Root zone infiltration irrigation affects plastic root developmental traits of fruit trees and root zone habitat in saline-alkali soil

Studying how fruit tree roots respond in saline-alkali soil to root architecture and habitat is critical for understanding water and nutrient cycling in these ecosystems. Irrigation is a essential farming practice that improves the root zone environment and root structural configurations. Analyzing shifts in root zone conditions induced by root zone infiltration irrigation and trade-offs in root system architecture is important for improving sustainable agricultural production practices. We conducted a two-year field experiment in a pear orchard with saline-alkali soil in the arid Korla region of Xinjiang, China. Different irrigation quotas (375, 525, and 675 mm) and infiltration tube burial depths (20, 30, and 40 cm) were used to investigate the responses of root zone soil physicochemical properties, enzyme activities, nutrient availability, bacterial community alpha diversity, and root geometric/spatial architecture to root zone infiltration irrigation (RZII). The results found that higher the irrigation quota reduced soil pH and electrical conductivity by 4.1 % and 10.3 %, respectively, and increased available phosphorus by 23.2 % and soil organic matter (SOM) by 20.4 %. Deeper burial depths shortened the irrigation source-to-root zone distance, increased nutrient leaching, and reduced phosphatase activity. Linear mixed-effects models (LMMs) and piecewise structural equation modeling (SEM) revealed the causal relationships between root architecture and habitat factors under RZII. RZII reshaped root development and foraging strategies by increasing the root length, surface area, and fractal dimension and reducing the topological index, thereby lowering root construction costs and enhancing soil resource acquisition. SEM and LMMs indicated that soil nutrients and physicochemical properties are the main factors affecting root architecture, and SOM positively affected geometric and spatial configurations by altering organic matter input. However, bacterial communities in the root zone did not directly affect root architecture. Our findings provide fresh perspectives on how soil habitat factors relate to root architecture trade-offs in saline-alkali orchards, advancing our understanding of fruit tree root adaptation to saline-alkali stress.