Reyes-Díaz Marjorie, Ivanov Alexander G, Huner Norman P A, Alberdi Miren, Corcuera Luis J, Bravo León A
Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Concepción, Chile.
Tree Physiol. 2009 May;29(5):651-62. doi: 10.1093/treephys/tpp003. Epub 2009 Feb 3.
Nothofagus dombeyi (Mirb.) Blume and Nothofagus nitida (Phil.) Krasser, two evergreens in the South Chilean forest, regenerate in open habitats and under the canopy, respectively. Both overtop the forest canopy when they are in the adult stage, suggesting that their photoprotective mechanisms differ in ontogenetic dynamics. We postulated that N. nitida, a shade-tolerant species increases its capacity to tolerate photoinhibitory conditions (low temperature and high irradiance) by thermal energy dissipation of excess energy during its transition from the seedling to the adult stage, whereas N. dombeyi, a shade-intolerant species, maintains a high capacity for photoprotection by thermal energy dissipation from the seedling to the adult stage. To test this hypothesis, the main photoprotective mechanisms in plants - the fast- and slow-relaxing components of thermal energy dissipation (NPQ, non-photochemical quenching) NPQ(F) and NPQ(S), respectively, and state transitions - were studied in seedlings and adults of both species grown in their natural habitats and in a common garden. In adults, NPQ(F) and NPQ(S) did not differ between species and seasons. The greatest differences in these parameters were observed in seedlings. The xanthophyll cycle was more active in N. dombeyi seedlings than in N. nitida seedlings at low temperature and high irradiance, consistent with a higher NPQ(F) in N. dombeyi. Under all study conditions, N. nitida seedlings had higher NPQ(S) than N. dombeyi seedlings. The state transition capability was higher in N. nitida seedlings than in N. dombeyi seedlings. Therefore, although (shade-intolerant) N. dombeyi was able to thermally dissipate the excess absorbed energy, under natural conditions its photochemical energy quenching was efficient in both developmental stages, decreasing its need for thermal dissipation. In contrast, the seedlings of N. nitida were more sensitive to photoinhibition than the adult trees, suggesting a change from shade-grown to sun-exposed phenotype from the seedling to the adult stage. These results help to explain the differences in the regeneration patterns of N. nitida and N. dombeyi and the presence of N. nitida adult stage in the upper canopy.
假山毛榉（Nothofagus dombeyi (Mirb.) Blume）和亮叶假山毛榉（Nothofagus nitida (Phil.) Krasser）是智利南部森林中的两种常绿植物，分别在开阔生境和树冠下更新。成年后，它们都高于森林树冠，这表明它们的光保护机制在个体发育动态上有所不同。我们推测，耐荫物种亮叶假山毛榉在从幼苗到成年阶段的过渡过程中，通过多余能量的热能耗散来提高其耐受光抑制条件（低温和高光照）的能力，而不耐荫物种假山毛榉从幼苗到成年阶段都通过热能耗散保持较高的光保护能力。为了验证这一假设，我们研究了生长在其自然栖息地和共同花园中的这两个物种的幼苗和成年植株中植物的主要光保护机制——热能耗散的快速和慢速弛豫成分（分别为NPQ，非光化学猝灭NPQ(F)和NPQ(S)）以及状态转换。在成年植株中，NPQ(F)和NPQ(S)在物种和季节之间没有差异。在幼苗中观察到这些参数的最大差异。在低温和高光照条件下，假山毛榉幼苗的叶黄素循环比亮叶假山毛榉幼苗更活跃，这与假山毛榉中较高的NPQ(F)一致。在所有研究条件下，亮叶假山毛榉幼苗的NPQ(S)都高于假山毛榉幼苗。亮叶假山毛榉幼苗的状态转换能力高于假山毛榉幼苗。因此，尽管（不耐荫的）假山毛榉能够通过热耗散吸收的多余能量，但在自然条件下，其光化学能量猝灭在两个发育阶段都很有效，从而降低了其对热耗散的需求。相反，亮叶假山毛榉的幼苗比成年树对光抑制更敏感，这表明从幼苗到成年阶段存在从耐荫生长表型到喜光表型的转变。这些结果有助于解释亮叶假山毛榉和假山毛榉更新模式的差异以及亮叶假山毛榉成年阶段在上层树冠中的存在。
