EFFECTS OF SLOPE ASPECTS AND STAND AGE ON THE PHOTOSYNTHETIC AND PHYSIOLOGICAL CHARACTERISTICS OF THE BLACK LOCUST (ROBINIA PSEUDOACACIA L.) ON THE LOESS PLATEAU

Abstract

To investigate the effects of slope aspects and stand age on the photosynthetic and physiological characteristics of black locusts on the Loess Plateau, the responses of photosynthesis and physiology to light radiation and CO2 concentration between juvenile (6-year-old) and mature (18-year-old) black locusts located on the sunny (southeast-facing) and shady (northwestfacing) slopes were compared and analyzed. Mature black locusts on the shady slopes present significantly higher Amax, Vcmax, AQY, ACE, Rd, Rp, Rubisco, LSP but lower Jmax/Vcmax, LCP, CSP than those on the sunny slopes, and the responses of E and WUE to PAR and [Ci] show considerable discrepancies at different slope aspects, which is mainly due to the variations in the microclimatic conditions between the sunny and shady slope aspects. Juvenile black locusts have significantly greater Amax, Jmax, Jmax/Vcmax, Rd, LCP, CCP, CSP, E but lower AQY, WUE compared to mature trees, which is likely associated with agerelated differences in physiological activities. It is oncluded that the mature and juvenile black locusts perform various effective acclimations of photosynthetic physiology to different slope conditions on the Loess Plateau.