Effect of stabilized organic amendments on biodegradability of poly-3-hydroxybutyrate, soil biological properties, and plant biomass

Abstract

Poly-3-hydroxybutyrate (P3HB) is a biodegradable polymer with a potential extensive use in agriculture. However, while P3HB biodegradation boosts microbial enzyme activity, it significantly reduces plant biomass due to nutrient competition. In this study, we test the hypothesis that these detrimental effects can be mitigated though the co-application of nutrient-rich organic amendments, such as compost and digestate. A pot experiment with lettuce (Lactuca sativa), grown in soil amended with P3HB lone or combined with either compost or digestate. Six variants were tested: Control, Compost, Compost + P3HB, Digestate, Digestate + P3HB, and P3HB alone. We evaluated degradation of the P3HB polymer, biological soil properties, and both the dry and fresh biomass of the lettuce. We observed that adding P3HB alone enhanced dehydrogenase and urease activities, as well as all types of respiration, except for L-arginine-induced respiration. However, it strongly and negatively affected the biomass of lettuce (both aboveground and root). The strong adverse effects of P3HB on plant growth were also observed when compost was co-applied, although this combination enhanced all enzyme activities except for suppressed β-glucosidase. Conversely, co-applying digestate with P3HB alleviated the negative effect of P3HB on both the dry and fresh biomass together lettuce. Additionally, this combination increased the activity of several enzymes (dehydrogenase, arylsulfatase, N-acetyl-β-D-glucosaminidase, urease), and enhanced all types of respiration, except for L-arginine-induced respiration. The use of biodegradable plastics in agriculture is on rise, but it may be compromised, because their biodegradation my negatively impact plant growth. The results showed that co-application of digestate is an effective solution to alleviate these effects, while co-application of compost failed. Generally, organic amendments seem to be an option to alleviate the negative effects of bioplastics biodegradation, and offers options how to handle the treatment of waste bioplastics or their residues, but further investigation is needed to understand the underlaying mechanisms involved. Graphical Abstract