The Impact of Litter from Different Belowground Organs of Phragmites australis on Microbial-Mediated Soil Organic Carbon Accumulation in a Lacustrine Wetland

Abstract

Although belowground litter decomposition critically influences lacustrine wetland soil carbon dynamics, the organ-specific microbial mechanisms driving soil organic carbon (SOC) accumulation remain unclear. Existing research has predominantly focused on aboveground litter, leaving a significant gap in the understanding of how roots and rhizomes differentially regulate carbon cycling through microbial community assembly and survival strategies. This study took Phragmites australis (a plant characteristic of lacustrine wetland) as the research object and examined how decomposing belowground litter from different organs affects microbial-mediated SOC accumulation through a one-year in situ field incubation in Jingyuetan National Forest Park, Changchun City, Jilin Province, China. Our findings reveal that root litter exhibited the highest decomposition rate, which was accelerated by intermittent flooding, reaching up to 1.86 times that of rhizome. This process enriched r-strategist microbial taxa, intensified homogeneous selection, and expanded niche width, directly promoting SOC accumulation. Rhizome litter decomposition enhanced dispersal limitation, promoted K-strategist microbial dominance, and indirectly modulated SOC through soil acidification. Mixed-litter treatments significantly enhanced SOC accumulation (up to three times higher than single-litter treatments) through synergistic nutrient release (non-additive effects < 0.04) and reinforced microbial network interactions. SOC accumulation varied significantly with the flooding regime as follows: non-flooded > intermittent flooding > permanent flooding. This study provides new insights into the microbially driven mechanisms of plant-organ-specific decomposition in the carbon cycling of wetland ecosystems.

Keywords: belowground plant litter; community assembly; soil microorganisms; soil organic carbon; survival strategies.

Figure 1

Maps of the sample plot in Jingyuetan National Forest Park in Changchun City, Jilin Province.

Figure 2

Non-additive effects of mixed litter. (a) Litter C nutrients remaining, (b) litter N nutrients remaining. LO indicates non-flooded, ME indicates intermittently flooded, and HI indicates permanently flooded. The standard error is used to represent the error bar in the figure.

Figure 3

Changes in soil (a) T PLFA (total microbial biomass), (b) B PLFA (bacterial microbial biomass), and (c) F PLFA (fungal microbial biomass) under different flooding conditions after litter decomposition. LO indicates non-flooded, ME indicates intermittently flooded, HI indicates permanently flooded, CK represents the blank control without adding litter, L represents rhizomes, LR represents roots, and M represents a mixture of the two. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 4

Soil microbial characteristics after litter decomposition under different flooding conditions: (a) bacterial and (b) fungal community relative abundance; α-diversity differences in (c,e) bacteria and (d,f) fungi across flooding conditions and litter addition methods. PCoA analysis based on Bray–Curtis distance showing (g) bacterial and (h) fungal community composition under varying flooding conditions and litter addition methods. LO indicates non-flooded, ME indicates intermittently flooded, HI indicates permanently flooded, CK represents the blank control without adding litter, L represents rhizomes, LR represents roots, and M represents a mixture of the two. * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 5

Soil microbial network analysis after different litter decomposition treatments: (a–d) bacterial and (e–h) fungal communities. (a,e) Control (no litter), (b,f) rhizome litter, (c,g) root litter, and (d,h) mixed litter treatments.

Figure 6

Neutral community model (NCM) analysis of soil (a–d) bacterial and (e–h) fungal communities following different litter decomposition treatments: (a,e) control (no litter), (b,f) rhizome litter, (c,g) root litter, and (d,h) mixed litter treatments. The solid blue line represents the best-fit values of the neutral community model, the dashed blue line represents the 95% confidence interval of the model (estimated through 999 bootstraps), and OTUs with occurrence frequencies higher or lower than predicted by the neutral community model are displayed in different colors.

Figure 7

Community assembly characteristics of bacteria and fungi after litter decomposition. Niche breadth of (a) bacteria and (b) fungi; βNTI distributions of (c) bacterial and (d) fungal communities; proportional contributions of assembly processes for (e) bacterial and (f) fungal communities. CK represents the blank control without adding litter, L represents rhizomes, LR represents roots, and M represents a mixture of the two. * p < 0.05, ** p < 0.01, **** p < 0.0001.

Figure 8

Direct and indirect relationships between litter decomposition dynamics (a) rhizome, (b) root, (c) mixed) and soil microbial biomass, community composition, assembly processes, niche breadth, physicochemical properties, and organic carbon. Standardized effects in SEM for (d) rhizome, (e) root, and (f) mixed litter. Red and black solid lines indicate significant negative and positive relationships, respectively; dashed lines denote non-significant path coefficients. Numbers adjacent to arrows represent standardized path coefficients, with arrow width corresponding to effect size.