Earthworms are known to improve compacted soil structure, water movement, and crop root growth. However, it remains unclear whether these benefits vary among earthworm species because of differences in their burrowing traits. The objective of this study was to determine the effects of three earthworm species on burrow structures, water movement, and the growth of maize roots in compacted red soil, using X‑ray computed tomography (CT) and potassium iodide (KI) tracer techniques. We established soil columns by packing the upper 50 mm of each column to a bulk density of 1.2 g cm−3 and the lower 90 mm to a bulk density of 1.5 g cm−3. The three earthworm species used in this study represent distinct ecological categories: the small epigeic Eisenia fetida (E. fetida), the large anecic Amynthas aspergillum (A. aspergillum), and the medium‑sized endogeic Pheretima guillelmi (P. guillelmi). Owing to its larger size, A. aspergillum formed burrows that penetrated more deeply and had significantly greater volume, surface area, length and diameter than E. fetida and P. guillelmi (P < 0.05). P. guillelmi exhibited the highest burrow connectivity (0.87), followed by A. aspergillum (0.60), whereas E. fetida showed the lowest connectivity. A. aspergillum increased the KI tracer volumes in the compacted subsoil by 167 % and 152 % compared with that in the Control and E. fetida, respectively (P < 0.05). Compared with the Control (no earthworms), all the earthworm treatments increased the rooting depths. The A. aspergillum burrows were most frequently colonized by maize roots, whose intersection volume, surface area, and length were significantly greater than those of P. guillelmi and E. fetida. Interestingly, increased root colonization levels of burrows did not always correspond to enhanced root growth. Compared with the Control treatment, only the E. fetida treatment significantly increased root volume (71 %), surface area (65 %), and length (57 %), whereas the A. aspergillum and P. guillelmi treatments failed to significantly alter these traits. E. fetida produced the smallest burrows (1.47 mm), which matched the maize root diameters (0.84–0.97 mm) better than the larger burrows of A. aspergillum (5.34 mm) and P. guillelmi (3.88 mm), resulting in superior root–soil contact. We conclude that A. aspergillum burrows enhance subsoil water movement and that when burrow structures are consistent with the root sizes, these burrows most effectively promote crop growth. Whether earthworm-mediated nutrient redistribution and drought-induced water uptake from the subsoil by deep roots further stimulate crop growth warrants future investigation.
Alpine grasslands on the Tibetan Plateau (TP) store vast amounts of soil organic carbon (SOC) but are highly sensitive to climate change. Although topography creates distinct microenvironments between slope aspects, its effects on SOC characteristics, mineralization rates, and temperature sensitivity (Q10) remain poorly understood. Here we collected paired soil samples from shady and sunny slopes of an alpine grassland in the Animaqing Mountains on the TP. We found that the shady slope contained substantially higher levels of total SOC and multiple carbon fractions, including mineral-associated organic carbon, heavy particulate organic carbon, and microbial necromass carbon (MNC). Short-range-ordered (SRO) and organically complexed Fe-Al oxides were also enriched on the shady slope relative to the sunny slope. Additionally, the two slopes exhibited pronounced differences in microbial properties, including the abundance and diversity of bacterial and fungal communities. Specifically, bacterial α-diversity was higher on the shady slope, while fungal α-diversity and abundance were higher on the sunny slope, and community composition differed significantly between slopes. A 200-day microcosm incubation experiment showed that soils from the shady slope had significantly lower SOC mineralization rates and Q10 compared to the sunny slope. These reductions were associated with distinct mineral protection modes: SRO Fe-Al oxides restrict substrate accessibility through ligand exchange and physical occlusion, whereas exchangeable Ca2+/Mg2+ stabilize SOC via cation bridging. Crucially, SRO Fe-Al oxides enriched on the shady slope act synergistically with MNC to fortify MAOC sequestration. This demonstrates that substrate availability, rather than intrinsic carbon quality, acts as the dominant controlling factor, overriding thermodynamic ‘carbon quality-temperature’ predictions by physically isolating organic compounds from enzymatic degradation. Moreover, microbial community analyses revealed contrasting roles of bacteria and fungi in regulating SOC mineralization: bacterial and fungal α-diversity were negatively and positively correlated with mineralization rates, respectively, whereas their β-diversity exhibited opposite relationships with Q10. Overall, our findings provide new insights into how topography regulates carbon cycling in alpine grasslands and highlight the importance of incorporating landscape heterogeneity into predictions of soil carbon–climate feedbacks on the TP.
Warming and changing litter inputs jointly influence soil organic carbon dynamics in subalpine and alpine ecosystems, yet the molecular-scale interactions in these soils remain poorly understood. We incubated subalpine pasture and forest mineral soils for 360 days at three temperatures (12.5, 16.5, 20.5 °C), representing the current growing-season temperature and projected end-of-century warming under RCP8.5 in the European Alps, with and without addition of Lolium perenne grass litter, and analysed free extractable lipids as molecular tracers of decomposition. In soils without litter addition, warming alone caused little change and revealed low temperature sensitivity in the native free extractable lipid pool. With litter addition, decomposition of litter-derived lipids was strongly temperature dependent during the early incubation phase (first weeks to months, 0–56 days), but this temperature effect weakened and largely disappeared during the remainder of the 360-day incubation. Pasture soils showed faster early decomposition of litter-derived lipids than forest soils, indicating an effect of land cover history. A biomarker-based inverse model (VERHIB, Vegetation Reconstruction with the Help of Inverse Modelling and Biomarkers) estimated a strong early decline of litter-derived lipids (decreases of up to ∼80%) and a partial convergence of remaining litter-derived fractions in all temperatures after one year. Our findings demonstrate that fresh litter availability and land cover history, rather than temperature alone, control molecular-level decomposition of soil organic carbon in these subalpine soils, underscoring the importance of vegetation-driven inputs for predicting soil carbon responses to climate warming.
The origin of the common very fine granular structure of Ferralsols remains debated, particularly the processes responsible for its development and long-term maintenance throughout thick tropical soils. We investigated a 14m-deep Ferralsol developed under native Cerrado vegetation using an integrated approach combining detailed field observations, scanning electron microscopy, mercury intrusion porosimetry and soil chemical and physical analyses. The degree of development of the very fine granular structure progressively decreased with depth. The upper part of the profile was dominated by loose- and close-packed granular groundmasses associated with low bulk density and high macroporosity, whereas deeper horizons progressively evolved towards a compact and continuous groundmass. Nevertheless, the very fine granular structure remained clearly expressed within biological galleries and chambers. These structural changes were consistently reflected in the evolution of bulk density, pore-size distribution and the size distribution of soil structural units. The observations reported here provide multiple independent lines of evidence consistent with a mechanism in which deep burrowing by social insects fragments and redistributes the soil groundmass, followed by progressive gravitational compaction. In the studied Ferralsol, active burrowing by Nasutitermes corniger was directly observed at depths exceeding 12 m, demonstrating that this species contributes to the process, while not excluding contribution from other termite species or even ants. Our results therefore suggest that the characteristic very fine granular structure of Ferralsols represents a depth-dependent dynamic structural state maintained by the interaction between deep bioturbation by social insects and the progressive loading imposed by the overlying soil.
High-throughput ITS metabarcoding is the dominant approach for characterizing soil fungal communities and inferring their functional roles. However, metabolically inactive fungal spores accumulate in soil and may distort these community profiles. We tested this by adding spores of a saprotrophic (Agaricus sp.) and an ectomycorrhizal (Hebeloma sp.) species to a single homogenized soil at five doses (0.015–1.5 mg g−1 dry soil, approximately 105-107 spores g−1). Spore-derived reads increased monotonically with dose, from 5 to 7% at the lowest dose to 71–87% at the highest, and exceeded the biomass-based expectation at every dose. Expressed as a scale-free enrichment, spore material yielded approximately six-fold (Agaricus sp.) and three-fold (Hebeloma sp.) more ITS reads per unit dry mass than the resident soil fungal community, with no trend across the dose gradient. Ergosterol, a proxy for active fungal biomass, showed no significant response to spore dose. Spores can therefore substantially distort ITS community profiles without reflecting active fungal biomass or community function.
