Departamento de Biologia Vegetal, Universidade Federal de Viçosa, 36570-000 Viçosa, MG, Brazil.
J Plant Physiol. 2010 Sep 1;167(13):1052-60. doi: 10.1016/j.jplph.2010.03.001. Epub 2010 Apr 8.
Coffee is native to shady environments but often grows better and produces higher yields without shade, though at the expense of high fertilization inputs, particularly nitrogen (N). Potted plants were grown under full sunlight and shade (50%) conditions and were fertilized with nutrient solutions containing either 0 or 23 mM N. Measurements were made in southeastern Brazil during winter conditions, when relatively low night temperatures and high diurnal insolation are common. Overall, the net carbon assimilation rate was quite low, which was associated with diffusive, rather than biochemical, constraints. N deficiency led to decreases in the concentrations of chlorophylls (Chl) and total carotenoids as well as in the Chl/N ratio. These conditions also led to qualitative changes in the carotenoid composition, e.g., increased antheraxanthin (A) and zeaxanthin (Z) pools on a Chl basis, particularly at high light, which was linked to increased thermal dissipation of absorbed light. The variable-to-maximum fluorescence ratio at predawn decreased with increasing A+Z pools and decreased linearly with decreasing N. We showed that this ratio was inadequate for assessing photoinhibition under N limitation. Expressed per unit mass, the activities of superoxide dismutase and glutathione reductase were not altered with the treatments. In contrast, ascorbate peroxidase activity was lower in low N plants, particularly under shade, whereas catalase activity was lower in shaded plants than in sun-grown plants, regardless of the N level. Glutamine synthetase activity was greater in sun-grown plants than in shaded individuals at a given N level and decreased with decreasing N application. Our results suggest that the photoprotective and antioxidant capacity per amount of photons absorbed was up-regulated by a low N supply; nevertheless, this capacity, regardless of the light conditions, was not enough to prevent oxidative damage, as judged from the increases in the H(2)O(2) and malondialdehyde concentrations and electrolyte leakage. We demonstrated that N fertilization could adequately protect the coffee plants against photodamage independently of the anticipated positive effects of N on the photosynthetic capacity.
咖啡原产于阴凉环境，但在没有遮荫的情况下往往生长得更好，产量更高，尽管这需要高施肥投入，特别是氮（N）。盆栽植物在全阳光和遮荫（50%）条件下生长，并使用含有 0 或 23mM N 的营养液施肥。测量在巴西东南部进行，该地区冬季的夜间温度相对较低，白天太阳辐射较高。总的来说，净碳同化率相当低，这与扩散限制而非生化限制有关。氮缺乏导致叶绿素（Chl）和总类胡萝卜素的浓度以及 Chl/N 比降低。这些条件还导致类胡萝卜素组成的定性变化，例如，在高光下，基于 Chl 的花药黄质（A）和玉米黄质（Z）库增加，特别是与吸收光的热耗散增加有关。黎明前的可变到最大荧光比随 A+Z 库的增加而降低，并随氮的减少呈线性降低。我们表明，该比率不足以评估氮限制下的光抑制。按单位质量表示，超氧化物歧化酶和谷胱甘肽还原酶的活性不因处理而改变。相比之下，在低氮植物中，尤其是在遮荫下，抗坏血酸过氧化物酶活性较低，而在遮荫植物中的过氧化氢酶活性低于阳光充足的植物，无论氮水平如何。在给定的氮水平下，与遮荫个体相比，阳光充足的植物中的谷氨酰胺合成酶活性更高，并且随着氮施用量的减少而降低。我们的结果表明，低氮供应上调了吸收一定数量光子的光保护和抗氧化能力；然而，无论光照条件如何，这种能力都不足以防止氧化损伤，这可以从 H（2）O（2）和丙二醛浓度以及电解质渗漏的增加来判断。我们证明，氮施肥可以充分保护咖啡植物免受光损伤，而无需考虑氮对光合作用能力的预期积极影响。
