Responses Of Community Structure And Ecosystem Multifunctionality To The Addition Of Plant Species During The Restoration Of Abandoned Cropland

Abandoned cropland is a type of broken land in the agro-pastoral ecotone in northern China that has the potential to be restored and utilized.Previous studies have shown that the addition(reseeding)of multiple species is a rapid recovery measure to improve the ecosystem structure and enhance its multifunctionality.However,the use of soil legacy and species priority effects to build the expected plant communities on different types of abandoned cropland and promote the rapid improvement of community structure and ecosystem multifunctionality of reclaimed grassland still remains unknown.In this study,the abandoned cropland was selected as the research object.The experiment was conducted at the National Soil Quality Observation and Experimental Station of the Institute of Grassland Research,Chinese Academy of Agricultural Sciences(Hohhot,China).Leymus chinensis,Melilotoides ruthenica,Allium ramosum and other common grassland plants in Inner Mongolia were selected experimental material.This study determined the responses of plant community structure and ecosystem function to the addition of species on a time scale during the restoration of abandoned cropland using outdoor control experiments of plots in which different types of species were added to the land to create different plant functional groups.The differences of ecosystem multifunctionality were evaluated in different treatments.These experiments were combined with those in an indoor pot control experiment on the priority effect.This experiment controlled the sowing order of species that were sown at different times.It clarified the impact of species priority effect on early community development and its regulatory mechanism,as well as the effects of process of the addition of species on their coexistence and the subsequent community development.This study utilized control experiments in the laboratory to clarify the influences of soil legacy effects on community development at the early stage that were mediated by plants and the regulatory mechanism of combining species diversity and soil legacy effects.A quantitative analysis was used to illustrate the differences of ecosystem multifunctionality in different communities.The relationship between the historical soil(soil legacy)and the species or combination sown,as well as their effects on the development of subsequent communities,were clarified further.The primary results of this study were as follows:1.Treatments that utilized different plant functional groups improved the structure of subsequent plant communities to some extent.From 2019 to 2021,the proportion of perennials in the species added treatments showed an increasing trend,and the maximum in 2021 was 23 times compared with 2019,and those of grasses,legumes and mixtures treatments were significantly higher than the control.Theα-diversity indices increased,and the β-diversity indices decreased.The heterogeneity of community composition gradually decreased in the treatments with different plant functional groups.2.The addition of species significantly affected the ecosystem multifunctionality of the restored grassland.The different plant functional groups all promoted the colonization of perennial plants,increased the underground biomass production,improved the community stability,and increased the comprehensive nutrients of the community.They affected the composition and function of soil fungi and bacteria to varying degrees.The improvement in ecosystem multifunctionality was more apparent in the mixture of three functional groups and forbs treatments than in the other treatments.3.Based on the different responses of plant communities,the mechanism study found that the priority effects of different species can lead to diverse overall biomass and overyielding effects by changing the competitiveness of species and resource partitioning in mixed-planting communities.The strength of the priority effects was influenced by the sowing order,root isolation,plant removal,and their interactions.The magnitude of priority effects also depended on the identities of species that were sown early and those that were sown late.This study found that when the species that were sown early and were less competitive had potential advantages during community assembly,particularly owing to a decrease in the cost(biomass loss)incurred by delayed sowing,and there was a higher overall net benefit of the resulting community.4.During the process of restoring abandoned cropland,different species or combinations can lead to varying soil legacy effects,which differ in their degrees of influence on the growth of subsequent community plants and ecosystem multifunctionality.The soil legacy effects were species-specific,and their magnitude and direction were determined by both soil legacies and plant species.The biomass,biodiversity net effect,and functional diversity indices of non-legume plant communities were higher in soil legacies conditioned by multiple species than those of the other soil legacies.Moreover,the diversity of species can compensate for the soil legacy effect mediated by non-legume plants to some extent.The ecosystem multifunctionality was stronger in soil legacies controlled by legumes and the mixture of three functional groups.In conclusion,the community development and ecosystem multifunctionality were significantly limited by the types of species that were added and the priority effects and soil legacy effects during the restoration and succession of abandoned cropland.During the early stage of community construction,the rational use of the synergistic effects of plant-specific soil legacy and functional group richness could be a key to ensure the successful establishment and management of the expected community.According to the restoration objective,the selection of an appropriate combination of species can create a favorable priority effect,which can promote the realization of expected goal.Thus,this study highlights the importance of selecting suitable species or combinations in the restoration of vegetation in the abandoned cropland and fully utilizes the priority effects and the soil legacy effects during the process of adding species to promote the successful construction of community and enhancement of ecosystem multifunctionality.