Data from: Microplastic biodegradability does not modify plant carbon input in soil but accelerate soil carbon loss in agroecosystems

Microplastics (MPs) are emerging contaminants that disrupt terrestrial
carbon (C) cycling, yet how their biodegradability modulates the turnover
of plant-derived C remains unclear. Here, we investigated how two widely
used MPs—non-biodegradable polyethylene (PE) and biodegradable polylactic
acid (PLA)—affected the fate of photosynthetically fixed C in dryland
agroecosystem. The goal was to explore how MPs influenced C fluxes across
soil-plant-atmosphere continuum (SPAC) and assess their implications on
climate change. We conducted a two-year field experiment to evaluate how
PE and PLA-based MPs affected plant photosynthetic C fixation and its
subsequent turnover in soil. Using 13CO2 pulse-labeling, we traced the
flow of photosynthetically fixed C across the SPAC under low, medium and
high MPs concentrations. We quantified: (i) 13C distribution in plant
shoots, roots, and bulk soil; (ii) 13C allocation among soil aggregate
size fractions; and (iii) microbial EEAs, CAZy gene abundance, and soil
respiration dynamics. Soil C sink capacity tended to decline for both MPs
types, as cumulative soil CO2 emissions increased. On average, 13C
retained in soil decreased from 50.8 to 41.1 mg m-2 in MPs treatments,
relative to the control. Interestingly, the underlying mechanisms differed
from MP types. Non-biodegradable PE-MPs weakened soil aggregation and
reduced 13C retention in macro-aggregates. However, biodegradable PLA-MPs
generated marginal effects on aggregation, and enhanced the activity of
microbial hydrolase, which negatively affected C retention. Moreover,
metagenomics confirmed that PLA-MPs enhanced microbial decomposition
capacity by enriching C degradation and energy metabolism genes. Finally,
photosynthetic C assimilation remained unchanged with increasing MPs
concentrations, regardless of MPs types. Synthesis and applications. Both
MP types can evidently impair soil C pools and differentially alter soil C
cycling via the biodegradation-dependent mechanisms. These findings
challenge the widely held assumption that biodegradable MPs are inherently
environmentally benign, as their presence in soils undermines C storage
capacity. The findings offer insights into future applications as: 1) to
phase down the increment and stock of soil MPs, in favour of truly green
alternatives of plastic mulching; 2) to update the estimation methods of
soil C emission in global terrestrial ecosystems considering the presence
of soil MPs.