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

This study focuses on the influence of nitrogen (N) availability and specie s on rhizodeposition and on decomposition of rhizodeposits, roots and soil organic matter. Four perennial grass species were studied that are characte ristic of grassland habitats that differ in nutrient availability. These pe rennial grass species, Holcus lanatus L., Festuca rubra L., Anthoxanthum od oratum 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 rem aining amount of rhizodeposits in the soil were measured. C-14-labelled roo ts were incubated in fresh soil. Decomposition was measured of 1) the label ed rhizodeposits in the soil in which the plants had been growing and 2) th e 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 re sponse to N. Higher N supply increased total rhizodeposition of H. lanatus and the decomposability of rhizodeposited carbon compounds of this high fer tility 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 rela tion between root decomposition rate and the nutrient availability of the h abitat of the four species. Overall, we suggest on the basis of the results that species can affect nutrient cycling by differences in rates of rhizod eposition and litter production. This offers a mechanism whereby species ca n influence species replacement during succession.