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

Interspecific competition in natural plant communities is highly dependent on nutrient availability. At high levels of nutrient availability, competit ion is mainly for light, As light is a unidirectional resource, high-nutrie nt habitats are dominated by fast-growing perennials with a tall stature an d a rather uniform vertical distribution of leaf area. Moreover, these spec ies have high turnover rates of leaves and roots and a high morphological p lasticity during the differentiation of leaves. There is less consensus, ho wever, about the importance and intensity of interspecific competition in n utrient-poor environments. It is argued that selection in nutrient-poor hab itats is not necessarily on a high competitive ability for nutrients and a high growth rate, but rather on traits which reduce nutrient losses (low ti ssue nutrient concentrations, slow tissue turnover rates, high nutrient res orption efficiency), Due to evolutionary trade-offs plants can not maximize both growth rate and nutrient retention. Thus, the low growth rate of spec ies from nutrient-poor habitats should be considered as the consequence of nutrient retention rather than as a feature on which direct selection takes place. The contrasting traits of species from nutrient-poor and nutrient-r ich habitats mutually exclude them from each others' habitats. Moreover, th ese traits have severe consequences for litter decomposability and thereby also for nutrient cycling. This leads both in nutrient-poor and nutrient-ri ch habitats to a positive feedback between plant species dominance and nutr ient availability, thereby promoting ecosystem stability.