Background Red soil region of southern China is the severe soil and water erosion region following the Loess Plateau. Dicranopteris dichotoma, which plays an important role in soil and water conservation in the red soil area of southern China, is an excellent soil and water conservation plant. The phosphorus mass fraction in the soil is an important factor affecting the distribution and growth of D. dichotoma. However, the effect of phosphorus on the functional traits of D. dichotoma has not received much attention. In order to give full play to the water and soil conservation function of D. dichotoma, further study in this area is urgently needed.

Methods The pot experiment was used to set up the 6 gradients of phosphorus addition treatment control (CK), P1, P2, P3, P4 and P5. The soil used in the experiment came from Hetian town, Changting county, Fujian province. Each pot was filled with 7 kg soil and one seedling of D. dichotoma. From the CK group to the P5 group, 0, 400, 600, 1 000, 1 600, and 2 400 mg of phosphate fertilizer were applied respectively. Four replicates were set up per group and a total of 24 pots were planted and cultivated. The pot culture period was 90 d, then the indexes of D. dichotoma's functional traits were measured. All data were collated using Excel 2010 and analyzed using IBM SPSS 22.0. The different data were examined by One-way ANOVA and LSD method or nonparametric Kruskall-Wallis method, and the correlation of data was analyzed using Pearson method. All illustrations were generated using Origin 9.0.

Results 1) Phosphorus addition significantly increased the leaf area and root length of D. dichotoma (P < 0.05), which were 2.29 times and 1.12 times that of the corresponding CK group, respectively. While there was little effect on specific leaf area, leaf tissue density, and specific root length, and the increase in root tissue density was small. 2) Phosphorus addition now increased the plant height of D. dichotoma (P < 0.05), with the largest plant under P4 treatment being up to 20.43 cm, and significantly reduced the root-to-shoot ratio (P < 0.05). The growth rate of D. dichotoma also increased with the increase of the phosphorus addition gradient. 3) The phosphorus mass fraction in various organs of D. dichotoma showed the characteristics of leaf> petiole> underground stem and root. Phosphorus mass fraction in the leaves, petioles, and underground stems and roots of D. dichotoma increased with the increase of phosphorus addition gradient, in which the phosphorus mass fraction of underground stems and roots increased at a relatively high rate, and it reached 1.8 g/kg in P4 treatment. There was no obvious regular change in the C:N of the underground stems and roots and leaves of D. dichotoma, while petiole C:N increased with increasing phosphorus addition gradient. The C:P and N:P of organs of D. dichotoma had the characteristic of significantly decreasing with the increase of phosphorus addition (P < 0.05).

Conclusions This study reveals that the functional traits of D. dichotoma may respond to the changes of phosphorus elements in the surrounding environment, and it has stable material acquisition capabilities and strong environmental adaptability in different environments, thus it can adapt to harsh living environment.