The Effects Of Different Microplastics And Plant Species Compositions On Ecosystem Multifunctionality Of Wetlands

Microplastics are considered to be an emerging class of pollutants that pose a great threat to terrestrial ecosystem and have received widespread attention.Species composition is one of the important community attributes and has been shown to have an important impact on ecosystem multifunctionality.The Yellow River Delta is one of the important coastal wetlands in China with high ecological value,but due to the sensitive ecological environment,ecosystem multifunctionality in the wetlands of the Yellow River Delta may be more vulnerable to microplastic pollutions and species compositions.In this paper,greenhouse experiments were conducted with two microplastic types(polyethylene and polystyrene),two microplastic concentrations(0.15 g kg-1 and 0.5 g kg-1),and five community combinations composed of different species(the species compositions of the communities were Phragmites australis+Cynanchum chinense+Glycine soja,P.australis+C.chinense+Setaria viridis,P.australis+C.chinense+Artemisia capillaris,P.australis+ C.chinense+Suaeda glauca,and P.australis+C.chinense+Limonium sinensis,respectively),and the effects of different types and concentrations of microplastics and plant species compositions on ecosystem functions(plant productivity,soil microbial activity,and soil nutrient content)and multifunctionality were investigated.The main results are as follows:Compared to the control,total plant productivity was reduced by 19%under the low concentration of polystyrene treatment,and belowground productivity was reduced by 20%and 22%under the low concentration of polyethylene and low concentration of polystyrene treatments,respectively,where microplastics reduced plant productivity by inhibiting the growth of plant roots.Compared to the control,β-glucosaminidase was reduced by 50%,33%,and 39%under the low concentration and high concentration of polystyrene and low concentration of polyethylene treatments,respectively,while phosphatase increased by 177%,180%,and 169%under these three treatments,respectively.Microplastics decreased the nitrogen requirement of the microbial community,but increased its phosphorus requirement,thus altering the soil enzyme activities.Compared to the control,soil total nitrogen content was reduced by 14%,17%,and 9%in the low concentration and high concentration of polystyrene and high concentration of polyethylene treatments,respectively,and ammonium content was reduced by 71%,68%,and 56%in the low concentration and high concentration of polystyrene and low concentration of polyethylene treatments,respectively,and soil total phosphorus content was reduced by 21%in the high concentration of polystyrene treatment.Therefore,microplastics decreased soil nutrient content.Ecosystem multifunctionality calculated based on the average approach and the threshold approach was significantly inhibited under multiple microplastic treatments,indicating the potential damage of microplastics on ecosystem multifunctionality,and emphasizing the need to manage microplastic pollutions to maintain higher levels of ecosystem multifunctionality.In the control without microplastic addition,plant productivity was higher in the S.salsa and G.soja subdominant species communities than in the other communities.The soil total nitrogen content,β-glucosidase and phosphatase were significantly higher in the G.soja subdominant species community than in the other communities,but β-glucosaminidase was lower.The higher nitrogen fixation capacity of G.soja improved soil nitrogen content,alleviated soil nitrogen limitation,and reduced nitrogen requirement of microbial communities,hence decreased β-glucosaminidase,but the carbon and phosphorus requirement of the microbial community became relatively higher,resulting in higher β-glucosidase and phosphatase.In addition,multifunctionality of the G.soja subdominant species community was significantly higher than that of the other communities,indicating that G.soja was more conducive to maintaining higher levels of ecosystem multifunctionality than the other subdominant species.Compared to the control,total plant productivity and aboveground productivity of the G.soja subdominant species community were reduced by 27%and 29%in the high concentration of polyethylene treatment,respectively,and by 38%,28%,38%,and 28%in the low concentration and high concentration of polystyrene treatments for the S.salsa subdominant species community,respectively.These two communities had better plant growth and stronger adsorption of microplastics,resulting in higher negative effects of microplastics on plants and reduced plant productivity.Compared to the control β-glucosidase of the G.soja subdominant species community was reduced by 43%in the high concentration of polyethylene treatment,and β-glucosidase of the S.salsa subdominant species community was reduced by 33%in the low concentration of polyethylene treatment.Compared to the control,soil organic carbon content of the S.salsa subdominant species community increased by 26%in the low concentration of polyethylene treatment.By inhibiting the growth of plants in both communities,microplastics slowed the decomposition of soil organic matter,increased soil organic carbon content,and reduced the carbon requirement of the microbial community,thereby decreasingβ-glucosidase.Microplastics reduced the multifunctionality of the G.soja subdominant species community,but increased the multifunctionality of the S.salsa subdominant species community,which was related to the weaker stress resistance of G.soja and the stronger stress resistance of S.salsa,indicating that S.salsa are more conducive to maintaining and restoring ecosystem multifunctionality under microplastic stress conditions.In this study,the effects of different types and concentrations of microplastics and plant species compositions on plant productivity,nutrient cycling and ecosystem multifunctionality of wetlands were analyzed,and the influence mechanisms of microplastics and species compositions on ecosystem multifunctionality of wetlands was revealed,thus providing a theoretical reference for the maintenance and restoration of ecosystem multifunctionality in the wetlands of the Yellow River Delta.