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Biochar and microplastics interactively modulate morpho-physiology and growth of maize under soil drying-rewetting cycles
Summary
A factorial microcosm experiment found that polyethylene and polypropylene microplastics interacted with biochar soil amendments to alter maize water-use efficiency, leaf physiology, and root architecture, with effects varying by biochar pyrolysis temperature, microplastic polymer type, and irrigation regime. The findings caution that microplastic contamination can undermine the intended benefits of biochar as a soil amendment, with implications for agricultural productivity in microplastic-polluted soils.
Biochar (BC) is a desirable soil amendment to eliminate chemical pollutants, improve soil moisture and support plant growth. Microplastics (MPs) on the other hand are emerging contaminants deposited uncontrollably in the soils and altering their properties. The interplay between BC and MPs, and the underlying mechanisms of interaction and their effects on plant growth remain largely elusive. This full-factorial microcosm study investigated morpho-physiology and growth responses of maize cultivated in pots with added maize-straw BC pyrolyzed at either 450 (LTBC) or 800 ℃ (HTBC), with polyethylene (PE-MPs) and polypropylene MPs (PP-MPs), given either full irrigation (FI) or soil drying-rewetting cycles (DRC). Compared to no BC added, LTBC significantly reduced leaf photosynthetic performance, but improved soil water-holding capacity (WHC) and leaf growth and water status. These improvements decreased by PE-MPs, despite enhanced specific leaf area and increased instantaneous water use efficiency (WUE); whereas the responses were inconsistent under HTBC and PP-MPs. Interestingly, under DRC, PE-MPs increased total dry matter, leaf and plant WUE. Compared to the controls, the plants under LTBC with PE-MPs engaged in a resource acquisitive strategy by increasing specific root length, but HTBC with PP-MPs increased root tissue density to allow plant invest less resources, particularly under DRC. Collectively, LTBC showed significant potential to improve maize grown on soils with PE-MPs, whereas HTBC showed adverse effect, especially on PP-MPs added soils. These findings warrant further study in controlling MPs-based emerging soil contaminants.