Effects Of Fungal Endophyte On Intraspecific Competition Of Achnatherum Inebrians

Drunken horse grass(DHG,Achnatherum inebrians)is a poisonous grass widely distributed in the grasslands of northwestern China.It forms a symbiosis with Epichlo? endophyte,and has a strong growth advantage in the community.However,its mechanism of competition has not been understood yet.In this study,endophyte-infected(EI)and endophyte-free(EF)DHG plants were used in the field and greenhouse experiments based on the De Wit-type replacement series.EI plants were used as competitive species,and EF plants were the target species.The relative yield total(RYT)and aggressivity(A)were used to quantify the competitiveness between EI and EF plants(RYT?1 and A>0 indicates that there is a competitive relationship and the aggressivity of the competitive species is stronger than the target species).The effects of endophyte,plant density,and the nitrogen contents of pot soil on DHG plant competitiveness were studied.The main results obtained were as the follows:1.EI and EF plants were sown as the sowing rate of 1:1 in the field,so that a mixed pasture was established,and some management were under taken.The results showed that the RYT and A for EI was 0.95 and 0.12 respectively,which indicated that there was competitive effect between EI and EF,EI was more competitive than EF.Which results in EI plant had higher plant height and more tiller numbers than EF,with a relative increase of 11.8% and 20.4%.In addition,the EI shoot N and P content was higher than EF,with a relative increase of 7.7% and 10.0%.These results indicated that Epichloe? endophyte could improve the aggressivity of EI DHG plants through increasing host grass growth ability.2.The RYT of DHG growing in greenhouse condition were 0.85,0.84 and 0.90,respectively under the sowing rate of 1:1,3:1 and 1:3 between EI and EF,indicating that EI and EF were competed each other.And in the sowing rate of 3:1 and 1:1,the A of EI DHG was 0.25 and 0.09,indicating EI plants were more competitive than EF.However,the RYT was-0.10 in the mixture of 1:3.This result indicated that the positive effects of endophyte on DHG competitions were decreased with the decrease of the number of EI plants.The endophyte increased the POD activity,SOD activity,and soluble sugar content in mixture of 3:1 and 1:1,with a relative increase 47.8%?26.9% and 32.3%,respectively.These results indicated that the fungal endophyte could improve the growth state,antioxidant enzyme activity of DHG,further increasing the competitiveness of EI plants.3.Under 0.1 mM and 1 mM nitrogen concentrations,the A of EI and EF were 0.05 and 0.15,0.06 and 0.08,0.04 and 0.15 in mixture of 1:1,3:1 and 1:3 under the pot experiment of nitrogen limitation,respectively.On the contrary,under the of 7.5 mM nitrogen concentration,the A of EI and EF were-0.10,-0.06,and-0.05 in mixture 1:1,3:1 and 1:3.It showed that the presence of an Epichloe? endophyte could enhance the competitiveness of DHG under nitrogen limitation treatment,but the endophyte reduced the competitiveness of plants with the increase of soil nitrogen content.Under the 0.1 mM and 1 mM nitrogen concentrations,EI plants had a higher plants growth index,tiller,leaf dry weight and root dry weight than EF,with a relative increase of 15.0% and 5.2%,18.9% and 3.0%,23.7% and 15.9%,31.4% and 24.6%,respectively.The chlorophyll content and net photosynthetic rate of EI DHG were higher than that of EF,with a relative increase of 20.7% and 16.2%,72.0% and 23.0%,respectively.EI shoot P contents,root N and P contents were higher than EF,with a relative increase of 19.5% and 2.9%,10.8% and 9.2%,15.2% and 18.2%,respectively.EI nitrogen utilization efficiency(NUtE)increased by 21.5% and 17.2% than EF plants under the 0.1 mM and 1 mM nitrogen concentrations.But the presence of endophyte had no significant effect on plant growth indicators under 7.5 mM pot soil nitrogen concentration(P>0.05).It demonstrated that the presence of an Epichloe? endophyte enhanced the competitiveness of plants by improving their growth performance,photosynthetic capacity,and nitrogen use efficiency of DHG under the low-fertility environments.In summary,soil nutrient content and plant density could affect the growth and competitiveness of DHG.Under low nitrogen conditions,the presence of endophyte increased the competitiveness of DHG.However,with the increase of soil nitrogen content,the gain effect of endophyte on competitiveness decreased.At the same time,these studies have shown that with the decrease in the number of EI plants,the gain effect of endophytic fungi on the competitiveness of DHG gradually weakened.Therefore,it could be explained the DHG had a strong competitive advantage and a high endophyte infection rate in the harsh natural grassland.