# Effect of Planting _Portulaca oleraca_ L. on Improvement of Salt-Affected Soils
## 4 Discussion
### Planting P. oleracea Improves Soil Physiological and Biological Properties in Salt-Affected Soils  
Planting _P. oleracea_ could improve soil structure in salt-affected soil. Soil bulk density is an important physical indicator reflecting soil compactness and structural condition, often referred to as the physical structural fertility of soil [26]. Excessive bulk density indicates reduced soil porosity, which may lead to excessive water retention, thereby affecting the growth and development of plant roots. In this study, after planting _P. oleracea_, the bulk density significantly decreased (Figure 2), and porosity increased in the 0-10 and 10-20 cm soil layers (Figure 3), indicating that the root growth of _P. oleracea_ effectively improved soil structure and enhanced soil aeration and water permeability. Studies have demonstrated that cultivating salt-tolerant plants can mitigate salt buildup in soils by enhancing their structural properties. For instance, [PERSON] et al. found that halophyte cultivation reduced soil bulk density while enhancing porosity and hydraulic conductivity, facilitating the leaching of salts from saline-alkali soils [27]. Similarly, [PERSON] et al. observed that the plants improved soil physicochemical properties, promoting the removal of Na\({}^{+}\) and soluble salts through enhanced leaching [28].  
Planting _P. oleracea_ could increase soil fertility in salt-affected soil. In the present study, the significant decrease in pH in the 0-10 cm soil layer (Figure 4) could be related to the secretion of organic acids by roots and the acidic substances produced by the decomposition of soil organic matter [29; 30]. The reduction in pH helps improve the availability of nutrients such as phosphorus, iron, and zinc, promoting plant growth [31]. Additionally, the organic matter content in the 0-10 cm soil layer increased (Figure 5), indicating that _P. oleracea_ primarily increases surface soil organic matter content through aboveground litter and root exudates. The increase in organic matter content helps improve soil structure, enhance water and nutrient retention, and promote soil microbial activity, thereby improving soil fertility and promoting the health of the soil ecosystem [31]. Soil enzyme activity is an important indicator reflecting soil fertility and ecological functions [32]. In this study, the activities of invertase and urease in the 0-20 cm soil layer significantly increased (Figures 6 and 7), indicating that the cultivation of _P. oleracea_ promoted soil carbon and nitrogen cycling. The enhancement of invertase activity facilitated the decomposition of carbohydrates in the soil, providing an energy source for soil microorganisms. The increase in urease activity, on the other hand, promotes the decomposition of nitrogen-containing organic compounds such as urea, releasing ammonium nitrogen that is readily absorbable by plants [33]. Additionally, the activity of alkaline phosphatase in the 0-10 cm soil layer showed a significant increase (Figure 8), suggesting that the cultivation of _P. oleracea_ enhanced the mineralization of organic phosphorus in the soil, thereby improving the availability of soil phosphorus [34]. The soil microbial community composition possibly changed under the ameliorative effect of various halophytes or salt-tolerant plants on saline soils [25]. Hence, it is necessary to conduct metagenomic analysis to reveal the phytoremediation effects of halophytes or salt-tolerant plants in saline soils in future studies.