Effects of Composted Sewage Sludge on Photosynthesis and Growth Characteristics of Sophora japonica Linn. and Pinus tabulaeformis Carr. Seedlings

Abstract

The application of urban sewage sludge as an organic fertilizer in garden plants has obtained an increasing attention. As conducted to study the responses of photosynthetic and growth (at harvest) characteristics of Sophora japonica Linn. (Determining photosynthesis in two seasons of July and August) and Pinus tabulaeformis Carr. (Determining photosynthesis in August)) seedlings to the application of composted sewage sludge (CSS). A greenhouse pot experiment was carried out. Five treatments were installed, i.e., low dosage CSS [LS, 30 ton/(ha year)], medium dosage CSS [MS, 60 ton/(ha year)], high dosage CSS [HS, 90 ton/(ha year)], inorganic compound-fertilizer (IF) and control (no application of sewage sludge and inorganic fertilizer，CK). With the increase of CSS dosage，the net photosynthetic rates (Pn) of Sophora japonica Linn. seedlings leaves decreased. In two seasons of July and August, the Pn was the greatest in treatment IF, followed by CK, And the Pn in treatments LS, MS and HS was lower than that in IF and CK. The Pn of Pinus tabulaeformis Carr. seedlings leaves in August was the greatest in treatment LS，but treatments MS and HS decreased the Pn compared with CK and IF. The plant height and tap root length in Sophora japonica Linn. seedlings were the greatest in treatment MS, while treatment IF induced the greatest basal diameter. Treatments LS, MS and HS in Sophora japonica Linn. seedlings increased the plant height, tap root length and basal diameter by 4.0%～13.0% , 9.4%～34.2% and 10.1%～16.5% compared with CK, respectively. In addition, Treatment LS in Pinus tabulaeformis Carr.seedlings resulted in the greatest plant height and basal diameter, while the tap root length and above-ground biomass in treatment LS were lower than those of IF but still higher than those of CK. Treatment LS in Pinus tabulaeformis Carr. seedlings increased the plant height, basal diameter, tap root length and above-ground biomass by 6.3%, 14.8%, 74.9% and 14.9% compared with CK, respectively. However, the applications of MS and HS induced the wilting and death of Pinus tabulaeformis Carr. seedlings. The results indicated that responses of photosynthesis in Sophora japonica Linn. and Pinus tabulaeformis Carr. seedlings to the application of CSS varied with dosage of CSS and between species, and MS and HS dosage clearly inhibited the photosynthesis. The appropriate application of CSS benefited the plant growth, especially, promoted the root system. The results suggested that the low dosage CSS application 30 ton/(ha year) of Pinus tabulaeformis Carr. seedlings was little worse than and equal to marketable compound fertilizer, and the dosage of CSS for Sophora japonica Linn. seedlings should be lower than 60 ton/(ha year).