Aridity was observed to affect the C-bonded stable H isotope ratios (δ²H_n values) of aboveground plant organic matter but not δ²H_n values of associated soil organic matter (SOM). Instead, δ²H_n values of SOM correlated spatially with long-term mean δ²H values of local rainfall. To explain this discrepancy, we investigated if and to which degree C-bonded H was replaced by ambient water-H during leaf litter decomposition in laboratory microcosms.

In a four-week incubation of leaf litter (Fagus sylvatica l. - beech, Acer pseudoplatanus l. - maple) with two H-isotopically labeled waters (δ²H_iw: +50‰, +250‰), we found a small incorporation of isotopically labeled H into the C-bonded H pool (<5% of total C-bonded H) in beech litter. For the leached, more reactive total organic matter in solution (TOM), we estimated that 8–9% of C-bonded H was replaced by the isotope label during incubation. We suggest that the small incorporation of H from ambient water can be attributed to microbial processes.

However, the small incorporation of H from ambient water during microbial processing would not be sufficient to overprint the aridity signal present in plant organic matter and shift δ²H_n values of SOM towards those of long-term rainfall. This supports the suggestion, that SOM originates from belowground sources including roots and microorganisms, which inherently show δ²H_n values related with those of long-term rainfall.

观察到干旱会影响地上植物有机质的 C 键合稳定 H 同位素比率（δ ² H _n值），但不会影响相关土壤有机质 (SOM) 的δ ² H _n值。相反，SOM 的δ ² H _n值与当地降雨的长期平均δ ² H 值在空间上相关。为了解释这种差异，我们研究了在实验室微观世界中的落叶分解过程中，C 键合的 H 是否以及在何种程度上被环境水 H 取代。

在用两种 H 同位素标记的水 (δ ² H _iw : +50‰, +250‰)对凋落物 ( Fagus sylvatica l. -山毛榉, Acer pseudoplatanus l. -枫树) 进行为期4 周的孵化过程中，我们发现了一个小的将同位素标记的 H 纳入山毛榉垃圾中的 C 键合 H 池（< 总 C 键合 H 的 5%）。对于溶液中浸出的、反应性更强的总有机物 (TOM)，我们估计在孵育过程中 8-9% 的 C 键合 H 被同位素标记取代。我们认为，环境水中少量的 H 掺入可归因于微生物过程。

然而，在微生物加工过程中，环境水中少量的 H 并不足以覆盖植物有机质中存在的干旱信号，并将SOM 的δ ² H _n值向长期降雨的值转移。这支持了以下建议，即 SOM 源自地下来源，包括根和微生物，它们固有地显示与长期降雨相关的δ ² H _n值。