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Background <p>Agroforestry integrates trees with crops to leverage biochemical processes for improved nutrient cycling and sustainable agricultural production. Understanding of the nitrogen (N) dynamics is fundamental to accurately determine the role of agroforestry systems and their potential contributions to socio-environmental benefits. This study investigates the spatiotemporal biochemical dynamics of soil N cycling in a traditional kapok <i>(Bombax ceiba)</i>–rice agroforestry system in western Hainan, China, focusing on tree-induced effects on microbial pathways and nutrient availability. We assessed soil properties, soil microbial biomass carbon (SMBC) and nitrogen (SMBN), N-acquiring enzyme activities leucine-aminopeptidase (LAP) and N-Acetyl-β-D-glucosaminidase (NAG), bacterial/fungal communities, and net N mineralization (No) along a three distance gradient from kapok trees and across five rice growth stages.</p> Results <p>The results revealed significantly elevated soil nutrient availability, SMBC (397.97&#xa0;mg&#xa0;kg⁻<sup>1</sup>), SMBN (131.56&#xa0;mg&#xa0;kg⁻<sup>1</sup>), and enzyme activities (LAP: 88.68&#xa0;μmol&#xa0;h⁻1&#xa0;g⁻1; NAG: 24.88&#xa0;μmol&#xa0;h⁻1&#xa0;g⁻1) at the maturity stage and closest to trees (D0). A 90-day incubation demonstrated highest net N mineralization potential (N<sub>o</sub>: 63.15&#xa0;mg&#xa0;kg⁻1) and mineralization rate constant (k) at maturity near trees (D0), well-fitted by a pseudo-first-order model (R2 = 0.95–0.99). Both tree proximity and rice reproductive stages significantly influenced microbial alpha diversity. Soil properties emerged as the strongest direct predictor of net N mineralization (R2 = 0.42), with microbial biomass and enzyme activities acting as key indirect pathways.</p> Conclusions <p>These findings indicate that kapok trees enhance N availability by creating localized hotspots of microbial activity and enzyme production, thereby improving soil N cycling and supporting sustainable rice production in tropical systems.</p> Graphical abstract <p></p>

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Kapok tree–induced biochemical hotspots regulate microbial nitrogen cycling and mineralization in tropical kapok–rice agroforestry soils

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月24日

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  • Sehrish Ali,
  • Wen-Qian Xiang,
  • Waqas Ahmed,
  • Avelino Núñez-Delgado,
  • Muhammad Qaisar Naeem Khan,
  • Ming-Xun Ren

摘要

Background

Agroforestry integrates trees with crops to leverage biochemical processes for improved nutrient cycling and sustainable agricultural production. Understanding of the nitrogen (N) dynamics is fundamental to accurately determine the role of agroforestry systems and their potential contributions to socio-environmental benefits. This study investigates the spatiotemporal biochemical dynamics of soil N cycling in a traditional kapok (Bombax ceiba)–rice agroforestry system in western Hainan, China, focusing on tree-induced effects on microbial pathways and nutrient availability. We assessed soil properties, soil microbial biomass carbon (SMBC) and nitrogen (SMBN), N-acquiring enzyme activities leucine-aminopeptidase (LAP) and N-Acetyl-β-D-glucosaminidase (NAG), bacterial/fungal communities, and net N mineralization (No) along a three distance gradient from kapok trees and across five rice growth stages.

Results

The results revealed significantly elevated soil nutrient availability, SMBC (397.97 mg kg⁻1), SMBN (131.56 mg kg⁻1), and enzyme activities (LAP: 88.68 μmol h⁻1 g⁻1; NAG: 24.88 μmol h⁻1 g⁻1) at the maturity stage and closest to trees (D0). A 90-day incubation demonstrated highest net N mineralization potential (No: 63.15 mg kg⁻1) and mineralization rate constant (k) at maturity near trees (D0), well-fitted by a pseudo-first-order model (R2 = 0.95–0.99). Both tree proximity and rice reproductive stages significantly influenced microbial alpha diversity. Soil properties emerged as the strongest direct predictor of net N mineralization (R2 = 0.42), with microbial biomass and enzyme activities acting as key indirect pathways.

Conclusions

These findings indicate that kapok trees enhance N availability by creating localized hotspots of microbial activity and enzyme production, thereby improving soil N cycling and supporting sustainable rice production in tropical systems.

Graphical abstract