Abstract: The application of urban sewage sludge as an organic fertilizer for garden plants has obtained an increasing attention. Taking Buxus microphylla seedlings as test objects, a greenhouse pot experiment was conducted to study the responses of their photosynthetic characteristics and growth to the application of sewage sludge (SS). Five treatments were installed, i.e., low dosage SS (LC), medium dosage SS (MC), high dosage SS (HC), inorganic fertilizers (IF), and control (no application of sewage sludge and inorganic fertilizers, CK). The application of SS increased the chlorophyll and N contents in B. microphylla seedlings leaves, but with the increase of SS dosage, the net photosynthetic rate (P_n) decreased. In August, treatments LC and MC increased the P_n but HC decreased the P_n by 259% and 89%, respectively, compared with IF and CK. In October, treatments LC, MC and HC decreased the P_n, compared with IF, but the P_n in LC was still higher than that of CK. The P_n in treatments MC and HC was lower than that of CK, and the P_n in HC was 48.4% and 29.2% lower than that in IF and CK, respectively. The plant height, basal diameter, and root length were the greatest in treatment IF, followed by in LC. Treatment LC induced the greatest above ground biomass; MC increased the plant height and the above ground biomass, but decreased the basal diameter and root length, compared with CK; while HC seriously restrained the root growth. Our results indicated that the dosage of sewage sludge for B. microphylla seedlings should be lower than 30 t·hm^-2.

Key words: Buxus microphylla, composted sewage sludge, organic fertilizer, photosynthesis, growth, Phascolosoma esculenta, enrichment, heavy metal, growth, protein, lipid.