Interspecific competition in natural plant communities: mechanisms, trade-offs and plant–soil feedbacks

Introduction Interspecific competition in natural plant communities Most plant scientists agree that interspecific competition is highly dependent on nutrient availability. At high is an important determinant of the structure and the levels of nutrient availability, competition is mainly for dynamics of plant communities. There is, however, much light. As light is a unidirectional resource, highless agreement about the mechanisms of interspecific nutrient habitats are dominated by fast-growing perencompetition. The literature about competition has long nials with a tall stature and a rather uniform vertical been dominated by the ‘Grime–Tilman’ debate (Tilman distribution of leaf area. Moreover, these species have 1985, 1987, 1988; Tilman and Cowan, 1989; Grime, 1979, high turnover rates of leaves and roots and a high 1988; Grime and Hodgson, 1987; Thompson, 1987; morphological plasticity during the differentiation of Thompson and Grime, 1988). These authors disagree leaves. There is less consensus, however, about the about the traits of successful competitors and about the importance and intensity of interspecific competition importance of competition in nutrient-poor environments. in nutrient-poor environments. It is argued that selecMoreover, there is still much discussion about biomass tion in nutrient-poor habitats is not necessarily on a allocation patterns of successful competitors and about high competitive ability for nutrients and a high growth the relative importance of aboveand below-ground rate, but rather on traits which reduce nutrient losses competition for the outcome of competitive interactions. ( low tissue nutrient concentrations, slow tissue turnFinally, some authors claim that, in nutrient-poor envirover rates, high nutrient resorption efficiency). Due to onments, traits which lead to high nutrient retention are evolutionary trade-offs plants can not maximize both far more important for plant performance than traits growth rate and nutrient retention. Thus, the low which lead to a high competitive ability for nutrient growth rate of species from nutrient-poor habitats uptake (Berendse and Aerts, 1987; Aerts, 1990, 1997a; should be considered as the consequence of nutrient Berendse, 1994a, b). retention rather than as a feature on which direct A surprising aspect of many papers on competition is selection takes place. The contrasting traits of species that it is not specified for which resources species are from nutrient-poor and nutrient-rich habitats mutually competing. This certainly contributes to much of the exclude them from each others’ habitats. Moreover, confusion about the traits of successful competitors these traits have severe consequences for litter because it will be shown in this paper that there is a decomposability and thereby also for nutrient cycling. trade-off between traits which lead to a high fitness in This leads both in nutrient-poor and nutrient-rich habnutrient-poor environments and traits which lead to sucitats to a positive feedback between plant species cess in more fertile environments. Moreover, both suites dominance and nutrient availability, thereby promoting of traits have important implications for nutrient cycling ecosystem stability. processes which may reinforce patterns of species distributions along gradients of soil fertility.