Ecological responses of soil bacteria and fungi to global change manipulations. CLIMAITE annual study

The seasonal dynamics of soil fungal and bacterial communities are important for understanding the future ecosystem responses to global change due to their role in nutrient cycling and organic matter decomposition. After four years of global change manipulations in a full-factorial experimental setup on a Danish heathland including increased temperature, extended drought and elevated CO2, soil samples were collected four times during one year to gain insight into how seasonal fluctuations affect climate change effects on both fungal and bacterial communities. We combined quantitative PCR and 454-pyrosequencing of the fungi and bacteria with analyses of total soil pools of carbon, nitrogen and phosphorus. During the study period, the bacterial community composition remained stable across both season and treatments without any major shifts in bacterial phyla. In contrast the fungal abundance, community composition and functionality changed due to season and were altered by the global change manipulations with some treatments affecting the seasonal fluctuation of the fungal communities, e.g. an extended growing season due to elevated temperature increased the relative abundance of free-living fungi and decreased the relative abundance of root-associated fungi in November. The main drivers of these changes were the single-factors while the predicted single-factor effects were generally extinguished by multi-factor treatments. In conclusion, our results highlight the importance of considering the entire principle decomposer community when investigating the impact of global change factors on future ecosystems.

土壤真菌与细菌群落的季节动态，因其在养分循环与有机质分解中的关键作用，对于解析未来生态系统对全球变化的响应机制至关重要。本研究在丹麦石楠荒原开展了为期四年的全球变化调控实验，采用全因子实验设计，设置增温、延长干旱期与CO₂浓度升高三个处理组；于一年内分四次采集土壤样本，以解析季节波动如何调控气候变化对真菌与细菌群落的影响。本研究结合真菌与细菌的定量PCR（quantitative PCR）及454焦磷酸测序（454-pyrosequencing）技术，并对土壤总碳、总氮与总磷储量进行了测定分析。研究期间，细菌群落组成在季节与各处理组间均保持稳定，细菌门类未发生显著变化。与之相反，真菌的丰度、群落组成与功能特性均随季节发生变化，且受全球变化调控实验的影响；部分处理可改变真菌群落的季节波动模式，例如：增温延长了植物生长季，使得11月自由生活真菌的相对丰度升高，而根系相关真菌的相对丰度降低。驱动这些变化的核心因素为单因子处理，但多因子处理通常会抵消单因子处理的预期效应。综上，本研究结果强调，在探究全球变化因子对未来生态系统的影响时，需将完整的核心分解者群落纳入考量范畴。