Are annual plants escaping the ‘root economics space’? Root functional traits in the annual model grass Brachypodium hybridum under increasing aridity.

• Applicant: Professor Dr. Johannes Metz
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 535094127

Roots are essential to plant performance as they ensure the uptake of water and nutrients. However, roots have received much less attention in functional ecology than aboveground organs. Moreover, most empirical and theoretical advances in understanding root systems were based on interspecific approaches that compared root traits across numerous species. Scarcely investigated is how root traits are adjusted within a species, namely across multiple populations along natural environmental gradients. Here, we propose an extensive greenhouse experiment investigating intraspecific root trait variation along a steep natural rainfall gradient in Israel. The key dimension and backbone of the project are 15 populations of the wide-spread Mediterranean annual grass Brachypodium hybridum that span from desert to Mediterranean conditions (89 – 926 mm rainfall) along the gradient. They show the species’ long-term evolutionary response to increasing aridity. The proposed study will be the first to combine this key dimension with three further dimensions that are predicted to shape root traits: One is the plastic response to high versus low irrigation levels, another is the ontogenetic change in root traits from juvenile to mature plants, and lastly the root response to high versus low colonization with mycorrhizal fungi. To this end, we will raise 1,800 plants belonging to 300 genotypes and 15 populations. Roots will be measured under i) high and low irrigation, ii) for juvenile, intermediate, and mature individuals, iii) and with and without mycorrhizal inoculation. A total of 14 root traits will be measured, including e.g. root mass fraction, specific root length, and mycorrhizal colonization. These 14 traits reflect major theories for root responses to increasing aridity, namely the theory of optimal resource partitioning, the root economics spectrum, and the root economics space. Based on these theories, we hypothesize higher root biomass allocation and a ‘slower’ trait strategy when water is more limiting, i.e. in drier populations along the rainfall gradient, under low irrigation, at older ontogenetic life stages, and with low mycorrhizal colonization. In sum, the proposed project will be the most comprehensive intraspecific study on how plants adjust their root system to increasing aridity. It will advance functional root ecology as well as our knowledge of plant adaptation to increasing aridity.

• DFG Programme: Research Grants