Grass cultivation regulates soil hydrogen cyanide formation in continuously cropped karst peach orchards by modulating precursor biosynthesis via nitrogen availability

Abstract

Aims Orchard grass cultivation is widely used to improve soil conditions and alleviate continuous cropping obstacles, yet its capacity to reduce soil hydrogen cyanide (HCN, an autotoxin in replant orchard soils) and associated mechanisms remain unclear. Methods A field trial was carried out in a degraded continuously cropped peach orchard in the karst mountains of southwest China. Two non-nitrogen-fixing grasses (Dactylis glomerata, Lolium perenne) and the nitrogen-fixing legume Trifolium repens were planted as monocultures and mixtures. We measured soil physicochemical properties, enzyme activities, bacterial and fungal communities, and quantified soil HCN concentrations. Results Monocultures of D. glomerata and L. perenne, plus the three-species mixture, markedly lowered HCN: 90.29%, 62.69% and 81.75% reduction in 0–20 cm topsoil, and 47.67%, 52.93% and 82.83% reduction in 20–40 cm subsoil relative to control. By contrast, white clover monoculture and its two-species mixtures did not reduce topsoil HCN and significantly increased subsoil HCN. PLS-SEM revealed total nitrogen, alkali-hydrolyzable nitrogen, sucrase and alkaline phosphatase as key drivers of HCN accumulation. Effective grass treatments reduced soil nitrogen availability, limiting nitrogen translocation to peach trees and suppressing biosynthesis of HCN precursors in plant tissues, thereby decreasing soil HCN. Conclusions This study highlights species-specific effects of cover crops on autotoxicity mitigation. We recommend monocultures of non-nitrogen-fixing grasses for managing HCN pollution in karst replant peach orchards.

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