Plant communtiy development is affected by nutrients and soil biota

1 Plant community development depends to a great extent on the availability of soil nutrients, but recent studies underline the role of symbiotic, herbivorous and pathogenic soil biota. We tested for interactions between these biotic and abiotic factors by studying the effects of additional nutrients and the removal of soil biota on the replacement of grassland plant species typical of different successional stages. 2 Species representing each of the early, mid and target phases of secondary succession in a grassland community (four per phase) were grown in mid-successional grassland soil. The mixed plant communities were grown in sterilized and non-sterilized soil, at three nutrient supply levels. The distribution of shoot biomass over the different plant species, and the total root biomass, were determined, as well as the composition of nematode and microarthropod communities and soil decomposition rates. 3 The effect of nutrient supply on plant community composition depended on soil sterilization. In sterilized soil, the plant community was initially dominated by grasses that increased in dominance even without fertilization. In non-sterilized soil, the plant community was more diverse and grass dominance decreased over time, except with high fertilization. Fertilization enhanced the productivity of the plant community in sterilized and, to a greater extent, in non-sterilized soil. 4 The abundance of root-feeding nematodes was positively related to increased root biomass, pointing to a strong bottom-up control. Increased levels of nutrient supply were associated with reduced abundance of omnivorous nematodes, the cause of this reduction being less clear. Increased soil fertility altered the functional diversity of the soil nematode community, which might, in the longer term, also affect their feedback effects on the plant community. 5 Increased nutrient supply reduced soil decomposition activity in the non-sterilized soil, but not in the sterilized soil. 6 Our results imply that soil biota may reduce the effects of nutrient supply on plant dominance. Incorporating the effects of soil biota on plant species interactions into studies on succession, plant species diversity and restoration may therefore considerably increase our understanding of the observed plant community patterns