"Life history tradeoffs and senescence in plants"

An increasing number of studies have shown that senescence, the functional decline in traits and increased risk of mortality with increasing age, occurs in organisms in wild populations, but there is a wide range of diversity in the patterns of senescence across species. The antagonistic pleiotropy and the disposable soma theories of senescence predict that there will be life history trade-offs between performance at early-and late-life stages. Plants show variation in senescence patterns and thus provide an opportunity to evaluate life history trade-offs and senescence. Many plant species can be easily followed demographically and their environments, resources and allocation to reproduction can be manipulated, which makes them particularly good models to address these theories. I compared the results from 22 studies of plant senescence in the wild and compiled 20 examples of life history trade-offs in plants. Some of the unique features of plants that may influence senescence patterns and trade-offs in the wild are highlighted through the results. I found all three age-specific patterns: age-decline, age-improvement, and no change with age for plants in the wild. The dominant pattern was an age-dependent decline in at least one trait but, even within a species, the age-specific patterns of traits varied. Results also showed that trade-offs vary across environments and that plants can manipulate their resource pool through increases in photosynthesis, which will influence the manifestation of trade-offs. I conclude that aspects of plant biology including dynamic resource pools, the impact of size, dormancy and below ground storage may influence both the patterns of senescence and life history trade-offs. The diversity of plant life forms and life cycles provide a wealth of opportunities to experimentally study senescence in the context of life history trade-offs.