Interspecific variation in RGR and the underlying traits among 24 grass species grown in full daylight

A growth analysis was conducted with 24 central European grass species in f ull daylight to test whether traits underlying interspecific variation in r elative growth rate (RGR) are the same in full daylight as they are at lowe r light, and whether this depends on the ecological characteristics of the studied species, i.e., their requirements with respect to nutrient and ligh t availability. In contrast to studies with herbaceous species at lower lig ht, net assimilation rate (NAR) contributed more than leaf area ratio (LAR) or specific leaf area (SLA) to interspecific variation in RGR. This was as sociated with a larger interspecific variation in NAR than found in experim ents with lower light. Without the two most shade-tolerant species, however , the contribution of LAR and its components to interspecific variation in RGR was similar or even higher than that of NAR. Leaf dry matter content co rrelated negatively with RGR and was the only component of LAR contributing in a similar manner to variation in LAIR and RGR. There was a positive cor relation between NAR and biomass allocation to roots, which may be a result of nutrient-limited growth. RGR correlated negatively with biomass allocat ion to leaves. Leaf thickness did not correlate with RGR, as the positive e ffect of thin leaves was counterbalanced by their lower NAR. Low inherent R GR was associated with species from nutrient-poor or shady habitats. Differ ent components constrained growth for these two groups of species, those fr om nutrient-poor habitats having high leaf dry matter content, while those from shady habitats had thin leaves with low NAR.