Proportional dry‐mass content as an underlying trait for the variation in relative growth rate among 22 Eurasian populations of Dactylis glomerata s.l.

1. Relative growth rate (RGR), proportional dry-mass content of leaf and stem tissues, and biomass-allocation pattern were assessed under controlled conditions for 22 populations of Dactylis glomerata s.l. from contrasting latitudes and altitudes in Europe, Israel and Kazakstan. Furthermore, width and thickness of leaves were measured in garden-grown mature plants. 2. All these parameters varied significantly among the populations. RGR correlated negatively with dry-mass content of leaves and stems, but not with biomass-allocation parameters, leaf thickness or leaf width. We argue that the close association of RGR with variation in dry-mass content among species and genetically distinct populations is a result of the larger volume of tissue, and correspondingly larger leaf area and longer root system, that a plant with a low tissue density can build per unit dry mass. 3. Leaf tissue dry-mass content decreased and RGR increased with increasing latitude and elevation of the originating site, indicating that a high growth rate may be an advantage in habitats with a short growing season. This contrasts with earlier findings of a negative correlation between inherent RGR and altitude.