不同生长阶段遮荫对番茄光合作用、干物质分配与叶N、P、K的影响

对番茄植株做了两种不同程度的遮荫处理，观测了夏季午间遮荫对光合速率，干物质积累量及其在根，茎，叶之间的分配，和叶N，P，K的含量以及经济产量的影响，发现不同时期遮荫影响不同。（1）遮荫增加三个阶段（开花早期，盛花期和开花后期）的气孔导度和胞间CO2浓度，显著降低开花早期中午的净化合速率，但盛花期中度遮荫（40%遮荫）使净光合速率随着时间的增加逐渐上升，在开花后期表现更加明显，平均净光合速率比对照高20%以上，蒸腾速率也增加较多。（2）开花早期和盛花期重度遮荫（如本实验中的75%遮荫）显著降低根，茎的干重，而开花后期中度遮荫的根，茎干重高于对照，但遮荫对叶干重的影响不明显。（3）开花早期和盛花期遮荫不明显影响叶片中N，P，K的含量，但开花后期中度遮荫使N，P，K含量增加，（4）开花早期两种遮荫对果实产量影响较小，但盛花期重度遮荫使产量降低，全部产量中无效部分所占的比例上升，开花后期中度遮荫的总产量和有效产量增加，单果重也增加，这些结果表明，在某些时期中度遮荫可以克服夏天辐射过强，气温过高对番茄的不良影响，对番茄生长，干物质积累和提高产量等有利，在生产上有意义。

Effects of Shading on Photosynthesis, Dry Matter Partitioning and N、P、K Concentrations in Leaves of Tomato Plants at Different Growth Stages

PAR (photosynthetic active radiation) is an important factor affecting tomato ( Lycopersicon esculentum Mill.) plant growth, development and yield. But high irradiation may not always be beneficial to the plant at all growth stages. The effects of two strengths of shading (40% and 75% increases in shaded area) for 8 days at three growth stages (i.e. early flowering (EF), peak flowering (PF) and late flowering (LF)) on photosynthesis, dry matter accumulation and allocation of dry matter to roots, stems and leaves, mineral nutrient (N, P, and K) in leaves and yield were measured. Different effects caused by shading at different growth stages were found: (1) Shading caused large increases in leaf conductance and intercellular CO 2 concentrations at all three growth stages, significantly reduced the leaf photosynthetic rates of EF stage, but the photosynthetic rates in 40% shaded leaves at PF stage were increased gradually depending on the length of shade time. This trend becomes more obvious and the average photosynthetic rates of 40% shaded leaves in an 8 day shading period at the LF stage was increased by 22%, (2) The 75% shading treatment at the EF and PF stages reduced the dry weights of root and stem tissues while the 40% shading at the LF stage caused a 22% to 43% increase, but shading did not affect leaf dry weight at most growth stages, (3) Shading at the EF and PF stages had no significant effects on total leaf N, P, and K concentrations, but 40% shading at the LF stage significantly increased the leaf N, P, and K concentrations by approximate 20%, 60% and 35% compared to unshaded controls. (4) Only shading at the LF stage significantly enhanced the marketable fruit yield of the 40% shaded tomato plants, but did not affect the fruit yield of shaded plants at the EF stage. These results suggested that the adverse influences caused by high irradiation and high temperatures could be overcome and a good growth, better dry matter accumulation and yield also could be obtained if some moderate shading was applied at the LF stage at the summer midday time, which might be useful in agriculture.