Chronic stress in humans has been implicated in heart disease, weight
gain, and diabetes, among a host of other health problems. Extreme
environments, a source of chronic stress, present a challenge even for
the hardiest organisms, and plants are no exception. Yet, some species
somehow manage to survive, and even thrive, in stressful conditions.
A recent article by Dr. Yuri Springer in the November issue of the American
Journal of Botany finds that certain wild flax plants growing in
poor soils have succeeded in balancing the stress in their lives —
these plants are less likely to experience infection from a fungal
pathogen. Walking the fine line between the costs associated with
surviving under stressful conditions and the benefits that may be
derived from growing in an environment with fewer interactions with
antagonistic species is a tricky balancing act.
For plants, serpentine soils are one example of an extreme
environment. Serpentine soils are those that provide a stressful medium
for plant growth, due to features of the soil, such as a rocky texture,
low water-holding capacity, high levels of toxic metals, and/or low
levels of necessary nutrients.
Springer assessed the prevalence of fungal infections in species of
the wild flax genus. Wild flax provides a model system to study
serpentine tolerance; the species exhibit a range of tolerance to soil
with low levels of calcium, a necessary nutrient for plant survival. He
examined the correlation between disease symptoms and tolerance to
serpentine soils in the context of evolutionary relationships among the
Springer found that wild flax populations growing in serpentine soils
displayed a reduction in fungal infection. These results support the
hypothesis that stressful environments may be attractive to plants
because they provide a refuge from pathogens; however, the plants need
to be able to survive in these extreme ecosystems. In wild flax, the
fungal pathogen may have difficulty infecting plants that have low
levels of calcium in their tissues due to low levels in the soil.
Alternatively, the plants growing in a low nutrient soil may allocate
much of their resources to defense against pathogens and herbivores due
to the high costs of replacing tissue.
Based on the putative evolutionary history of the wild flaxes,
tolerance to serpentine soils has evolved rapidly and repeatedly in the
genus or was present in the ancestors of these wild flaxes and lost in
several lineages. This is the first study to attempt to quantitatively
explain how plants have evolved a specialization to serpentine soils and
ultimately may help to explain floristic diversity in these unique
Source : American Journal of Botany