Lopes Marta S, Nogués Salvador, Araus José L
Unitat de Fisiologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain.
Funct Plant Biol. 2004 Nov;31(10):995-1003. doi: 10.1071/FP04031.
Water stress and nitrogen (N) availability are the main constraints on barley (Hordeum vulgare L.) yield in Mediterranean conditions. Here we studied the combined effects of N source and water regime (WR) on plant growth, photosynthesis and carbon isotope discrimination (ΔC) in barley grown under controlled conditions. The effects of these conditions on plant N isotope discrimination against the fertiliser (ΔN) was also examined to assess whether the natural variation in plant N isotope composition is a reliable indicator of N nutrition. Six experimental treatments were established with three nutrient solutions containing ammonium (NH), nitrate (NO) or a mixture of the two (NH : NO), each either well watered or moderately water stressed. The NH : NO treatment resulted in the greatest biomass accumulation and photosynthetic capacity in both WRs. The NH plants showed accelerated phenology and depressed growth. They also had the lowest photosynthetic rates in both WRs. This effect was mainly due to stomatal closure, while electron transport and carboxylation capacity of leaves were less affected. Consistent with lower stomatal conductance, leaf ΔC was lower in plants that received NH, indicating higher water use efficiency (WUE) not only when irrigated, but also under water stress. In addition, leaf ΔC and photosynthetic N use efficiency (PNUE) correlated positively with each other and with shoot biomass in both WRs. However, NO treatment produced the greatest ΔN, which was higher in leaves than in roots. Leaf ΔN was decreased by water stress only in plants in the NO treatment. We conclude that leaf ΔC is an adequate trait to assess the differences in growth, photosynthetic activity and WUE caused by distinct N sources. However, the usefulness of natural abundance of N in plant tissue as a nitrogen source marker is restricted by the effect of WR and internal plant fractionation, at least for plants that received NO.
水分胁迫和氮素有效性是地中海条件下限制大麦（Hordeum vulgare L.）产量的主要因素。在此，我们研究了氮源和水分状况（WR）对在可控条件下生长的大麦植株生长、光合作用及碳同位素分馏（ΔC）的综合影响。还考察了这些条件对植株相对于肥料的氮同位素分馏（ΔN）的影响，以评估植株氮同位素组成的自然变异是否是氮营养状况的可靠指标。设置了六种实验处理，采用三种营养液，分别含铵（NH）、硝酸盐（NO）或二者混合物（NH : NO），每种营养液又分为充分浇水或中度水分胁迫处理。NH : NO处理在两种水分状况下均导致最大的生物量积累和光合能力。NH处理的植株物候期提前但生长受抑。在两种水分状况下，它们的光合速率也最低。这种效应主要是由于气孔关闭，而叶片的电子传递和羧化能力受影响较小。与较低的气孔导度一致，接受NH处理的植株叶片ΔC较低，这表明不仅在灌溉时，而且在水分胁迫下，其水分利用效率（WUE）都较高。此外，在两种水分状况下，叶片ΔC和光合氮利用效率（PNUE）相互之间以及与地上部生物量均呈正相关。然而，NO处理产生的ΔN最大，叶片中的ΔN高于根系。仅在NO处理的植株中，水分胁迫降低了叶片ΔN。我们得出结论，叶片ΔC是评估不同氮源引起的生长、光合活性和WUE差异的合适指标。然而，至少对于接受NO处理的植株，植物组织中氮的自然丰度作为氮源标记的有用性受到水分状况和植株内部分馏效应的限制。
