Abstract The incidence of UV-B radiance on the surface of the earth has been intensifying in the tropics of the southern hemisphere. However, little is known about its effect on tropical trees, especially on sun-tolerant versus shade-tolerant plants. For this study we used two ecotypes of the tropical tree Paubrasilia echinata. These ecotypes diverge among themselves in relation to leaf morphology and ecological habitats as with respect to light availability. The small-leaf ecotype is shade-tolerant and the medium-leaf ecotype is sun-tolerant. The plants were submitted to UV-B for 45 days. The shade-tolerant ecotype proved to be negatively responsive to UV-B indicated by inhibition of stem growth, total biomass, CO2 assimilation (A) and photochemical efficiency (FV'/FM'), whereas the sun-tolerant ecotype showed to be positively responsive. This divergence of responses between the two ecotypes seems to be related to the capacity to produce phenolic compounds, total antioxidant capacity (TAC) and cell respiration (Rd). UV-B increased flavonoids, lignin, TAC and reduced Rd in the sun-tolerant ecotype. In the shade-tolerant ecotype, these responses were opposite, with increased leaf loss. As for cell wall polymers (CWP), the ultraviolet radiance increased the lignin content to the detriment of hemicelluloses in the sun-tolerant ecotype. However, it did not influence the cellulose content. In the shade-tolerant ecotype, in general, the proportions of the three CWP remained invariable in relation to the control. The results indicate that the ecotypes of P. echinata function as a good model to investigate the UV-B effects on sun-tolerant and shade-tolerant tropical trees. We presume that the increase in UV-B may be a compromise for populations of juvenile plants of the shade-tolerant ecotype and increase populations of the sun-tolerant ecotype.

中文翻译：

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UV-B对紫锥花耐阴和耐日生态型生长、光合作用、总抗氧化潜力和细胞壁成分的影响

摘要 UV-B辐射在地球表面的发生率在南半球热带地区不断增加。然而，人们对其对热带树木的影响知之甚少，尤其是对耐晒植物和耐阴植物的影响。在这项研究中，我们使用了热带树 Paubrasilia echinata 的两种生态型。这些生态型在叶子形态和生态栖息地以及光照可用性方面彼此不同。小叶生态型耐阴，中叶生态型耐晒。植物经受UV-B 45天。通过抑制茎生长、总生物量、CO2 同化 (A) 和光化学效率 (FV'/FM') 表明，耐阴生态型对 UV-B 呈负响应，而耐光生态型对 UV-B 呈正响应反应灵敏。两种生态型之间的这种反应差异似乎与产生酚类化合物的能力、总抗氧化能力 (TAC) 和细胞呼吸 (Rd) 相关。在耐晒生态型中，UV-B 增加了类黄酮、木质素、TAC 并降低了 Rd。在耐阴生态型中，这些反应相反，叶片损失增加。至于细胞壁聚合物 (CWP)，紫外线辐射增加了木质素含量，从而损害了耐晒生态型中的半纤维素。然而，它不影响纤维素含量。在耐阴生态型中，一般而言，三种 CWP 的比例相对于对照保持不变。结果表明，紫锥菊的生态型可作为研究 UV-B 对耐晒和耐阴热带树木的影响的良好模型。