臨時生物科学セミナー（第１５８回）

　　日　時：平成１９年１０月２２日（月）　１６：３０〜１８：００

場　所：理学部２号館　第二講義室（２２３号室）

講演題目：Ecological limits to plasticity

講演者名：Fernando Valladares

Instituto de Recursos Naturales, CCMA, CSIC. Madrid, Spain.

講演概要: Phenotypic plasticity is considered the major means of plants to cope with spatially heterogeneous and temporally dynamic environments. Although ubiquitous in nature, actual phenotypic plasticity is far from being maximal in most plant species and populations. This has been explained by the existence of internal limits to its expression. However, phenotypic plasticity takes place within an ecological context and plants are exposed to multifactor environments and to simultaneous interactions with many species. These external factors may limit phenotypic plasticity or curtail its adaptive value, but seldom have they been considered since limits to plasticity have typically addressed factors internal to the plant. Plastic responses to abiotic factors have been shown to be reduced under situations of conservative resource use in stressful habitats (1, 2). Extreme levels in a given abiotic factor can negatively influence plastic responses to another factor (3). However, our knowledge on multifactor interactive effects on plasticity is scant. We do know that patterns of plasticity can be very different depending on the target response variable. For instance, while net photosynthesis exhibited moderate sun-shade differences and seasonal acclimation, dark respiration was far more responsive to environment under Mediterranean, stressful conditions. Dark respiration responses to temperature exhibited a remarkable seasonal acclimation providing a homeostasis that was particularly relevant under low light, where minimizing carbon losses can be crucial for survival (4). But this acclimation was profoundly affected by water availability. Preliminary analyses of the triangular, interactive effects of temperature, water and light availability on dark respiration in a dominant woody species from a continental Mediterranean ecosystem revealed that seasonal acclimation was more pronounced in dry than in wet years

Biotic factors such as herbivory can also significantly limit plant phenotypic plasticity since damaged plants can only rarely attain the optimal phenotype in the challenging environment (5). Finally, it is examined how phenotypic changes involved in trait-mediated interactions can entail costs for the plant in further interactions with other species (5). Ecological limits to plasticity must be included in any realistic approach to understand evolution of plasticity in complex environments and to predict plant responses to global change.

参考文献:1) Valladares F. et al. (2002) New Phytologist 156:457-467. 2) Sánchez-Gómez D et al. (2006) Tree Physiology 26:1425–1433. 3) Sánchez-Gómez D, et al. (2007). Annals of Forest Science (in press). 4) Zaragoza-Castells Jet al. (2007) Plant, Cell & Environment 30:820-833. 5) Valladares F et al. (2007) Tansley review. New Phytologist (in press)

　東京大学理学部生物学科植物学コース