{
  "abstract": "Reforestation is a leading natural climate solution, but bulk soil organic carbon (C) often responds slowly, obscuring early belowground change. We tested whether soil aggregates reveal early structural reorganization that affects C retention pathways at a three-year-old experimental reforestation planting established on former pasture in Oregon, USA. We sampled soils at 0-20 and 20-40 cm beneath incense cedar (Calocedrus decurrens; arbuscular mycorrhizal [AM]), black cottonwood (Populus trichocarpa; AM and ectomycorrhizal [EcM]), ponderosa pine (Pinus ponderosa; EcM), and treeless controls. We measured bulk soil C concentration and C:N, aggregate size distribution and mean weight diameter (MWD), fraction-associated C, and, in a subset of surface aggregate fractions, natural-abundance {delta}13C to evaluate soil C pools, physical structure, C distribution, and C processing. After three years, reforestation did not produce significant differences in bulk soil C between planted trees and treeless controls. In surface soil, MWD averaged 36% higher under incense cedar and 58% higher under black cottonwood than under controls, whereas ponderosa pine remained similar to controls. The clearest treatment differences in C distribution occurred in macroaggregates. Incense cedar and black cottonwood had higher large (>2000 m) macroaggregate-associated C than controls, while black cottonwood combined a greater proportion of large macroaggregates with lower C concentrations, indicating that structural development and C accumulation were partly decoupled. Species patterns were broadly consistent with stronger early aggregate responses under AM-compatible species in former-pasture legacy conditions; by contrast, the EcM-associated ponderosa pine remained closer to treeless controls across multiple aggregate measures. Treatment effects weakened with depth and were limited in microaggregates (250-53 m) and silt-and-clay (<53 m) fractions. Smaller aggregate fractions were progressively enriched in {delta}13C, consistent with greater C processing in protected fractions, but treatment-level isotope differences had not yet emerged. Soil aggregates showed species-associated belowground reorganization, revealing how tree identity and former-pasture legacy may shape early soil C organization before consistent differences emerged in bulk soil C. Aggregate measures can complement bulk soil C measurements in restoration monitoring as early indicators of belowground soil C trajectories shaped by tree species identity and land-use legacy.",
  "abstract_shown": true,
  "affiliations": [
    "University of Oregon"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "C. E. Mathers"
    },
    {
      "name": "H. R. Dawson"
    },
    {
      "name": "E. Huckstead"
    },
    {
      "name": "L. C. R. Silva"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fc234d4vwd6aj.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.09.22.753307",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.09.22.753307v1.full",
  "id": "fc234d4vwd6aj",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.09.22.753307v1",
  "language": null,
  "licence": "CC-BY-NC-ND",
  "licence_label": "CC BY-NC-ND",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "biorxiv",
      "ecology"
    ],
    [
      "openalex",
      "1111|Soil Carbon and Nitrogen Dynamics"
    ]
  ],
  "openalex": "W7214111233",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.09.22.753307v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-22",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fc234d4vwd6aj.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:06Z",
      "native_id": "10.64898/2026.09.22.753307",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.09.22.753307v1"
    }
  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "biorxiv:ecology",
      "subfield": "ecology"
    }
  ],
  "title": "Soil aggregates reveal tree species and land-use legacy effects on early carbon storage pathways during reforestation",
  "title_text": "Soil aggregates reveal tree species and land-use legacy effects on early carbon storage pathways during reforestation",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:06Z",
  "url": "https://research.draconitic.com/paper/fc234d4vwd6aj",
  "venue": "bioRxiv",
  "versions": []
}