Data for: Cover crop functional types differentially alter the content and composition of soil organic carbon in particulate and mineral-associated fractions

Cover crops (CCs) can increase soil organic carbon (SOC) sequestration by
providing additional OC residues, recruiting beneficial soil microbiota,
and improving soil aggregation and structure. The various CC species that
belong to distinct plant functional types (PFTs) may differentially impact
SOC formation and stabilization. Biogeochemical theory suggests that
selection of PFTs with distinct litter quality (C:N ratio) should
influence the pathways and magnitude of SOC sequestration. Yet, we lack
knowledge on the effect of CCs from different PFTs on the quantity and
composition of physiochemical pools of SOC. We sampled soils under
monocultures of three CC PFTs (legume [crimson clover]; grass [triticale];
and brassica [canola]) and a mixture of these three species, from a
long-term CC experiment in Pennsylvania, USA. We measured C content in
bulk soil and C content and composition in contrasting physical fractions:
particulate organic matter, POM; and mineral-associated organic matter,
MAOM. The bulk SOC content was higher in all CC treatments compared to the
fallow. Compared to the legume, monocultures of grass and brassica with
lower litter quality (wider C:N) had higher proportion of plant-derived C
in POM, indicating selective preservation of complex structural plant
compounds. In contrast, soils under legumes had greater accumulation of
microbial-derived C in MAOM. Our results for the first time, revealed that
the mixture contributed to a higher concentration of plant-derived
compounds in POM relative to the legume, and a greater accumulation of
microbial-derived C in MAOM compared to monocultures of grass and
brassica. Mixtures with all three PFTs can thus increase the short- and
long-term SOC persistence balancing the contrasting effects on the
chemistries in POM and MAOM imposed by monoculture CC PFTs. Thus, despite
different cumulative C inputs in CC treatments from different PFTs, the
total SOC stocks did not vary between CC PFTs, rather PFTs impacted
whether C accumulated in POM or MAOM fractions. This highlights that CCs
of different PFTs may shift the dominant SOC formation pathways (POM vs.
MAOM), subsequently impacting short- and long-term SOC stabilization and
stocks. Our work provides a strong applied field test of biogeochemical
theory linking litter quality to pathways of C accrual in soil.