[Effects of shading on photosynthetic characteristics of Pinellia ternata leaves].

OBJECTIVE: To study the effects of shading on photosynthetic physiology and chlorophyll fluorescence of Pinellia ternata. METHOD: Plant growth, chlorophyll content, net photosynthetic rate (P(n)) and chlorophyll fluorescence in P. ternata were investigated under different shading treatments (0%, 70% and 90%) when it grew about 15 cm high. RESULT: The results showed that fresh weight of a tuber, height, leaf length, width, leaf area, specific leaf area (SLA) and contents of chlorophyll content were enhanced after shaded, and chlorophyll a/b rate declined. Compared with control, net photosynthetic rate, light compensation point (LCP) and light saturation point (LSP) of P. ternata decreased after shading, but apparent quantum yield (AQY) increased; quantum yield of PS II (PhiPS II), minimal fluorescence (F(o)), maximal fluorescence (F(m)), intrinsic photochemical efficiency of PS II (F(v)/F(m)) and photochemical quenching coefficient (qP) were enhanced. CONCLUSION: Compared with control, all data indicated that there were distinctive differences between the height, SLA, chlorophyll content, P(n) and chlorophyll fluorescence characteristics under the shading treatments (70% and 90%), the fresh weight of a tuber increased after 70% shading, and provided better environmental conditions for the growth of P. ternata.

Unit-cell scale mapping of ferroelectricity and tetragonality in epitaxial ultrathin ferroelectric films.

Typically, polarization and strain in ferroelectric materials are coupled, leading to the generally accepted direct relation between polarization and unit-cell tetragonality. Here, by means of high-resolution transmission electron microscopy we map, on the unit-cell scale, the degree of tetragonality and the displacements of cations away from the centrosymmetry positions in an ultrathin epitaxial PbZr(0.2)Ti(0.8)O(3) film on a SrRuO(3) electrode layer deposited on a SrTiO(3) substrate. The lattice is highly tetragonal at the centre of the film, whereas it shows reduced tetragonality close to the interfaces. Most strikingly, we find that the maximum off-centre displacements for the central area of the film do not scale with the tetragonality. This challenges the fundamental belief in a strong polarization-tetragonality coupling in PbTiO(3)-based ferroelectrics, at such thicknesses. Furthermore, a systematic reduction of the atomic displacements is measured at the interfaces, suggesting that interface-induced suppression of the ferroelectric polarization plays a critical role in the size effect of nanoscale ferroelectrics.