Dong Shuting

Rates of apparent photosynthesis, respiration and dry matter accumulation in maize canopies

The rates of canopy apparent photosynthesis (PC) and canopy respiration (Rc) were studied during vegetation season in two erectophile and two planophile hybrids of maize (Zea mays L.) grown at two canopy densities [7.5 plants m-2 (HD) and 4.5 plants m-2 (LD)]. Large differences in PC, Rc, RC/PC, leaf area index (LAI), dry matter accumulation and grain yield were found among hybrids and plant densities. Variations in PC and RC were associated mainly with changes in LAI. There was also found change in PC per unit LAI with time. The average RC/PC was 28.9 % for all treatments throughout the vegetation season. PC and RC per unit dry matter were higher in LD than in HD and decreased throughout the measurement period. The HD stand had higher PC and yield in hybrids with erectophile foliage, whereas LD stand had higher PC after male tetrad and got higher yield in hybrids with planophile foliage. Only RC in hybrids of the two foliage types was higher under HD than under LD throughout the vegetation period.

Effects of Shading on Photosynthetic Characteristics and Xanthophyll Cycle of Summer Maize in the Field

A field experiment was conducted to study the effects of shading on photosynthetic characteristic and xanthophyll cycle of summer maize. One non-shading treatment was used as control and three shading treatments with a shading degree of 60% were designed in growing period ranging from tasseling to maturity (S1), from jointing to tasseling stage (S2) and whole growing period (S3), respectively. Two cultivars Zhengdan 958 and Zhenjie 2 were used as experimental materials. Results showed that grain yield decreased significantly under shading condition. Effects of different shading treatments on grain yield showed S3 > S1 > S2, and there was a yield reduction of 96.87% and 90.78% for Zhengdan 958 and Zhenjie 2 in S3. Compared with CK, photo- synthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), chlorophyll content decreased and the intercellular CO2 con- centration (Ci) increased at first and then decreased, with the rame tendency for two maize cultivars. The stomatal factor and the non-stomata factor had double impacts decreasing photosynthesis. The actual photo-chemical efficiency (ΦPSII), the xanthophyll cycle pool (A+Z+V) and the de-epoxidation extent of xanthophyll cycle (A+Z)/(A+Z+V) increased, and the maximal photo- chemical efficiency (Fv/Fm) and non-photochemical quenching (NPQ) increased. In other words, in a long time shading, the dis- tribution of sunlight captured by leaves changed and the start of the xanthophyll cycle promoted the heat dissipation of excess light energy. Meanwhile, the ratio of the energy of photosynthetic electron transport to the absorbed light reduced. Finally, the (A+Z)/(A+Z+V) and NPQ increased rapidly in early days after ceasing shading, showing that leaves adapted shading are sensitive to normal illumination in initial stage of light recovery and the enhancement of xanthophyll cycle restrains the damage of photo- synthetic structure by sunlight.

Comparison of photosynthetic characteristics of leaves in pop corn, sweet corn, and glutinous corn during the late growing period.

以爆裂玉米、甜玉米和糯玉米3种类型特用玉米为试材,系统比较研究了生育后期叶片光合特性在类型间和叶位间的差异。结果表明,玉米叶片的光合特性存在类型间差异,糯玉米叶片的光合特性明显优于爆裂玉米和甜玉米,叶片的光合速率（Pn）、叶绿素含量（Chl）、蒸腾速率（Tr）和气孔导度（Gs）均表现为糯玉米〉甜玉米〉爆裂玉米;3类玉米的光合特性存在叶位间差异,中部叶片光合速率表现为糯玉米〉甜玉米和爆裂玉米,下部叶片光合速率的类型间差异不显著,上、中部叶片叶绿素含量表现为甜玉米〉爆裂玉米〉糯玉米;相关分析表明,叶绿素含量、蒸腾速率、气孔导度与光合速率显著或极显著正相关。总之,各类型玉米的上部和中部叶片光合特性都优于下部叶片,其中糯玉米上部和中部叶片的光合速率、光合速率高值持续期、叶绿素含量和蒸腾速率都大于甜玉米和爆裂玉米,甜玉米和爆裂玉米下部叶片光合性能的衰减在时间上早于糯玉米。