One fundamental question in plant ecology is why certain species occur in a wide range of habitats while others are limited to specific ecological niches. The impact of ongoing and future climate change on plant communities will be largely determined by species tolerance, resistance and resilience to rapid changes in their growth conditions, thus outlining the importance of this question. Nowadays, it is assumed that the differential plasticity in functional traits may mechanistically explain the width of a species’ ecological niche. In situations where water limitation is an issue, functional traits of the water-conducting system in the xylem, carbohydrates (NSC) and other energy reserve pools appear to be particularly crucial to withstand drought periods during which stomata are closed. Little is known about the plasticity of functional xylem traits, particularly in herbaceous species. This lack of knowledge contrasts with the importance of herbaceous plants in many biomes such as the alpine and arctic zones, as well as for production in agriculture.

The MOUNTLAND experiment has analyzed the reactions of pasture-woodlands to simulated climate change by means of a transplantation experiment performed along an altitudinal gradient using soil turfs taken at 1400 m and transplanting them downhill at 1000 and 600 m. During an earlier study on the functional above-ground responses of two herbaceous species, Taraxacum officinale and Alchemilla monticola, no change in the foliage gas exchanges and leaf structure was observed whereas the leaf turnover and phenological development of both species were accelerated, thus suggesting that climate change may affect the growth and reserve storage inside perennial roots.

Project Aims

The aim of this project is to investigate functional xylem traits in the roots of two dominant species of pasture-woodlands, which above-ground reactions were analyzed in a previous study within the framework of the MOUNTLAND experiment, and to compare above- to below-ground reactions to simulated climate change. More specifically, we will:

1. quantify secondary growth and xylem hydraulic traits (vessel size and arrangement) and storage tissue (ray parenchyma, phloem, pith)
2. quantify the amount of starch, lipid and protein reserves stored in the roots
3. relate changes in these parameters to above-ground growth, ecophysiological micro- and macro-morphological reactions to simulated climate change

Overall, we thus seek to gain novel insight into whole-plant responses to climate change.

Methods

Root anatomical traits related to water transport will be quantified and compared to the amount of stored energy reserves in two dominant herbaceous species from the pasture-woodlands. Therefore, structural and functional traits in xylem of perennial roots (i.e. annual rings width, size and spatial arrangement of, vessels and reserve-storing parenchyma, amounts of starch, lipids and proteins reserves) will be quantified in anatomical thin sections treated with specific histochemical staining agents. The obtained data will be compared to those characterizing the leaf physiology, micro- and macro-morphology, as measured during the preceding vegetation season and using the same plants, and analyzed in the context of soil processes characterized in other MOUNTLAND sub-projects.