Trait‐based ecology uses phenotypic characteristics of plants to study responses to environmental change and to investigate ecological hypotheses. These phenotypes that are associated with plant functioning are called functional traits. One example of a widely known functional trait is the ratio of leaf dry mass and leaf area, also known as leaf mass per area (LMA). The LMA is an important functional trait because it is a key characteristic in plant growth and a critical indicator of plant strategies often associated with functional attributes of a leaf such as lifespan, nitrogen concentration, photosynthetic rate and defence chemistry. Leaves with high LMA are thought to have longer lifespan because of their higher physical strength and coordination with other traits such as defence chemistry, and lower growth rate while low LMA leaves tend to have shorter lifespan and higher growth rate. Provided that a functional trait is measurable, it can then be used to study plant responses to environmental change in the past (Soh et al. 2017).
We presented an application of functional trait in deep-time ecology in a case study on ancient ginkgos and cycad-like plants, bennettite. These plants inhabited much of the Earth’s surface million years ago and they would have experienced the mass extinction event that occurred at the boundary of the Triassic and Jurassic period. To understand how these ancient plants cope with the extremity at the time, we infer their leaf weight by using cuticles that were still intact in fossilised leaves (Fig. 1). By using this palaeo-LMA proxy, we showed that plant with thicker and heavier leaves, i.e. high LMA, were more likely to survive the Triassic-Jurassic mass extinction event caused by global warming 200 million years ago. Our study also suggests that extreme global warming selected for plants with high LMA associated with a stress-tolerant strategy and that adaptive plasticity in leaf functional traits such as LMA contributed to post-warming ecological success (Soh et al. 2017).
Figure 1. Cross section of a 200 million years old ginkgo leaf under fluorescence microscope.
Details of funding and collaborator can be found in the listed publication. In addition to LMA, future work will focus on other traits such as seed buoyancy and winter bud size.
Soh W.K., Wright I.J., Bacon K.L., Lenz T.I., Steinthorsdottir M., Parnell A.C. & McElwain J.C. 2017. Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event. Nature Plants 3, 17104. DOI: 10.1038/nplants.2017.104