Studies On Eco-physiological Characteristics And Propagation Technology Of Macropanax Rosthornii

Macropanax rosthornii is an evergreen shrub or small arbor of Araliaceae. It is one of high-quality wild ornamental plant resources for it is shade-tolerant, eaay to be pruned and has a higher ornamental value in tree shape, leaf shape and leaf hue. And It can be applied to city greening, bonsai-making and indoor ornamentation as a good new shade-tolerant plant. Introduction and cultivation of M. rosthornii is of importance to enrich the city garden plants, to improve the city ecological benefit and to enrich city landscape. In this paper, by the introduction of M. rosthornii from Yongshun County to Changsha City, its eco-physiological characteristics and propagation technology were comprehensively studied initially. The main results were as follows.(1) M. rosthornii had the undeveloped root system, and the poor differentiation of vascular bundles inside both root and stem, and spongy tissue was obviously more than palisade tissue in the leaf, and this plant had a longer growing season and a good shoot-growing ability within a year, and grew well under a proper shading environment.(2) The diurnal course curves of the net photosynthetic rate of M. rosthornii planted in the garden forests had a single peak at 14:00 without "midday depression" and also the yearly course curve of the net photosynthetic rate had a single peak during the months of June and July. No strong light suppression was found on the photosynthetic light response curve of of M. rosthornii. The maximum net photosynthetic rate, light saturation point, light compensation point, dark respiration rate simulated by modified rectangular hyperbola were 6.902 μmol·m-2·s-1,1013.163 μmol·m-2·s-1,4.794 μmol·m-2·s-1 and 0.290 μmol·m-2·s-1 respectively, and thereby it indicated that M. rosthornii had a good shade-tolerance and adaptation to weak light. It was advisable for the plant to be grown under shading conditions.(3) The photosynthesis and growth of either ground-grown or potted M. rosthornii varied distinctly in different light intensities. The results showed that growth rate, plant height, basal diameter, size of leaf of the ground-grown M. rosthornii in full light(canopy density 0) were significantly higher than those in half light(canopy density about 0.5) or week sun light(canopy density about 0.8), but less was the ornamental value for the dark green and sunburned leaves. Lamina mass per unit area (LMA) increased with rising light intensity. Although chlorophyll a, chlorophyll b and the total chlorophyll content increased with the rising light intensity, chlorophyll a/chlorophyll b decreased. The photosynthetic light response curve of the ground-grown M. rosthornii was an intensive suppression type in half or week light, but a saturation and approach type in full light, ant its maximum net photosynthetic rate (Pmax), light saturation point (LSP), light compensation point (LCP) and respiration rate (Rd) increased with rising light intensity, and apparent quantum yield (AQE) was highest in half light. In addition, Fo and Fv/Fm of the ground-grown had no significant difference in different light environments. The contents of total chlorophyll, chlorophyll a and chlorophyll b in leaves of potted M. rosthornii under the shading treatments(70% sunlight intensity and 40% sunlight intensity) were significantly higher than in full sunlight intensity(100% sunlight intensity), and the chlorophyll contents was increased with the enhanced intensity of shading. However, the variation trend of chlorophyll a/b was on the contrary. Compared with full sunlight intensity, the apparent quantum yield (AQY) and the maximum net photosynthetic rate (Pmax) were increased, and the light saturation point (LSP) and light compensation point (LCP) were distinctly decreased. The efficiency of primary light-energy conversion (Fv /Fm) and potential activity (Fo/Fm) of PS II were increased by shading treatments in this study, in particular, Fv/Fm and Fo/Fm were significantly (P<0.05) higher under 40% sunlight intensity than those in fullsun light intensity. The non-photochemical quenching coefficient (NPQ) were significantly(P<0.05) lower under shading treatments than those in fullsun light intensity, and NPQ was further decreased with increasing shading intensity in which heat dissipation was reduced to increase the efficiency of light-energy conversion of PS II. The chloroplasts in the M. rosthornii leaves were subject to injury in full sunlight intensity in summer. The grana thylakoids became loose and swollen, the stroma lamellas were distorted and the liposomes increased in number in full sunlight intensity, but the injuries of chloroplasts were rather reduced under 70% sunlight intensity and there hardly were injuries of chloroplasts under 40% sunlight intensity.(4) The Photosynthesis, Physiological and biochemical responses of M. rosthornii under natural drought stress were studied in the pot experiment. The results showed that photosynthetic rate of Macropanax rosthornii was significantly inhibited under drought stress. Stomatal conductance and photosynthetic capacity decreased under drought stress. The initial fluorescence and the maximal photochemical efficiency decreased significantly with the drought stress increasing. In the meantime, photosynthetic organ was damaged, and photosynthesis ceased. The relative water content, protein content and chlorophyll content decreased, but relative membrane permeability, MDA content, soluble sugar content, proline content and POD activity increased under the drought stress. Endogenous hormone including ABA, IAA, ZR and GA increased under the stress of drought.(5) The experiments were conducted on the M. rosthornii seed germination and seedling growth. The results showed that light made seed germination easier, and the appropriate temperatures of seed germination were from 15℃ to 35℃; the substrates from high to low of seed germination rate were agar(27%), filter paper(24%), soil(15%), sand(13%), perlite(7%); 50 mg-L"1 GA3 promoted significantly germination of seed(p<0.05); the seeds by sand storage treatment had a significant germination(p<0.05). The growth difference in various culture media was significant, and the best seedling growth medium was selected by comparison in the combination of garden soil, dung and pearl rock.(6) The cutting rooting capability of M. rosthornii was studied in this paper and the results showed that 3-year-old hard-wood cuttings had a notably better rooting effect than 1-year-old soft-wood cuttings(.P<0.05), and yellow subsoil and coconut chaff were better than river sand and chaff but perlite had the poorest rooting effect. The types and concentrations of growth regulators were also important factors that affected cutting rooting. Treated with IB A at a concentration of 2000 mg·L-1, the cuttings had a rooting rate of 98.8%,; the mixture of different growth regulators made against cutting rooting of M. rosthornii. In the paper the cutting substrate of yellow subsoil and 3-year-old hard-wood cuttings shortly dipped with 2000 mg-L"1 IBA were appropriate to the cutting rooting of M. rosthornii. The cutting rooting mechanism of M. rosthornii was also studied in this paper and the results showed that the new rooting originated from cortex and there was no callus formation at the base, and rooting process included root-induced stage, root formation stage and root elongation stage, wherein there obviously were physiological and biochemical changes. The soluble sugar content was decreased either in root-induced stage or in early production stage, and the maximal decrement was 64.75% compared with that of pre-cutting, while, it increased in root formation stage. The soluble protein content was decreased by 69.18% in root-induced stage and increased both in root formation stage and in root elongation stage, with a maximal increment of 55.51% compared with those of pre-cutting. The activity of PPO was increased to the maximum with a 515.85% increment in root-induced stage and decreased to the lowest in root formation stage, and then increased to the maximum with a 590.24% increment in the root elongation stage compared with those of pre-cutting. The activity of POD reached its peak either in root-induced stage or in root elongation stage with a maximal increment of 59.20% compared with that of pre-cutting. The activity of IAAO was increased gradually in root-induced stage, it reached to a peak with an increment of 14.84% in root formation stage compared with that of pre-cutting, and then decreased to the pre-cutting level in root elongation stage. The root number, sugar content and protein content of cuttings in the treatment of IBA were higher than those of in the control, while, the activity of PPO, POD and IAAO were hardly affected by the treatment of exogenous IBA.