Effect Of Plant-soil Feedback On Plant Growth And Soil Nitrogen Utilization And Loss

The development of agriculture and animal husbandry in China has led to an increasing demand for food and pasture,but while expanding the scale and increasing the yield,crop rotation barriers such as reduced yields,poor soil quality,and reduced soil fertility caused by long-term cultivation of the same family or species have not only severely restricted the development of agriculture and animal husbandry,but have also caused a series of ecological problems.To effectively reduce the negative impact caused by continuous cropping,the crop rotation is considered as the first biological pathway which can increase crop yields and improve soil quality.However,the mechanisms that crop rotation improve crop yield and soil quality are not well understood.Plant-soil feedback has now become one of the hot issues in ecological research and has been applied to agricultural systems because it can effectively links aboveground and belowground.Plant-soil feedback play key roles in understanding the mechanism that determines the ecosystem community structure and functional stability.In this study,two greenhouse pot experiments were conducted to simulate continuous and rotational cropping systems in agricultural and pastoral ecotone in Northeast China,two grasses(Leymus chinensis,Medicago sativa)and crops(Zea mays,Glycine max)were selected to investigate the effects of plant-soil feedback on plant growth and development,soil physicochemical properties and nitrogen(N)turnover,and to explore the mechanisms underlying the plant-soil feedback process mediated by soil microorganisms.The main results were as follows:(1)Different cropping systems had no effect on the biomass of grassland ecosystems,and its effect in agroecosystem was higher than grassland ecosystem.In grassland ecosystems,no significant changes in plant growth characteristics between the studied two grass species.However,in agroecosystems,crop rotation significantly increased plant growth characteristics,crop height,net photosynthetic rate,aboveground,belowground,and total biomass.The different cropping systems significantly affected soil physicochemical properties.In agroecosystems,crop rotation significantly reduced soil p H and alleviated soil salinity;and crop rotation significantly increased soil total N and available phosphorus(P)content and significantly reduced the ratio of carbon-to-nitrogen.For soil nutrients(total N and available P),different planting sequences had different effects on soil physicochemical properties,with Z.mays-G.max and L.chinensis-M.sativa sequences increasing soil nutrient content.(2)For soil bacteria,Amoebacteria and Acidobacteria were the dominant species in all bacterial communities across all treatments;for soil fungi,Cysticercus fungi were the dominant species.The cultivation of different plants significantly affected soil microbial diversity.The fungal α-diversity of soils domesticated by Leguminosae species(G.max,M.sativa)were much higher than that in the soil domesticated by Gramineae species(Z.mays,L.chinensis).The changes in soil fungal community composition were mainly influenced by soil available P and soil total nitrogen contents,while soil p H was the main factor influencing changes in soil bacterial community composition.Although plants had a significant effect on soil microbial community composition,the changes of soil microbial diversity had no effect on second crop yield.(3)The present results found that planting different plants had no significant effect on the N content of the aboveground of the subsequent crop,but crop rotation significantly increased the total soil N content.In agroecosystems,Z.mays-G.max rotation reduced soil N loss,but in grassland ecosystems,L.chinensis-M.sativa rotation significantly increased soil N loss.Cropping systems had no effect on soil nitrification and N mineralization rates in grassland ecosystems;in agroecosystems,Z.mays-G.max rotations significantly increased soil nitrification and N mineralization rates.(4)The legacy effects of the first-stage of the plant-soil feedback have an impact on the growth and development of second-stage plants,but this species-specific.At phase I,soil physicochemical properties were significantly correlated with the growth characteristics of subsequent crops in both grassland and agroecosystems,and which were mainly influenced by soil p H,total carbon and total N content.In contrast,the composition and diversity of the soil microbial community in the first stage had no effect on the growth and development of subsequent crops in agroecosystems.In summary,the present study provides preliminary insight into the mechanisms of plantsoil feedback on plant growth and development and soil N turnover in agricultural and pastoral ecotone in Northeast China.In addition,the specific feedback effects of different plants on the soil reaffirmed the "bottom-down" theory,for instance,soil physical and chemical properties and soil biology can regulate the growth of above-ground plants.Significant difference in plantsoil feedback influence on soil N turnover was observed between grassland and agroecosystems.In agroecosystems,crop rotation reduced soil N loss in farming systems,but in grassland systems,L.chinensis – M.sativa rotation significantly increased soil N loss.The results suggest that crop rotation is a potential pathway to reduce N loss and increase crop yield in agroecosystem,while the grass rotation might aggravate the N loss in the grassland ecosystems.