Leaf life span and the leaf economic spectrum in the context of whole plant architecture. (Special Feature: The tree of life in ecosystems: evolution of plant effects on carbon and nutrient cycling.)

摘要

The leaf economics spectrum (LES) has been an organizing framework of plant functional ecology for the past decade. The LES describes a set of trade-offs among traits related to plant carbon balance. Species with a long leaf life span (LLS) invest additional material for leaf protection and structural support and consequently tend to have a lower leaf photosynthetic rate per unit mass than species with a shorter LLS. While the LES is most apparent in comparing species with extreme differences in their traits, it has nonetheless been adopted as a general explanation of leaf trait variation at all scales and in all plants. It highlights the 'trait-based' approach to plant ecology, which has generally used a small set of traits to predict whole organism and even whole ecosystem attributes. Few studies have investigated the relationships between LES traits and organismal attributes not directly related to carbon economy. We explored the LES in 32 deciduous woody species of Viburnum (Adoxaceae). We found no evidence for any mass-based LES trade-offs. Rather, on an area basis, photosynthetic rates were positively correlated with leaf mass per area (LMA); higher LMA was associated with greater investment in photosynthetic tissue, with most of the variation due to changes in the thickness of photosynthetic mesophyll. Species' mean LLS varied between 19 and 26 weeks and was not correlated with other LES traits. Instead, LLS was strongly associated with the diverse set of whole-plant branching patterns in Viburnum. In the most common growth pattern, LLS was significantly correlated with flowering time, because branches end in terminal inflorescences, and all leaves and inflorescences are pre-formed in overwintering buds. Synthesis. Plants may recover the cost of their leaves early in the growing season, allowing LLS to vary independently of the plant carbon budget. In deciduous species, LLS may be strongly influenced by whole plant architecture, which, in Viburnum, is evolutionarily conserved. In general, positive area-based LES trait relationships will limit the relevance of LLS to this spectrum and allow LLS to vary for reasons that are not directly related to carbon economy.