Figure 4

Proline, soluble protein and malondialdehyde (MDA) contents under different intercropping treatments (maize monocrop (MMC), wheat monocrop (WMC), intercropping maize (IM), and wheat (IW) crops) and nitrogen treatments in 2019 and 2020. Different lower-case letters show a significant difference among intercropping treatments under both N rates. “*” above bars indicates a significant difference between the monocropping and intercropping treatments at *P < 0.05; **P < 0.01.