Objectives Two plant growth retardants, PP333 and TIBA, have been widely applied in chemical pruning of hedge plants because of having dwarfing effects on plants growth. In this study, both PP333 and TIBA were applied by spraying seedlings foliage to probe the responses of nitrogen accumulation in roots and leaves of the hedge plants.

Methods A field experiment with a two-factor completely randomized design was conducted by foliar spraying the detacthment seedlings of Buxus megistophylla (3-year old). The applied concentrations of PP333 were composed of 4 levels: 0, 20, 50 and 80 mg/L, and TIBA application included 3 levels: 0, 50 and 100 mg/L. In detail, a total of 1 L of prepared solution was sprayed into each experimental plot in an interval of 25 days from 5 April, 2017. Twenty-five days after the third spraying, the whole seedlings of Buxus megistophylla from each plot were sampled to measure the total-N, free amino acid, nitrate-N in roots and leaves, and the soluble protein and photosynthetic pigment contents in leaves were determined.

Results 1) Spraying PP333 significantly promoted the contents of total-N, nitrate-N and free amino acid in radicula and medium roots and TIBA application with high concentration obviously affected the contents of total-N content, nitrate-N and free amino acid in radicula. The interactions between the PP333 and TIBA significantly promoted the accumulations of total-N content, nitrate-N and free amino acid in radicula of the seedlings of B. megistophylla treated. 2) PP333, TIBA and their interactions dramatically increased the total-N, soluble protein and photosynthetic pigment content in leaves too, the content of free amino acids was improved by PP333 of 50 or 80 mg/L, and that of nitrate-N was improved by PP333 of 80 mg/L. 3) Compared with the TIBA treatment, the PP333 application significantly affected the nitrogen accumulation in B. megistophylla.

Conclusions The nitrogen metabolic accumulation in B. megistophylla is regulated by PPP333, TIBA and their interactions. Compared with TIBA, PP333 could affect the metabolic process of nitrogen in B. megistophylla. In landscape maintenance, the nitrogen metabolic process in radicula and the contents of protein and photosynthetic pigments were improved dramatically by spraying both PP333 of 80 mg/L and TIBA of 100 mg/L. Spraying PP333 of 80 mg/L alone promoted the contents of nitrate-N and free amino acid.