Mycorrhiza-mediated nitrogen cycling depends on earthworm behavior under different straw management regimes

Arbuscular mycorrhizal fungi (AMF) play important roles in some key steps of nitrogen cycling in agroecosystems, such as the transformation of soil nitrogen and plant nitrogen uptake. However, whether AMF-mediated nitrogen cycling can be affected by other soil organisms, such as earthworms, remains to be elucidated, particularly under straw incorporation. A factorial microcosm experiment was conducted to test the effects of AMF-earthworm interactions on nitrogen cycling by including two earthworm species with different feeding behaviors (Eisenia fetida, epigeic, EP and Metaphire guillelmi, endogeic, EN) under different straw management strategies (no straw, NS; straw mixing with soil in 0–10 cm depth, SM; and the deep burial of straw at 20 cm deep, DB). Our results showed that AMF significantly increased the aboveground plant nitrogen uptake under NS (+27.01 %), SM (+7.63 %) and DB (+14.42 %) treatments. However, interactions between earthworms with different feeding types and straw management could affect AMF-mediated nitrification and denitrification in soils. In addition, earthworms were found to promote the uptake of mycorrhizal 15N uptake in the SM treatment but reduced it under the DB treatment. However, the interaction between AMF and EN earthworms promoted the total plant N uptake in the DB treatment. Our study suggests that AMF can affect the transformation of soil nitrogen and plant nitrogen uptake, but their impacts could be altered by agronomic management, such as straw incorporation, which induced changes in the activities of soil fauna, such as earthworms.