Considering the potential enhancement of soil water repellency (SWR) due to the increased accumulation of soil organic matter (SOM) under grassland enclosure, there may be an increased risk of soil erosion and degradation as it can reduce water infiltration and penetration into the soil. There remains a knowledge gap pertaining to the relationship between SWR and plant growth, soil physicochemical properties, SOM composition, and particle size in enclosed grassland. The main objective is to investigate the impact of different grassland enclosure years (14a, 23a, 32a, 40a, and 51a) on SWR in temperate grasslands of the Loess Hilly Region using the water drop penetration time (WDPT) method. Results showed that, at the early stage of enclosure (<32 years), in-situ grassland soils mainly showed slight water repellent and hydrophilic characteristics. In contrast, grassland soils at the late stage of enclosure (>32 years) exhibited a transition towards strong water repellency, accompanied by the emergence of severe hydrophobicity. The potential SWR also exhibited a significantly higher trend in the 40a and 51a grassland compared to the previous 32 years of enclosed grassland. Moreover, the SWR increased as the soil particle size decreased, and exhibited an upward trend with increasing years of grassland enclosure. Notably, in the 40a and 51a grasslands, SWR for sieve size of soils <0.05 mm was significantly higher than that observed in the initial 32a grasslands, reaching a strong water repellent level. These findings highlight that grassland enclosure significantly promoted the development of the SWR. Correlation analysis and random forest models showed that NO3--N, litter biomass, plant height, TN, CO, C–H, bulk density and plant richness were identified as the primary factors controlling SWR. The structural equation model (SEM) analyses further suggested that grassland enclosure indirectly affected SWR through aliphatic C–H groups, which was influenced by plant properties. Consequently, the consideration of SWR formation mechanism is imperative in order to mitigate the risk of soil erosion and degradation in enclosed grassland ecosystems.

中文翻译：

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脂肪族碳调节黄土丘陵地区草原围封时间序列中的土壤拒水性


考虑到草地围护下土壤有机质 （SOM） 积累增加可能会增强土壤拒水力 （SWR），因为它可以减少水的渗透和渗透到土壤中，因此土壤侵蚀和退化的风险可能会增加。在 SWR 与封闭草地植物生长、土壤理化性质、SOM 组成和粒径之间的关系方面仍然存在知识差距。主要目的是使用水滴穿透时间 （WDPT） 方法研究不同草地圈封年限 （14a、23a、32a、40a 和 51a） 对黄土丘陵区温带草原 SWR 的影响。结果表明：圈封初期（<32 a），原位草地土壤主要表现出轻微的憎水性和亲水性特征。相比之下，圈地后期（x3E32 年）的草原土壤表现出向强拒水性的过渡，并伴有严重的疏水性。与前 32 年的封闭草原相比，40a 和 51a 草地的潜在驻波比也表现出显著更高的趋势。此外，SWR 随着土壤粒径的减小而增加，并随着草地圈封年限的增加而呈上升趋势。值得注意的是，在 40a 和 51a 草原中，土壤筛粒尺寸 <0.05 mm 的驻波比显著高于初始 32a 草原，达到较强的拒水水平。这些发现表明，草地圈封显著促进了 SWR 的发展。 相关性分析和随机森林模型表明，NO3--N、凋落物生物量、株高、TN、CO、C-H、容积密度和植物丰富度是控制SWR的主要因素。结构方程模型 （SEM） 分析进一步表明，草地围护通过脂肪族 C-H 基团间接影响 SWR，脂肪族 C-H 基团受植物特性的影响。因此，为了减轻封闭草原生态系统中土壤侵蚀和退化的风险，必须考虑 SWR 形成机制。