| Plant invasion has caused a serious threat to China’s ecosystem and biodiversity.With the advancement of global climate change and frequent acid rain,acid rain was considered to be one of the three major ecological and environmental disasters in the world.China has become the third major acid rain pollution area after Europe and North America.The influence of acid rain and its acid deposition on plant invasion is complex and changeable.Therefore,it is of great significance for the management of invasive plants in acid rain areas to study the ecological adaptability and tolerance of invasive plants under acid rain stress,so as to understand the invasion mechanism of plants in acid rain areas.In this experiment,the invasive plant Alternanthera philoxeroides（Mart.Griseb）and indigenous plant Alternanthera sessilis（L.）DC.were taken as the research objects.The pot control experiment was carried out indoors to explore the changes of plant growth physiological indexes,soil physical and chemical properties and soil microbial indexes under different p H values（p H 2.5,p H 3.5,p H 4.5,p H 5.6 and p H 7.0）simulated acid rain treatment.（1）The effects of simulated acid rain on the growth and physiological indexes of A.philoxeroides and A.sessilis were studied.The results showed that acid rain stress would inhibit the normal growth and development of A.philoxeroides and A.sessilis.Compared with the control（p H 7.0）,the aboveground biomass,chlorophyll a,chlorophyll b,total chlorophyll and net photosynthetic rate of A.philoxeroides were significantly inhibited under the treatment of simulated acid rain（p H≤3.5）,with the maximum decreases of25.4%,14.0%,7.8%,11.8%and 44.3%respectively,Under the treatment of simulated acid rain（p H2.5）,the content of MDA in A.philoxeroides leaves increased significantly by28.4%,and the activities of SOD,POD and CAT decreased significantly by 16.0%,16.5%and 23.5%respectively;Under the treatment of simulated acid rain（p H≤5.6）,the plant height,aboveground biomass,chlorophyll a,chlorophyll b,total chlorophyll content and net photosynthetic rate of A.sessilis were significantly inhibited,with the maximum decrease of 25.2%,33.2%,40.5%,31.3%,39.1%and 54.1%.Under the treatment of simulated acid rain（p H≤4.5）,the MDA content of A.sessilis increased significantly,with the maximum increase of 29.8%,and the activities of SOD,POD and CAT were inhibited,with the maximum decrease of 19.0%28.4%and 20.4%.The results showed that both A.philoxeroides and A.sessilis had acid resistance,but the resistance to acid rain of A.philoxeroides was stronger than that of A.sessilis.（2）By studying the effects of simulated acid rain on the physical and chemical properties of A.philoxeroides and A.sessilis soil,the results showed that acid rain would lead to soil acidification of A.philoxeroides and A.sessilis and improve soil conductivity.The buffering capacity of A.philoxeroides soil to acid rain is greater than that of A.sessilis.Compared with the control,the exchangeable Mg2+,exchangeable K+and organic matter of A.philoxeroides soil were lost under the treatment of simulated acid rain（p H≤3.5）,with the maximum decrease of 34.3%and 20.7%.The contents of exchangeable Ca2+,ammonium nitrogen and available phosphorus decreased significantly by 7.4%,10.5%and10.4%under the treatment of simulated acid rain（p H 2.5）.The contents of total nitrogen,total phosphorus and total potassium were not significantly affected by acid rain;The contents of exchangeable Ca2+and ammonium nitrogen in A.sessilis soil decreased significantly under the treatment of simulated acid rain（p H≤4.5）,with the maximum decrease of 8.8%and 26.2%respectively.The contents of exchangeable K+,organic matter,total potassium and available phosphorus decreased significantly under the treatment of simulated acid rain（p H≤3.5）,with the maximum decrease of 23.9%respectively.The contents of exchangeable Mg2+and exchangeable Na+decreased significantly under the treatment of simulated acid rain（p H≤5.6）,with the maximum decrease of 32.7%and10.8%.This showed that acid rain can lead to the loss of soil nutrients,and the range of soil nutrient loss of A.philoxeroides was less than that of A.sessilis.（3）The effects of simulated acid rain on soil microbial communities of A.philoxeroides and A.sessilis were studied.The results showed that simulated acid rain improved the diversity index of fungi and bacteria in A.philoxeroides and A.sessilis soil.Compared with the control,under the treatment of simulated acid rain（p H 2.5）,the Chao1,ACE and Shannon indexes of A.philoxeroides bacterial communities were significantly increased by6.8%,8.8%and 5.5%,Simpson index was significantly reduced by 30.2%,and the Chao1Ace and Shannon index increased significantly by 18.0%,17.0%and 14.8%,and Simpson index decreased significantly by 27.9%;The bacterial flora richness index（Chao1 and ACE）and diversity index（Shannon and Shannon）of A.sessilis were not significantly affected by acid rain.The fungal flora Chao1,ACE and Shannon indexes increased significantly by 14.5%,12.4%and 30.4%respectively under simulated acid rain（p H 2.5）,and the Simpson index decreased significantly by 37.3%;p H2.5 simulated acid rain significantly changed the bacterial and fungal communities of A.philoxeroides and A.sessilis.The redundancy analysis results showed that soil EC and TP were the main factors leading to the change of bacterial community,and AP,OM,soil EC and soil p H were the main factors leading to the change of fungal community.In conclusion,it was speculated that the damage threshold of acid rain to A.philoxeroides was between p H2.5 and 3.5,the damage threshold to A.sessilis was between p H4.5 and 5.6,compared with A.sessilis,A.philoxeroides can better maintain soil nutrient content,increase soil microbial diversity and change microbial structure to improve the acid resistance of A.philoxeroides under acid rain stress.The results of this study can provide a theoretical basis for studying the invasion mechanism of alien plants under acid rain conditions. |
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