Unraveling consequences of the co-exposure of polyethylene microplastics and acid rain on plant-microbe-soil system

Emerging microplastics (MPs) pollution and continuing acid rain (AR) co-exist in terrestrial ecosystems, and are considered as threats to ecosystems health. However, few data are available on MPs-AR interactions in plant -microbe-soil systems. Here, a microcosm experiment was manipulated to elucidate the co-exposure of poly-ethylene MPs (PE MPs; 1%, 5% and 10%) and AR (pH 4.0) on soil-lettuce system, in which the properties of soil and lettuce, and their links were explored. We found that 10% PE MPs increased soil CO2 emission and its temperature sensitivity (Q(10)) in combination with AR, while 1% PE MPs reduced soil CO(2 )emission irrespective of AR. PE MPs addition did not influence lettuce production (total biomass) though its photosynthesis was affected. PE MPs exerted negative impact on soil water availability. PE MPs treatments increased NH4+-N content of soil without AR, and dissolved organic carbon content of soil sprayed with AR. 10% PE MPs combined with AR reduced soil microbial biomass, while soil microbial community diversity was not affected by PE MPs or AR. Interestingly, 10% PE MPs addition altered soil microbial community structure, and promoted the complexity and connectivity of soil microbial networks. 5% and 10% PE MPs addition decreased soil urease activity under AR, but this was not the case without AR. These findings highlight the critical role of AR in regulating PE MPs impacts on plant-microbe-soil ecosystems, and the necessity to incorporate other environmental factors when evaluating the actual impacts or risks of MPs pollution in terrestrial ecosystems.

Automated summary

This study investigated the interactions between microplastics (MPs) pollution and acid rain (AR) in plant-microbe-soil systems. The results showed that 10% poly-ethylene MPs (PE MPs) combined with AR increased soil CO2 emission, while 1% PE MPs reduced soil CO2 emission. The addition of PE MPs did not affect lettuce production, but it did affect the photosynthesis of lettuce. PE MPs also had a negative impact on soil water availability. Addition of PE MPs increased NH4+-N content of soil without AR, and dissolved organic carbon content of soil with AR. Interestingly, 10% PE MPs altered the soil microbial community structure and promoted the complexity and connectivity of soil microbial networks. However, the addition of 5% and 10% PE MPs decreased soil urease activity under AR. These findings highlight the importance of considering AR when evaluating the actual impacts or risks of MPs pollution in terrestrial ecosystems.