Effects Of Invasive Plants,Alternanthera Philloxeroides And Triadica Sebifera,on Soil Nematode Communities

Plant invasion often exerts destructive impacts on biodiversity and ecosystems in the invasive range,which is considered one of the important research topics in the field of ecology.Previous studies mainly focused on aboveground communities,while a growing body of studies showed that plant invasion may also have potential to affect belowground biotic communities.Soil nematode community,which is one of the major components in the soil ecosystem and food webs,is considered an important driver for plant invasion.In this study,we examined the effects of invasive and native plants on soil nematode communities using invasive plant Alternanthera philoxeroides which is native to South America and invaded China in 1930s,as well as its congener Alternanthera sessilis which is native to China.We also examined the effects of invasive plants from native and invasive populations on soil nematode communities using Triadica sebifera which is of eastern Asia origin and invaded the United States in 1772.In addition,our study investigated the spatial distribution patterns of soil nematode comirmnities along latitudinal and altitudinal gradients and examined the effects of biotic factors(including plant species and aboveground herbivores)and abiotic factors(including soil properties and climatic variables)on soil nematode communities.(1)To examine the effects of A.philoxeroides and A.sessilis on soil nematode communities and whether these effects changed along latitude,we conducted filed surveys along the latitudinal gradient(23.63°?36.47°N)in China.Our results showed that soil nematode abundance of the two plant species significantly increased with increasing latitude,whereas the increase in nematode abundance of A.philoxeroides was weaker than that of A.sessilis.In addition,we also examined the relative importance of soil properties and climatic variables to latitudinal patterms of soil nematodes of the two plant species.The results showed that,along the latitudinal gradient,soil nematode abundance of A philoxeroides was only positively correlated with soil pH,whereas soil nematode abundance of A.sessilis was positively correlated with soil moisture,negatively correlated with annual mean temperature and annual precipitation.These results indicated that the responses of soil nematode communities of the two plants to abiotic factors were quite different.(2)To examine the responses of soil nematode communities of A.philoxeroides and A.sessilis to biotic factors,we applied different herbivory treatments(no herbivory,specialist Agasicles hygrophila herbivory and generalist Cassida piperata herbivory)to the two plant species.The results showed that the nematode abundance of A.philoxeroides was significantly lower than that of A.sessilis in the absence of herbivores.However,herbivory had profound effects on soil nematodes,with increasing nematode abundance of A.philoxeroides,while decreasing nematode abundance of A.sessilis.There was no difference between the effects of the specialist A.hygrophila and generalist C.piperata.In addition,the herbivore-induced effects of invasive plant A.philoxeroides on soil nematodes waned with time after removal of herbivores.(3)To examine the effects of T.sebifera from invasive(US)and native(China)populations on soil nematode communities,we used seeds collected from six populations in the invasive range and six populations in the native range.Our results showed that there was no significant difference between the soil nematode abundance of invasive and native populations.However,there were significant differences in the nematode trophic groups between invasive and native populations.The native populations have more microbial feeding nematodes and richer trophic diversity,comparing to invasive ones.Moreover,the soil nematode communities significantly differed from each other within invasive and native populations.(4)To reveal the spatial distribution patterns of soil nematode communities of T.sebifera,we conducted field surveys along the latitudinal(19.44°-33.56°N)and altitudinal(Tianzhu mountain,100?1000 m a.s.l.)gradients in China,Our results showed that latitudinal patterns of soil nematode community structure are mainly quadratic(low nematode abundance at mid-latitude),whereas altitudinal patterns are mainly linear(low nematode abundance at high altitude).In the latitude survey,soil nematode communities were significantly affected by soil properties(soil total carbon,total nitrogen and pH)and climatic variables(annual precipitation).However,soil nematode communities were not correlated with the soil properties measured in the altitude survey,which indicated that the correlations between soil nematode communities and abiotic factors might also be different in the different gradient surveys.Overall,our study examined the relationships between invasive plants and soil nematode communities through comparing invasive and native plants,as well as comparing invasive plants from invasive and native populations.These results revealed invasive plants had significant impacts on soil nematode communities,while these impacts were species-specific.Furthermore,biotic and abiotic factors had different impacts on the interactions of invasive plants and soil nematodes,resulting different spatial distribution patterns of soil nematode communities.