Eftects Of Soil Heterogeneity And Earthworm On Plant Growth And Commuity Productivity

Soil heterogeneity is prevalent in natural habitats,and significantly affects various ecological patterns and processes.Environmental heterogeneity related to soil nutrients or physical space,interacting with other trophic levels(e.g.,detritivores,and phytophagous insects),can combinedly influence the dynamics of plant individuals,populations and communities.So far,however,the effect of soil heterogeneity on the interactions among plants,detritivores,and phytophagous insects have rarely been explicitly investigated.Taking various plant species(clonal and non-clonal),phytophagous insects and earthworms as target species,five controlled experiments were conducted to test interaction effects of soil heterogeneity and other environmental factors(including soil moisture,earthworms and aphids)on the growth and foraging behavior of plants.1.Compared to native plants,soil heterogeneity exerted a more significant positive effect on the growth and competitive performance of Alternanthera philoxeroides,and such an effect depended on soil moisture.In the treatments of interspecific competition,A.philoxeroides reduced the growth of three native plants,and the negative effects on the growth of Hemarthria altissima and Cynodon dactylon were more pronounced in the heterogeneous than in the homogeneous soil.Across native species,the competitive response of A.philoxeroides was more negative in the heterogeneous than in the homogeneous soil at a lower moisture level.2.Clonal integration in A.philoxeroides induced a developmental-programed division of labor between ramets with different ages,via increasing either the investment of the root growth in(older)central ramets or the aboveground growth in(younger)peripheral ramets.Clonal integration thus improved the growth of the central and peripheral ramets,clonal fragments,as well as the expansion of the whole ramet population.3.Increasing soil depth not only facilitated the individual growth of legume and forb species,but also increased the overall productivity of the community.Species diversity significantly affected the community productivity,and greatly contributed to the responses of legume and forb species to the heterogeneity of soil space.In particular,forb species from the high-diversity commununity were more susceptible to soil depth and its heterogeneity.Legume species from the low-diversity community responded more significantly to soil depth and its heterogeneity,whereas the legumes from the low-diversity community often grew better in the shallow soil.4.Soil resource heterogeneity triggered the foraging response of Hydrocotyle vulgaris,thereby increasing the performance of the whole clone.Herbivory by aphids severely decreased biomass accumulation and ramet production of H.vulgaris,especially in the homogeneous condition,i.e.,soil heterogeneity to some degree alleviated the negative impact of aphids.The presence of earthworms did not cause any influences on plant performance.However,the survival rate and fresh mass of earthworms were significantly affected by soil heterogeneity and aphids,and improved in the heterogeneous condition or under herbivory by aphids.5.Different plant species exhibited various foraging responses to soil heterogeneity and activity of earthworms.Grass species including Agrostis stolonifera,Elymus dahuricus,Festuca rubra,Lolium perenne,and Paspalum notatum,performed better in the heterogeneous than in the homogeneous soil.Or Festuca rubra,Lolium perenne,Paspalum notatum,Zoysia matrella and Zoysia tenuifolia performed better in the presence than in the absence of earthworms.Besides,the presence of earthworms modified the positive effects of soil heterogeneity on plant growth in some species,for example,weakened the positive effect on the growth of P.notatum.In conclusion,heterogeneity of soil nutrients or space can influence the foraging behavior of plants,improve individual growth,and alter the competitive relationship between invasive and native species.Meanwhile,both biotic and abiotic factors can influence the impacts of soil heterogeneity on the growth of plants.