Aims

In cold biomes, snow cover mitigates the harsh winter soil conditions, thereby enhancing overwinter decomposition of organic matter which controls the availability of nutrients for plants and microbial uptake at the beginning of the growing season. Yet, how this buffering effect is modulated by litter traits, soil characteristics and herbivory remains poorly studied.

Methods

We conducted a litter-bag experiment in four types of subalpine grasslands, two of which being naturally free of snow during most of the winter. Litter bags were filled either by grasses or forbs sampled in plots submitted the preceding summer to grasshopper grazing treatments.

Results

Snow cover strongly increased the decomposition of forbs, but not of grasses. Litter quality (low C:N and polyphenols triggering a priming effect) and soil ammonium content were correlated with litter decomposition rate in the presence of snow only, whereas soil organic matter content was positively associated with decomposition rate under both snow regimes. Herbivory did not affect decomposition.

Conclusions

Our findings may be explained by the functional differences between copiotrophic and oligotrophic microbes, copiotrophs being more sensitive to harsh abiotic conditions than oligotrophs. As long as copiotrophs are favored by high litter quality and nutrient-rich soils (high ammonium content), litter decomposition is enhanced in the absence of snow only.

中文翻译：

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凋落物和土壤特性调节积雪对凋落物分解的缓冲作用

目的

在寒冷的生物群落中，积雪减轻了严酷的冬季土壤条件，从而增强了有机物的越冬分解，从而控制了植物生长季节开始时植物养分的利用率和微生物的吸收。然而，如何通过凋落物性状，土壤特性和食草性来调节这种缓冲作用的研究仍很少。

方法

我们在四种类型的亚高山草原上进行了垃圾袋试验，其中有两种在冬季的大部分时间里自然没有积雪。乱扔垃圾的袋子装满了草或草，这些草是在去年夏天提交给蚱hopper放牧处理的土地上取样的。

结果

积雪强烈增加了草的分解，但没有草的分解。仅在有雪的情况下，凋落物质量（低的C：N和多酚类物质会引发启动效应）和土壤铵含量与凋落物分解速率相关，而在两种雪域下，土壤有机质含量与分解速率均呈正相关。食草不影响分解。

结论

我们的发现可能是由于营养缺陷型微生物和营养缺陷型微生物之间的功能差异而引起的，营养缺陷型微生物比营养缺陷型微生物对恶劣的非生物环境更敏感。只要高营养质量的土壤和高养分含量（高铵含量）的土壤中有营养菌，在没有积雪的情况下，垃圾的分解作用就会增强。