1 The development of general principles regarding biotic interactions involving plants, or plant species effects in ecosystems, is best achieved through simultaneous evaluation of several species. We utilized a comparative approach involving 20 dicotyledonous herbaceous species, to explore possible relationships between several plant ecophysiological traits and plant litter decomposition, interactions involving competition and herbivory, and plant species effects on soil properties.
2 Decomposition rates of plant stem and leaf litter were negatively related to plant mass, time until flowering and vegetative growth rate, and positively related to stem nitrogen content. Root decomposition was also related to several traits. Multiple regression relationships showed that 74% and 84% of the variation across species for stem and root litter decomposition, respectively, could be predicted by plant traits; this suggests that plant traits may be powerful predictors of decomposition and have potential as alternative predictors to the litter quality characteristics that previous studies have concentrated on.
3 Palatability of both seedlings and leaf discs by the invertebrate herbivores Deroceras reticulatum and Listronotus bonariensis were frequently related to plant traits. Those traits that showed the strongest relationships with the palatability data included various vegetative growth characteristics and (for the leaf disc data) nitrogen concentrations of flowering plant stems.
4 Competitive effects of the dicotyledonous species against a phytometer species, the grass Lolium perenne, were negatively related to leaf nitrogen concentration, and multiple regression relationships involving this trait in combination with others explained over 50% of the variation across species. The competitive response of both plant mass and total seed production to L. perenne was poorly related to plant traits.
5 The effects of plant species on soil properties including microbial biomass and activity, pH, nitrate concentration and total nitrogen were often closely related to various plant traits. Multiple regression relationships revealed that combinations of several traits were often important in determining these effects; the strongest relationships found were for effects of senescent plants on soil respiration and for the effects of flowering plants on soil nitrate. Plant traits were therefore clearly important in determining plant species effects on soils.
6 Our study emphasizes the importance of plant traits in understanding (and predicting) species interactions and effects in communities and ecosystems, and shows that properties considered at the whole plant level have the potential to manifest themselves over much larger scales. We therefore conclude that there are clear linkages between plant ecophysiological traits, biotic interactions involving plants, and ecosystem level properties and processes.