Polytrichum commune from relative drought habitat and Plagiomnium acutum from wet habitat were used as materials,their difference in reactive oxygen species metabolism,lipid peroxidation and response of antioxidative system were studied under dehydration and rehydration stress.(1)During process of dehydration and rehydration,moisture content alternation under summer sunlight is similar to changes on silica gel fast desiccation.(2)Membrane permeability of P.acutum recovered rapidly after rehydration,but its alternation was dramatic.On contrary,permeability of P.commune sustained a stable lower level.(3)In the procedure of desiccation and rehydration,malondiadehyde (MDA) content of both bryophytes displayed opposite trends of moisture content alternation,that is to say,increased under desiccation and then decreased under rehydration,and content in P.commune was obviously lower than that in P.acutum.(4)During dehydration and rehydration,superoxide anion (O^-·₂) reproductive rate and hydrogen peroxide (H₂O₂) content of both species manifested a tendency similar to MDA content,and their value in P.commune was obviously higher than that in P.acutum.(5)Induced by ROS,activities of antioxidative enzymes of both bryophytes,such as superoxide dismutase (SOD),catalase (CAT) and ascorbic peroxidase (APX) manifested the same tendency of ROS alternation,in other words,possessed a peak during dehydration and rehydration,and their activities in P.commune was much more sensitive to dehydration oxidative stress than that in P.acutum.(6)The ascorbic acid (AsA) content decreased under desiccation and then increased under rehydration, and content in P.commune was obviously lower than that in P.acutum.Results mentioned above indicated that both bryophytes contains powerful ability to adapt desiccation oxidative stress,especially,the repair ability in rehydration process.Nevertheless,bryophytes from deferent habitat should reflect distinct response on desiccation.P.commune from relative drought habitat possess stronger desiccation tolerance than P.acutum from wet habitat for its higher antioxidtive ability.