Cadmium transfer in the ecosystem of soil-wheat-aphid under dual stress of cadmium and drought

There have been several reports regarding the effects of both drought and heavy metals on aphids. However, although aphids often experience dual stresses and even multiple stresses, such as a combination of heavy metals, drought, and other stress factors, in the natural environment, there have been few reports on dual or multiple stresses. To explore the effects of dual stresses from drought and heavy metal on the Cd transfer in the soil-wheat-aphid system, this study took Sitobion avenae (Fabricius) as the research object and used an atomic absorption spectrophotometer to measure the Cd contents of S. avenae and of the roots and leaves of wheat following treatment with different soil contents of heavy metals (100 and 200 mg·kg^-1) and exposure to different degrees of drought stress (well-watered, moderate drought stress and severe drought stress). The results revealed that both soil Cd content and drought stress had significant effects on the Cd contents of both wheat and aphids (P < 0.05). The interactive effect of soil Cd content and drought stress was significant (P < 0.05) on Cd content of wheat roots and leaves, but it was not significant (P > 0.05) on Cd content of wheat stems and aphids. Cd accumulation in wheat was in the order of root > stem > leaves, under the same stress conditions. As drought stress increased, the Cd content of wheat roots and the Cd transfer coefficient from soil to roots gradually decreased, and the stem Cd content and transfer coefficient from roots to stems gradually increased. In S. avenae, the Cd content under 100 mg·kg^-1 soil Cd content was higher than that under 200 mg·kg^-1. Moderate drought stress increased Cd accumulation in the bodies of the aphids, whereas severe drought stress reduced the Cd accumulation. The Cd transfer coefficient from leaf to aphid was >1, and significantly larger than that from soil to root and that from root to stem and stem to leaf, indicating biomagnification of Cd in the aphids. In summary, drought stress promotes the transfer of Cd from soil to stems of wheat and its accumulation in roots, but it inhibits the transfer of Cd from root to stem and its accumulation in stem. Moderate drought stress promotes Cd accumulation in S. avenae, whereas severe drought stress inhibits Cd accumulation in aphid.