Abstract:

A potting experiment in greenhouse was conducted to study the effects of municipal sewage sludge (MSS) on the photosynthetic parameters, including net photosynthesis rate( P _n)、transpiration rate( Tr )、chlorophyll content and nitrogen content in leaves of poplar seedlings ( Populus × euramericana 'Guariento’). Six treatments were set, i.e. , four different dosage MSS as follows: 30 t ·hm^-2(LS), 60 t ·hm^-2(MS), 90 t ·hm^-2(HS), 120 t ·hm^-2(SS), and inorganic compound fertilizer 0.45t ·hm^-2 (F) and control (without application of sewage sludge and inorganic fertilizer). The results showed that the P _n and Tr in treatment F were greatest with 22.59% and 3.57% higher than those of control treatment, respectively. With the increase of MSS dosage,the chlorophyll and nitrogen contents in leaves tended to increased, but the P _n and Tr had a decreased. Treatments LS,MS,SH and SS treatment led to a decrease in P _n by 13.10%~37.03% and 29.11%~48.63%, and the Tr by 14.31%~31.38% and 17.27%~33.74%, respectively, compared with control and F treatment. Furthermore, the stomatal limitation ( L_s ) decreased with P _n decrease, suggesting that the decrease of P _n might be mainly caused by nonstomatal limitation. Our results suggested that the above changes in photosynthetic and the related physiological characteristics of poplar seedlings might be induced by the interaction between nutrition level and heavy metal in MSS.

Key words: poplar seedlings, municipal sewage sludge, photosynthesis, chlorophyll content, nitrogen content of leaf