Effects of polyethylene microplastics with different particle sizes on photosynthesis，biomass and root characteristics of maize seedlings

Objective With increasing plastic pollution，microplastics have become an important issue in the global environment.Understanding the effects of microplastics on plant growth can help to assess the potential threat of plastic pollution to agro-ecosystems，especially its long-term effects on crop growth and agricultural production.This study was conducted to investigate the effects of polyethylene（PE）microplastics of different particle sizes on the growth of maize（variety：Zhengdan 958）seedlings. Method Through soil pot experiment，the control group（CK），small particle size（13 μm，M1）and large particle size（150 μm，M2）PE microplastic treatment group were set up，and the microplastic mass concentration was 5%.The plant height，leaf area，chlorophyll content（SPAD），biomass accumulation，root traits and plant health index（PHI）of maize were measured to comprehensively evaluate the effects of microplastics on crop growth. Result The results showed that the SPAD values of maize seedlings were significantly reduced by 11.52%（P<0.05）under the treatment of small-sized microplastic（P<0.05）.Although M1 and M2 did not significantly change plant height and leaf area，they both contributed to biomass accumulation，which showed that the biomass of organs in maize seedlings showed a trend of M1>M2>CK（P>0.05）.The enhancing effect of M1 on the total root length，root volume，and root surface area was particularly significant，with increases of 148.87%，175.78%，and 104.29% respectively（P<0.05）.M1 significantly increased the PHI of maize seedlings by 50.43%（P<0.05）compared with CK，indicating that small-sized microplastics have a positive effect on the growth and health of maize seedlings.The results of principal component analysis（PCA）showed that both M1 and M2 samples were significantly separated from CK，indicating that the two microplastic treatments significantly affected the growth of maize seedlings.In addition，the plant height，leaf area，biomass of each organ，total root length，root volume and root surface area were the important driving factors affecting the growth of maize seedlings with different particle sizes of microplastics. Conclusion In summary，the results of this study showed that polyethylene microplastics with different particle sizes had significant effects on the growth of maize seedlings，and the effect of small particle size was stronger than that of large particle size.In the future，the cumulative effects of long-term exposure to microplastics on soil health and plant growth should be considered in order to better assess the full impact of microplastic pollution on agroecosystems.