Effects of Soil Water Content on Photosynthetic Characteristics of the Populus×euramericana cv."74/76"Seedlings

Net photosynthetic rate(Pn)of one-year-old potted Populus×euramericana cv74/76was determined through controlling soil water content(SWC).There were 6 treatments of SWC(7.8% ,8.5%,10.1% ,11.7%, 14.0% and 17.1%)and the treatment time was 60 d.The results showed the curves of Pn response to PAR were different under SWC.The discrepancy of maximum Pn was very obvious under different SWC.Photosynthetic quan- tum yield and the light saturation points increased with the improvement of soil moisture status but the light compen- sation points declined.The curve representing the diurnal course of the photosynthetic rate under different SWC was twin or single peaked patterns.The daily average Pn increased with the increase SWC.The discrepancy was very remarkable between the treatments of 10.1%,11.7%,14.0% and the treatments of 7.0%,8.5%,17.1%.The relationship model curves of Pn with SWC showed that the range of 10.1%SWC14.0% was transitional range of it,which was favorable to enhance efficiency of light use and water use.It is considered that 10.1%SWC14.0% was the rational water providing range of Populus×euramericana cv.74/76seedlings.