Aridity is known to influence the structure and function of the soil microbiome and their connection with ecosystem functions, however, whether aridity leads to gradual (or abrupt) and systemic (or specific) changes in the microbiome-ecosystem functions relationships in alpine ecosystems is largely unknown. Here, we conducted a survey of 60 sites along an aridity-gradient transect across the Tibetan Plateau to investigate changes in microbial diversity and functions and to evaluate their relationship with soil functionality. We found that plant richness and biomass, soil microbial richness (e.g., bacteria, fungi, diazotrophs, saprotrophs, pathotrophs and symbiotrophs), the relative abundance of copiotrophs and soil functionality (e.g., C-, N-, and P cycling, multifunctionality) decreased along the aridity gradient, whereas the proportion of genes associated with organic matter decomposition and denitrification increased (obtained from metagenomic sequencing). Above an aridity threshold of ∼0.6, soil multifunctionality decreased slowly and supported a larger proportion of genes associated with cellulose, hemicellulose, chitin, lignin and pectin degradation as well as genes associated with denitrification (e.g., Z, Z atypical 2, B-cNor and B-qNor). In drier habitats (>0.6 aridity level), microbial diversity and genes involved in organic matter decomposition and N cycling were strongly correlated with soil multifunctionality, whereas plant diversity was closely associated with soil multifunctionality in wetter habitats (<0.6 aridity level). Plant biomass and soil organic C play a key role in regulating microbial compositional and functional diversity and further affect soil multifunctionality in drier habitats. These findings suggest that soil microbiomes may play a larger role in maintaining soil multifunctionality in more arid environments than in less arid environments. Our results highlight the threshold responses of microbial diversity and functions to aridity and provide novel insight into mechanisms by which climate change affects ecosystem functions.

中文翻译：

---

高山生态系统气候干旱梯度微生物组-土壤功能关系的干旱阈值

众所周知，干旱会影响土壤微生物组的结构和功能及其与生态系统功能的联系，然而，干旱是否会导致高山生态系统中微生物组-生态系统功能关系的逐渐（或突然）和系统（或特定）变化在很大程度上是未知的。未知。在这里，我们对青藏高原干旱梯度样带沿线的 60 个地点进行了调查，以调查微生物多样性和功能的变化，并评估它们与土壤功能的关系。我们发现植物丰富度和生物量、土壤微生物丰富度（例如细菌、真菌、固氮生物、腐生生物、病养生物和共生生物）、富养生物的相对丰度和土壤功能（例如碳、氮和磷循环、多功能性）沿干旱梯度下降，而与有机物分解和反硝化相关的基因比例增加（从宏基因组测序获得）。高于~0.6的干旱阈值时，土壤多功能性缓慢下降，并支持较大比例的与纤维素、半纤维素、几丁质、木质素和果胶降解相关的基因以及与反硝化相关的基因（例如，Z、Z非典型2、B-cNor）和 B-qNor)。在较干燥的生境（>0.6 干旱水平）中，微生物多样性和参与有机质分解和氮循环的基因与土壤多功能性密切相关，而在较湿润的生境（<0.6 干旱水平）中，植物多样性与土壤多功能性密切相关。植物生物量和土壤有机碳在调节微生物组成和功能多样性方面发挥着关键作用，并进一步影响干燥生境中的土壤多功能性。这些发现表明，在较干旱的环境中，土壤微生物组在维持土壤多功能性方面可能比在不太干旱的环境中发挥更大的作用。我们的结果强调了微生物多样性和功能对干旱的阈值响应，并为气候变化影响生态系统功能的机制提供了新的见解。