ARES inhibite the positive effect of nitrogen fertilizer on the L.chinensis.(3)ARES significantly increased soil pH and the content of available phosphorus.ARES reduced soil electrical conductivity and microbial biomass carbon.Within no nitrogen fertilizer treatment,the effects of ARES on available nitrogen and microbial biomass carbon in soil interpreted non-significant results.However,ARES dramatically increased soil available nitrogen,and obviously decreased microbial biomass carbon under the condition of nitrogen fertilizer addition.(4)The nitrogen treatment has a significant negative effect on soil pH value and available phosphorus content,meanwhile,there is also an apparent positive effect on soil conductivity and available nitrogen content.In addition,nitrogen addition did not significant affect soil microbial biomass carbon within no ARES treatment.However,the nitrogen application has a significant negative effect on microbial biomass carbon under the treatment of ARES.The above results determined the inhibition of ARES on the growth and nutrient utilization efficiency of L.chinensis.In conclusion,the poisonous plant may inhibit the growth of neighboring grasses by releasing the allelochemicals to affect soil chemical property,particularly nitrogen utilization.So,in the primary stage of grassland degradation,poisonous plants with low density(eg: S.chamaejasme)can promote the growth of L.chinensis.However,S.chamaejasme with high density can inhibit the nitrogen absorption of neighboring plants to gain competitive advantage in severely degraded grassland. |
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