Biological soil crusts (BSCs) are typical covers in arid and semiarid regions. The dissolved organic matter (DOM) of BSCs can be transported to various aquatic ecosystems by rainfall-runoff processes. However, the spatiotemporal variation in quality and quantity of DOM in runoff remains unclear. Herein, four kinds of runoff plots covered by four successional stages of BSCs were set up on slopes, including bare runoff plot (BR), cyanobacteria crust covered runoff plot (CR), mixed crust covered runoff plot (MIR), and moss crust covered runoff plot (MOR). The quantity and quality of DOM in runoff during rainfall was investigated based on the stimulated rainfall experiments combined with optical spectroscopy and ultra-high resolution mass spectrometry analyses. The results showed that the DOM concentrations (i.e., 0.30 to 45.25 mg L) in runoff followed the pattern of MOR>MIR>CR>BR, and they were exponentially decreased with rainfall duration. The DOM loss rate of BR (8.26 to 11.64 %) was significantly greater than those of CR, MIR, and MOR (0.84 to 3.22 %). Highly unsaturated compounds (HUCs), unsaturated aliphatic compounds (UACs), saturated compounds (SCs), and peptide-like compounds (PLCs) were the dominated compounds of the water extractable DOM from the original soils. Thereinto, PLCs and UACs were more easily leached into runoff during rainfall. The relatively intensity of HUCs in runoff generally decreased with rainfall duration, while the relatively intensities of UACs, PLCs, and SCs slightly increased with rainfall duration. These findings suggested that the DOM loss rate was effectively decreased with the successional of BSCs during rainfall; meanwhile, some labile compounds (e.g., PLCs and UACs) were transported into various aquatic ecosystems by rainfall-runoff processes.

中文翻译：

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不同强度降雨下不同演替阶段生物土壤结皮溶解性有机质的流失：洞察不同降雨阶段分子成分的变化


生物土壤结皮（BSC）是干旱和半干旱地区的典型覆盖物。 BSC的溶解有机物（DOM）可以通过降雨径流过程输送到各种水生生态系统。然而，径流中 DOM 的质量和数量的时空变化仍不清楚。本文在斜坡上设置了4种连续阶段BSC覆盖的径流样地，包括裸露径流样地（BR）、蓝藻结皮覆盖径流样地（CR）、混合结皮覆盖径流样地（MIR）和苔藓结皮覆盖径流样地。径流图（MOR）。基于模拟降雨实验，结合光谱和超高分辨率质谱分析，研究了降雨过程中径流中DOM的数量和质量。结果表明，径流中DOM浓度（0.30~45.25 mg·L）遵循MOR>MIR>CR>BR的规律，且随降雨持续时间呈指数下降。 BR 的 DOM 损失率（8.26%~11.64%）显着高于 CR、MIR 和 MOR（0.84%~3.22%）。高度不饱和化合物(HUCs)、不饱和脂肪族化合物(UACs)、饱和化合物(SCs)和类肽化合物(PLCs)是原始土壤中水可提取DOM的主要化合物。其中，PLCs和UACs在降雨期间更容易渗入径流中。径流中HUCs的相对强度总体上随降雨持续时间的增加而减小，而UACs、PLCs和SCs的相对强度则随降雨持续时间的增加而略有增加。这些结果表明，降雨期间随着BSC的演替，DOM损失率有效降低；同时，一些不稳定的化合物（例如、PLCs和UACs）通过降雨径流过程被输送到各种水生生态系统中。