Abstract:Effects of leaf age and longitudinal location on photosynthesis heterogeneity in Viola baoshanensis and V. yedoensis were studied using Imaging-PAM exposed to the special and different photosynthetically active radiation (PAR). Under special PAR, Fv/Fm, ΦpsⅡ, qP, Abs and PS/50 decreased from the apex to the base of the young and maturate leaves of the two Viola species，while NPQ/4 and qN showed the opposite pattern. Fv/Fm and ΦpsⅡ showed spatial homogeneity by no obvious difference among the apex, middle and basal of the leaves of the two species. Other significant differences in fluorescence parameters varied along the longitudinal with the plant species and leaf age. There was significant difference in PS/50 among the base, middle and apex in the young leaves of two Viola species, while significant difference of qP was found only in the young leaf of V. banshanensis. NPQ/4 and qN were significant different among the apex, middle and base of the young and old leaves of V. baoshanensis, but significant difference in NPQ/4 and qN was found between the apex and the basal in the mature and young leaf of V. yedoensis, respectively. Rapid light curve (RLC) showed no effects of leaf age and longitudinal on the efficiency of light capture in the two Viola species, as indicated by light-limited photosynthetic efficiency (α). The highest Pmax was found at the apex, the lowest at the basal in the young and old leaves of the two Viola species in RLC, Pmax of the middle parts of leaves was different from that at the basal and apext because of leaf age. The highest of Ik was all determined at apex of the different leaf age in the two Viola species. The above data showed a clear pattern of photosynthesis heterogeneity in the leaf longitudinal, which might relate to the basal meristem and leaf age.