Data-Integrated microbial–enzymatic pathways driving carbon sequestration in plant litter crusts of semi-arid sandy soils

Field sampling was conducted in July 2018 and 2019 in degraded sandy soils at litter crust monitoring sites, following the methodology of Cheng et al. (2025). Three representative sites, spaced more than 1000 m apart, were selected in vegetation-free areas (within a one-meter radius). At each site, four treatments were established: bare sandy soil (control), early-successional litter crust (1-3 years), mid-successional litter crust (3-5 years), and late-successional litter crust (5-8 years) (Fig. 1a). Naturally formed litter crusts, consisting mainly of Populus simonii Carr. and other plant litter, persist for several years and typically as discrete patches or belts in low-lying or flat sandy areas. The age of the litter crust was determined in the field based on established morphological characteristics, including litter color and the degree of adhesion between soil and litter (Jia et al. 2018). Sampling was conducted in two consecutive years, providing six replicates per treatment (3 sites × 2 years). For each treatment, three replicate plots (1 m × 1 m) were established at each site, spaced more than 10 m apart. Within each plot, composite soil samples were collected from the 0-10 cm depth using a 5-cm-diameter soil auger. Each composite sample consisted of five sub-samples obtained via the five-point sampling method. All samples were immediately placed in insulated coolers with ice packs and transported to the laboratory on the same day. One portion was stored at -80 ℃ for DNA extraction, another at 4 ℃ for enzyme activity assays, and the remainder was air-dried for physicochemical soil characterization. Prior to analysis, visible plant debris was removed by sieving through a 2-mm sieve.本研究于2018年和2019年7月，参照Cheng等人（2025）的方法，在枯落物结皮监测样点的退化沙质土壤中开展野外采样。选取3个间距超过1000米的代表性样地，均位于无植被覆盖区域（半径1米范围内）。每个样地内设置4种处理，分别为：裸沙土壤（对照组）、早期演替枯落物结皮（1~3年）、中期演替枯落物结皮（3~5年）以及晚期演替枯落物结皮（5~8年）（见图1a）。自然形成的枯落物结皮主要由小叶杨（Populus simonii Carr.）及其他植物枯落物组成，可存续数年，在低洼或平坦沙地区域通常呈离散斑块或条带状分布。枯落物结皮的形成年限可通过野外已确立的形态学特征判定，包括枯落物颜色及土壤与枯落物的黏结程度（Jia等，2018）。本研究连续两年开展采样，每种处理共设置6个重复样（3个样地×2年）；每个样地内针对每种处理设置3个重复样方（1 m × 1 m），样方间距超过10米。每个样方内，采用直径5 cm的土壤钻采集0~10 cm土层的混合土样，每份混合土样由通过五点采样法获取的5份子样混合而成。所有样品需立即放入装有冰袋的保温冷藏箱中，并于当日运送至实验室。其中一部分样品保存于-80 ℃环境中用于DNA提取，另一部分保存于4 ℃环境中用于酶活性测定，剩余样品经风干处理后用于土壤理化性质表征。分析前，需通过2 mm孔径的筛网去除样品中的可见植物残体。