Abstract: Zanthoxylum bungeanum is an important ecological and economic tree species in karst rocky desertification area of China. We measured the photosynthetic productivity of Z. bungeanum in the fragile habitat with rocky desertification, including lightly degraded (LD), moderately degraded (MD) and severe degraded (SD) Z. bungeanum. Daily photosynthesis variations of Z. bungeanum and their relationships with environmental factors were examined. Moreover, the path analysis method was used to analyze the direct or indirect effects of environmental factors on the net photosynthetic rate (P_n) ofZ. bungeanum. Average daily P_n of LD, MD and SD were 3.53, 2.85 and 2.32 μmol·m^-2·s^-1, respectively. Diurnal photosynthesis assimilations of LD, MD and SD were 141.21, 113.44 and 94.97 mmol·m^-2, with significantly lower value of SD than those of LD and MD. LD had higher water use efficiency and instantaneous carboxylation efficiency than MD and SD. Z. bungeanum with different degraded degrees showed no significant difference in average daily stomatal limiting value. P_n of LD was mainly influenced by CO₂ concentration and photosynthetically available radiation (PAR). The interaction between air temperature (T_a) and relative humidity (RH) jointly restricted the value of P_n.PAR and RH were dominant factors influencing MD and SD respectively, with T_a as the major limiting factor. In conclusion, photosynthesis of different degraded Z. bungeanum was sensitive to the dynamics of physiological conditions and natural environment conditions, with relatively low photosynthetic productivity.

Key words: ecosystem services, urban ecology, landscape pattern, assessment, tradeoff.