Abstract：
The combined cadmium (Cd) and acid rain pollution poses a significant threat to the global ecological environment. Previous studies on the combined adverse effects have predominantly focused on the aboveground plant physiological responses, with limited reports on the microbial response in the rhizosphere soil. This study employed Populus beijingensis seedlings and potting experiments to simulate the impacts of combined mild acid rain (pH=4.5, MA) or highly strong acid rain (pH=3.0, HA), and soil Cd pollution on the composition and diversity of microbial communities, as well as the physiochemical properties in the rhizosphere soil. The results showed that Cd decreased the content of inorganic nitrogen, resulting in an overall decrease of 49.10 % and 46.67 % in ammonium nitrogen and nitrate nitrogen, respectively. Conversely, acid rain was found to elevate the content of total potassium and soil organic carbon by 4.68 %-6.18 % and 8.64-19.16 %, respectively. Additionally, simulated acid rain was observed to decrease the pH level by 0.29-0.35, while Cd increased the pH level by 0.11. Moreover, Cd alone reduced the rhizosphere bacterial diversity, however, when combined with acid rain, regardless of its intensity, Cd was observed to increase the diversity. Fungal diversity was not influenced by the acid rain, but Cd increased fungal diversity to some extend under HA as observed in bacterial diversity. In addition, composition of the rhizosphere bacterial community was primarily influenced by the inorganic nitrogen components, while the fungal community was driven mainly by soil pH. Furthermore, \"Metabolism\" was emerged as the most significant bacterial function, which was markedly affected by the combined pollution, while Cd pollution led to a shift from symbiotroph to other trophic types for fungi. These findings suggest that simulated acid rain has a mitigating effect on the diversity of rhizosphere bacteria affected by Cd pollution, and also alters the trophic type of these microorganisms. This can be attributed to the acid rain-induced direct acidic environment, as well as the indirect changes in the availability or sources of carbon, nitrogen, or potassium.
摘要：
镉（Cd）和酸雨污染对全球生态环境构成重大威胁。以前对联合不利影响的研究主要集中在地上植物的生理反应，关于根际土壤微生物反应的报道有限。本研究采用了北京杨树幼苗和盆栽实验来模拟轻度酸雨（pH=4.5，MA）或高度强酸雨（pH=3.0，HA）的影响。土壤Cd污染对微生物群落组成和多样性的影响,以及根际土壤的理化性质。结果表明,Cd降低了无机氮含量,导致铵态氮和硝酸盐氮总体下降49.10%和46.67%，分别。相反，酸雨使土壤总钾和有机碳含量分别升高4.68%-6.18%和8.64-19.16%,分别。此外,观察到模拟酸雨使pH值降低0.29-0.35，而Cd使pH值升高0.11。此外，Cd单独降低了根际细菌多样性，然而,当与酸雨结合时，不管它的强度，观察到Cd增加了多样性。真菌多样性不受酸雨的影响，但是在细菌多样性中观察到，在HA下，Cd增加了真菌多样性。此外,根际细菌群落的组成主要受无机氮成分的影响，而真菌群落主要由土壤pH驱动。此外，“代谢”是最重要的细菌功能，受到综合污染的显著影响，而Cd污染导致真菌从共生向其他营养类型转变。这些发现表明，模拟酸雨对受Cd污染影响的根际细菌多样性具有缓解作用，也改变了这些微生物的营养类型。这可以归因于酸雨引起的直接酸性环境，以及碳的可用性或来源的间接变化，氮，或者钾.
