Soils are typically subjected to multiple wetting–drying (WD) cycles due to irrigation and seasonal climate cycles, which directly impact soil pore structure and soil aggregate stability. Poly-γ-glutamic acid (γ-PGA) is a polymer used to improve soil water holding capacity and plant growth. However, the impact of γ-PGA on soil pore structure requires further research, particularly under WD cycles. Therefore, we investigated the different amounts of γ-PGA on soil structure, including soil aggregate stability, macropore (>100 μm) structure characteristics and the relationship between macropore characteristics (equivalent pore diameter, pore shape factor, soil porosity, fractal dimension (FD), soil connectivity and the percentage of aggregate content with particle size larger than 0.25 mm) and soil aggregate stability by structural equation modelling (SEM) under WD cycles. A sandy soil and a loam soil were studied, and amended with γ-PGA at three different concentrations: 0 (P0), 0.4% (P4) and 0.8% (P8) (w/w, %). Results showed that γ-PGA amendment increased the mean weight diameter (MWD) and the percentage of aggregate content with particle size larger than 0.25 mm (R_0.25) under WD cycles in both sandy and loam soils, while the MWD between P4 and P8 did not differ significantly. As the number of WD cycles increased, soil porosity (TP) increased due to an increase in pores of 100–500 μm. With γ-PGA added to soil, large microporosity (>1000 μm) increased in sandy soil, but decreased in loam soil. In addition, 8WD cycles also increased the FD (2.6%–4.2%) and pore connectivity (Con) compared with 4WD. Structural equation modelling (SEM) revealed that soil pore characteristics accounted for 74% and 98% of the variation in sandy and loam soils, respectively. TP, FD, Con and R_0.25 directly contributed to MWD, according to the SEM. These findings improve our understanding of pore characteristics and aggregate stability, which are key factors influencing soil quality when amended with γ-PGA during the seasonal WD period.

中文翻译：

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干湿循环条件下聚-γ-谷氨酸改良土壤大孔隙特征及团聚体稳定性

由于灌溉和季节性气候循环，土壤通常会经历多次干湿循环 (WT)，这直接影响土壤孔隙结构和土壤团聚体稳定性。聚-γ-谷氨酸 (γ-PGA) 是一种用于提高土壤持水能力和植物生长的聚合物。然而，γ-PGA 对土壤孔隙结构的影响需要进一步研究，特别是在 WD 循环下。因此，我们研究了不同用量的γ-PGA对土壤结构的影响，包括土壤团聚体稳定性、大孔隙（>100 μm）结构特征以及大孔隙特征（当量孔径、孔隙形状因子、土壤孔隙率、分形维数（FD） )、土壤连通性和粒径大于0的团聚体含量百分比。25 mm) 和土壤团聚体稳定性，通过 WD 循环下的结构方程模型 (SEM)。研究了沙质土壤和壤土，并用三种不同浓度的 γ-PGA 进行了改良：0 (P0)、0.4% (P4) 和 0.8% (P8)（w/w，%）。结果表明，γ-PGA 修正增加了平均重量直径 (MWD) 和粒径大于 0.25 mm 的聚集体含量百分比 (R_{0 .25} ) 在 WD 循环下在沙土和壤土中，而 P4 和 P8 之间的 MWD 没有显着差异。随着 WD 循环次数的增加，土壤孔隙率 (TP) 由于孔隙增加 100-500 μm 而增加。随着γ-PGA添加到土壤中，大微孔隙率（> 1000μm）在沙土中增加，但在壤土中减少。此外，与 4WD 相比，8WD 循环还增加了 FD (2.6%–4.2%) 和孔连通性 (Con)。结构方程模型 (SEM) 表明，土壤孔隙特征分别占沙土和壤土变异的 74% 和 98%。TP、FD、Con 和 R _{0 .25}根据 SEM，直接对 MWD 做出了贡献。这些发现提高了我们对孔隙特征和团聚稳定性的理解，这些是在季节性 WD 期间用 γ-PGA 修正时影响土壤质量的关键因素。