Responses And Mechanisms Of Rhizosphere Nematode Communities To Different Plant Species In Abandoned Farmland Of Red Soil Region

Plants play pivotal roles in resource input of terrestrial ecosystem.Since the industrial revolution,the land-use intensity eacerbated the rate of soil degradation,particularly for soil biota.The feedback of soil biota could affect soil ecological process and subsequently modulate the aboveground plant community.In fact,the interaction of plant community and soil community co-determine and co-drive the structure and function of terrestrial ecosystem.Compared with the aboveground plant community,soil community was have not receiving enough attention that they deserved given their critival roles in ecosysterm functioning.Soil nematode are one of the most abundant groups of soil fauna.They have various trophic groups and occupy a central position in the soil food web as well as in soil nutrient cycling and energy flow,thus having great potential in indicating soil ecosystem state.Red soil is important for food security and environment procteion,but inappropriately agricultural use has resulted in severe degradation,speeding up its degradation particularly in light of soil biota and function.It is well-kown that main soil organic matter is inseparate from soil structure,fueling soil community.Promoting soil organic level is considered the bases of soil restoration form degraded soil.Despite different plant species could return distinct organic compounds into soil,which change rhizosphere conditions and soil community,however,there is even no awareness on inter-relationship and the mechanism between plant species and nematode community.Combining field investigation and laboratory analysis,five representative pioneer plants of red soil abandoned field were selected in the year of 2015 for nematode community investigation including Setaria viridis(Set.),Xanthium sibiricum(Xan.),Polygonum perfoliatum(Pol.),Phytolacca Americana(Phy.)and Aeschynomene indica(Aes.).Based on the results of 2015,in 2016 we chose some typical plant functional types including compositae Conyza Canadensis(Con.),Gramineae Paspalum natatu(Pas.),and legume Cassia rotundifolia(Cas.)and Lespedeza bicolor(Les.),further validating whether plant functional type have a greater impact on soil nematode communities than species.Samples of plants and rhizosphere soil were collected at vigorous and mature growth stage.We explored response and the mechanism of rhizosphere nematode communities to different plants.1.The main results from 2015 showed that:(1)Rhizosphere nematodes were affected significantly by plant species and growth stage.At the vigorous growth stage,nematode abundance of Aes.(45.7 ind.g-1 soil)was significantly higher than that of the other 4 plants(P<0.05,same below).And there was no significant difference among the remained 4 plant species.At mature stage,nematode abundance followed the order:Set.<Xan.<Aes.<Phy.<Poy.The difference between Gramineae(Set.)and Leguminosae(Aes.)was most apparant.(2)The proportion of herbivorous nematodes was highest(64.2%-88.4%)among all trophic groups.At the vigorous growth stage,Aes.had the highest proportion,while Set.had the lowest one.Microbivorous nematodes(bacterivores and fungivores)were lowest in Aes.while highest in Set.irrespective of growth stage.(3)Regardless of growing stage,nematode abundance positively correlated to the root/shoot ratio and root nitrogen content,while negatively correlated to root length and surface area.Rhizosphere soil physicochemical properties were associated with nematode abundance,the trophic group proportion and several ecological indexes.But the complex pattern suggested complicated mechanism determined nematode community.2.The main results from 2016 showed that,(1)Besides the growth stage,at the level of same family or function guild,the difference of rhizosphere nematode abundance was small.At the vigorous growth stage,nematode abundance of Pas.(35.1 ind.g-1 soil)was significantly higher than other plants(P<0.05)and Gramineae had more nematodes than Leguminosae or Compositae.In same family,the perennial had more nematodes than the annual plant.At the mature stage,nematode abundance followed the order of Gramineae(Set.and Pas.)>Leguminosae(Cas.and Les.)>Compositae(Con.).(2)Herbivorous nematode also had the highest proportion among all trophic groups(45.2%-77.9%).Different from the year of 2015,the herbivorous nematodes were highest in Gramineae,while lowest in Compositae at the vigorous growth stage.The proportions of microbivorous and predatory nematodes were highest in Con.At the mature stage,the proportion of herbivorous nematodes was highest in Set while lowest in Pas.(3)The quantity and quality of resources in rhizospher was distinctly at the fuctional guild or family level.The rhizosphere nematode abundance was positively related to root biomass,root length and root surface area,while was negatively correlated toroot nitrogen content.Relationships between rhizosphere nematodes and soil physicochemical properties depended on growth stage and specific nematode index.In conclusion,plant species especially the function guild type are the determinant factors of rhizosphere nematode community characteristics.The direction(promotion or inhibition)and extent of effects depended on plant root traits and related soil properties.This study provides a basis for understanding the changes and controlling factors of soil food webs during the succession of plant community in the abandanced farmland field.The ecosystem structure and function remains to be further studied in order to use suitable plants for the restoration of degraded red soils.