Rhizosphere microbial activities in response to combined effects of drought and microplastic 

The human’s well-being is challenged by various global issues such as environmental pollution and climate change. While plastic waste, particularly microplastic, is an emerging environmental pollution, drought becomes a more frequent natural hazard to cropping system. Two hypotheses were proposed in this research as (i) drought is more dominated as compared to microplastic existence regulating microbial activities; (ii) the effects of microplastic on enzyme activities and distribution are enzyme specific and depends on microplastic types. Zymography was acquired to demonstrate the distribution of β-glucosidase (GLU) and acid phosphatase (APT) within soybean rhizosphere amended with either biodegradable microplastics or nondegradable microplastics. In addition, enzyme activities of GLU, APT, leucine aminopeptidase (LEU), and microbial biomass phosphorus (MBP) were assayed to prove the hypotheses. Five-time lower hotspot percentage in dry soil than moist soil regardless of microplastic types implied an overwhelming impacts of water stress as compared to microplastics on the microbial degradation of soil organic matter in the plant-soil ecosystem. A shortened rhizosphere extent was found in microplastic treatments also demonstrated its negative influence on rooted microbial activities. In conclusion, the co-influence of two distinguished abiotic factors should increase the complexity of plant-microbe association and unpredicted regulation of nutrient and C flux in the crop land. Keywords: rhizosphere, enzyme activities, microbial biomass, drought, zymography