The corn straw used in the study was collected from Changping
District, Beijing City, China. The straw was air-dried to final moisture contents (MCs) of 7–8%. The air-dried was then chopped with
a paper chopper (PC500, Staida Co., Tianjing, China) to a particle
size of approximately 3 cm and then ground into 5–10 mm particles by a hammer mill (FE130, Staida Co., Tianjing, China). The samples were then packed in plastic bags and placed under 62 ± 1%
relative humidity and 2 ± 0.5C until use