Plant species and nutritional-mediated control over rhizodeposition and root decomposition

This study focuses on the influence of nitrogen (N) availability and species on rhizodeposition and on decomposition of rhizodeposits, roots and soil organic matter. Four perennial grass species were studied that are characteristic of grassland habitats that differ in nutrient availability. These perennial grass species, Holcus lanatus L., Festuca rubra L., Anthoxanthum odoratum L. and Festuca ovina L., were homogeneously labeled with (CO2)-C-14. Plants were grown on soil without N addition and with N addition (14 g N m(-2)). After 8 weeks, plants were harvested and root production and the remaining amount of rhizodeposits in the soil were measured. C-14-labelled roots were incubated in fresh soil. Decomposition was measured of 1) the labeled rhizodeposits in the soil in which the plants had been growing and 2) the labeled dead roots incubated in fresh soil, by trapping the evolved (CO2)-C-14, over 69 days. In general, decomposability of both roots and rhizodeposits increased when nitrogen availability increased. Moreover, the species differed in their response to N. Higher N supply increased total rhizodeposition of H. lanatus and the decomposability of rhizodeposited carbon compounds of this high fertility species was greater than of the low fertility species F. ovina, but lower than of A. odoratum. The presented study gives no evidence for a relation between root decomposition rate and the nutrient availability of the habitat of the four species. Overall, we suggest on the basis of the results that species can affect nutrient cycling by differences in rates of rhizodeposition and litter production. This offers a mechanism whereby species can influence species replacement during succession.