Species‐specific root–shoot ratios in a diverse grassland community

Abstract Existing studies of root/shoot ratios (R/S) in the field show large differences among environments, from high values in unproductive environments to low values in productive environments. However, virtually, all such studies are community‐wide, that is compare biomasses of roots and shoots summed over all coexisting species. Therefore, we do not know to what extent this is due to innate interspecific differences in the R/S ratios or to plastic response to nutrient limitations. This is due to methodological difficulties in assigning roots into species, which preclude the contribution of species‐specific differences to the community‐wide R/S ratio. These limitations can be overcome by DNA analyses. We used qPCR to determine species‐specific R/S ratios in a montane grassland and compared these values to R/S ratios from a two‐season long single‐species pot experiment. To translate the qPCR data to root biomass units, we extracted DNA from the experimental plants to perform calibration for each species and to take into account potential change during the ontogeny of root systems. We used these calibration relationships to recalculate gene copies estimated in a set of field samples to species‐specific root biomass values. All species except one showed fairly high correlation between above‐ground biomass (determined by weighing) and below‐ground biomass (determined by qPCR) across all studied plots in the field. Root/shoot ratios determined from the field were for most species slightly lower than the aggregate values of the whole community determined by weighing both roots and above‐ground biomass. They showed significant correlation with the R/S ratios from the pot experiment, indicating innate differences among species that persist across two very different sets of conditions (multispecies community in the field, single species culture in pots). The field R/S ratios based on qPCR root estimation are informative on the true field patterns. This is supported by their correlation with the pot‐derived values. While the values seem to be slightly underestimated, they are well in the reasonable range of values. This opens a new field of study, namely examination how R/S ratios in the field respond to changed nutrient availability and diversity and species composition of neighbouring species. Read the free Plain Language Summary for this article on the Journal blog.