Spatiotemporal variations of arbuscular mycorrhizal fungal communities and their infective potential with rice in kapok-rice agroforestry systems

Abstract

Agroforestry is increasingly recognized as a vital sustainable land-use strategy. Arbuscular mycorrhizal (AM) trees within these systems modify soil properties and serve as a source of AM fungal inoculum. Kapok (Bombax ceiba L.), a typical AM tree species, is traditionally maintained in tropical rice fields. However, kapok’s influence on AM fungal communities in rice fields, and whether these changes subsequently affect AM colonization of rice roots in kapok-rice agroforestry systems, remain unclear. We collected 96 soil and 64 rice root samples along distance gradients from kapok trees (DK: 1, 3, 6 and 12 m from tree bases) across three stages of rice field (SR: tillering, maturity and fallow) in a representative kapok-rice system on Hainan Island, China. Soil properties, AM fungal spore density, hyphal density, community composition and rice root colonization rates were measured. Results demonstrated that both AM fungal spore density and hyphal density varied significantly with DK and SR, exhibiting higher values proximal to kapok trees and during tillering than maturity. AM fungal community structure was primarily driven by SR rather than DK, with variations explained by associated changes in soil properties (pH, nitrogen, soil organic matter, potassium). SR indirectly affected rice root colonization through mediation of soil properties and AM fungal communities, whereas DK exerted direct effects. Available potassium significantly reduced rice root colonization and inhibited AM fungal activity. In conclusion, kapok trees have potential as AM fungal inoculum sources for rice, though the underlying mechanisms require further investigation in kapok-rice agroforestry systems.