Enhanced irrigation volume reduces salinity and improves deep root zone soil nutrients, phosphatase activity and changes root traits of fruit trees

Saline soils pose complex environmental challenges that limit fruit tree root function. Understanding the mechanisms by which environmental factors drive root traits in the root zone soil is crucial for improving fruit tree productivity through irrigation-based regulation of root structure. This study aimed to identify the primary drivers and driving mechanisms of soil environment on root traits, as influenced by root zone soil water content in saline fruit trees. A 2-year field experiment was conducted in Korla, Xinjiang, to investigate the effects of root zone soil physicochemical properties, enzyme activities, nutrients and active state trace elements on root traits by setting different irrigation gradients (Low: 3750 m3 ha−1; Moderate: 5250 m3 ha−1; High: 6750 m3 ha−1). Compared to low-irrigation treatment, the results showed that high-irrigation treatment decreased soil electrical conductivity and pH by 21.6–30.5 % and 1.4–5.5 %, respectively, and increased soil organic matter, available phosphorus, and available potassium by 4.4–5.1 %, 11.7–17.6 %, and 14.8–34.6 %, respectively. Additionally, catalase, urease, and phosphatase activities increased by 30.0–33.1 %, 21.6–22.0 %, and 30.0–30.2 %, respectively, enhancing irrigation amount promote nutrient migration to deeper soil layers and providing a stable and suitable environment for the main root zone. Concurrently, a total dataset (TDS) was established using four categories of 15 indicators, including physicochemical properties, nutrients, active trace elements, and enzyme activities of the 0–80 cm root zone soil. The machine learning models were used to screen the root zone soil driving factors and reveal the mechanism of environmental factors on root traits. The Random Forest model identified phosphatase, effective phosphorus, and temperature as the main drivers of root traits, with an increase in MSE (%) range of phosphatase (10.3–15.6 %), AP (6.8–10.9 %), and temperature (8.3–16.9 %). Additionally, water-mediated soil nutrients and soil enzyme activities had a positive effect on root traits. Therefore, this study provides a theoretical basis for irrigation regulation programs in the root zone soil environment of saline fruit trees.