FIGURE 4 The root system secretes catalase activity in the culture medium. (a), (b), and (c) respectively represent the changes in catalase under the superimposed environmental factors of nitrogen, phosphorus and nitrogen-phosphorus deficit stress. (d) indicates the changes in catalase under the superimposed drought and high temperature. * indicating a significant difference to the N, P, NP, D, and CK treatment, p < 0.05.