Tall fescue (Festuca arundinacea Schreb.) leaf blades elongated 33% faster at continuous low than at continuous high irradiance (60 versus 300 micromoles per second per square meter photosynthetic photon flux density) when temperature of the leaf elongation zone was held constant at 21°C. Increased rate of elongation was associated with a near proportional increase in length of the elongation zone (+38%). In contrast, growth in width and thickness was decreased at low irradiance, resulting in only a 12% increase in leaf area production and 5% less total growth-associated water deposition than at high irradiance. At low irradiance dry matter (DM) import into the elongation zone was 28% less, and 55% less DM was used per unit leaf area produced. DM use in synthesis of structural components (i.e. DM less water-soluble carbohydrates) was only 13% less at low irradiance, whereas water-soluble carbohydrates (WSC) deposition was 43% less. The lower rate of WSC deposition at low irradiance was associated with a higher net rate of monosaccharide deposition (+39%), whereas net deposition rates for sucrose (−27%) and fructan (−56%) were less than at high irradiance. Still, at low irradiance, net fructan accumulation accounted for 64% of WSC deposition, i.e. 25% of DM import, demonstrating the high sink strength of the leaf elongation zone.
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机译：当叶片伸长区的温度保持恒定在21°时，高羊茅（Festuca arundinacea Schreb。）叶片在连续低辐射下的伸长比连续高辐照度（60 vs 300微摩尔每平方米光合光子通量密度）快33％。 C。伸长率的增加与伸长区的长度几乎成比例的增加有关（+ 38％）。相反，在低辐照度下，宽度和厚度的增长会降低，与高辐照度相比，叶面积产量仅增加12％，与生长相关的总水沉积量减少5％。在低辐照度下，进入伸长区的干物质（DM）进口减少了28％，而每单位叶片面积使用的DM减少了55％。在低辐照度下，DM用于合成结构组分（即DM较少的水溶性碳水化合物）仅减少13％，而水溶性碳水化合物（WSC）沉积减少43％。低辐照度下WSC沉积率较低与单糖沉积的净率较高（+ 39％）有关，而蔗糖（-27％）和果聚糖的净沉积率（-56％）低于高辐照度。尽管如此，在低辐照度下，果聚糖净积累量占WSC沉积量的64％，即占DM进口量的25％，表明叶片伸长区的沉陷强度高。
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