Subsoils contain more than half of global soil organic matter (SOM) stocks. Given that sequestration and turnover processes of SOM are slower in the subsoil than in the topsoil, subsoil carbon (C) stocks are likely to be vulnerable to shifts in precipitation patterns. Therefore, we investigated the responses of different sources of tropical forest soil organic C (SOC) pools to a delayed onset and increased intensity of seasonal precipitation in a 10-year rainfall manipulation experiment. While total SOC varied with soil depth, regardless of shifts in rainfall pattern, we observed that changes in precipitation patterns affected the composition of SOC pools. A delayed wet season increased both the content and proportion of the light fraction C in the SOC at the 0–10 cm depth, potentially due to a decrease in the light fraction decomposition. The delayed wet season also led to a higher content of iron (Fe)-bound organic C, due to impacts on free iron (Fe) and aluminum oxides. In addition, wetter wet season led to a higher content of lignin phenols in the top- and subsoil (0–70 cm), due to anoxic conditions preventing lignin decomposition. However, this precipitation shift decreased both the content and proportion of fungal necromass in the SOC in the subsoil (50–70 cm), this was attributed to fungal necromass decomposition by microorganisms facilitated by increased N-acquisition enzyme activity. Overall, greater precipitation intensity increased the vulnerability of subsoil C to losses, primarily due to greater microbial decomposition under increased N limitation. Our study demonstrates the subsoil C-cycling processes in shaping SOM stocks to global changes in precipitation patterns.

中文翻译：

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热带森林土壤有机质库对降水模式变化的响应


底土含有全球土壤有机质 (SOM) 储量的一半以上。鉴于地下土壤有机质的封存和周转过程比表土慢，因此地下土壤碳 (C) 储量可能容易受到降水模式变化的影响。因此，我们在为期 10 年的降雨操纵实验中研究了不同来源的热带森林土壤有机碳 (SOC) 库对季节性降水延迟出现和强度增加的响应。虽然总 SOC 随土壤深度而变化，但无论降雨模式如何变化，我们观察到降水模式的变化会影响 SOC 池的组成。雨季延迟增加了 0-10 厘米深度 SOC 中轻组分 C 的含量和比例，这可能是由于轻组分分解减少所致。由于对游离铁 (Fe) 和铝氧化物的影响，雨季的推迟还导致铁 (Fe) 结合的有机碳含量较高。此外，由于缺氧条件阻止木质素分解，潮湿的雨季导致表土和底土（0-70厘米）中木质素酚的含量较高。然而，这种降水转移降低了底土（50-70 cm）SOC中真菌坏死物的含量和比例，这归因于微生物对真菌坏死物的分解，而微生物对真菌坏死物的分解是由于氮获取酶活性增加而促进的。总体而言，较大的降水强度增加了底土碳损失的脆弱性，这主要是由于在氮限制增加的情况下微生物分解更大。我们的研究表明，地下土壤碳循环过程会影响土壤有机质储量，从而影响全球降水模式的变化。