Validity of Photo-oxidative stress markers and stress-related phytohormones as predictive proxies of mortality risk in the perennial herb Plantago lanceolata

Oxidative stress and hormonal regulation are hallmarks of a/biotic stress responses in plants. However, little is known about their linkage with whole-organismal mortality in long-lived species. Here, we examined the validity of photo-oxidative stress markers and stress-related phytohormones as predictive proxies of mortality risk in the perennial herb Plantago lanceolata. Capitalizing on its broad ecological niche, we examined photo-oxidative stress markers (Fv/Fm ratio, contents of chlorophylls, carotenoids, and tocochromanols, and the extent of lipid peroxidation) and stress-related phytohormones (ABA, salicylic acid and jasmonates contents) as proxies of mortality in three populations of sub-tropical and Mediterranean habitats: Virginia (VA, U.S.A.), Catalonia (CAT, Spain), and Queensland (QLD, Australia). Stress markers were measured together with the vital rates of survival, growth, and reproduction on a total of 279 individuals. Stress marker data were collected during the summer and death/survival was monitored after two and four months. Whole-organism mortality was similarly high in both sub-tropical non-native populations (ca. 30 % after a drought in VA and QLD), but lower in the native population (ca. 10 % in CAT). The contents of antioxidants (lutein, zeaxanthin, β-carotene) and the de-epoxidation state of the xanthophyll cycle (DPS) were good proxies of mortality risk in VA and QLD. DPS and all carotenoid contents per unit of chlorophyll were lower four months in advance in dead than in alive plants in VA and QLD, thus suggesting reduced photoprotective capacity increased the mortality risk in non-native populations. We show that whole-organismal mortality in P. lanceolata is associated with a reduced capacity to enhance photoprotection under abiotic stress conditions. The validity of various stress markers as predictive proxies of mortality risk is discussed

Data from: Aging in an herbaceous plant: increases in mortality and decreases in physiology and seed mass

1. Little is known about plant age-dependent trait expression and how environmental conditions might affect aging in the wild. This study evaluates age variation in multiple traits of a short-lived perennial herb using a manipulative field experimental design. 2. Two different-aged cohorts were followed in a field plot for over a year to evaluate trait expression in response to a competition treatment and seasonal stress. Traits measured included size, mortality, reproduction, and physiology, including photosynthetic efficiency and chlorophyll content (SPAD). We hypothesized that the stress of competition and seasonal changes would accentuate age-dependent trait declines in older plants. 3. The results highlight consistent age differences in plant size, mortality, and seed size with older plants being smaller, more likely to die, and producing smaller seeds. Some of the aging declines were sensitive to environmental conditions such that it was only during certain seasons when older plants had higher mortality, lower photosynthetic efficiency, and lower chlorophyll content than young plants. Age-dependent trait expression also varied in response to competition such that age differences in size were only present in the ‘no competition treatment,’ and old individuals in the competition treatment had a higher mortality than all other age-environment combinations. 4. Synthesis. These findings show that aging in plants is a complex phenotype where declines in traits are uncoordinated and can be, but are not always, sensitive to environmental conditions. This study shows age-dependent maternal effects on offspring quality which, together with the decline in performance of older individuals, may have impacts on an individual’s fitness and on natural population demography