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<p>Continuous cropping severely limits the sustainable production of watermelon (<i>Citrullus lanatus</i> L.) by inducing soil degradation, yet the mechanisms of microbial succession and interaction remain unclear. We monitored rhizosphere soils across 11 consecutive cropping seasons in a greenhouse pot experiment to evaluate the impact on bacterial and fungal communities. Available nitrogen, available potassium, total carbon, and total nitrogen declined with cropping duration, whereas available phosphorus showed a hump-shaped pattern. Soil pH reached a minimum in the seventh season, and soil enzyme activities increased markedly from the fifth season. Quantitative Real-time PCR (qPCR) and amplicon sequencing showed sustained rises in bacterial abundance, while fungal abundance initially decreased before recovering. Bacterial Shannon diversity hit a nadir in the fifth season with subsequent partial recovery, whereas fungal diversity continuously declined. Principal coordinate analysis (PCoA) revealed abrupt community shifts in both domains at the fifth season. Co-occurrence networks simplified sharply thereafter, with bacterial network complexity strongly negatively correlated with enriched <i>Bacillus</i> abundance (R² = 0.91). Structural equation modeling indicated that soil chemical changes and reduced fungal diversity were associated with increased <i>Fusarium</i>, whereas <i>Bacillus</i> enrichment did not suppress <i>Fusarium</i>. Sterilized soil bioassays confirmed that biotic factors induced broad-spectrum growth inhibition in both watermelon and tomato, suggesting broader microbial community imbalance. These results identify the fifth season as a critical threshold for <i>Fusarium</i> enrichment and network simplification, highlighting an actionable time window for early interventions to restore microbial functions before dysbiosis becomes entrenched.</p>

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Dynamics of soil health and microbial interactivity during 11 seasons of watermelon cropping: identifying the critical threshold for dysbiosis

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Wei Fang,
  • Yingyu Zhang,
  • Chenfei Liang,
  • Shuai Shao,
  • Junhui Chen,
  • Hua Qin,
  • Qiufang Xu,
  • Tongxing Wu

摘要

Continuous cropping severely limits the sustainable production of watermelon (Citrullus lanatus L.) by inducing soil degradation, yet the mechanisms of microbial succession and interaction remain unclear. We monitored rhizosphere soils across 11 consecutive cropping seasons in a greenhouse pot experiment to evaluate the impact on bacterial and fungal communities. Available nitrogen, available potassium, total carbon, and total nitrogen declined with cropping duration, whereas available phosphorus showed a hump-shaped pattern. Soil pH reached a minimum in the seventh season, and soil enzyme activities increased markedly from the fifth season. Quantitative Real-time PCR (qPCR) and amplicon sequencing showed sustained rises in bacterial abundance, while fungal abundance initially decreased before recovering. Bacterial Shannon diversity hit a nadir in the fifth season with subsequent partial recovery, whereas fungal diversity continuously declined. Principal coordinate analysis (PCoA) revealed abrupt community shifts in both domains at the fifth season. Co-occurrence networks simplified sharply thereafter, with bacterial network complexity strongly negatively correlated with enriched Bacillus abundance (R² = 0.91). Structural equation modeling indicated that soil chemical changes and reduced fungal diversity were associated with increased Fusarium, whereas Bacillus enrichment did not suppress Fusarium. Sterilized soil bioassays confirmed that biotic factors induced broad-spectrum growth inhibition in both watermelon and tomato, suggesting broader microbial community imbalance. These results identify the fifth season as a critical threshold for Fusarium enrichment and network simplification, highlighting an actionable time window for early interventions to restore microbial functions before dysbiosis becomes entrenched.