Microbial life-history strategies are linked to stratified accumulation of plant- and microbial-derived carbon during subtropical revegetation

Abstract

Vegetation restoration is a key pathway to enhance soil carbon sinks in degraded ecosystems, but the depth-dependent accumulation patterns of plant- and microbial-derived carbon and their links to microbial life-history strategies remain poorly understood. Using a restoration chronosequence (severely degraded woodland, plantations restored for 5, 20, and 40 years, and a > 100-year undisturbed secondary forest) in a subtropical eroded red soil region, we analyzed lignin phenols (plant-derived carbon, VSC), amino sugars (microbial necromass carbon, MNC), and microbial life-history strategies in topsoil (0–20 cm), subsoil (20–50 cm), and deepsoil (50–100 cm). The results showed that bacterial K -strategist phyla decreased in abundance with restoration but remained dominant across all layers, whereas fungal communities shifted from r -strategy dominance to K -strategy at the UF stage. Long-term vegetation restoration significantly increased soil organic carbon (SOC) and MNC in all soil layers and topsoil VSC, but transient declines occurred in topsoil and subsoil MNC at the early stage (F5). The contribution of plant-derived carbon to SOC (2.78%–33.95%) increased in topsoil but decreased in subsoil overall; the contribution of MNC (2.82%–60.62%) generally increased and became dominant (mainly fungal necromass); both contributions were greater in topsoil. PLS-PM indicated a positive effect of VSC on MNC, and the positive correlation between lignin degradation degree and MNC further suggested that the dominant contribution of MNC is closely linked to the microbial degradation-reassembly of plant-derived carbon. Soil nutrients and microbial properties jointly influenced carbon fraction accumulation, with bacterial life-history strategies positively correlated with carbon fractions, but predictors shifted with depth: topsoil VSC and MNC were dominated by soil physicochemical properties (TN, TP, sand) and Proteobacteria/Acidobacteriota; subsoil MNC shifted to association with microbial biomass and Gemmatimonadota/Acidobacteriota; deepsoil MNC remained primarily associated with soil physicochemical properties and the specific r -strategist Gemmatimonadota. These findings demonstrate that long-term restoration effectively promotes soil carbon sequestration and highlight the depth-specific role of microbial life-history strategies, providing insights for stratified carbon management in eroded red soils.