Warren C R, Bleby T, Adams M A
School of Biological Sciences, The University of Sydney, Sydney, NSW, 2006, Australia.
Oecologia. 2007 Nov;154(1):1-10. doi: 10.1007/s00442-007-0803-2. Epub 2007 Jul 18.
Two of the ways in which plants cope with water deficits are stomatal closure and "osmotic adjustment". We sought to assess the contributions of these processes to maintenance of leaf hydration in field-grown, 7-year-old Eucalyptus marginata. Plants were exposed to their normal summer drought (controls) or supplied with additional water (irrigated). Irrigation increased photosynthesis by 30% in E. marginata. These increases in photosynthesis were related to an 80% increase in g (s). However, there was no difference in substomatal CO(2) concentrations between treatments, or in chloroplast CO(2) concentrations, as indicated by carbon isotope composition of leaf soluble sugars. This suggests that impaired mesophyll metabolism may partially explain slower rates of photosynthesis in plants exposed to their normal summer drought. There was no difference in concentrations of solutes or osmotic potential between non-irrigated and irrigated individuals, perhaps because relative water content was the same in non-irrigated and irrigated plants due to stomatal sensitivity to water deficits. Irrespective of the absence of osmotic adjustment, analysis of leaf solutes gave a clear indication of the major groups of compounds responsible for maintaining cell osmotic potential. Soluble sugars were three times as abundant as amino acids. Proline, a putatively osmotically active amino acid, contributed less than 1% of total solutes. These patterns of solutes in E. marginata are consistent with a growing body of literature arguing a greater role for carbohydrates and cyclitols and lesser role for amino acids in maintaining osmotic potential. Our data suggest the primary mechanism by which E. marginata coped with drought was partial stomatal closure; however, we cannot discount the possibility of osmotic adjustment under more severe water deficits.
植物应对水分亏缺的两种方式是气孔关闭和“渗透调节”。我们试图评估这些过程对田间生长的7年生边缘桉树叶水合作用维持的贡献。将植物暴露于正常的夏季干旱（对照）或额外供水（灌溉）条件下。灌溉使边缘桉的光合作用提高了30%。光合作用的这些增加与气孔导度（gs）增加80%有关。然而，处理之间的胞间CO₂浓度或叶绿体CO₂浓度没有差异，叶可溶性糖的碳同位素组成表明了这一点。这表明叶肉代谢受损可能部分解释了暴露于正常夏季干旱的植物光合作用速率较慢的原因。未灌溉和灌溉植株之间的溶质浓度或渗透势没有差异，这可能是因为由于气孔对水分亏缺敏感，未灌溉和灌溉植株的相对含水量相同。尽管没有渗透调节，但对叶溶质的分析清楚地表明了负责维持细胞渗透势的主要化合物类别。可溶性糖的含量是氨基酸的三倍。脯氨酸是一种假定具有渗透活性的氨基酸，其占总溶质的比例不到1%。边缘桉的这些溶质模式与越来越多的文献一致，这些文献认为碳水化合物和环醇在维持渗透势方面发挥更大作用，而氨基酸发挥较小作用。我们的数据表明，边缘桉应对干旱的主要机制是部分气孔关闭；然而，我们不能排除在更严重的水分亏缺下渗透调节的可能性。
