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Earthworms counteract drought-induced impairment of wheat performance at the jointing stage regardless of microplastic type
Summary
Researchers ran a 120-day microcosm experiment showing that earthworms (Eisenia fetida) significantly offset drought-induced wheat biomass loss at the jointing stage — increasing biomass by 57.5% under drought — regardless of whether conventional polyethylene or biodegradable PLA microplastics were present, with soil nitrate nitrogen and aggregate stability identified as the key mediating pathways.
Increasing frequency and severity of drought events severely constrain wheat production systems across arid and semi-arid landscapes. Plastic film mulching is widely used to mitigate drought in Chinese dryland agriculture, yet its extensive application has caused increasingly prominent microplastic contamination in soils. However, whether and how earthworms, key soil macro-decomposers, alleviate crop stresses from the combination of drought and microplastics remains unclear. Here, we conducted a full-factorial microcosm experiment to disentangle the individual and interactive effects of drought, microplastics, and earthworms on wheat jointing-stage biomass. Drought treatments (ambient 60% soil water-holding capacity vs. extreme 30% soil water-holding capacity) were initiated at wheat sowing and maintained continuously for 120 days with no post-drought recovery. The experiment included three microplastic treatments (no-microplastic control vs. 2.5% w/w non-biodegradable low-density polyethylene vs. 2.5% w/w biodegradable polylactic acid) and two earthworm treatments (absence vs. presence of Eisenia fetida at 2.5% w/w), with partial E. fetida survival observed across all treatments at trial termination. Our results revealed that drought significantly reduced wheat jointing-stage biomass by 8.87 g (65.6%). Biodegradable polylactic acid (PLA) microplastics significantly increased biomass by 1.14 g (13.3%), whereas non-degradable low-density polyethylene (LDPE) microplastics had no significant effect. Earthworms significantly elevated biomass by 4.08 g (57.68%); crucially, they significantly mitigated drought stress, leading to a 2.08 g (57.5%) increase in wheat jointing-stage biomass under drought conditions. Further, structural equation modellings (SEMs) confirmed that drought reduced wheat jointing-stage biomass mainly by direct pathways; these detrimental effects were effectively mitigated by earthworms through increasing soil properties (e.g. soil nitrate nitrogen content, 15.63 mg kg, +131.26%; soil mean weight diameter, 0.34 mm, +5.55%). These findings suggest that soil macrofauna (e.g. earthworms) substantially buffer the adverse effects of global environmental change, enhancing crop performance in arid and semiarid regions. This evidence underscores the potential of harnessing soil biological processes to strengthen resilience of sustainable agricultural systems under global change pressures.