Effects of vegetation restoration on soil properties in soda saline-alkali soils of the Songnen Plain: A meta-analysis

Description

Soda saline-alkali soils, characterized by Na2CO3/NaHCO3 dominance and pH commonly exceeding 9.5, are among the most challenging salt-affected soils to remediate. The Songnen Plain in Northeast China, one of the worlds three major soda saline-alkali regions, contains approximately 3.7 million hectares of such soils, yet no quantitative synthesis has evaluated vegetation restoration effectiveness in this system. Here, we conducted a meta-analysis synthesizing 1,018 paired observations from 26 field studies to quantify vegetation restoration effects on soil physicochemical properties. A key methodological advance is the conversion of pH values to hydrogen ion concentrations ([H+] = 10-pH) with variance propagation via the Delta method, correcting the log-scale bias inherent in conventional pH meta-analysis. The overall effect was significantly positive (lnRR = 0.253, 95% CI [0.163, 0.342], p < 0.0001), though heterogeneity was extremely high (I2 = 99.98%). The effect was predominantly driven by pH reduction (lnRR for [H+] = 2.092), while electrical conductivity decreased by 58.5% (lnRR = -0.880), soil organic matter increased by 97.2% (lnRR = 0.679), and soil organic carbon increased by 46.7% (lnRR = 0.383). Sensitivity analysis confirmed that excluding pH observations rendered the overall effect non-significant (lnRR = 0.025, p = 0.511). Vegetation type strongly moderated outcomes: Alfalfa produced the largest improvement (lnRR = 0.756, p < 0.0001), followed by Puccinellia spp. (lnRR = 0.299, p = 0.026). Initial degradation severity was a critical moderator: severely degraded sites exhibited substantially greater restoration responses than moderately degraded sites (Qm = 29.58, p < 0.001). Recovery duration showed no significant linear relationship with outcomes (p = 0.321). Publication bias assessment confirmed robustness (Rosenthals fail-safe N = 7,557). These results provide quantitative support for a threshold-based graded restoration framework for soda saline-alkali soils.

Institutions

• Northeast Forestry University

  Heilongjiang, Harbin

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